EPOXYWORKS Number 18, Fall 2001 1 of 3

Wood/epoxy composite tank guidelinesBy Patrick Ropp

Builders have successfully constructedtanks for potable water, sewage, graywater, ballast and diesel fuel tanksand a limited number of gasolinetanks using WEST SYSTEM epoxysince the early 1970’s. The regulatoryenvironment has evolved within thelast thirty years and has placed safetyrestrictions on various aspects of tankbuilding, specifically potable waterand gasoline.

U. S. Coast Guard (USCG) regula-tions, Food and Drug Administration(FDA) regulations, American Boat &Yacht Council (ABYC) standards, andinsurance restrictions should be care-fully considered by anyone, profes-sional and homebuilder alike,planning to build a composite tank.Tank construction material and con-struction processes have been investi-gated thoroughly over the years, andthe lowest grief option is choosing acertified tank from a manufacturer.Certified fuel tanks have already beentested in accordance with strict fireand flame regulations, and haveproven themselves in the field. Certi-fied potable water tanks have beenmade to minimize or eliminateextractives.

While professional builders are boundby tough USCG regulations andABYC standards regarding tanks,backyard-boat builders have the op-tion to follow or disregard them.However, if the builder decides to sellthe boat, the federal regulations be-come applicable because he/she hasbuilt the boat for the purposes of sale.A good reference for individualsbuilding boats for their own use andnot for sale is Safety Standards forBackyard Boat Builders,

COMDTPUB P16761 3B, availablefrom. USCG Headquarters or its website. (See resources at the end of thisarticle.)

Before using Gougeon Brothers’products in tank construction, we ad-vise that customers review the rele-vant federal, state and local safetyregulations, standards, and recom-mended marine practices, as well ascontacting their insurance carriers forrestrictions. A wood/epoxy diesel fueltank may be an uneconomical choiceif insurance premiums increase or ifstate licensing/federal documentationproblems are encountered.

Wood/epoxy tank construction

Once the epoxy leaves our shippingdock, Gougeon Brothers cannot con-trol how the epoxy will be used.Some customers will use, and haveused, the epoxy to build all types oftanks. For those who decide to pro-ceed with making tanks, here aresome guidelines to help make the pro-ject as successful as possible. The keyto a durable tank is a thick,well-cured epoxy coating. To mini-mize long-term performance prob-lems, we recommend the following:

1 Coat all interior surfaces with 5or 6 coats of rolled epoxy

The inside of the tank should betreated similar to the outside of a hull.We recommend a minimum of 20-milcoverage, which is five or six rolledcoats of epoxy, for all interior surfacesof tanks. This is similar to the cover-age recommended as a “barrier coat”for the exterior of a hull. After it isrolled on, brush the epoxy out tominimize any entrapped air. Install

surge baffles to minimize free surfaceeffect, using generous fillets and giv-ing them the same 5-6 coats of epoxyas the rest of the tank interior.

Any tank openings, such as fill, vent,inspection or clean out, should beoversized and also receive 5-6 coats ofepoxy. We recommend that fastenersbe epoxy bonded in place to secureany hardware to the tank or in theconstruction of the tank (See detailsof hardware bonding in the WESTSYSTEM User Manual & ProductGuide.)

2 Use a slightly resin-rich/hardener-lean epoxy mixture

Carefully metered resin/hardener ra-tio is critical to any epoxy’s perfor-mance. In all projects, with oneexception, we recommend dispensingand mixing epoxy at the target ratiowithin our acceptable range. Tankbuilding is the exception to the rule.When mixing epoxy for tank coat-ings, we recommend a resin-rich/hardener-lean mixture at the outerlimits of the acceptable range asshown in Table 1.

This is because excess resin in epoxy isless likely to adversely affect the phys-ical properties of cured epoxy thanexcess hardener. When excess hard-ener is in the epoxy matrix, it cannotfully react with the resin and will be-come suspended in the mixture. Be-cause amines (in the hardeners) arewater soluble, they can potentiallyleach out and cause odd tastes, con-taminates in the liquid, and porosityin the epoxy film, among other per-formance defects. The maximumresin-rich ratios noted in Table 1 areat the end of acceptable ranges for

Building tanks

with WEST SYSTEM® epoxy

When it comes to boats, WEST SYSTEM

epoxy is unbeatable at keeping liquids out.

It makes sense that it would work just as

well at keeping liquids in. If only it were as

simple as turning a boat inside out.

EPOXYWORKS Number 18, Fall 2001 2 of 3

WEST SYSTEM epoxy. These ratiosshould not be taken any farther fromthe target. These maximum resin-richratios meet specification to obtain aproperly cured epoxy film and tominimize extracts leaching out of theepoxy. When using 300, 301 or 303Mini Pumps, one way to obtain theresin-rich/hardener-lean ratio withinthe acceptable range is to dispense thefollowing:

Epoxy Combination Pumps PumpsResin Hardener

105 Resin +205 or 206 Hardener 6 5

105 Resin +207 or 209 Hardener 7 6

3 Mix thoroughly, using adouble-pot method

We recommend using a double-potmixing method when building orcoating tanks. Completely thoroughmixing of epoxy is difficult to achievewhen resin and hardener are pumpedand mixed in one container. A film ofresin or hardener will cling to the bot-tom or side of the container leavingareas of unmixed or under-mixedcomponents. This can be readily seenwhen tinted epoxy is mixed together.

To ensure thorough mixing, first dis-pense and mix resin and hardener inone container, carefully scraping thesides and bottom. Scraping is key be-cause it incorporates the majority ofthe single components into the mix-ture. Second, transfer this mixed ep-oxy into another clean mixingcontainer. Use a new stir stick to mixa second time. This transfer will elim-inate any clinging unmixed materialand additional mixing will assurethorough cross-linking of bothcomponents.

4 Post cure at an elevatedtemperature

Post cure at a minimum of 120° F for 4to 8 hours (after the epoxy has cured atroom temperature and can no longer bedented with your thumbnail). You canuse a temporary oven or radiant heaterto apply an elevated temperaturepost-cure. A high-wattage incandescentor halogen light bulb can raise the tem-perature in a tank high enough to do thejob. This is often the only way to do anintegral tank. However, watch the firehazard as some light bulbs can get hotenough to cause the epoxy to char orpossibly ignite.

5 Scrub cured epoxy thoroughlywith water

Scrubbing with water and a scour-ing/abrasive pad, such as 3M’s ScotchBrite™ pad, removes any surface con-tamination, specifically any potentialamine blush that may form on thesurface. Amine blush is water-solubleand can be removed with tap water.The scrubbing action agitates the sur-face to help removal. Solvents don’tnormally remove the amine blush be-cause of its water solubility. So leavethe lacquer thinner, acetone, vinegar,alcohol, and other solvents in thestorage bin, and use water. Afterscrubbing, rinse again with water anddry with paper towels.

Considerations for holding tanks andgray water tanks

Sewage holding tanks are Type III ma-rine sanitation devices (MSD) and areregulated under Title 33, Code of Fed-eral Regulations Part 159 (33 CFR159)-Marine Sanitation Devices. A TypeIII MSD is considered a certified tank ifit (1) is used solely for the storage ofsewage and flush-water at ambient air

pressure and temperature, and (2) pre-vents the overboard discharge of treatedor untreated sewage or any waste de-rived from sewage (33 CFR 159.3,159.12a, and 159.53). Type III MSDsmay not be labeled. For Coast Guard In-spected vessels, the Type III MSD mustalso comply with 33 CFR 159.97. Forthe specific tank construction, make surethe internal surfaces are very smooth andthat all burrs or wood splinters are re-moved so they don’t cause anything tocling to the surfaces. This should help al-low the tank to be cleaned efficiently.

Type I and Type II MSDs are morecomplex systems and are beyond thescope of this article; refer to the Codeof Federal Regulations for guidance.

We know of no federal regulations orother standards regarding the manufac-ture of gray water tanks. Use the abovegeneral guidelines for construction andyou should not have any problem usingWEST SYSTEM epoxy.

Considerations for potable watertanks

We have adopted the broad policy of notrecommending epoxy for drinking watertanks because of regulatory and safety is-sues. The potential problems outweighthe benefits. To date, none of GougeonBrothers’ epoxies meet FDA regulationsor any other drinking water certified ap-proval. The major long-term concernwith any plastic water tank is extractivesleaching out in the water. Off-ratio,poorly cured epoxy can release extract-ives, as noted above. In the fabrication ofwater tanks and food handling equip-ment, the successful use of epoxy re-quires thorough mixing and adequateelevated temperature post-cure to assurethe maximum cross-linking and cure ofthe polymer. These process controls arenot always possible with the home-builttank. Unfortunately, neither GougeonBrothers, Inc. nor any certificationagency can verify the level of qualitycontrol exercised in the fabrication ofthe tank.

What about the builder who weighs therisks and decides to go ahead against ourrecommendation? For the homebuilder itis a personal choice. If you build a potablewater tank, follow the general guidelinesnoted above; in addition, you may want toinstall an in-line filter to help remove any

Resin/HardenerCombination

Weight Ratio Volume Ratio

Target Max Resin-Rich Target Max Resin-Rich

105/205 5.1:1 6.16 :1 4.7:1 5.68 :1

105/206 5.3:1 6.35 :1 4.7:1 5.58 :1

105/207 3.5:1 4.16 :1 3.1:1 3.69 :1

105/209 3.7:1 4.13 :1 3.1:1 3.50 :1

Table 1—Maximum resin-rich ratios

EPOXYWORKS Number 18, Fall 2001, ©2001 Gougeon Brothers, Inc., All rights reserved. 3 of 3

possible extracts and odd tastes. Profes-sional builders should understand, again,that there are no formal approvals(awarded or pending) for GougeonBrother’s epoxy products for use in pota-ble water tanks. Where certification is re-quired, it is usually application specific. Wehave looked at the 2000 Title 21 of theCode of Federal Regulations, Part 175.300(Food and Drug Administration, HHS)and found that the testing is specific forend-use conditions, container sizes, andfrequency of use. If you have a specific de-sign/use in mind, it may be appropriate tocontact the American or Canadian agencyto identify their requirements. As withmany things, the care used in the construc-tion of the tank is the key to the overallquality.

ABYC also has a section dedicated tothe general installation of potable wa-ter systems; the specific standard isH-23-Installation of Potable WaterSystems for Use on Boats.

Another great agency to get informa-tion from regarding potable watercoatings is NSF International, ThePublic Health and Safety Company.They are dedicated to testing and is-suing certifications of various coatingsand materials for public health andsafety. See their web site to find cur-rent products that meet their variousstandards.

Considerations for fuel tanks

Fuel tank building is a controversialarea. There are several USCG regula-tions and ABYC standards governingfuel systems. Because of gasoline’slower flash point, higher volatilityand combustibility, gasoline systemsare more regulated than diesel fuelsystems. These regulations are veryspecific and contain stringent require-ments for the fill systems, vents,installation, testing and labeling.

The USCG regulatory informationcan be obtained at USCG Headquar-ters and at each Coast Guard Dis-trict’s Boating Safety Division. Theguiding regulations for gasoline tanksin recreational boating are containedin Title 33 of the Code of FederalRegulations, Part 183.501 through183.590. The regulations may befound online at no charge or obtained

for a nominal fee from theGovernment Printing Office. TheABYC standards for gasoline systemsare found in Standard H-24-GasolineFuel Systems and H-25-PortableGasoline Fuel Systems.

Although the USCG doesn’t publishany regulations for recreational boatdiesel fuel systems, ABYC publishes awritten a standard, StandardH-33-Diesel Fuel Systems. It wouldbehoove customers to obtain a copyto ensure all safety precautions andrecommended practices are followed.

Conclusion

All types and variations of tanks havebeen successfully constructed withWEST SYSTEM Brand epoxy andused in the field with great results.However, Gougeon Brothers does notcondone or recommend that certaintanks be built because of various is-sues noted above. In our testing, vari-ous epoxy combinations have provento be resistant to various liquids, in-cluding gasoline, diesel fuel, motoroil, potable water, sea water, sewage,gray water, etc. Regarding gasolinespecifically, some epoxy combinationsare more resistant than others. Withthe increasing use of alcohol andother high-tech additives, we are un-sure how the epoxy will resist them inthe future. We do know that manytypes of alcohol vigorously attack ep-oxy; we can only conclude that gaso-line with a higher percentage ofalcohol may break down an epoxycoating over a long period of time.

Before building gasoline tanks andpotable water tanks, do your home-work and take into consideration theinformation above. The resources andvarious agencies noted should helpyou make informed decisions regard-ing tanks and whether or not youshould build your own. The final de-cision rests on the builder, and it is vi-tal that you make sound, educatedchoices. As always, please contact theTechnical Staff if specific questionsarise.

References and Resources:American Boat & Yacht Council3069 Solomons Island RoadEdgewater, MD 21037-1416

phonel: 410-956-1050fax: 410-956-2737info@abycinc.orgwww.abycinc.org

Food and Drug Administration:

5600 Fishers LaneRockville, MD 20857-0001

www.ac-cess.gpo.gov/nara/cfr/waisidx_00/21cfr175_00.html

Government Printing Office

Code of Federal Regulations:

Superintendent of DocumentsAttn: New OrdersPO Box 371954Pittsburgh, PA 15250-7954

Customer Service: 202-512-1803

Internet accessFuel Tanks:www.ac-cess.gpo.gov/nara/cfr/waisidx_00/33cfr183_00.html

Marine Sanitation Deviceswww.ac-cess.gpo.gov/nara/cfr/waisidx_00/33cfr159_00.html

Fuel tanks for USCG Inspected Vessels (d GT):www.ac-cess.gpo.gov/nara/cfr/waisidx_00/46cfr182_00.html

Gougeon Brothers Inc.

PO Box 908Bay City, MI 48707-0908

phone: 989-684-7286fax: 989-684-1287www.gougeon.comwww.westsystem.comTS@gougeon.com

NSF InternationalPO Box 130140789 N. Dixboro RoadAnn Arbor, MI 48113-0140

phone: 734-769-8010toll free (USA): 800-NSF-MARKfax: 734-769-0109www.nsf.org

U.S. Coast Guard

Commandant (G-OPB-3),US Coast Guard,2100 Second Street, SW,Washington, DC 20593-0001

phone: 202-267-0984USCG Infoline: 800-368-5647www.USCGBoating.org

Recreational Boating Safety

Safety Standards for Backyard Boat Builders,COMDTPUB P16761 3Bwww.uscg.mil/d8/mso/louis-ville/WebStuff/comdtpubp16761_3b.pdf�