historic lighthouse preservation: windows · architectural style upon which the ornament of the...

Historic Lighthouse Preservation Handbook Part IV. E,

Historic Lighthouse Preservation:

WINDOWS

With their functional and decorativefeatures such as keystone lintels, multi-lightsashes, arched pediments, and architrave(trim or molding which surrounds thewindow opening), windows can beextremely important in defining the overallcharacter of a lighthouse. Usuallywindows were integral components of ahistoric lighthouse�s stylistic design andfeatured hallmark elements that defined thearchitectural style upon which theornament of the structure was based.

The predominant window type found inhistoric lighthouse towers is a wood,double-hung sash variety. This windowtype has been used since the late 18thcentury. Other window types associatedwith lighthouses are wood and metalcasement windows.

The primary cause of lighthouse windowdeterioration is moisture penetrating thevarious components through rain drivenagainst and into windows, standing water

on sills, and interior condensation. In amarine environment, deterioration causedby moisture penetration is exacerbated byextended periods of damp weather, whichprevent windows from drying out, therebyencouraging expansion and rot. Otherfactors that contribute to windowdeterioration are poor design, vandalism,insect/fungal attack, settlement over time,paint buildup, broken glazing, deterioratedputty, and deferred maintenance.

Windows admit light and air into alighthouse. Both of these functions shouldbe maximized, but in a controlled manner.Because most lighthouses are unoccupied,mechanical methods are not always viableas a means of interior climate control. Well-maintained, operable windows willtherefore be an important and preferredcomponent in creating an efficient passiveventilating system. Replacement windowsand components, when needed, should beconstructed of materials of the highest

Figure 1. Close-up of a window foundin a Chesapeake Bay "spark plug"lighthouse . The integral cast-iron trimis a typical character-defining feature ofthis lighthouse type from the late 19thcentury

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Figures 2 and 3. Wood and metal window details (source: The Window Handbook).


quality that can withstand a harsh marineenvironment. Where vandalism andsecurity require the temporary blocking of awindow to better secure the structure,sensitive measures can effectively block theopening with minimal damage to thehistoric window. The following is adiscussion of preferred preservationmethods to consider when preservinghistoric lighthouse windows.

Window Types

The two primary types of windows found inhistoric lighthouses are identified by howtheir moving parts operate. The wooddouble-hung sash is the most common.

The moving parts of the window consist oftwo wood frames, called sashes, thatcapture the glass �lights� or panes of thewindow. These frames are housed in awood frame, called a jamb, that allows thesashes to slide up and down. The top of thewood frame is called the head and thebottom portion is called the sill on theexterior and the stool on the interior. Thesill is responsible for shedding water awayfrom the window opening. The secondmost common window type found inhistoric lighthouses is the metal casement.The moving parts of a metal casementwindow operate like a door. Theterminology remains the same for the partsof the casement window.

Inspection and Evaluation

The first step to repairing historic windows is a thorough inspection of each window unit.

Inspection Chart for Lighthouse Windows

Look For: Possible Problems:

Wood Windows

Areas of paint failure This may indicate the wood is in poor conditionand in need of repair. Wood is frequently insound condition, however, beneath unsightlypaint. After noting areas of paint failure, inspectthe condition of the wood. Use an ice pick or anawl to test wood for soundness. Pry up a smallsection of the wood. Sound wood will separate inlong fibrous splinters. Decayed wood will lift upin short irregular pieces caused by breakdown offiber strength.

Deteriorated wood If deterioration has begun from within the woodmember and the core is badly decayed, the visiblesurface may appear to be sound. Pressure on aprobe can force through an apparently soundouter layer to penetrate deeply into decayedwood. This technique is especially useful forchecking sills where visual access to the undersideis restricted.

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This may indicate the paint is at the end of itseffective life span or the window has been bent ordeformed. Bending makes the less flexible paintfracture and �pop� off the window frame.

Look For: Possible Problems:

Metal Windows

Areas of corrosion on all surfaces of the sash,frame, sub-frame (if visible), and hardware

This may indicate a moisture infiltration problem.Corrosion in the form of rust will occur typicallyinside the frame channel and along the bottomedge of the sash.

Bowing or misalignment of window parts Deformation could be the result of misuse/abuseor corroding components that have deformedbecause of rust-jacking or deterioration.

Both Window Types

Water entering around the edges of the frame The joints or seams should be caulked to eliminatethis danger. Check the glazing for cracked, loose,or missing sections. Examine the sill for adownward slope which allows water to drain.

Condition of glass and glazing to determine theextent of required repairs

Careful probing of the glazing with an awl will aidin determining its soundness.

Gaps or cracks in the joint between the windowframe and the lighthouse wall

Cracks or gaps are possible water infiltrationpoints.

Moving parts of the windows Bound or tight operating windows may simply bepainted shut or may be stuck because ofdeteriorating frame members or sash frames, orbound because of corroded hardware.

Areas of paint failure


PRESERVATION TREATMENTSThe following are protection/stabilization (mothballing) and repair treatments designedspecifically for windows found in historic lighthouse towers. For a discussion of windowtreatments in ancillary structures, see NPS Preservation Briefs 9: The Repair of HistoricWooden Windows and Preservation Briefs 13: The Repair and Thermal Upgrading ofHistoric Steel Windows.

Protection and Stabilization (Mothballing)

Lighthouses which have been mothballed usually have had the openings on the lowerlevel covered to protect fragile glass windows from breaking and to prohibit entry points.Infill materials for closing window openings include plywood, corrugated sheet-metalpanels, metal grates or grills, brick, and cinder or cement blocks (in masonry lighthouses).The method of installation should not damage the opening or window jamb. During thisprocedure all associated sash, shutters, and frames should be protected. If removed, allwindow parts should be labeled to indicate which window they came from and stored forfuture reuse. Special care must be taken to ensure no further damage is incurred duringthe removal of the window parts.

� For windows, the most common security featureis the closure of the openings; this may beachieved with wooden or preformed panels or,as needed, with metal sheets or in the case ofmasonry towers concrete blocks or bricks maybe used. Plywood panels, properly installed toprotect window frames and which are properlyventilated, are the preferred treatment from apreservation standpoint. (To provide adequateventilation the louvered opening should have anarea that is approximately half of the originalsash opening.)

� There are a number of ways to insert ventedplywood panels into window openings to avoiddamage to frame and sash. One commonmethod is to bring the upper and lower sash ofa double-hung unit to the midpoint of theopening and then to install pre-cut plywoodpanels on the inside face of the window usinglong carriage bolts anchored into horizontalwooden bracing, or strong backs (see Figures 4and 5).

� The type of ventilation should not underminethe security of the building. The most secureinstallations use custom-made grills wellanchored to the window frame, often set inplywood security panels. In upper-levelwindows vents formed using heavy millworklouvers set into existing window openings areanother possibility (see Figure 6).

Figure 4. A good example of a blocked window using ametal panel fitted with a hooded vent. For more adequateventilation, the vent should be larger.

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� Plywood panels are usually 1/2- to 3/4-inch(1.25-1.875 cm.) thick and made of exteriorgrade stock, such as CDX, or marine-gradeplywood. They should be painted to protectthem from delamination and to provide a neaterappearance. These panels may be painted toresemble operable windows or treateddecoratively.

� As a temporary treatment, acrylic or other highimpact clear sheeting could be used to cover anentire window. The sheeting could either beattached to the actual window frame withscrews, being careful not to damage any historicmolding profiles or split the wood frame. Abetter attachment method (especially formasonry lighthouses) would be to construct asub-frame within the window opening using 2-by 4-inch framing members and then attach thesheeting to the sub frame. If this method isused, the interior sash should be opened andthe sheeting fitted with large screened louvers.

(To provide adequate ventilation, the louveredopening should have an area that isapproximately half of the original sash opening.)When using this treatment, the sheeting must beventilated to ensure that condensation, whichcould accelerate the deterioration of thewindow, does not build up between the paneland the window.

� Another effective method of ventilating alighthouse during mothballing is to lower theupper sash and install a large screened, hoodedvent. These vents, together with the louversfitted in the tower entry door, keep the interiorof the tower free from condensation year round.

Figure 5. Interior view of the blocked window. Ifpossible, a better solution would have been to raise thelower sash and lower the upper sash and pass the boltsthrough the openings.

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Figure 6. Detail of wood louver system designed to beinserted into lower sash opening after sash has beencarefully removed. (Drawing by Thomas Vitanza, WPTC)


RepairThe following is a discussion of maintenance and repair philosophy and treatments forhistoric lighthouse windows. These instructions conform with the principle that the leastmodification to an existing window often yields the greatest return�accepted preservationpractice and simple economics; the ratio of investment to return is often greater whenrepairing and upgrading an existing window than when replacing it.

� Identify, retain, and preserve windows (theirfunctional and decorative features) that areimportant in defining the overall historiccharacter of the building. Such features caninclude frames, sash, muntins, glazing, sills,heads, hood molds, paneled or decoratedjambs, moldings, hardware, and interior andexterior shutters and blinds.

� When determining its historic significance,consider a window�s place as a principlecharacter-defining component of the exteriorfacade and its contribution to an interior space.

� Avoid changing the historic appearance ofwindows through the use of inappropriatedesigns, materials, finishes, or colors whichnoticeably change the sash, depth of reveal, ormuntin configuration; the reflectiveness andcolor of the glazing; or the appearance of theframe.

� Conduct an in-depth survey of the conditions ofwindows early in preservation planning so thatrepair and upgrade methods and possiblereplacement options can be fully explored.

� When possible preserve all remaining originalglazing. Historic glass often has distortions andimperfections that are not found in modernglass�an irreplaceable character-definingelement.

� Evaluate the overall condition of materials todetermine whether more than protection andmaintenance are required, i.e., whether repairsto windows and window features are needed.

� Keep glazing clear to maximize the natural lightsource. Glass is preferred to plastics such asacrylic and polycarbonate which may scratcheasily, tend to look oily, and will yellow andhaze with time.

� Preserve operating systems for historicwindows, (e.g., weights on double-hungwindows), repairing or replacing components asneeded. This should done even though thewindows may not be currently used.

� Repair all broken, cracked, or missing glassimmediately. If immediate replacement is notfeasible, a temporary patch should be used toprohibit the entry of water, pests, and vandals.When funds are available the missing glassshould be replaced.

� Where building or life-safety code requires,install safety glass into existing window sashes,carefully retaining frame and hardwarecomponents. If possible, salvage original glassfor later reinstallation or use elsewhere in thestructure. These codes are enforced at a local orstate level and typically apply to lighthouses thatare privately owned where visitors haveunsupervised access to the tower.

� Remove rust and paint from metal windows byhand scraping. Low pressure (80-100 psi)sandblasting may be used to remove heavycorrosion, with careful protection of glass andsurrounds. Do not use heat to remove rust orpaint from metal windows; this can distort themetal members, release toxic fumes, and maycause the glazing compound to fail. If the sashis removed from the frame, the paint can beremoved through a chemical dip process, butthe metal surface should be neutralized beforerepainting.

� Do not obscure historic window trim withmetal, vinyl, or other material.

� Do not strip windows of historic material suchas wood, cast iron, or bronze.

Figures 7 through 9 illustrate forms ofdeterioration typical to lighthouse windows.All of these conditions are repairable anddo not require total replacement. Thefollowing guidelines are intended to aid inthe repair of such deterioration.

� Once the damage and deterioration have beenidentified, the affected areas must be treated.Repair window frames and sash by patching,splicing, consolidating, or otherwise reinforcing.Such repair may also include replacement of

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those parts that are extensively deteriorated ormissing, using surviving prototypes such asarchitraves, trim, hood molds, sash, sills, andinterior or exterior shutters and blinds.

� Repair defective sills to permit positive drainageaway from the window sash. Poor design of theexterior window sill is a frequent problem;window deterioration usually begins onhorizontal surfaces and at joints where watercollects, saturating wood and corroding metal.

� Repair of historic windows is always preferredto replacement. Usually the sill must bereplaced first, then lower sash parts. Splicingand dutchmen can be effective repair methodsfor both wood and metal window elements.

� If replacement is required, limit it to severelydeteriorated components.

� Clean and oil hardware that has been paintedover; in most cases, repair, rather thanreplacement, should be possible.

� Remove built-up paint on sashes and frames thatcauses sashes to be inoperable. Wherepossible, remove paint only to the next soundlayer. In order to provide a paint chronology, a

patch of sound paint should be left undisturbedfor future reference.

� When possible, remove earlier repairs that havebeen insensitive to the historic features andmaterials, and repair according to acceptedstandards.

� Document all work through written andphotographic means as a record for futurereference.

Removing Paint from WoodWindows

NOTE ABOUT LEAD PAINT: In thefollowing treatment explanations referencesare made to the removal of loose, flaking, andblistering paint finishes; in carrying out thistreatment, all precautions should be taken toprotect the workers from exposure to lead-based paint.

Figure 7. Deteriorated glazing putty and peeling paint on amultilite wood sash.

Figure 8. Deterioration of the bottom rail and sill on awooden double-hung window.

Figure 9. Rust occurring on the inside of the steel channelthat forms the sill of this metal casement window.

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Historic wood windows tend to accumulatemany layers of paint. This paint is likely tointerfere with the proper operation of thewindow and is usually visually unattractive.Over time, partial peeling leaves a pittedsurface that encourages moisture to collect.Excessive paint layers also obscure theshape of original molding profiles, whichadd definition to the window�s appearance.

The extent of paint removal requireddepends on the condition of the paint.Treatments for common paint conditionsfound on historic lighthouse windows:

� Chalked paint: Clean with a mild detergentsolvent, hose down, and allow to dry beforerepainting.

� Crazed paint: Sand by hand to the next soundlayer before repainting; exposure of bare woodis not necessary.

� Peeling and blistering: Analyze between coatsas to the source. If salts or impurities havecaused peeling, scrape off the defective surface,hose off the underlying surface, and wipesurface dry before repainting. If the peeling orblistering was caused by incompatibility of thepaints or improper application, scrape off thedefective surface, and sand the underlyingsurface to provide a better bond with the newpaint. Peeling, cracking, and alligatoring tobare wood require total removal of the defectivepaint followed by drying out of the woodsubstrate and treatment for any rotted areasbefore repainting. Sand or scrape only to thenext sound layer of paint, exposure of barewood is not necessary.

Paint Removal Methods

Paint is typically removed from wood surfaces by scraping after it has been softened with heatguns or plates or brushed with commercially available chemical stripping solvents. Regardlesswhich method is chosen for paint removal, after the stripping process is complete, all affectedareas will need at least light sanding.

Chemical Strippers

WARNING: When chemical paint removers are used, take care to protect your skin and eyes, provideadequate ventilation, and prevent spillage onto adjacent materials. These solvents can etch or otherwisedamage the surrounding masonry, painted surfaces, and glazing. It is best not to use these chemicals on ordirectly adjacent to glass.

Paint on historic lighthouse window sash can be removed by softening with commercial chemicalstrippers such as methylene chloride, toluol, or xylol. To maximize the chemical’s effect, thestripping agents have been combined with a thickener which holds them in place while thechemicals soften the paint. The softened paint is scraped with special scraping tools designed notto damage existing molding profiles. The scrapers can be formed on site by grinding the trimprofile on the end of a large (2-inch-wide) scraper. Commercially available scrapers are designedwith different sized curves and shapes that can be used in combination to fit the various curvesand shapes of the molding profile.

Another commercially available method sandwiches the paint, softened by a solvent paste,between the wood substrate and a disposable membrane. Although materials for this method aremore costly, it is less labor intensive than using traditional strippers and scraping. Even with thissystem some scraping is required. With either stripping method all stripped surfaces must beneutralized for the new paint to properly adhere. The neutralization method depends on theparticular stripper.

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Applied Heat

WARNING: Under no circumstances should a torch or other open flame be used to remove paint. Whenusing heat to strip paint, be sure to provide adequate ventilation, properly protect skin and eyes, and wear arespirator designed for vapors. Take all precautions to protect workers from lead-paint exposure.

There are two commercially available applied-heat paint-removal systems for use on historicwindows: heat guns and heat plates. Heat guns will soften paint in only a small concentrated area,making heat guns good for removing paint in trim profiles and other tight spaces. A heat gun canbe used to soften and remove glazing compound only if certain precautions are taken to protectthe glass. When a heat gun is used near glass, carefully cover the glass with a piece of hardboardwrapped with aluminum foil. This measure will help reflect heat away from the glass and reducethe chances of localized overheating, which can crack the glass.

To facilitate complete paint removal, remove the existing sash from the frame. To do this, pryloose the stops and parting beads as carefully as possible so that the wood does not split. All partsshould be labeled and positions documented to ease reinstallation. If parts are damaged duringremoval they should repaired or reproduced to maintain the historic appearance of the window.Because window stop profiles have changed very little over the last 100 years, the variety of sizesavailable at many lumber yards will likely match the historic profile to be replaced.

Once the paint has been removed, revitalize the bare wood by rubbing it with fine-grade steelwool soaked in turpentine or mineral spirits and boiled linseed oil.

After the excess paint from the window frame and sash has been removed, it may be advisable totreat the surfaces with a wood preservative coating. Choose a commercially availablepreservative, taking care that it is compatible with the finish or paint system to be appliedafterward. Solutions containing copper arsenate, for example, give treated wood a greenish toneand are not approved for use by most government agencies.

Removing Paint from MetalWindows

NOTE ABOUT LEAD PAINT: In thefollowing treatment explanations, referencesare made to the removal of loose, flaking, andblistering paint finishes; during this processall precautions should be taken to protectworkers from exposure to lead-based paint.

Historic metal windows often haveaccumulated many layers of paint, which islikely to interfere with the proper operationof the window and is usually visuallyunattractive. Over time, partial peelingleaves a pitted surface that collectsmoisture. Excessive paint layers alsoobscure the shape of original moldingprofiles, which add definition to thewindow�s appearance.

The extent of paint removal requireddepends on the condition of the paint.Treatments for common paint conditionsfound on historic lighthouses:

� Chalked paint should be cleaned with a milddetergent solvent, hosed down, and allowed todry before repainting.

� Crazed paint should be sanded by hand or witha power sander before repainting.

� Peeling and blistering between coats should firstbe analyzed as to the source. If salts orimpurities have caused peeling, the defectivesurface should be scraped off and theunderlying surface hosed off and wiped drybefore repainting. If peeling or blistering wascaused by incompatibility of the paints orimproper application, scrape off the defectivesurface and sand the underlying surface toprovide a better bond with the new paint.Peeling, cracking, and alligatoring to bare woodrequire total removal of the defective paint,


followed by drying out of the wood substrateand treatment for any rotted areas beforerepainting.

Removing paint from metal frames and sashusually includes removing some built-upcorrosion and scaling. Use a wire brush,being careful not to damage the remainingglass or other surfaces. Particular attentionis required to remove rust buildup atconstruction joints and along the crackperimeter of the sash and frame. Becauseolder metal windows were typically primedwith lead-based paint, wear a respiratorrated for lead protection when using a wirebrush. An alternative to abrading thesurface, particularly when only lightcorrosion is present, is to use a liquid gelcontaining phosphoric, ammonium citrate,or oxalic acid. After the gel has beenbrushed on and has set, wipe clean and drythe steel substrate. Again, protectsurrounding materials, particularly masonryand glass, during all these procedures.After removing the paint, wipe the baremetal with a solvent such as benzene ordenatured alcohol to remove all chemicalresidue.

WARNING: Heat should not be used toremove paint from metal windows becausepossible distortion may result.

If corrosion is extensive, sandblasting maybe necessary. Remove the sash from theframe and the glass panes from the sash. Alow-pressure blast (80 to 100 psi) with smallgrit in the range of #10 to #45) applied withan easily controllable pencil blaster isrecommended.

Because corrosion begins as soon as thebare metal is exposed to the air, apply arust-inhibiting paint immediately afterremoving old paint. Two coats of zinc-richchromate paint as a primer arerecommended and the finish coat of paintshould be from the same manufacturer asthe primer to ensure compatibility.

Repainting

NOTE ABOUT PAINTING: The followingtreatments provide only general information.In preparing surfaces and applying paint,follow manufacturer’s specifications andguidelines included with the product (eitherdirectly on the label or as included literature)for more specific instructions.

The most time-consuming maintenanceprocedure is repainting windows. Carefulsurface preparation is the key to asuccessful job. In repainting woodwindows once the wood has beenpreserved and its moisture content reduced,select a paint that resists moisture butallows the wood to breathe. Steel windowsshould be primed with an anticorrosiveprimer and finished with a compatiblepaint.

A complex array of paint options have beendeveloped by the modern coating industry.Paints containing lead, used in the past onboth wood and metal windows, are nolonger readily available. Solvent- andwater-based paints used today are generallythicker in composition than the solvent-based paints used historically. Whenselecting a paint, seek assistance frommanufacturers or suppliers aboutcompatibility and methods of application.

When selecting a paint consider thesefactors:

� drying and recoating time

� coverage

� environmental factors, such as toxicity andflammability

� color and gloss durability

� moisture permeability (in wood windows)

� expected service life

� compatibility with window putty

� tolerance to adverse weather conditions

� adhesion between contacting surfaces

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Wood Windows

The earliest water-based paints, now oftenreferred to as latex, were developed for useon interior surfaces and performed poorlyon exterior surfaces. For wood windowsexterior water-based vinyl acrylic paints aregenerally more compatible with existingpaint layers containing lead and providebetter moisture permeability than water- orsolvent-based alkyd paints. If the paintlayer is impermeable, it may trap water thatpenetrates past the paint film. Alkyd paintsavailable in flat, semigloss, and glossfinishes are fast drying, flexible, resistant tochalking, and retain color and gloss well,but are incompatible with existing paintlayers containing lead.

Metal Windows

Before painting, pits that were created bycorrosion should be filled by melting steelwelding rod into the pits; then grind flushor use a steel-based epoxy than can beground or sanded flush with thesurrounding material. After the voids havebeen filled, all bare metal surfaces shouldbe wiped with a solvent-metal-preparationsolution. This will remove any chlorides(salt deposits) that may have settled on thesurface from the sea air as well asmicroscopic rust or corrosion that may havestarted to form. All bare metal surfacesshould be coated with a corrosion-inhibiting primer. A solvent-based alkydpaint rich in zinc or zinc chromate isgenerally recommended as a primer forsteel windows along with two impermeablealkyd finish coats.

Caulking and Glazing Compounds

Caulking and glazing compounds are usedto seal a window�s nonoperable joints.Because their expected service life variesfrom 5 to 30 years when the window unit isproperly maintained, they are considered adisposable part of the window system and

therefore receive periodic maintenance.Replacing cracked or missing compounds issomewhat complicated because newmaterials have been developed in recentdecades.

Most traditional caulks and glazingcompounds had a base of linseed oil, whichtended to became hard and brittle overtime. Today, more than a dozen genericcompounds are commercially available tofill seams and joints. Most are based onmore complex plastic and siliconecompounds and tend to remain pliant for alonger time, but not all are useful inwindow rehabilitation. Because ofwindows� exposure to temperatureextremes and the stresses that develop atthe joints where dissimilar materials meet,compounds should be durable, flexible, andresilient.

Caulking

Caulking is used to bridge the jointsbetween the frame and the windowopening. These should not be consideredstationary joints, for they are constantlymoving as the wall and window materialsexpand and contract because of changes intemperature and moisture content.Selecting an appropriate caulking alsodepends on the window material itself. Thedimensions of a metal window within awindow opening, for example, change lessthan a wood window does. Both, in turn,are more stable than an aluminum window,which has the highest coefficient of thermalexpansion and thus requires the mostsophisticated caulking.

When selecting caulking be sure toconsider the following:

� the material of the window opening (somecompounds do not adhere well to porousmaterials)

� the width of the joint to be sealed (somecompounds have a limited gap range)


� the season when caulking is to be applied andthe curing time (some of the better compoundsrequire extended periods of warm temperaturesabove 60o Fahrenheit)

� the caulking�s integral color range, oftenavailable by custom order

� its adherence to paint

Commonly used window caulks:

� Oil-based caulks: can seal joints of up to 1/2inch and are the least expensive, but can requireup to a year to cure and temperatures above40° Fahrenheit for application. They dry hardand can deform permanently. Not paintable.

� Butyl rubber caulks: can seal joints of up to 1/2inch, adhere well to metal and masonry, andcan be painted upon cure, but require extendedtemperatures above 40° Fahrenheit forapplication. They are subject to shrinkage, andsome degrade under exposure to ultravioletlight.

� Polysulfide caulks: can seal joints of up to 1inch, are flexible and resilient, but are moreexpensive. They require temperatures above60° Fahrenheit for application, as well ascareful surface preparation and application of aprimer over porous surfaces.

� Silicone caulks: can seal joints of up to 1 inch,are flexible and resilient even at lowtemperatures, and can be applied attemperatures as low as O° Fahrenheit. They arethe most expensive, have limited integral colorrange, cannot be painted in most cases, andrequire careful surface preparation andapplication of a primer over porous surfaces.Only special silicone formulations are paintable.

� Polyurethane caulks: used in some metalwindows, can seal joints of up to 3/4 inch, areflexible and resilient, and adhere well tomasonry. They require application attemperatures above 40° Fahrenheit, carefulsurface preparation, and application of a primerover most surfaces. Not paintable.

When caulking a window, carefully scrapeout the existing compound and residuebefore applying new caulking. If the joint islarge and deep, use a filler, known asbacker rod, to fill a majority of the void,leaving a gap for the caulk that isapproximately as deep as the gap is wide.

Then fill this gap with the caulkingcompound. Protect adjacent masonrysurfaces before caulking, since somecompounds will stain these materials.Review and strictly follow manufacturer�srecommendations and instructions.

Glazing Compounds

Glazing compounds are used to seal thejoints where the panes of glass meet themuntins and sash members in older, single-glazed windows. An oil-based putty istypically used on wood sash, whilespecially formulated glazing compoundsare used in steel sash. Most compoundsshould be protected by paint, but hardenwith age and rapidly deteriorate whenexposed to the elements. Sections ofdeteriorated glazing compound can oftenbe replaced without removing the sash fromthe frame. Complete replacement of thecompound, however, is best accomplishedwith the sash on a horizontal surface andthe glass removed.

Preparing the Sash

When completely replacing the glazingcompound, remove all deteriorated materialmanually by scraping, taking care not todamage the rabbet, where the glass ispositioned. During all operations takeevery precaution to protect the historicglass.

Wood Windows

If the putty or other compound hashardened in the rabbets, it can be softenedby applying heat. A heat gun may be usedif the glass is protected by a heat shield(hardboard wrapped with aluminum foil).A better heat source is a heat plate withonly a perimeter element and a built-in heatshield that is designed for the purpose ofsoftening putty in wood windows. Beforethe glass panes are replaced, the surfaces ofsash members should be prepared. Cleanand finish bare surfaces of wood sash by

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rubbing the surface with a fine-grade steelwool or a fine grade of high-qualitysandpaper, and then apply a solution ofequal parts of boiled linseed oil andturpentine. Finally, prime and repaint.

Metal Windows

First, carefully remove all damaged glazingcompound and the mounting clips thatretain the glass pane. This must be donemechanically. Do not use applied heat,which may cause the window frame todistort. Use a wire brush or, for moresevere conditions, a pencil sand blaster atlow pressure (80-100 psi) to remove anycorrosion. Paint all surfaces with a solvent-based alkyd paint rich in zinc or zincchromate as an anticorrosive primer. Thenapply two coats of a compatible,impermeable alkyd-finish top coat.

Setting the Glass

With wood sash and most steel sash, applya thin bed of putty along the inside face ofthe rabbet. This process, known as back-puttying, provides a tight seal andprotective cushion for the glass. Insert theglass, replace glazing points (in woodwindows) or retaining clips (in metalwindows), and putty the exterior face in aneat triangular bead. For metal windows,use only a glazing compound designed formetal windows. For wood windows, useeither a linseed-oil putty that is thickenedwith commercial whiting or a pre-mixedglazing compound. Paint the glazingcompound only after it has completelycured. When painting, allow the brush tooverlap and drag slightly over the glass toform a durable seal.

Repairing Damaged orDeteriorated Windows

Window repairs, such as splicing newwood, fitting dutchmen, consolidatingwood sections, welding steel sections,

bending steel sections, replacing glass (seeprevious section on glazing compounds),and adjusting hardware are generallyperformed as needed during the course ofmaintaining a building. Such repairs greatlyimprove the performance of older windowsby returning them to an operable condition.

Splicing and Dutchmen

Deteriorated portions of wood windows canbe effectively repaired using like-kindsplices or dutchmen. Splicing of a woodmember is required when a portion of thewindow, i.e., a frame rail, has beendamaged or has deteriorated and only thatportion needs removal and a new sectionattached in its place. All deterioratedmaterial should be removed, and the endwhere the replacement member will beattached should be cut on a diagonal toincrease the gluing surface area. Thereplacement member should match theexisting members in grain orientation andin any existing shape or profile. The newmember can even be made from matchingsalvaged stock. To attach the new member,

Figure 10. Close-up of a recently restored replacementmetal window at Cape Hatteras Lighthouse. Now that therepair work is done, all that this window needs is thehardware lubricated and periodic maintenance to remain inoperable condition for the next 50 years. At the time of thislighthouse restoration, it was discovered that the originalwindows were not repairable and funds were not availableto replicate the original cast-iron frame design. Theoriginal windows were more like a shutter, constructed intwo parts, hinged at both sides and meeting in the middle.The new landing windows were installed as a temporarymeasure until additional funds are available.

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probe the deteriorated area to determinethe approximate depth of the deterioration.Second, cut a wood patch or dutchmanwith its grain aligned with the existingmember�s. The dutchman can berectangular or diamond shaped. Bothshapes will work; however, a diamondshape is a little more difficult to fit but willprovide more gluing surface and blend withthe grain better if the window is finishedwith varnish instead of paint. Be sure thedutchman is large enough to cover theaffected area and thicker than thedeterioration is deep. Slightly bevel all ofthe edges of the dutchman so that thewidest face is the top. This will ensure atight cork-like fit. Next, trace the outline ofthe dutchman�s narrowest face on theexisting member over the deterioration.Using the outline as a guide, carefullyremove all of the deteriorated wood with achisel. Test-fit the dutchman, and trim thehole until the dutchman bottoms out andfills the affected area entirely; the dutchmanshould be slightly higher than the existingmaterial. Glue and clamp the dutchman inplace. Once the glue has cured, use achisel or hand plane to make the dutchmanflush with the surrounding material. Handsanding can be used for the final leveling ofthe two surfaces.

Figure 13. Close-up of a dutchman repair (light-coloredwood used to mend a window muntin).

cut the end diagonally to match the existingmember; then drill aligned holes in bothmembers for reinforcing dowels.

A �dutchman� is a fitted patch in a woodmember that has only localizeddeterioration. To fit a dutchman, first

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Figure 11. Example of a metal casement window in alighthouse dating from the 1870s

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Figure 12. Close-up of severely deteriorated bottom rail ofthe same window in Figure 11. This condition can berepaired by splicing a new piece of sash

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WINDOWSPart IV. E,

twisted or warped, as when the surfaces ofsills, lower portions of the frame, andbottom rails of sash have become erodedbut have not cracked or split. Filling andconsolidation of most frame members isperformed in place, while sashconsolidation is usually done in a shop.

When only wood surfaces are eroded, voidscan be eliminated by applying a paste orputty filler. Apply fillers after the wood hasdried and has been treated with a fungicideand a solution of boiled linseed oil.

In cases where a limited amount of rot hasprogressed well into the substrate, interiorvoids are filled in by saturating the woodwith a penetrating epoxy consolidantformulated for wood. Surface voids, as wellas decayed or missing ends near joints, arethen filled or built up with an epoxycompound. When sash are in such poor

Figure 14. A wood windowsplice repair. (Illustration byEric Ford, WPTC)

Epoxy, Fillers, and Consolidants

NOTE ABOUT EPOXY, FILLERS, ANDCONSOLIDANTS: Epoxy treatments areirreversible, may not be approved forNational Historic Landmark structures, andshould be used only after a careful study hasbeen made of more traditional repairtechnologies such as splicing and dutchmen.Some epoxy, filler, and consolidanttreatments require training in the applicationof the system. Individuals not familiar withthe use, effectiveness, and results of thistechnology should be trained in its use beforefield application.

Wood Windows

Repair of deteriorated wood sash and framemembers is possible where there has beenloss of material. It should be considered aprimary option when joints have not


condition that they require consolidation,puttying and painting are typically alsoneeded. Moreover, the joints connectingstiles and rails are likely to have becomeloose. After the glass and paint in affectedareas have been removed, the sash isplaced in a jig on a horizontal surface.Separated corners should first be repairedby pulling the joints together with a pipeclamp, drilling holes through adjacent stilesand rails, and securing each joint with ablind dowel. Rotted, missing, or erodedsections are then treated with the saturatingepoxy, allowed to cure, and resurfaced withthe epoxy paste. Surfaces are then sandedand painted as required.

Splicing and Bending Metal Window Parts

Damaged or severely corroded metalwindow sections can be removed andmatching sections welded into place. Somerolled steel window stock is stillmanufactured or can be located inarchitectural salvage yards. Depending onthe extent of deterioration, this repair canbe done in situ or the sash may be removedand repaired in a shop. Because specialskills are required for this type of repair, acertified window repair contractor shouldbe consulted.

Deformed windows can be reshaped bygently applying pressure in the right

location. This process may take a few daysto complete. Depending on the extent ofdeformation, this repair can be done in situor the sash may be removed and repaired ina shop. Because special skills are requiredfor this type of repair, a certified windowrepair contractor should be consulted.

Adjusting Hardware

Properly cleaned and adjusted hardwarewill greatly extend the operable life ofwood or metal windows. For routinecleaning use fine steel wool or a fine brass-wire brush and a cleaning solvent. Allmoving parts should be lubricated with anoncorrosive lubricant.

Limited Replacement In Kind

Windows are character-defining features ofthe historic lighthouse. Replacement ofexisting historic sash, no matter itscondition, is a last-resort treatment.Replacement is usually the most expensivealternative and results in total loss ofhistoric fabric. Replacement may beconsidered only if the historic sash aremissing or too deteriorated for repairtechniques. This decision should be madeby a preservation professional such as ahistorical architect, engineer, or facilitymanager trained in preservation.

If replacement windows are put in a historiclighthouse, they should match thecharacteristics of the historic sash: numberand size of lights, muntin width and profile,stile and rail dimensions and profiles,setback in window opening, and window-frame size and profile. For moreinformation refer to NPS PreservationBriefs: 9, 13, 16, 17, and 18.

Use the following as a guide whenconsidering window replacement:

� Always keep replacement to a minimum.Where sash replacement is called for, attempt toretain the window frame, hardware, and trim.

Figure 15. This window sash frame was repaired withtraditional (replacement wood hammerhead key) andmodern epoxy filler (material to left and right of thehammer head key) techniques.

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WINDOWSPart IV. E,

� Replacement may be the only feasible optionwhen substantial structural damage to a windowhas occurred. Choose a replacement windowwith particular care. Ideally the new windowshould be an exact match of the old one. If thisis not possible, carefully consider all of thewindow�s characteristics, both interior andexterior, and its importance in the facade, whenselecting a replacement.

� When a window is deteriorated to the pointwhere it is no longer weathertight, the openingmay be temporarily blocked in a manner whichdoes not damage the historic window features.Reference the previous mothballing section forsensitive window blocking methods designedfor historic windows.

For more information on the replacement oflighthouse windows refer to Part V.,Beyond Basic Preservation.

historic lighthouse preservation: windows · architectural style upon which the ornament of the...

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