Tanking on new plaster

[joe-90]

If time and money are no object then fine, go tank it. But that isn't the reason for this forum. We try to specify what actually needs doing not belt and braces all the time. Any mug can specify belt and braces. I bet you say tank Mermox and Aqaupanel too (though the manufactures say not to bother).

 

[Paul C.]

Aquapanel is water resistant, so it can take in moisture but will not swell. Tanking advised (for belts and braces) but not essential. Marmox, like PDC, Wedi and the Schluter Kerdiboard, is completely waterproof. For all of these, including the Aquapanel, the joints of the board need to be waterproof taped to seal them.

Next........

 

[joe-90]

So you do tank Aquapanel then? Why doesn't the manufacturer agree with you then?

 

[Paul C.]

Told you.... belts and braces. Aquapanel as standard is adequate because of the limited amount moisture getting to it (providing its tiled correctly). But a job won't fail if tanked. Each to their own i guess. But the bit about the joints is a must.

 

[Kitsune]

Thanks for the replies you've demonstrated perfectly why I'm struggling to decide whether or not to tank!

Our plumber thinks it's going over the top especially as we are now using large porcelain tiles which are pretty water resistant and we'd have few grout lines, he keeps telling me it's not necessary and the manufacturers sell the fear factor to make money.(he has a good point it seems to have worked on me)

Likewise my boyfriend doesn't really want to spend the extra money or time unless it is really necessary.

Me, I think of what could happen if we are one of the unlucky ones who do get a problem and end up having to rip everything out and redoing it, especially if it can be avoided by spending £50 and a couple of hours. We are doing the tiling ourselves and although I have done a bit before we haven't done it to this extent. Also the first two posts I looked at after posting this were about cracking grout causing a leak and a wall drying out due to water getting behind the tiles.

 

[Kitsune]

On different but similar point we have been recommended to use flexible adhesive and to use Mapei we've been left with an empty bag so would know what to get but it is called 'Super Flexible Adhesive' and only seems to be sold at B&Q, is it made specially for them as it also mentions a primer on the back that only them and screwfix sell. If so is it the same as the normal Mapei adhesives and which one?

We are fixing 600mm x 300mm porcelain tiles to both the wall and floor, floor is floorboards over boarded with Ply so I know it needs to be flexible. Walls are straight as have new dot and dab plasterboard, (were pretty wiggly before). The website I'm going to buy my tiles from also sell Mapei and I'm not sure whether what I would need would be the Keraflex Maxi?

 

[Paul C.]

Is this in a different room? The first one you said was plaster skim but your last post suggested plasterboard?

 

[Kitsune]

Same room the plasterer skimmed the walls after, we are having a mix of paint and tiles and he wanted to skim it all (I know that's not necessary what he should have done in the tile area now, but when I said about leaving it as the board for tiles he said it was best to skim it as well!)

 

[Paul C.]

Ummm... Not really helped you much.

Whether you decide to tank the area or not, you will need to prime the plaster. The Mapei "Primer G" is the one to go for unless you go for a tanking kit that has one included (Like the BAL WP1 Showerkit which includes their APD primer). Because of the size and the fact it is porcelain, it has to be a cement based adhesive, so the Keraflex Maxi will be a good one to go for.

Only thing you will need to check is the weight of the tile. Plaster skim should only hold a maximum weight of 20kg per sq.m including the weight of the adhesive (3-4kg approx). Plasterboard would have catered for 32kg and would not have been a problem.

 

[joe-90]

I agree with Paul, you MUST use a primer or the adhesive won't stick.

 

[tictic]

That was fun reading the replies there.....takes me back a good bit on this forum...

 

[Kitsune]

Tiles are borderline in the weight department about 18kg and then the adhesive on top, we had changed from natural stone because of weight but the porcelain ones are pretty heavy too. Just out of interest what is meant to happen if the tiles are too heavy, do they pull the skim off the wall has anyone known this to happen?

 

[Paul C.]

To be honest, I have only seen it happen 3 times. One instance was 20mm thick limestone. Weighed 37kgs.... Not suprising that happened.

The second was 10mm thick 600x400 porcelain, 25kg. 5 blobs of adhesive on the back, so again, not surprising. That was mainly to do with water having room to move and soaking the plaster until it pretty much turned to mush but only released from the plasterboard behind the 5 blobs. Hard to tell if it would have held if fitted correctly.

The 3rd was fitted with full coverage of adhesive.... 600x300, but it was a ready-mixed adhesive, so it never dried properly. The moisture dispersed into the plaster, softened it, and when the tile came down, about 75% of the skim followed. tile weight was 22kg, but in all 3 instances, the plaster wasn't really given a chance.

I know there are many times that a showroom has advised against it but the customers do it anyway, but its not very often I called out to people who have knowingly gone against the advise, so for all I know, they may not have even had any problems.

I have a feeling that the 20kg's will be on the safe side to cover many backs, but if anything does happen, you have gone against the guarantee of the tile and the adhesive, so it is a risk, but you will only be over by 2kg. If you have 100% coverage of adhesive to spread the weight, you "might" be ok.

The safest would be to chip all the plaster off down to the bare plasterboard, tank it, tile it. Or the messy way is to rip all the plasterboard down, replace with Marmox or PDC boards, tape the edges and tile it but not essential unless as Joe says, you want to spend more money to get the "belts and braces" prep.

 

[Kitsune]

Thanks Richard I think we will risk it as it is only a little over and we are using Keraflex adhesive and the walls are nice and flat now, so won't be like the situations you mentioned.

With tanking, which we have decided to do, we have a small window in the shower area, so we would need to tape external corners, internal corners, onto shower tray and what about where it meets the window inside the revel?

 

[Paul C.]

You will not need a tape up to the window but macke sure to go slightly round the edge with the membrane. When tiling, leave a 2mm gap between the tiles and the window and fill it with silicone. That will be fine.