Oi! Experts! I've a bone to pick with you....

A while ago I asked about rendering internal thermalite walls, and you advised to use a scratch coat with waterproofer etc.

Well, I prepared the walls with battens, all nicely levelled and flat. Did the rendering as advised, with a plasterer friend. Got the skim on a couple of days later. The most beautiful flat wall you have ever seen....

But within a couple of days, the plaster had cracked, and now the render is cracked, and floating off the wall by a good few mm.

So I guess there's something wrong with what I did. Now my dilemma is whether I do anything about it, or whether I just go ahead and fit the kitchen and tile over the suspended sheets of rendering.

Any thoughts?

Perhaps it should have had dot & dab plasterboard?

Perhaps I should have used hardwall?

Perhaps I should have used pva?

PS The render and skim on concrete blocks is fine, as is the skim on plasterboard.

 

you should not use sand/cement on lightweight blocks.

 

it seems to me that the render may have dried out to quick did u conrol the suction? if it was my kitchen i would take the lot off, as you say its just hanging there sounds like u can scrape it off with a scraper your asking for trouble fitting the kitchen on walls that have blown the tiles will just fall off along with the render attatched to them, along with anything else for that matter
my advice is to start over, myself i would use hardwall

 

If it’s blown it has to come off I'm afraid but can you provide a link to your original thread pls?

 

It's probably this one.
http://www.diynot.com/forums/viewtopic.php?p=1137502#1137502

Roughcaster.

 

pva would have been good the suction has been too fast like above never use sand and cement. brown, bond or plasterboard

 

I used sand and cement on thermalite blocks on my own kitchen, and it's fine. but I did totally soak the walls first.

 

Too much suction, how well did you damp the blocks down? Lightweight blocks need lots & lots of water before you start, more like a dousing with a sprinkler hose rather than a splash with a brush or spray bottle. To say you can’t render lightweight blocks is wrong, of course you can; if it falls off or blows, either the blocks are too dry or the mix is wrong.

 

I have always used sand and cement on thermalite blocks without any problems although i will admit hardwall is better but with either one i always pva the walls first

 

I've spoken to plasterers who say s+c render on lightweight blocks is ok.
I think the mate didn't wet the walls enough on the scratch coat, so it basically turned to dust. The float coat just didn't stick to it. Although it took a few days to pop off.
But I've done a terrible thing and fitted the units anyway.
They have really helped clamp the render back on (!).
Give it ten years, I might fit a new kitchen and do it properly then.....
Oh the anguish!!!

 

i hope its your kitchen and no one elses if its your kitchen then thats up to you reg

 

Its always a good idea to dampen the blocks down thoroughly before you start to render

Another favourite is to make slurry with cement and water and dash all the wall with this ,equivelent to pva and this will stop the rapid suction wich is what you want to slw down

Thats the reason unfortunately for the blown render and nothing else

Ah well you live and learn next time you will get it right

 

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