Repairing cracks in external rendered walls

Thoroughly clean the area

Before repairing cracked render, it is essential to ensure it is sufficiently clean. If the render has been in situ for a while, it will first need cleaning. Drench the affected are with undiluted weber CL150 using a brush or sprayer and leave for 48 hours to ensure all algae on the elevation has been killed.

Wash the area using a pressure washer on low pressure with a fanned jet action, taking care at exposed edges.

Open thickness of crack

Using a mini disc cutter or oscillating tool, run a cut through the crack to increase its width to that of the cutter blade.

Mix products

Mix weberpral M (or weberpral D in Ireland) with weber accelerateur monocouche at a dose of 100ml per 25kg bag. Then mix in a dilution of 2 parts clean water with 1 part EVA or waterproof external grade PVA to produce a workable consistency.

Please note: It is important that the additive to water ratio is measured correctly – if the dilution is too strong, the colour of the repair will be affected.

Filling cracks in render

Fill a cartridge with the mixture and load into a cartridge gun. Cut the nozzle to the width of the crack and apply a bead of the mixture into the crack.

Ensure the mixture doesn't overlay the existing render but form a protruding nib of material 2-3mm in front of the line of the existing render.

Allow to dry and remove nib

Allow the repair material to stiffen for a period of between 20-40 minutes — dependent on temperature — then remove the nib carefully using the edge of a small filling knife.

Please note: If left to dry for longer than 40 minutes, it's likely a much lighter shade will be achieved than the existing render.

Paint the elevation

If there is a noticable colour difference between the existing render and the repaired crack, you may wish to paint the elevation with webersil P. webersil P is a high performance mineral paint that gives exceptional long term durability and performance, and is available in over 100 colours (including weberpral colours).

Providing all areas to be painted are clean, dry, and sound, a direct application of webersil P is appropriate. The first coat should be diluted with between 10-15% clean water and applied with a medium pile wool paint roller. A second coat can be applied undiluted after 24 hours. Application should be in a criss-cross pattern ensuring that the paint is applied evenly, minimising any effect on the scraped texture of the monocouche.

Spillages are susceptible to staining, and difficult to remove. Vulnerable areas should be thoroughly protected.