Tiling Dilemma With Damp Wall Substrate

[mika_98]

Hello all,

I seem to be in a dilemma with the tiler and tiling my bathroom. First of all, things to bear in mind are that the walls are slightly damp and I have gone for porcelain tiles. The walls have been treated with a damp proof course but I have been advised any previous damp may remain for a while.

With that in mind, I'm assuming the best method is to fit a board of some sort to tile onto. If that is correct, which method should I use - dot and dab with adhesive or studwork?

I'd rather go with the dot/dab as my bathroom is very small (1.8 x 1.5m). Batons plus boards, followed by tiles will take up what little space I already have. If I go down this route, which boards (apart from plaster/MR) can I fit using adhesive? I'd love to use something like Aquapanels but was advised they have to be fitted using batons. Are there any other alternatives?

However, if its best to go with batons+boards, which combination can I go with (again apart from plaster/MR) that will take up less space? Aquapanels I believe require a 38mm baton according to the manufacturer!

Also, I've never heard of this but the tiler wishes to add some kind of waterproof additive to the grout I prefer, which is one from the Mapei range. Anyone ever heard of such practice?

I would be very grateful of any advice as it's causing me some bother 😳

 

[Dan]

Dot and dab plasterboard and then tank the shower area. I assume the damp is visibly gone and just still in the wall? When was the course put in?

Not heard of a waterproof additive for grout.

Only epoxy is waterproof and can be used as a grout, or adhesive. Expensive to do a whole bathroom though and a bit of an overkill.

Tank it and use the normal Mapei grout and it'll be fine.

If the damp is still quite bad you might need to avoid plasterboard. That won't mix well with moisture.

 

[Dave]

First off, what's caused the damp walls ?

 

[Unused Account 1]

Dry the room out totally ,then see if damp comes back ,worth it ,rather than tile it then mess up ,then decide wether to board or any other method ,its there for ten years ,do it right

 

[WetSaw]

Damp problem needs to be confirmed as completely eliminated before any type of finish. Is the damp coming from inside or outside?

 

[mika_98]

Thanks for the response guys.
The moisture in the walls was due to rising damp. A dpc was done about 3 weeks ago. So hopefully, there will be no further damp but just taking precaution with what moisture is left and if rising damp causes issues in future again.

If I dot/dab, are there any boards that I can use with this fixing method which are better than plaster/MR?

 

[SJPurdy]

Wedi Boards of 20mm thick or more can be dot/dab fixed over uneven walls, thinner Wedi boards can be fixed on a notched trowel bed of adhesive over flat walls (additional dowels/screws and washers also required). Very easy to use, lightweight and good surface to tile onto. Impermeable to water. Expensive?
"No More Ply" boards of 6mm can also be fixed dot/dab again with additional screw fixings. Will also need priming (SBR) both sides to improve adhesion.
"Google" both for full details, confirmation of my notes and fixing instructions.

 

[AliGage]

After 3 weeks.........How much damp is still in the wall. Is the wall an external wall, or internal brick partition?

 

[White Room]

I wouldn't be putting anything on the walls until any damp has gone, you also don't want any gypsum products on the wall...Over the years I've used Sovereign Render lite after damp injection or sand/cement with an integral waterproofer.

 

[p4ulo]

Might be worth running a de-humidifier in the room for a week to really try and drag the moisture out....leaving it damp will only store up problems for the future (unless you are selling the place soon of course?!)

 

[Unused Account 1]

P4ulo ,good advice ,ive done this a couple of times over the years ,just hired a de humidifier ,it solved the. Problem

 

[mika_98]

I like the idea of using No More Ply boards. A decent board for a reasonable price.
Assuming if I go with the dot/dab then screw in process, the idea would be to let the adhesive set and then screw in?

Not sure how much damp remains to be honest, its down to bare brick. Could always get someone in to check with the damp meter again. As for the dehumidifier, that's something I was considering so thanks for the reminder.

 

[Unused Account 1]

If its down to brick. Heat will dry the bricks out ,then youll see if its coming in from the outside.

 

[p4ulo]

@mika_98 - you screw whilst the adhesive is setting, so it squidges down tighter....

 

[Old Mod]

@mika_98 - you screw whilst the adhesive is setting, so it squidges down tighter....

Surely p4ulo u'd knock it out of plumb that way, u make sure it's bedded well, plumb and level it then mechanically fixed once dry?
Unless I'm doing it wrong?

 

[mika_98]

Sorry if this sounds silly but I assume this means pre-drilling holes for the plugs and screws. Is that correct?

Been looking at No More Ply boards. The process on their site advises to use a 'Mega Strength Adhesive' on the joins. Is that an absolute requirement?

 

[Unused Account 1]

Keep away from all that ,just go in when ready to tile ,dont tke chances ,only as good as last job

 

[p4ulo]

Surely p4ulo u'd knock it out of plumb that way, u make sure it's bedded well, plumb and level it then mechanically fixed once dry?
Unless I'm doing it wrong?

I personally like to screw it down whilst its going off, ok - maybe doing it til it squidges is a bit much, but using my level at the same time I ensure its still flat once fitted.

 

[p4ulo]

Sorry if this sounds silly but I assume this means pre-drilling holes for the plugs and screws. Is that correct?

Been looking at No More Ply boards. The process on their site advises to use a 'Mega Strength Adhesive' on the joins. Is that an absolute requirement?

Yeah, you will need to pre-drill and rawl-plug before fitting the board.
Dunno about No More Ply boards, I'm a HardieBacker man meself, cos I get it cheap at Topps.

 

[Doggit]

Damp bricks take about a month per inch to dry out. If you're down to bare brick, then the normal way would be sand and cement with a waterproof render in it, but you should use a washed sand. The drawback is it'sll take a few weeks to dry. If you want to get on with the work quickly, then you could go for the Dryzone system. Not cheap, but you can get the plasterboard up in a day. Last method to think about, is to blackjack the wall to stop the damp coming though, batten the walls using tanalised timber, and stainless steel screws, then plasterboard - but make sure the blackjack goes on the ground as far out as the plasterboard will go.

 

[mika_98]

Thanks. What is blackjack?

If I use adhesive and galvanised screws to attach something like Aquapanel/Hardiebacker board, do I have to prime the bare bricks first?

 

[mika_98]

If yes to priming, what should I prime with?

 

[White Room]

Thanks. What is blackjack?

If I use adhesive and galvanised screws to attach something like Aquapanel/Hardiebacker board, do I have to prime the bare bricks first?

Bitumen type substance, used for tanking and waterproofing.

 

[Doggit]

Okay, back to basics. A damp wall will loosen off any normal adhesive you use to tile with, or soak into plasterboard that you dot and dab. The trick is to stop the damp coming through, so you either use the hardibacker/Aquapanel type board to seal the wall, but this will create damp air behind the boards. By using blackjack DPM (google it), or the dryzone system, is that the moisture is forced to evaporate to the outside of the wall. Having put the Blackjack on, you can then safely batten the wall (as adhesive may not stick well to it), and then use plasterboard - which works out pretty cheaply, and to be honest, stainless steel screws aren't really necessary, just an added precaution. I'd only use the adhesive and screw method on a drywall, not a damp one, as the primer isn't going to stop the damp coming through.