FrTedCrilly
New Member
Hi all, I am currently in the process of self-building our house and we are at the plastering stage. The house is constructed from Juwo Poroton clay blocks and we are using a lime render for breathability on the outside. My plan is to use sand and cement with a skim coat on the inside as this is what my plasterer has quoted for but the block supplier said "We recommend you use a gypsum-based plaster or lime plaster" and does not recommend sand and cement for clay block or any other block system. I don't really understand why they said that and they haven't replied when I asked them to expand on their reasons. Lime-based plaster on the inside will work out much more expensive than sand and cement.
Has anyone here worked with clay blocks before and can you think of a logical reason why sand and cement plaster on the inside would be an issue?
edit: my block supplier just replied with this:
"Sand and cement is too stiff for all types of blocks not just ours and will result in it cracking. Worst of all is sand and cement render to the outside as the cracks allow water in which freezes in cold weather or in warm weather expanded to even boiling point on a southerly facing external wall and blows the render, which I’m sure you have seen all over Ireland as I know I do in the UK.
The secret of all good rendering is that the render inside and outside should be softer and more flexible than the substrate is apply to which onto a clay block isn’t sand and cement."
Any opinions? If its that bad then why is every plasterer I talk to doing it?
Has anyone here worked with clay blocks before and can you think of a logical reason why sand and cement plaster on the inside would be an issue?
edit: my block supplier just replied with this:
"Sand and cement is too stiff for all types of blocks not just ours and will result in it cracking. Worst of all is sand and cement render to the outside as the cracks allow water in which freezes in cold weather or in warm weather expanded to even boiling point on a southerly facing external wall and blows the render, which I’m sure you have seen all over Ireland as I know I do in the UK.
The secret of all good rendering is that the render inside and outside should be softer and more flexible than the substrate is apply to which onto a clay block isn’t sand and cement."
Any opinions? If its that bad then why is every plasterer I talk to doing it?
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