Bathroom tiling - advice needed

[Bilis]

Hi all,

I have recently came across this forum which is a real treasure trove for the DIYer like me (redecorating our first house). I've read dozens of posts and the stickies/wiki articles but still have a few questions that someone will hopefully be able to answer me.

I am planning to tile the floor and two walls floor to ceiling in the bathroom.

I have replaced the floorboards with 18mm ply. I will lay No More Ply backer boards on top and tile on them. Joists are approx. 40cm centres and I am not planning to install any noggins due to time/skill constraints.

The walls are stud walls. I have bought standard 12.5mm plasterboard for the stud wall (I wasn't aware of the green water resistant plasterboards or tile backer boards at the time). I will be tanking the plasterboard in the immediate shower/bath area.

My tiles are 30x60cm and ~5mm thick for the floor and 25x40 and ~3-4mm thick for the walls. I am jot sure but I think they are ceramic tiles.

I am not quite clear on the following:
1. How much of a problem is not having the noggins installed? Is it worth installing decoupling mat to compensate for some potential flex in the ply?
2. Standard advice is to use 6mm No More Ply board doe the floors. Is it OK to use 12mm as I want to raise the bathroom floor to minimise the step (the rooms will be fitted with 20mm engineered flooring ot op of the existing floor boards plus underlay and probably overboarding but that's a different subject)?
3. Will the plasterboard hold the weight of the wall tiles or should I install the backer board instead? I have already bought the plasterboard so don't want to waste it unless I have to.
4. Does the plasterboard need to primed where it's not tanked? I've read something about priming with PVA - does it need to be diluted with water? To what ratio?
5. Sticky post mentions 20mm notch U shape trowel foe the floor. What size notch and shape trowel should be used for my wall tiles?
6. What's the best way to cut out a rectangle in a tile (make it an L shape) so it would fit around the boxed in soil stack? Not sure if scoring would work here?

Thanks!
Vilius

 

[foxhole]

5mm tiles sounds like a wall tile .

 

[Bilis]

5mm tiles sounds like a wall tile .

I measured incorrectly - the floor tile is actually 7-8mm thick.

 

[JaimieH]

Here's my advice to help you along -
1. If your floor still has any flex when you walk across it then I'd take up the plywood and add noggings to strengthen. I know it will be a pain but it's best to do it now. Decoupling membranes are designed primarily to relieve lateral movement between the substrate and the tiles and won't offer much protection against flexing of the floor or prevent any vertical movement.
2. 12mm NMP will be fine to use if that helps with the finished floor level. Make sure you use the Mega Adhesive along the joints as well as underneath.
3. Bare plasterboard will take up to 32kg sqm including adhesive so your choice of wall tiles should be well within that limit. Certain tile backer boards can take up to 100kg sqm but obviously that is much more than you need.
4. Personally I prime everything that will absorb water and that includes plasterboard. Don't use PVA though, acrylic tilers primer is the one to use and ideally use the same one as your adhesive manufacturer, although to be honest I don't very often follow my own advice.
5. 20mm u-notch trowel or 12mm square notch will be fine for your floor tiles. Make sure you back skim each floor tile before you lay them, this will greatly improve the bond and also help to achieve a greater coverage. For your 25x40 wall tiles I'd probably go for a 10mm square notch. Try to get your walls bang on flat and plumb when you reboard and tiling will be much easier.
6. You can't score and snap a L-shaped cut, you'll need to firstly either wet cut or angle grind the short cut. You can score and snap the other side following this if you want to.
Good luck with everything.

 

[Bilis]

Here's my advice to help you along -
1. If your floor still has any flex when you walk across it then I'd take up the plywood and add noggings to strengthen. I know it will be a pain but it's best to do it now. Decoupling membranes are designed primarily to relieve lateral movement between the substrate and the tiles and won't offer much protection against flexing of the floor or prevent any vertical movement.
2. 12mm NMP will be fine to use if that helps with the finished floor level. Make sure you use the Mega Adhesive along the joints as well as underneath.
3. Bare plasterboard will take up to 32kg sqm including adhesive so your choice of wall tiles should be well within that limit. Certain tile backer boards can take up to 100kg sqm but obviously that is much more than you need.
4. Personally I prime everything that will absorb water and that includes plasterboard. Don't use PVA though, acrylic tilers primer is the one to use and ideally use the same one as your adhesive manufacturer, although to be honest I don't very often follow my own advice.
5. 20mm u-notch trowel or 12mm square notch will be fine for your floor tiles. Make sure you back skim each floor tile before you lay them, this will greatly improve the bond and also help to achieve a greater coverage. For your 25x40 wall tiles I'd probably go for a 10mm square notch. Try to get your walls bang on flat and plumb when you reboard and tiling will be much easier.
6. You can't score and snap a L-shaped cut, you'll need to firstly either wet cut or angle grind the short cut. You can score and snap the other side following this if you want to.
Good luck with everything.

Thank you Jamie for your detailed response, this has been really helpful.

I am planning to use No More Ply primer for the walls as I have already got it, unless it's in a tanked area where I'm using the primer from the tanking kit.

One more question about priming - do I need to prime the tanked area after the tanking has been completed, ie between the tanking "paint" and the tile adhesive to improve the adhesion?

Many thanks!

 

[JaimieH]

No problem Bilis, no need for anything else after the tanking, just tile straight onto it once it's dry.

 

[Bilis]

No problem Bilis, no need for anything else after the tanking, just tile straight onto it once it's dry.

Great, thanks Jamie. Fingers crossed the bathroom will be finished by the end of the week!

 

[JaimieH]

Nice, hope it all goes well.