Extensive plaster cracking after heat pump installation - thermal cracking? subsidence?

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HJBHome

(@hjbhome)

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Topic starter 07/01/2022 11:03 am

Hi,

Perhaps a long shot, but wondering if anyone has had issues with thermal cracking following a change of heating system. We’re in a 1930s converted bungalow with old plaster walls and ceiling. We switched to a heat pump from a combo boiler in August and had underfloor insulation installed at the same time which significantly reduced draft and damp from the foundations through the wood floors. We had some ceiling cracking prior to this, but have had widespread and quite worrying cracking in walls and ceiling this winter. We’re property surveyed as we are worried it could be land slip or subsidence, but I’m wondering if a more benign explanation is possible in terms of thermal / moisture changes related to the new heating system?

Would be really interested if anyone’s had a similar experience.

Thanks

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batalto

(@batalto)

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07/01/2022 11:27 am

if there was a lot of damp in the lower walls and foundations the cracking could be caused by the drying out. How large are the cracks?

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Kev M

(@kev-m)

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07/01/2022 11:34 am

I suspect also that it's the floor insulation and reduction in damp. That sort of thing happens when you mix modern insulation/damp proofing with the original in an old house. I suspect it will settle down and at worse you'll need to do a bit of filling. But make sure you use the correct sort of plaster/filler (same as the original) if you do.

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Flowboy

(@flowboy)

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08/01/2022 8:51 pm

@hjbhome Before you open up a can of worms re. potential subsidence - insurance claims, underpinning etc 😱.

Unless the cracks are large enough to see into the brickwork, or they are actually following the brick courses to some extent, the only way to be absolutely certain would be to hack off the plaster on the worst wall, (or perhaps an affected wall in a small room to look at the brickwork - then you only have a smallish area to re-plaster...) External signs of cracking along brick courses would be more worrying - although can also be caused by rusting cavity wall ties.

However... When you say 1930's property, I would think you quite likely still have a lot of natural lime plaster. This "breathes" - takes up & gives out moisture - adapts to humidity levels. How much it has been able to do this fully naturally, I suspect will have been reduced by the layers of modern emulsion or other paints, partially sealing the walls in modern times. They may have been breathing to some extent but taking much longer to do so with the modern paint coatings.

Your serious thermal improvements & draught reduction are no doubt keeping more heat in the property than you previously managed. It may be that the sudden change in air temp / dryness - without the previous possibly slightly damp draughts, may have caused the plaster to dry out very rapidly. Hence the cracking. There are a number of lime & eco specialist companies that supply fillers that might do the job. A bit more expensive. On the other hand if there are innumerable coats of modern paints then a modern flexible filler might be ok, I would leave it for some time until the cracking activity has stopped. If you still have lath & plaster ceilings then I should think the same would apply - they do become more vulnerable with age anyway - plaster detaching from laths.

I would think that drying out below floor / dpc level would be unlikely, as the drying will surely only / mostly be in the occupied parts, unless you also have a heated basement. If you can see your basement / underfloor walls they might reveal if the cracking has more worrying implications or not.

👍

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