Water tight external rendering options

Question

Water ingress only when sustained heavy rain driving into south facing wall. Believe it's getting through cracks in render and running down external surface of wall where it continues down past lintel support beam due to extension roof flashing installed short of wall and going through gap.

What are my best options to stop this please ?

Rui · Answer

I believe using a resign based render would be Beneficial to your water ingress issues, it uses a fiberglass mesh underneath the top coat to reduce the chance of cracking. It's price is comparable to normal cement render and can be tinted to suit your colour choice.

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Lukasz · Answer

1  Hydrophobic wall treatment

Apply a silane/siloxane-based water-repellent to healthy render.

Popular UK products include Stormdry Masonry Protection Cream, Dryzone, Thompsons Water Seal.

These make rain bead on the surface instead of soaking in, while keeping the wall breathable.

2. Modern render systems

If the existing render is heavily cracked or aged, consider a new insulation/render system with silicone render.

Silicone render is highly water-repellent, flexible, and self-cleaning – widely used in UK refurbishments.

Michael · Answer

Were cavity trays installed when the extension was built? If not this could be the issue.

Andy · Answer

Krend silicone render with a choice of coloured finishes

William · Answer

To stop it you would have to address the damp proofing of the wall, and require a suitable damp resistant option.

Jason · Answer

No easy way to answer this question without inspection of problem, would just be guesswork.

Justin · Answer

I would look at the flashing and guttering first ,water is not supposed to run down your walls

Michael · Answer

South-facing wall gets hammered by wind-driven rain.
Cracks in the render let water in.
 Water runs down behind the render, past the lintel, due to the roof flashing being too short (not sealed against the wall).

This is a classic combination problem:
 Cracks in the render allow penetration.
poor flashing detail channels water into the wall.

Good news: both issues can be fixed—fairly standard building work.

Adam · Answer

Unless the cracks are large in the render is mostly likely due to poor weather detailing at intersections of various elements.

Adam · Answer

The main causes are as follows: Building faults – damaged or deteriorating mortar can lead to water ingress through the render. Any cracks in the brickwork or substrate will also allow water to get in. This can occur for a number of reasons including more serious structural issues.

Water tight external rendering options

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