Extensions Question

Cracks in rendering and crumbling render

We had an extension built on to our cottage, which was completed in Feb 2008. The extension provided an extra bedroom with ensuite and new kitchen. The extension was made from building a timber framed first floor on top of an existing stone built lower floor. The lower floor was already rendered. When the extension was complete the builder rendered the entire timber frame with two coats and the lower pre existing render with one coat.

Six months later we had cracks, he arranged to have them filled. Now we have huge cracks all over, and some fine cracks also. In places you can tap the render and it sounds hollow, and the render crumbles off the wall when you touch it. We have sent samples of render from both top and bottom of the extension to be tested for mix proportions etc, results came back that the render was lean on cement.

We have approached the builder to ask what he can do about it, he will only fill the cracks, nothing else. We do not have the money to spend on a re render, but we are concerned just filling the cracks will not be enough and it will happen again. Does our property need re rendering or can it be fixed. Didn't expect it to look like this after a few years. Older parts of the cottage have been rendered for years and do not have any problems with these walls.

3 Answers

Best Answer

There are render systems with flexible, anti-crack properties specifically designed for timber frame buildings. In our experience it would be safe to say that 'most' general builders are not conversant and up-to-date with modern and technologically advanced render systems. For long term durability (and if you want, for example, a 15 year anti-crack guarantee) then you need a calcium silicate board substrate, a mesh-reinforced polymer base-coat and a flexible acrylic topcoat. That's your full render system. The big question: can this problem be rectified without removing the existing, failed render? If you would like a full consultation specific to your problem, then please feel free to contact us.

Answered 23rd Oct 2014


Member since 13 Jun 2010

Well, the builder is responsible, that is for sure. Just repairing cracks is no good. Water will also get trapped behind the render, then when it freezes, this pushes even more render off. The render and technique that should have been used is specific for timber framed houses, I assume this was not done, so it is sure to crack and fall off. Render on brick or stone is usually fine if done properly, should last many decades but does need maintenance to seal any small cracks. But you have a far different situation to routine maintenance. I think all the render on the timber framed part needs removing. It may not need replacing, many properties are half rendered. But you would need advice from a surveyor, I cannot tell from your email. Hope this helps. Good luck, this is not a good situation to find yourself in.

Paul Albright

Answered 10th Jun 2013

Aspire Housing

Member since 23 Nov 2011

If the render sounds hollow when you tap it than I'm afraid it has blown.
The render is not fixed / stuck to the timber base.
Filling the cracks will help it look better but will not solve the problem
Without looking I couldn't say for sure but I would say it will need pulling off and done again

Answered 10th Jun 2013

Coles & Collins

Member since 7 Jun 2013

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