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Making good and finishing

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INTRODUCTION

Published by British Cement Association Century House Telford Avenue Crowthorne BerksRGll 6YS Telephone 0344 762676 Fax 0344 76 1214

45.208 First published 1993 ISBN 0721014402

Price group AB

British Cement Association 1993

All advice or information from the British Cement Association is intended for those who will evaluate the signillcance and limitations of its contents and take responsibility for its use and application. No liability (including that for negligence) for any loss resulting from such advice or information is accepted. Readers should note that all BCA publications are subject to revision from time to time and should therefore ensure that they are in possession of the latest version.

The eleven booklets in the Concrete on site series are updated replacements for the well-known Man on the job publications, which were first issued in 1968, and became the standard guides on concreting for site personnel.

The titles of the Concrete on site booklets are listed on the back cover. The scope ofconcreting operations featured is similar to the original series except that, as most site concrete is now supplied ready-mixed, the series no longer deals with site mixing or the selection and testing of materials for concrete.

The Technical Consultant for this series was Tony Binns and the Editor was Bob Tattersall.

SAFETY ON SITE When Portland cement is mixed with water, or even becomes damp, alkalis are released that can be harmful to the skin. The effect depends on the length ofcontact, any abrasion, the individual, and the part of the body involved. Suitable protective clothing should be worn. If eyes are affected they should be washed out immediately and medical attention sought.

Many construction activities are potentially dangerous so care is needed at all times. Current legislation requires all persons to consider the effects of their actions or lack of action on the health and safety of themselves and others. Advice on safety legislation may be obtained from any of the area offices of the Health and Safety Executive.

Making good and finishing CONTENTS Making sure of a high-quality finish 2

To make good or not? 3 Colour matching 3 Controlling suction 3 Bonding 3 Curing 3

Mixes for making good 4 The mixes to use 4

Blemishes you might have to deal with 4 Grout runs 4 Lippingat joints 5 Grout fins 5 Arrises 5 Bolt holes 5 Blow-holes 7 Sandy texture 7 Honeycombed areas 7 Exposed aggregate 8

How it works out in practice 9 Making good and finishing fair-faced concrete 9 Remedial work to board-marked concrete 10

Tools and materials 12 Further reading 12

MAKING GOCI) ANt) FINISHING 1

Making sure of a high-quality finish Ifyou are working on a project in which the ultimate appearance of the concrete is important, right from the start you should spend time and care on achieving a high- quality finish.

It is wrong to rely on later remedial work to disguise defects and blemishes. Such making good, as it is known, is time consuming, and therefore costly. More importantly, it is seldom completely successful.

So what steps must one take to avoid surface defects Quite simply, top quality finishes demand a concrete that is properly proportioned, properly mixed, properly placed and compacted in well designed and well made formwork, then thoroughly cured. In short, a high standard ofworkmanship is required at all stages.

Unfortunately, even with the best intentions, mistakes can sometimes occur, and the surface of the concrete will need to be made good. Here, too, care must be taken, for poor workmanship and the use of the wrong materials can produce a remedy that is worse than the original fault.

That is where this booklet comes in, for it describes and gives guidance on the cement- based products and techniques that have been found satisfactory for remedying most of the common defects and blemishes that occur during construction.

Repairs and techniques using epoxide resin and similar materials are not dealt with. If you wish to use proprietary products based on them, you should seek the guidance of the manufacturers.

Where a high-quality finish exposed to view is required including textured (e.g. board- marked), exposed-aggregate and plain smooth surfaces making good will be necessary on

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honeycombed areas and tie-bolt holes in order to ensure durability. And the patching must be as indistinguishable as possible from the rest of the area. Other blemishes, such as excessive blow-holes and sand streaking, will also require making-good, so that the final appearance is reasonably uniform.

For surfaces that will not be visible perhaps because they will later receive a decorative treatment, or be covered by applied finishes blemishes such as blow- holes, sand streaking and lack of colour uniformity are not important. The sole objective is to achieve a repair that will be durable and protect the reinforcement, so making-good can be restricted to honeycombing and tie-bolt holes.

Surface blemishes that need to be made good: a. Honeycombing b. Large blow holes c. Grout loss d. Grout runs

To make good ... or not? Everybody agrees that the making-good of honeycombed areas and the filling of tie-bolt holes are essential.

But should such blemishes as blow-holes and sand streaking be treated? There are conflicting views on this question. In coming to a decision on your site, you should bear in mind the following points. Plain, unblemished concrete of uniform colour is extremely difficult to obtain with any certainty. The best that can be achieved may well fall short of what the client expects. Acceptance of this fact, plus a willingness to compromise on the part of everyone involved, are therefore desirable. Blemishes that are small in number and extent as a proportion of the total area are often best left untreated. Defects that maybe unsightly if looked at from one or two metres may be less or not at all noticeable from further away. So never inspect a concrete finish from closer than the distance from which it will normally be seen. This applies particularly to buildings higher than two storeys. In fact, it is a good rule never to check a surface finish from closer than three metres unless it will regularly be seen from closer than that. It is easier to achieve uniformity of colour with white, than grey, concrete.

Any patching or making good, no matter how well done, is unlikely to match the

surrounding concrete perfectly. So the techniques recommended in this booklet generally call for a subsequent overall surface treatment of the affected area to mask any localised repairs you have carried out.

In the pages that follow we give advice on methods and materials to be used for making good and finishing. In some cases, it may be necessary to use a combination of two or even more of them. COLOUR MATCHING As already pointed out, it is difficult to match the colour of any patching or making-good with that of the surrounding concrete. True, you can get a good match at the start by using the same materials in the same proportions as in the original concrete, or even adding a little white cement to the repair mix to achieve the same tone of grey.

But different curing conditions and slightly different surface characteristics brought about by the fact the patch is trowelled into place, whereas the concrete will have been cast against formwork can result in different weathering. As a result, the repair will become more obvious as time goes by.

The techniques and materials we describe have been developed with this in mind.

CONTROLLING SUCTION Cement-based repair mixes should never be applied to dry concrete, for it will absorb

moisture from the new mortar, and so prevent a good bond from being formed, thus reducing the quality and durability of the repair.

Areas to be made-good or finished should first be damped down to control any suction. This is done with clean water, preferably the day before, so that the surface is just damp when the repair is carried out.

BONDING A bond is likely to be more successful, particularly where the defective area is deep, if a bonding coat of cement and styrene butadiene rubber (sbr) is applied first.

The bonding coat must not be allowed to dry out before the repair mix is applied, so you should start to make good immediately.

CURING Just like the original concrete, cement-based repairs need to be properly cured. The method to be used will depend on the circumstances.

On concrete that will not be seen, one or two coats of bituminous emulsion, applied some two to three hours after the repair is complete, will be quite sufficient.

To cure small areas of repair, cover them with polythene taped down all round the edges, and left in position for at least seven days.

Larger areas should.be cured in the same way as the parent concrete. See No 6: Curing.

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For high-quality finishes, two mixes are required Mix A for patching, bolt hole filling and making good; Mix B for the finishing coat. Where a finishing coat is to be used to hide the making-good, both mixes must be of similar materials.

Keep some of the dry Mix B handy in case it is needed to stiffen the mortar slightly. This may be necessary when the original concrete surface is being exposed by rubbing back with the rubber-faced float as in the sketch on page 7.

Where surface finish is unimportant, no overall finishing coat will be required, and you will need just one mix for patching and making-good bolt holes. This is Mix C.

THE MIXES TO USE Mixes A, B and C are mentioned frequently in this booklet, so refer to this section when you need to use one. Mix A: Mix together Portland cement and dry crushed limestone sand, in proportions rangingfrom 1:1 to 1:2, depending on the colour ofthe surface to be matched. Mix a styrene butadiene rubber dispersion (sbr) with an equal amount of water. Add this gauging liquid to the mixed dry materials until a mortar ofjust- moist consistency is obtained. The mixing must be thorough, and is best done on a spot board, using steel trowels.

When you are aiming for a dark grey colour, a small amount of black pigment may be added.

Or use sulfate-resisting Portland cement, which is usually darker, instead of normal Portland cement.

For a light grey, add white Portland cement to normal Portland cement. The pro- portions will depend on the colour you wish to achieve, and they may need adjusting. Unfortunately, the colour can be judged only when the mortar has dried, so you will probably have to carry out trials. However, 3 parts white to 1 part of normal Portland cement is normal.

When cements are blended this way, 1 part of blended cement should be mixed with 1 to 2 parts of the aggregate. Mix B: This is again made with Portland cement and dry crushed limestone sand. Screen the fines through a sieve. For rougher textured finishes, a 600 micron sieve will usually be satisfactory, but for smoother finishes, such as those obtained from plastic-faced plywood, it is better to use a 300 micron sieve.

Make any colour adjustments to the cement needed to match it to Mix A, then mix cement and limestone in equal parts.

Dilute 1 part sbr with 3 parts ofwater in a bucket, and add the dry mixture, stirring well until a creamy mortar of brushing consistency is obtained. Mix C: Pass a sharp concreting sand through a 2.36 mm sieve, and add 2 parts sand to 1 part Portland cement. Mix sbr and water in equal proportions, and add to the dry mix to obtain a creamy consistency.

Blemishes

GROUT RUNS Grout or mortar will ooze out of imperfectly sealed gaps in formwork, and run down the face of the completed work.

If the surface will not be seen, then in general this does not matter. However, the run should be removed if the surface appearance is important

Ideally, the grout is best wiped off immediately, but you might not spot it in time. In that case leave it until it has become brittle enough to be removed by careful chipping with a piece of hardwood or a bolster.

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Mixes for making good

Grout leakage causes blemishes

Chippingoff excess grout

you might have to deal with There are places where grour

runs are nnt acceptable, even though surface appearance may not be important. One such place is the inside of a silo. Here, too, a hardened run can be cleanly removed by careful chipping without damaging the underlying surface, as already described. Or you can use grinding.

Never use grinding not even hand stoning where you want a good finish, because the surface of the surrounding concrete is likely to be affected by the scouring action.

LIPPING AT JOINTS If the formwork at a construction joint either horizontal or vertical has not been properly tightened on to the hardened concrete of the preceding pour, grout runs are likely, and there may as a result be lipping, sandy areas and slight honeycombing.

As with other minor blemishes, such faults do not usually require any treatment where appearance is not important.

For high-quality finishes, though, it will be necessary to cut back the lip, tapering it to suit the scale of the defect. Patching and finishing can then be carried out.

GROUT FINS Grout oozing out of leaking joints, either between or within individual sections offormwork, can cause fins as it hardens. Such fins may be considered a

desirable feature on board- marked surfaces, but elsewhere they are usually unwanted. Even so, if they are not objectionable at a distance of up to 3 m, they are best left untreated, especially if they are narrow, and do not protrude more than, say, 2 mm.

Where there is loss of water .rhrough the joint, a darkening of the surface usually occurs, too. And a more severe leak might cause a sandy-textured surface, some 5 mm or more in width and running along the length of the faulty joint.

If the decision is taken to chop off the fin, do so with a hammer and bolster held at an angle to its root , so that it comes away cleanly. This removal may cause a line of sandy-textured concrete to be left behind. Should this be no more than 2 mm wide, it is usually best left untreated.

However, if the fin was accompanied by surface darkening and a wider sandy- textured area, it should be disguised, using treatmeist similar to that given under the heading'Where appearance is important on page 7.

An alternative technique is to use a fine-grained carborundum stone, but there is a danger that it could scour the adjacent face of the concrete. However, if you start immediately after striking, while the concrete is still green, you may achieve some blending of colour by carefully filling-in the sandy texture with cement paste worked up with the carborundum stone.

control suction, then make the repair with Mix A, adjusted for colour.If the resulting match is not good enough, see Where appearance is important on page 7.

BOLT HOLES As with all making-good, it is almost impossible to fill bolt

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ARRISF.S Chipped or spalled arrises and corners, caused by accidental knocks or careless removal of formwork, are difficult to mend satisfactorily, particularly if the repair has to blend visually.

This could mean that small chipped corners and arrises (up to about 10mm long) ate best left alone since they will then be less conspicuous than if they are made good.

Should you decide on remedial work, a lasting repair calls for great care, especially in the preparation.

Begin by squaring off the edges around the perimeter feather edges must be avoided if a good bond is to be achieved.

Squaring off the edges

Damp down the area to

holes so that they merge-in with the test of the concrete. Even if you start off with a good colour match, the tepair mortar will tend to weather diffetently from the concrete and the parch will soon be visible.

Rather than telying on subsequent repairs, it is a good idea with exposed conctete surfaces to site the bolt holes in a predetermined pattern that can be made into a decorative feature.

There are two possibilities if this course is adopted. Firstly, you can recess the filling, leaving a series of small cavities that should all be of the same depth.

This method also has the advantage that the shadow it makes will draw attention away from the datk surround that water leakage will inevitably have caused round the perimeter of the holes.

Alternatively, if it is preferred to fill the holes flush, they can be picked out in a different colour. However,the drawback with flush filling is that the mortar might spread on to the adjacent

concrete and the repair will not then look so neat.

A small, improvised tool, made of a U-shaped length of metal attached to a hardwood block that acts as a handle, will help you to prevent this. The device is designed to hold the mortar as it is being pushed home, and to stop any excess from spreading.

Whether you fill the holes flush with the surface, or recess the filling, you must make sure that the filling will be durable and watertight. To ensure this, thoroughly clean out the hole by pushing a clean rag through it to remove any grease and loose material. Then damp down irs inside to control suction,

Make up a quantity of Mix A for the repair, if the appearance is important, otherwise you can use Mix C.

Fill the hole in a series of layers each no more than 25 mm deep. Ifyou tr to push in more than this at one go, the compaction will probably be incomplete. Press home the mix

using a hardwood or metal rammer that is a fairly loose fit with a diameter about 5 mm less than that of the hole.

With holes up to about 300 mm in depth, the filling and ramming can be done from one side only, with a piece of board held on the other side to act as a stop.

For recessed filling, use a purpose-made circular plug to push the mortar firmly home until the top of the plug is level with the surface of the concrete.

Thus the plug acts as a gauge to ensure that all the recesses are the same depth.

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Fillinga bob hole with a small rammmer

This improvised tool makes it easier tofillboltholes

Recessed ho It holes

Purpose-made plugfor recessed filling ofa ho It hole

When flush-filling where the appearance is not important but a smooth finish is required, leave the mortar slightly proud, then, once it has stiffened, level it with a suitable tool, such as a wooden float faced with sponge rubber. But if the finish does matter, strike off the filling flush with the surface, taking care not to spread mortar over the surrounding area. No attempt should be made to treat any dark rings or sandy- textured areas surrounding the hole, unless the whole unit is to be colour-matched as described later, in which case Mix A should be used for the filling, followed by Mix B over the whole area.

The mortar should be moist- cured for at least seven days. If a high-class finish is wanted, cover it with a piece of polythene taped at all edges. Where the concrete will not be seen, you need merely give the filling and its immediate surround a coat of bituminous emulsion.

BLOW-HOLES It is neither usual, nor necessary, to fill blow-holes if they are small and insconspicuous. But if they are larger than about 5 mm, and the surface is likely to be seen from closer than, say, 3 m, some surface treatment should be carried out.

Where appearance is not important Isolated blow-holes may be filled individually with mortar applied by a small trowel or, perhaps, a

putty knife. Alternatively, try stoning. Strike the formwork early while the concrete is still green, and rub the surface with a carborundum block, which will work up a mortar that can be pushed into the holes to fill them.

Another possibility is bagging-in. Fill the holes with a freshly mixed mortar pushed home with a piece of hessian rolled into a ball. Or you can apply mortar to the surface and rub it into the holes with a float faced with sponge rubber see sketch (right). Where appearance is important As with all making-good when a high-class finish is important, the objective is to stop-up the holes completely so that the filling will be durable, and, secondly, to achieve as close a match as possible with the parent concrete.

The following steps are recommended for achieving a high degree of colour uniformity after other making-good has been completed.

They are best carried out in overcast conditions, or in the late afternoon or evening. Never attempt in conditions of hot sunshine. Thoroughly damp down the surface. While the surface is still just damp, use a rwo-knot stock brush to apply a coat of Mix B, in a thick creamy consistency, over an area of about 1 m2. Use a wooden float faced with

sponge rubber to rub the creamy mortar into the surface of the concrete, working it well into the holes.

Make a dry mix of cement and crushed limestone sand in the same proportions as used for Mix B. Before the mortar in the holes has set, wet the sponge rubber face of the float, and use it to rub this dry mix over the entire surface. The mortar in the holes will then be stiffened, ensuring a flush, tight filling. Continue rubbing to remove all excess soft mortar until the original concrete is exposed. SANDY TEXTURE No making-good is necessary when the finish is not important. On important finishes, use the technique recommended for blow-holes in the previous column.

HONEYCOMBED AREAS Honeycombed areas of a depth greater than about 10mm should be made good.

Begin by cutting back to as uniform a depth as possible until you reach sound concrete. Do

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Stopping-up blow holes for a high-class finish

not cut deeper than any reinforcement you expose, unless the honeycombing extends beyond it.

Next, the perimeter to be patched should be carefully chiselled to give a clean sharp edge at least 10mm deep. It is essential that all exposed surfaces be clean and free from dust, especially in the corners. Clean them with a soft brush. The exposed surfaces should be damped down, and repairs left until they are almost dry.

Shallow repairs For repairs up to about 25 mm deep, a mortar maybe used, the type depending on the required finish.

Where finish is important, use Mix A, and punch it tightly home with suitable tools (normally a short length of hardwood and a club hammer). Make sure that all corners are completely filled, that no air is entrapped and that a good tight finish is obtained around the edges. Ifyou want a rough- board effect, rub back the surface with a float faced with sponge rubber; for a smooth finish use a steel trowel.

The patch should be kept damp until next day, when the whole area should be finished with Mix B as described later.

Deep repairs Thicknesses between approxi- mately 25 and 75 mm are best reinstated with a fine concrete (10 mm maximum-size aggregate). A number of

manufacturers produce suitable cement-based materials, batched dry and ready to mix with water.

Thicknesses greater than about 75 mm should be repaired using a mix similar to the orginal concrete, placing it behind formwork with a 'letter box' entry at the top.

EXPOSED AGGREGATE Exposed aggregate and abrasive- blasted finishes are usually a feature ofhigh-quality work, so they demand a good finish.

Any physical blemishes visible after the formwork is struck are likely to be accentuated rather than masked by tooling and abrasive blasting, but slight variations in colour maybe less noticeable after the removal of the surface skin.

There is little that can be done with shallow water-scoured surfaces, sandy-textured areas where grout and water loss has occurred, or blow-holes, other than to increase the depth of the texturing. This is likely to be very costly, and may reduce the reinforcement cover too much.

Shallow honeycombed and scoured areas, such as those in the sketch below, may be made good with Mix A, carefully adjusted to the colour of the original mortar or concrete. Rub in the mix with a float faced with sponge rubber, then cure it well for seven days before tooling or abrasive blasting.

Deeper honeycombed areas present more of a problem. It is recommended that they be cut back carefully to a depth of at least 50 mm. Then they should be filled with concrete of the same proportions as the orginal, but mixed to a stiffer consistency so that it can be tightly punched home and trowelled, particlar attention being paid to the joint lines. Allow the repair to cure for at least seven days, then wait a few more days before tooling or abrasive blasting.

Small areas that are a slightly darker colour or texture after tooling may sometimes be improved by careful hand pecking with a sharp pointed hammer.

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Letter box technique for repairing deep honeycombing Honeycombingca used by grout

loss

How it works out in practice So far we have outlined the methods and materials for making good the various faults that can develop in concrete work.

In this section we take a closer look at how things work out in practice on site, and offer some tips and suggestions.

MAKING GOOD AND FINISHING FAIR- FACED CONCRETE

The sketch shows part of a concrete wall after the formwork has been removed from the second lift. There are various defects and blemishes that have to be made good and finished to ensure a satisfactory job. Slight tipping and honeycombing along the line of the horizontal joint. Spatted and honeycombed arris in the second lift. The lipping on the end occurred because, as a check with a straightedge revealed, the end of the lower lift was out of tine. U Blow-holes. U Water scour this is more noticeable on the second lift.

Colour variations within the lower lift, and between the tifts.

It was thought best to tackle the making-good on one day attending to upping and honeycombing and then carry out the finishing work on the second day, treating the remaining items and reducing the prominence of the repair as a whole.

Procedure This is the procedure that should be followed for these repairs. There are eleven stages for making-good and a further six stages for finishing. Day one Making-good 1. Remove the grout runs below the horizontal joint with a coarse carborundum stone; alternatively, you could chip them ofiwith a hammer and bolster.

2. Remove the lip above the joint by bush-hammering. (Because in this case the lip was slight, it was feathered off over a distance of 50 to 75 mm; had

3. Cut back the broken and honeycombed arris with a hammer and bolster until sound concrete is reahed. 4. Bush-hammer the end below the joint to provide a good key for the later application of a dry- pack repair. The key should extend at least 150mm below the joint in order to improve the alignment between the two lifts. 5. Wire-brush the treated areas, then use a soft brush to remove any loose particles and dust still clinging to the concrete. Damp down the area, and allow to become almost dry before you proceed. 6. Make up a quantity of Mix A, but do not make it too wet; a stiff consistency is needed.

\IAKIN(, (001) ANI) I 1NI io 9

the tip been much larger, it would have been necessary to extend the bush-hammering higher up the second lift in order to fade it out.)

Continue bush-hammering, if necessary, to remove any honeycombing, and cut back the defective areas to sound concrete.

Defects in a concrete wall that need to be made good

Removing the isp above a joint by bush-hammering

Removing grout runs with a hammer and bolster (left) anda carborundum stone

7. Apply a bonding coat of sbr and cement to the prepared surfaces on the end and the arris. Immediately you have done this, fix and wedge a board along the line of the arris.

A bonding coat beingappliedby brush to the defective area

8. Whilst the bonding coat is still wet, force Mix A into the area to be repaired, using either a small trowel or putty knife. Finish off the repair flush with the surrounding surface, using a steel trowel.

9. Apply freshly mixed bonding coat to the honeycombed area,

and immediately force Mix A into the surface. Finish off flush with the surrounding concrete.

10. Fill the bolt holes by dry- packing with Mix A. 11. Lightly spray the repaired areas with clean water, and leave them overnight. Day two Finishing 1. Work over the entire surface with an abrasive disc to remove any projections. 2. Remove any dust with a soft brush. 3. Damp down the entire surface to reduce suction when the repair is applied. 4. Apply Mix B to the whole panel while the surface of the concrete is still damp. 5. Before the slurry dries out and stiffens, rub it with a rubber- faced float to fill small blow- holes and water-scour marks. Then rub it back to expose the original concrete surface. Scrape the float occasionally to remove excess slurry that might have collected on it. 6. When the finishing has nearly

dried out, spray it lightly with water, and cure it under

the leakage of grout along the line of the joint. There is also a slight amount of lipping.

The requirement is to improve the appearance of the joint, hiding the repair as far as possible. Because complete uniformity of colour and texture across a joint is virtually unattainable, it was decided to make a feature of the joint.

Only a relatively small amount of remedial work needs to be carried out here, so it is possible to combine the making- good and finishing operations. Where more needs to be done, it is better to make-good one day and tackle the finishing the next.

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polythene.

REMEDIAL WORK TO BOARD-MARKED CONCRETE

Using a steelfloat, MixA is forcedfrom a hawk into a honeycombed area

Defects you mightfindin a board-marked concrete wall

The main defect (see above) is

MxA is applied while the bonding coat is still wet. Use either a small trowel, as here, or aputtyknft Procedure

1. Remove dribbles by gently tapping them with a piece of wood (see sketch on page 4).

2. To help you to see the joint more clearly, draw a pencil line along it, using a straightedge as a guide. 3. Remove excess grout below the line with a bolster and club hammer (see sketch on page 9). 4. Working on only three or four boards at a time, damp down the surface with clean water to remove dust and reduce suction.

5. Honeycombed areas should be made good by forcing Mix A into the surface of the concrete.

6. Blend-in the treated area with the rest of the concrete by drawing a float faced with sponge rubber upwards. You should work on just one board at a time, making sure that you leave a false joint at the side of the board.

7. Apply Mix B with a soft brush to the lower and upper parts of the panel. This time, however, you should work over a wider area of, say four boards.

8. Holding a timber straight- edge along the line of the vertical

joint, apply the rubber-faced float to each board in turn, first to rub-in the slurry and then to remove excess mortar by rubbing back to the original surface. Careful dabbing of the float can reproduce realistic- looking board marks in the surface.

9. Fill the bolt holes by dry- packing with Mix A. Leave the holes flush, but as a feature as in the sketch below. 10. When the whole panel is finished, spray the surface with water, and cure under polythene sheet.

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Blending-in the treated area using afloatfaced with sponge rubber

Damping down with clean water

Rubbing-in the slurry. CareJIil d.abbing can produce board marking

Making-good honeycombed areas

App lyingMzx B with a soft brush

Thefinished result

TOOLS AND MATERIALS FOR MAKING-GOOD AND FINISHING

The following items are not always readily available on site, and may have to be ordered specially. Below is a list of suppliers. It was correct in June 1993, but there may have been changes since. Two-knot stock brush Bromley Brush Co (Kent) Ltd, 1 Pembroke Road, Bromley, Kent BR1 2TJ. Tel: 081-464 1707 Crushed limestone sand Tilcon plc, Ballidon Quarry, P0 Box 6, Ashbourne, Derbyshire DE6 1GU. Tel: 0335 25301 Sieves Endecotts Ltd, 9 Lombard Road, London SW19 3BR. Tel: 081-542 8121 F W Potter & Soar plc, Beaumont Road, Banbury, Oxon 0X16 7SD. Tel: 0295 253344 Ready-made floats faced with sponge rubber Concrete Tool Sales & Hire Ltd, Lowdham Lodge, Pole Hill Road, Hillingdon, Middlesex UB 10 OQE. Tel :081-848 8899

FURTHER READING

Styrene butadiene rubber dispersion (sbr) Builders' merchants

Materials and method for making a float, faced with sponge rubber 12mm medium-density sealed-face sponge rubber WMannering & Co plc, 64-66 Redchurch St, London E2 7DP. Tel: 07 1-729 4145 Marine-quality plywood Builders' and timber merchants Bostik D Builders' merchants and others Mount the rubber on marine-quality plywood, glucing it with Bostik D. Trim the rubber with avery sharp knife so that a straight, dean cut with sharp arrises is left. Do not leave either proprietary or self- made floats in water for long periods because they tend to distort.

Visual concrete: Design andproduction, byW Monks. 1988. Published by the British Cement Association. (Address on inside front cover.) The Control ofbemishes in concrete, by W Monks. 1981. Published by the British Cement Association. (Address on inside front cover.)

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