How to Fill Cracks in Brickwork and Concrete

Cracks often occur in a rendered finish (a sand and cement finish 10 to 15mm thick which is applied lo the external side of a brick wall). They may be an early warning that the rendering is starling to lose its adhesion tap the area around the crack and listen for any hollow sounds. In severe cases, you may need to patch render a considerable area of wall. If you ignore cracks in rendering, rain-water may soak down between the brickwork and the rendering, causing damp inside the house. Fine hair-line cracks can be covered up with masonry paint. Diy cracked wall repair kits are available for easy repair of cracks.

Larger cracks in brickwork can be filled with a mix of one part of cement to three parts of builders” sand by volume (small quantities can be purchased ready-mixed) or with Commercial Epoxy or a cement-based ready-made filler.


First, clean any loose material out of the crack by gouging down it with a suitably shaped metal tool – a triangular paint scraper, say. If you suspect poor adhesion but you cannot pull the rendering away from the wall with a scraper, carefully knock it away with a hammer and cold chisel (ideally you should use a club hammer and bolster). Thoroughly mix the sand and cement and add water to make a wet paste just dry enough lo retain its shape. Brush water into the crack and wet it thoroughly (unless the instructions on the filler pack warn against this) and then pack in the filler using a filling knife. You should use a wallpaper scraper (or any other flat-edged tool) but a filling knife has a narrower and more flexible blade and makes the job easier. Make sure that you press in the filling material as tightly as possible. With deep and narrow cracks push the filler down into the crack to avoid making a bridge. Fill wide deep cracks in stages, using a depth of filler around 10 to 15mm each time. If possible, allow the filler to dry for two to three days between coats.

Fill Cracks in Brickwork

Make sure you leave a smooth finish to the final coal as these fillers set too hard to rub down. You can do this by leaving the filler flush with the original surface and then running the wet fiat edge of a filling knife along the filler.

Rendering which has cracked away from the external corner needs special treatment. Clean the crack and attach a wood batten vertically so that one straight edge lies along the corner. You can use masonry nails but do not knock them in too far as they will have to be removed later. Mix the filler, wet the area and apply the filler up to the edge of the wood batten. (If a large area has to be filled then use a rendering trowel instead of a filling knife.) Finally, finish off as before. Once the filler is bard, gently remove the wood batten and fill the other side of the crack.

Before painting over the filler, it should be left for a week to dry out and then given two coats of alkali-resisting primer or masonry paint.

Filed Under: Home & Maintenance


About the Author: Jason Prickett loves to write about home maintenance and stuff you can do yourself instead of hiring any professional. His step by step guides will assist you in completing your home maintenance tasks.

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