Render repair: repairing cracks in external rendered walls

Monocouche render, a type of through-coloured render, is known for its durability and resistance to cracking. However, over time, environmental factors, settlement, or other issues may lead to the development of cracks.

Repairing the cracks to retain a similar level and texture to the existing render is a common practice in maintaining the appearance and integrity of a building's exterior. However, with more noticeable cracks, it is harder to achieve colour shade matching, especially with strong-pigmented colours, and renders which have been in situ for a while.

Step-by-step guide

Our Application Manager, Phill Powell, guides you through the process of how to repair cracks in monocouche render. 

Scroll down to read through the individual steps in this process.

  1. 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.

  2. 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.

  3. Mix products

    Mix weberpral M (or weberpral D in Ireland) with weber monocouche accelerator 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.

  4. 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.

  5. 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.

  6. 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.

If you're unsure

Larger cracks in the render which could suggest hollow or defective render, or damage to render, will require a more specialised approach. In this circumstance, please contact our technical team.

Please contact us if you are unsure about whether this process is appropriate for the type of crack you have. If repairs are not carried out correctly, the situation could be made worse. Contact our technical team:

Our technical team is available Monday to Friday, 8:30am until 5:00pm.

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