New plaster coming away from wall

[stevethespreader]

Why has the render got to come off?

 

[adam911]

I told him the old plasterer didn't scratch the old render and is possibly why the old plaster has come off so he's said its best to go back to brick as he cant guarantee his work if the old render doesn't come off as the render could come away from the wall anytime. So what would the correct procedure be starting from brick? How long should he wait between coats of render and how long should he wait until the new render is plastered also where and when does he need to pva. Im want to know so i know if he's doing it right or wrong. Thanks.

 

[stevethespreader]

Well I think what he's saying is cr@p that's like saying every time you go to skim a wall you have to take all the render off just in case the plaster don't stick what a load of tosh. If the renders sound just skim it you should be able to make a judgement , if he goes back to brick he do not need to use PVA, I can't tell you how he's going to work he might try and get the floatcoat done in one day who knows ? If its text book your after scratch first day float next skim couple of days after no PVA , tbf he might float it in one day skim next and it will all be fine , but to take render off when nothing's wrong with it is not the right way to go

 

[adam911]

I know but i dont want him to turn around later and say i told you to remove the old plaster. In terms of cost he's not charging much more for the extra render its just the cost of materials really. So he can put both coats of render in one day and next day he can multi finish and all will be fine?

I really hope he can do a better job.

 

[stevethespreader]

I know but i dont want him to turn around later and say i told you to remove the old plaster. In terms of cost he's not charging much more for the extra render its just the cost of materials really. So he can put both coats of render in one day and next day he can multi finish and all will be fine?

I really hope he can do a better job.

Here read this from an old friend "micilin"from back in 2007 here he explains in good detail of the processes involved times mixes ect etchttp://www.diynot.com/diy/threads/sand-cement-plastering.107172/

 

[roy c]

Is micilin still with us?

 

[stevethespreader]

Last time I spoke to him must be about 8 months ago or more

 

[adam911]

Right just a update, had the new plasterer in today and its not a good start. Hes taken all wall previously plastered back to brick. He put on first coat of Sharp sand and cement render and there is one wall the render has started to crack after 1 day and some areas now sound hollow . I told him to use renderguard water proofer in the first coat.
What has caused this? Its only 1 wall at the minute.

I told him im not happy with it and told him to redo it again. Hes using 3 Sharpe sand (25kg bags from b&q) and 1 cement as directed by dryzone dpc.

Any ideas why that would happen he sprayed the bricks with water before rendering too?

 

[roy c]

He wants to use 6-5 sand 2 lime and 1 cement (with plasticiser) (Not W/proofer as it shouldn't be put in with lime!) and his float coat can be the same and he should of killed the suction before he plasters.. The reason for using that mix is ,You dont know what mix the brickies used when they built the house but you can gaurantee that it wont be as strong as the mix he wants to use. no one knows the mix that was used so you make your mixes alot weaker than theirs. Always go weaker on scratch and float ..3-1 is far too strong for your job...

 

[stevethespreader]

So he has only scratch coated one wall? And its the scratch coat that has blown? Or did he do it all in one go? You would also have been better off with plastering sand because its washed

 

[stevethespreader]

Also how much water did he use? I drench my walls

 

[adam911]

I think it was spray bottle of flash but with water in it probably 1 litre or so.

 

[adam911]

Hes done few walls both in dining room and lounge but its only in the lounge to one side of the chimney breast thats cracking. It states on the dryzone to use Sharpe sand as its copes better with damp or summa? He took it back to brick and got a 2 litre pespsi bottle with several hole on the top and drench the bricks. Will see in the morning if the cracks reappear with the new render. First coat is 3:1 and ive told him ive read on here to have the second coat of render weaker 4:1 hope thats right.

 

[stevethespreader]

Pepsi bottle? Oh come on your not going to give the wall a thorough soaking with that , best way to soak a wall other than hose pipe is to get a long pile shaggy roller and a bucket of water, he's also taken down sound render because he can't guarantee his plaster will stick to it and now "his" render has blown ? Also first I've heard of sharp sand being better than washed sand for inside render, washed sand has virtually no silt , silt is a major contributor to cracking and crazing and failure "just saying"

 

[roy c]

Hi Steve. where we are we get, Builders sand (Brick and block laying) Sharp sand (which is plastering sand for inside and outside) and Concreting sand So might be different names for it in different parts of the UK..If we ask for plastering sand we get sharp sand.