help with cement rendering on thermalite

[cigamseinnub]

need to render a thermalite internal wall have read up on it and a bit confused.

was going to wet wall and put on a 5to1 diluted pva mix then when its tacky start to sand/cement render ,but have read of people putting on two coats, one on the day before then 2nd when they render. Are two coats better or would one do ?.
thought with the dried coat of pva it may seal the blocks and make it harder to get good suction on the render.

the other point was its recommended to do 6 /1/1 sand lime cement or 6/1 with plasticiser mix for thermalite . haven't used lime before so was going to just use the 6/1 plasticiser . but as the blocks are prone to cracking would i be better off adding lime for the extra flexibility is it worth the extra cost.
thanks

 

[Micilin]

need to render a thermalite internal wall have read up on it and a bit confused.

was going to wet wall and put on a 5to1 diluted pva mix then when its tacky start to sand/cement render ,but have read of people putting on two coats, one on the day before then 2nd when they render. Are two coats better or would one do ?.
thought with the dried coat of pva it may seal the blocks and make it harder to get good suction on the render.

the other point was its recommended to do 6 /1/1 sand lime cement or 6/1 with plasticiser mix for thermalite . haven't used lime before so was going to just use the 6/1 plasticiser . but as the blocks are prone to cracking would i be better off adding lime for the extra flexibility is it worth the extra cost.
thanks

You can use PVA inside, but I prefer not to on thermalites as it is less effective

You need to either soak the wall well the night before and the morning of application; or at least 24 hours before give it a coat of SBR slurry, rendaid or HPX to seal up and key.

Scratch coat of 4:1 with waterproofer. Ruled off and scratched.

Then float coat at least 24 hours after - 5:1:1

The blocks will cause cracking if you don't stablise the suction.

If in experienced you will need time and even suction.

Inside with lighting you are better off with a slow set than making a hames of it.

 

[stevethespreader]

one of the best ways to soak the wall if you cant use a hose is a long pile roller the longer the better

 

[stevethespreader]

duplicate

 

[stevethespreader]

duplicate

 

[cigamseinnub]

thanks for the advice
did the first wall today and as as suggested didn't pva just well wet down, a 4.5 meter wall took nearly two buckets (20 liters) of water and still absorbed more before i applied the mix ,thanks steve the roller idea worked a treat lot better than by brush
as its 12mm render tried doing it in one coat hopefully will work
how long will it take to cure before i know if has blown away from the wall or adhered well.don't fancy doing all the rooms and then finding out i have to take it down and start again.

cheers

 

[stevethespreader]

how long will it take to cure before i know if has blown away from the wall or adhered well.don't fancy doing all the rooms and then finding out i have to take it down and start again.

cheers

what are you planning on doing are you leaving the rooms just rendered or is there going to be a skim coat going on? your wall should be fine if you wet the walls anough and done a consistant mix what sand are you using?

 

[Micilin]

what are you planning on doing are you leaving the rooms just rendered or is there going to be a skim coat going on? your wall should be fine if you wet the walls anough and done a consistant mix what sand are you using?[/quote]

I should have asked the same - I assumed it was to be left rubbed up render!

 

[stevethespreader]

I should have asked the same - I assumed it was to be left rubbed up render!

i think so did most people i only thought different when he stated talking about doing his other rooms

 

[cigamseinnub]

sorry for not making it clear ,was render before a skim coat,hopefully will be able to speed up as i get used to it ,as i'm bloody slow at the moment and thats with battens as guides have three rooms to do kitchen ,utility an wet room, was thinking of doing the whole house render but if i keep up this pace will dot and dab the rest .
the wall i did yesterday seems to have bonded ok as you said used lots of water.
was using sharp sand left over from screeding floors .
cheers

 

[roy c]

You must "devil" the wall so you have a key for your skim coat, put 3 screws in the end of your float and adjust so the points are sticking thru (or knock 3 sheradised pins thru) then when your wall has "firmed " up and you have screeded it flat devil float it in figures of eight (easiest way to describe it) and that will give you your "key" for your skim... Have a look in my "Dabbing walls" album. Number 2 picture and you can just see the devilling on the left hand side wall...What I did with those walls was to use "dabs" plumbed up and screeded between, then filled in the bays in the middle...

 

[roughcaster]

Just been looking at your pics again Roy,, some good stuff on there as usual. I use the "dot" method too for setting out screeds on walls, and also use the same method for screeding floors etc.Once the datum dots are all set out, you can't go wrong. This is another part of plastering, rendering, floor screeding etc, that was taught as basic skill years ago, but nowadays not many plasterers are taught all these things together. The old plasterers that taught me are all long dead now, but i'll never forget them,, Bill Darrington,, Percy Gay,, and not forgetting our fantastic plasterers labourer, Bill (Whistle) Davis, the man who made the whole squad tick. I am proud to have been taught by them, and i can still sense them keeping an eye on me day by day.

 

[roy c]

Just been looking at your pics again Roy,, some good stuff on there as usual. I use the "dot" method too for setting out screeds on walls, and also use the same method for screeding floors etc.Once the datum dots are all set out, you can't go wrong. This is another part of plastering, rendering, floor screeding etc, that was taught as basic skill years ago, but nowadays not many plasterers are taught all these things together. The old plasterers that taught me are all long dead now, but i'll never forget them,, Bill Darrington,, Percy Gay,, and not forgetting our fantastic plasterers labourer, Bill (Whistle) Davis, the man who made the whole squad tick. I am proud to have been taught by them, and i can still sense them keeping an eye on me day by day.

Your right rc there are a lot of good plasterers gone now and they took alot of knowledge with them even tho they passed a lot on aswell. I remenber a few years ago I was knocking out holes in the side of a building to put windows in on the top floor in seperate rooms and had to make sure that when l went into each room I had them in line.There was a joiner working on the job and I asked him what the datum was (for the cill heights) and he told me the 22nd August,.And I had to explain to him what a "datum" was!!!!! Always raises a laugh when I tell that story. And now he is building houses and got a load of men working for him and a new van every two years. I still wonder if he remembers the days when he didn't know his "datum" from his Elbow