Plastering advice - large porcelain tiles

[Catty]

I would be grateful for some help please! Bathroom walls were bonded a few weeks ago but didn't apply skim at the time (long story). Is it too late to skim now? If not, how should the bonding be prepared / sealed prior to applying the skim coat now that some time has passed? I understand that PVA is out! Will be tiling with large porcelain tiles.

 

[Andy Allen]

Should imagine the tiles, if large porcelain will be to heavy for any plastered wall..
But definitely don't tile to bonding plaster

 

[Boggs]

I would imagine the tiles would be too heavy for a plaster skim.

 

[One Day]

You want the bad news or the bad news?
Bonding is totally 100% not suitable for any tiles yet alone large format porcelain.
Skimmed walls might take the weight of thin porcelain. What's the thickness?

 

[On one]

If you can swap the porcelain tiles for ceramics you might be able to pull it off without too much hassle.
The Bonding(undercoat) plaster should be brushed or rollered with numerous coats of diluted PVA until it won't absorb anymore (just a case of going round and round the room) Then a final coat of PVa diluted 1:1 ..... when that goes tacky apply your finish plaster.
Obviously your not looking for a paint finish......just a reasonably flat finish

 

[Catty]

Thank you everyone. The tiles are 9.5mm thick and weigh 18K per sq. meter, which with adhesive will take them a bit over the recommended load of 20K for plastered solid walls, so will risk that. I appreciate that we can't tile over bonding and will need to add a skim coat. My worry is whether we've left it too long to add the skim coat to the bonding as the bonding was put on a few weeks ago and will have dried out by now. Many have said on this forum that shouldn't use PVA in the bathroom due to the moisture - but would this be OK over a bonding coat before skimming? So, my question is, is there is another product I should put onto the bonding to seal it before skimming or is too late to do anything about it now and have to start again? Can't put up cement board up either as there's not enough room! Urgh!

 

[One Day]

The reason you can't tile onto bonding is a. It's so very porous it'll just suck the water out of the adhesive before it cures, and b. It's so weak, as adhesive cures it will pull the bonding apart.
There are always nay-sayers who will happily fix to bonding.
Muppets, all of them!

 

[Andy Allen]

You can't use PVA as a primer before tiling, using PVA on the bonding before applying the skim coat of plaster is fine, wait for the skim coat to dry apply an acyrlic primer then tile...
As for the 2 week gap between the bonding and the skim coat, I'm sure it will be fine, but I'm no spread, but im sure someone else can confirm this.

 

[Andy Allen]

I'm sure @widler is a common plasterer...

 

[One Day]

I'm sure @widler is a common plasterer...

Dead common!

 

[Waluigi]

PVA doesn’t matter on the coat between bonding and skim coat. It’s only unsuitable as a tiling primer.

As already mentioned- lots of coats of your PVA/water solution and really brush it into your bonding. Any gaps and it’ll set the skim coat instantly and it’ll craze. I would lightly brush the skim instead of polishing it.

 

[Catty]

Thank you everyone! You've been really helpful. Fingers crossed that my total weight of approx 22K per sq meter (including adhesive) will be OK!

 

[Boggs]

If it’s completely dry I think I would use a couple of coats of sbr instead of pva.

 

[Boggs]

Thank you everyone! You've been really helpful. Fingers crossed that my total weight of approx 22K per sq meter (including adhesive) will be OK!

Just remember to take your spacers out.

 

[widler]

Hi catty ,being a common plasterer , i can advise you to pva the bonding coat and skim, if your plasterer can’t handle suction.
As long as your tiles are what you say they are in weight, prime with a tile primer and tile .
Id of personally plasterboarded it and tiled, so much easier than a rough coat and skim.
Cheers
Common craig