- Thread starter Maria D
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Company have told me this is the best option for my house. Advised against woodfibre. I think their advice was mostly due to concerns about penetrating damp (although this isn’t a major issue for us). But I’m wondering if they will give us the thermal insulation we’re looking to achieve.
If you have penetrating damp, you should resolve the issue allowing damp to penetrate. If you don’t have penetrating damp then it’s back to the question: what selling point do these boards have vs the standard breathable IWI systems, namely wood wool, wood fiber and agglomerated expanded cork?
You should ask the people recommending them to you. If they can’t give you a clear, rational answer then it’s likely some BS ulterior motive.
Lacan07
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Can you put a link up to the product?
The inclusion of thermal plaster raises alarm bells for me, its not really a serious option for insulation unless you've got nice thick walls like aockenden. Wood fibre board is the tried and tested way that many people follow. If your walls suffer damp you need to eliminate that first before insulating. Incidents of rising damp are very rare (imho) unless you live on a high water table or rainwater management is poor or faulty, so its a mute point.
Agreed, I thought the board product PLUS an insulating plaster is a particularly strange recommendation that raised alarm bells for me as well. That insulating plaster won’t do much unless it’s built up thickly, but how’re you supposed to build up a few CMs of plaster onto a flat board product with no mechanical key.
To the OP: Typically you either build up a thick layer of insulating plaster directly onto the masonry substrate, OR you use an insulating breathable board option with just a standard, non-insulating coat of finishing plaster on top.
Agree with ao and lacan - it's a strange choice. It has about half the insulating capacity of wood fibre or cork and so you'd need a much thicker board to get the same insulating effect, which you probably don't want internally - the thinner the better.
If you're worried about damp penetration, wood wool would be a better choice - about the same thermal conductivity as calcium silicate board, but cheaper and with a much better key for your plaster.
Sounds to me as if your contractor either has a load of calcium silicate boards they want to get rid of or has some kind of arrangement with the supplier/manufacturer. Probably the former because that would explain the use of insulating plaster - the boards they have and want to use aren't thick enough to meet building regs (U = 0.3) and so need to supplement with plaster.
If you're worried about damp penetration, wood wool would be a better choice - about the same thermal conductivity as calcium silicate board, but cheaper and with a much better key for your plaster.
Sounds to me as if your contractor either has a load of calcium silicate boards they want to get rid of or has some kind of arrangement with the supplier/manufacturer. Probably the former because that would explain the use of insulating plaster - the boards they have and want to use aren't thick enough to meet building regs (U = 0.3) and so need to supplement with plaster.
One other thing, if the lime plaster already on the walls is in good condition, can I just insulate over it? I read a lot here about adhering the wood fibres boards directly to the masonry but it would be a big job to remove all the existing plaster.
If they're a good company, then they'll probably do a good job. Nothing really wrong with using calcium silicate board except that it needs to be thicker than most products to produce the same level of insulation. It is water resistant and highly fire resistant, so is a good choice in some situations for sure. It's also very light weight - makes it good for fireproof ceilings.
Provided there is no vapour impermeable plastic paint over your lime plaster, no reason not to leave it (as far as I can see), but it does add extra depth. Removing it would have the advantage of giving you an extra centimetre or two to offset the thickness of the boards (assuming the wall beneath is nice and flat).
Provided there is no vapour impermeable plastic paint over your lime plaster, no reason not to leave it (as far as I can see), but it does add extra depth. Removing it would have the advantage of giving you an extra centimetre or two to offset the thickness of the boards (assuming the wall beneath is nice and flat).