DIY Doctor

Damp rock wool filled cavity’s

Postby Ashleyhopkin » Wed Dec 23, 2020 1:00 pm

Hi, we have just started getting damp on one side of our house, we had a patch of rock wool removed previously in the year where the wall started blistering. On checking we have found the rock wool is soaked and this is penetrating to the inside wall. Since then a new patch has appeared. Does anyone know if it’s the rockwool causing this? And if so how easily is it removed? Apparently it’s not the stuff that’s been pumped in, it’s been installed in rolls when the house was built? I’ve attached some photos for info. Cheers.
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87BD26DE-F16D-489E-9D47-C43BE18B6608.jpeg
Wall damp
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Postby stoneyboy » Thu Dec 24, 2020 9:52 pm

Hi Ashleyhopkin
If it is the roll material this is intended as roof insulation and does not have the waterproof resin. Special cavity wall batts were/are made by rock wool for this purpose. There may also not be an air gap on the outside for ventilation.
Removal will be a nightmare probably entailing opening up the outer brickwork to give access/replacement.
Regards S
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Postby Ashleyhopkin » Sun Dec 27, 2020 8:28 pm

Hi stoney,

Thanks for the reply, this a photo when we opened up one of the walls in the summer to look at a damp patch? Do you know anything about this type of insulation? You can just about make it out in the cavity between the two bricks? I’m hoping it can be sucked out otherwise like you said it’s going to be a nightmare to do the whole house.
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CAC4B046-FB8A-44B8-B5A6-385A1BB6E4DA.jpeg
Photo of insulation in cavity wall
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Postby stoneyboy » Sun Dec 27, 2020 10:39 pm

Hi ashleyhopkin
It doesn’t look the right colour or fibre for Rockwool but it is difficult to tell. Suggest you get a bit out and contact Rockwool and see if they are prepared to identify the product and suggest a solution.
Regards S
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Postby Ashleyhopkin » Mon Dec 28, 2020 11:55 am

Thanks, will definitely look into that.

Do you think the insulation could dry out over time? Then maybe I could seal the outside wall, but would want to do this once all the moisture is removed from the cavity?
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Postby stoneyboy » Mon Dec 28, 2020 10:39 pm

Hi ashleyhopkin
It is really difficult to say. The damp low down on your internal wall may not be the insulation in the wall, it could be that snots fell onto the DPC area when the wall was built and this is providing a bridge for moisture the travel from the outside wall to the inner wall.
I would suggest specialist advice but sometimes you can get the wrong diagnosis.
Try getting bricks cut out opposite to the problem areas and see if this identifies the problem.
Regards S
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