How to Repair Cracked Masonry and Brickwork

Never ignore substantial cracks across large areas of brickwork, particularly if the brick, rather than the surrounding pointing, is cracked. This can indicate serious structural problems, such as subsidence, so consult a builder or local authority building control officer. If a crack is stable, you can repair it yourself.

Remove cracked mortar and then repoint the area in the usual way. If one or more brick is cracked through the middle, use a club hammer and cold chisel to remove and replace the brick. Follow the same steps for replacing a spalled brick.

Cracks running across a rendered or painted exterior wall should be filled with mortar mixed with a PVA bonding agent. This helps it to stick and also gives it some elasticity to move with the buiding (all buildings move slightly, to some extent.) Before repairing the crack, moisten the damaged masonry with a hose to help the mortar get deep into the crack.

Waterproofing Masonry and Brickwork

Use a colorless water repellent fluid to protect your masonry and brickwork. These moisture repellents will make your bricks and masonry impervious to water but will allow them to breathe.

Prepare the brickwork and masonry by repairing cracks and damaged areas. Apply the repellent generously and take care to stipple it into any joints. Apply a second coat as soon as the first has been absorbed.

Render and Brickwork Repair Guide

Exterior brickwork and stonework is often clad in textured render (a cement/sand coating). Rain, damp or frost can all damage render, causing cracks, stains and bulging. Prompt repairs to render will dramatically improve the final finish and also help to weatherproof the render and prevent further damage.

How to Repair Cracks and Bulges in Render

Before repairing a rendered wall, prepare the surface thoroughly by making good any damage and cleaning off any dirt or mould growth.

Rake out cracks with a cold chisel, dampen them with water and then fill them with an exterior filler. Repair larger render cracks with a mixture of one part cement, two parts lime, nine parts builder’s sand, and a dash of PVA bonding agent.

Bulges in render indicate that the cladding has come away from the stonework or brickwork. Assess the extent of the bulge by tapping it gently with a wooden mallet. Hack off render around the hollow areas and brush out the debris. Apply a coat of PVA bonding agent and, when this becomes sticky, trowel on a half-inch thick layer of render. Leave this to set properly. Once dry, scratch it with a chisel to form a key and then apply new render until it is level with the rest of the render surface. Use a wooden float to smooth the surface.

How to Reinforce a Render Crack

Render cracks are prone to open up again after they have been repaired. To prevent a render crack from re-forming then reinforce it with a glass fibre membrane covered with a base coat bitumen.

Rake out the crack to remove any loose material. Dampen the crack and then fill it with a mortar made from one part cement to four parts of builder’s sand. After the mortar has hardened, generously apply a coat of bitumen base coat, extending four inches either side of the edge of the crack. Apply strips of fibreglas scrim using a stippling action.

After 24 hours, apply another coat of bitumen base coat. When dry, cover with two coats of exterior masonry/render paint.

How to Remove Rust Stains from Render

Faulty guttering and rainworks can sometimes ruin render with rusty streaks and patches. Before redecorating render that has been stained with rust, prime the stains with an aluminium spirit-based sealant. If you fail to do this, the rust will migrate through the top layers of fresh paint.

After sealing, paint over the stains with two coats of exterior masonry/render paint.

How to Repair Spalled Masonry and Brickwork

Repairing spalled brickwork and stonework is possible, but the effectiveness of the repair depends on the extent of the damage. That’s why early action is imperative to prevent the spalling from getting worse.

If you have just a few spalled bricks or stone slabs, cut out the damaged areas and replace them with new bricks or stone slabs.

To replace a spalled brick or slab, use a cold chisel and club hammer to rake out the mortar pointing around the brick. Pull out the brick. If it doesn’t come out easily, drill holes in it with a large diameter masonry drill bit and then crack it into pieces with the chisel and club hammer.

Fit the replacement brick by dampening the opening and applying mortar to the base and one side. Spread mortar on one end and on the top of the dampened replacement brick. Slot the brick into the gap and then spread the pointing to match surrounding brick or stonework.

If spalling is extensive, repoint the masonry and apply a clear water and moisture repellent. This won’t improve the look of the damage but it will prevent it from getting worse. Read also the article about the reasons why brick tends to crack around doors and windows.