New Plaster problem

[adders21]

Hi All,

I recently removed some tiles in my bathroom. An area of plaster came away with tiles. I'm going to tile over the top so I decided that I would replace the plaster.

I had a bag of plaster left over from some building work 2 years ago so I decided to use that. I bought some PVA. Diluted it as instructed and painted the area. Before the PVA dried (instructions on tub said to plaster whilst tacky) I applied the plaster. It looked great, very pleased with my first effort.

Then, the next morning it all cracked, please see the pictures.

Untitled

• adders21
• 23 Feb 2012
• 1

Untitled

• adders21
• 23 Feb 2012
• 1

There is a small radiator in the bathroom that would have come on about an hour before I went back into the bathroom and saw the cracks. I plastered about 5:30pm in the evening and it looked fine around 9pm. So this all happened through the night.

Any ideas as to what I did wrong?

Cheers

 

[peaps]

I guess you used finishing plaster to fill the void..?

You should have used a backing plaster/render and the gave it a skim....

Finishing plaster should be mm not feet thick

 

[adders21]

Hi Peaps,

Yes, I'm guessing it was a finishing plaster. We had a kitchen extension and it was left over after the plasterers skimmed the plaster boards.

I've read on another site that I should use Thistle Hardwall as I'm plastering on to brick about 1.5cm thick. Apply PVA leave it over night then apply a second coat. Wait for that coat to go tacky and then apply the plaster.

Does that sound right?

As I will be tiling on the top is there any need to skim with a finishing coat?

Cheers

 

[stevethespreader]

As I will be tiling on the top is there any need to skim with a finishing coat?

Cheers

no theres not scrape all that cr@p off and patch with render
then tile

 

[peaps]

Hi Peaps,

Yes, I'm guessing it was a finishing plaster. We had a kitchen extension and it was left over after the plasterers skimmed the plaster boards.

I've read on another site that I should use Thistle Hardwall as I'm plastering on to brick about 1.5cm thick. Apply PVA leave it over night then apply a second coat. Wait for that coat to go tacky and then apply the plaster.

Does that sound right?

As I will be tiling on the top is there any need to skim with a finishing coat?

Cheers

Just hack it off and redo with a backing plasted, hardwall etc or render. no need to skim it over. You should not fill deep patches all at once or it can sag and crack. build up the layers.

 

[Alastairreid]

I had a bag of plaster left over from some building work 2 years ago so I decided to use that.

Plaster does have a limited shelf life.

 

[peaps]

I had a bag of plaster left over from some building work 2 years ago so I decided to use that.

Plaster does have a limited shelf life.

I use old finish, you can mix it 50/50 with sand to use a a filler for patching..

But yes the first thing we do is look at the date on the bag!!

 

[adders21]

Hi Everyone,

Thank you for your replies.

Cracked plaster chipped of. Fresh PVA applied last night mixed 5 to 1.
Radiator turned off. 2nd application of PVA today at 9am 3 to 1.
Hardwall plaster going on at 12 today.

Fingers crossed!

 

[peaps]

Hi Everyone,

Thank you for your replies.

Cracked plaster chipped of. Fresh PVA applied last night mixed 5 to 1.
Radiator turned off. 2nd application of PVA today at 9am 3 to 1.
Hardwall plaster going on at 12 today.

Fingers crossed!

No need to pva it but it's done now. PM me if you have a problem. I'm near Derby.

 

[Richard C]

Probably too late with this one but if you’re re-tiling, it’s easier & quicker to use a Rapidset cement based tile adhesive to fill out & true up (acrylic prime first) It doesn’t need to be smooth just flat & you won’t have to wait days for it to dry out before tiling; don’t tile over damp plaster, at best the adhesive won’t set & at worst the tiles may eventually fall off.

Sand/cement render is a good tile base but unfortunately base plasters (with the exception of Dri-coat) are not suitable as a tile base.

 

[adders21]

Richardc,

Would you consider Thistle Hardwall a suitable tile base?

 

[Richard C]

No, it’s a base plaster; Brititsh Gypsum, the Tile Association & all the tile adhesive manufacturers I use state specifically that base plaster (with the exception of Thistle Dri-coat) is not suitable for tiling. If you’ve already done it you might get away with it if it’s just small infill areas, well bonded & you prime it well but I wouldn't gurantee it, especially if you plan to use large format/heavy tiles. You should also be aware that finish plaster has a fairly low weight limit as well & if your tiles weigh any more than around 18 kg/sqm you could be in trouble with your tile base.

Rapidset tile adhesive or a quick set render would have been a much better choice.

 

[peaps]

Richardc,

Would you consider Thistle Hardwall a suitable tile base?

if you have used it give it a thin skim.

 

[Richard C]

if you have used it give it a thin skim.

Would be the best solution as long as your tiles don’t exceed the weight limit for finish skim; but even finish plaster is generally not a good tile base if large format tiles are planned because of the maximum weight restriction & additional prep required when using cement based tile adhesive.

Additionally, the bond strength of finish plaster will only be as good as the weakest link, if the bond of the base plaster/render is suspect that will be the limiting factor as far as max tile weight goes.

 

[adders21]

Well, the good news is that due to work commitments I had to abort todays plastering session.

So, cement based tile adhesive. If I go down this route what is acrylic prime and how do I use it? Will it go over the PVA I've already put on the wall?

The depth of the area I'm filling is about 1.5cm. The largest area, apart from the strips that you can see in the picture, is about 60cm x 40cm.

Thank you again for all your advice. I really do appreciate it.