Subfloor preparation - matting vs board on plywood

[muppetman74]

Bit of an intro - I'm a competent DIYer and have been refurbing the bathroom on and off for the last few months - currently the only bathroom in the house so am refurbing around the family using it, hence it's taking a while.

So I've got the shower cubicle in and installed (tanked and tiled) - tray was installed on a 10mm-ish bed of Mapei rapidflex on ply subfloor - the shower has been in use for about 6 months and the tray is absolutely solid with no movement.

Herein lies the problem - I fitted the subfloor a year ago before I had done any research. I ripped out the soggy 18mm T&G chipboard and replaced the entire subfloor with large sheets of 25mm WBP ply - 400mm joists, screwed at 200mm with 80mm screws (not cheap and bloody heavy on your own!) The floor has absolutely no noticeable deflection.

It's now time to tile the floor. Area is approx 4m x 3m. My original plan was to tile straight onto the plywood (hence the 25mm) as that's what out tiler did years ago. I now know things have moved on, and ideally should overboard with a tile backer but the issue is I already have a 7mm step into the bathroom, plus another 15mm or so for tile and adhesive so I don't want to add 6mm etc for tile backer.

Would it be safe to tile straight onto the plywood (25mm with no deflection) even though its not the accepted way? I understand why tiles can crack on a timber base, but with a solid 25mm ply floor? The shower tray has been rock solid, which is giving me some confidence. The other option is to use a matting like Ditra, but is seems as though that's more for concrete floors unless I'm mistaken.

The other thing I should mention is that I have NOT SBR'd the bottom and edges of the ply sheets as I rushed into this and its now too late!

This is our "forever" house so I'm not opposed to spending a bit more cash and effort for a lasting job.

 

[LM]

You must uncouple the floor for a few reasons and if your worried about height then Ditra stuck with Ardex AF200 for example would be the way to go for piece of mind. The only concern there would be the size of tile you intend to use, the minimum tile size is 50mmx50mm for Ditra.

 

[muppetman74]

Thanks for your reply - that's the bit I wasn't getting...lack of deflection is one thing but I hadn't considered the uncoupling element.

I haven't chosen the tiles yet so no issue with size.

As regards the Ardex adhesive, is there a Mapei equivalent? I can get a good deal on Mapei through a mate, but would go for the Ardex if essential.

 

[Dave]

Thanks for your reply - that's the bit I wasn't getting...lack of deflection is one thing but I hadn't considered the uncoupling element.

I haven't chosen the tiles yet so no issue with size.

As regards the Ardex adhesive, is there a Mapei equivalent? I can get a good deal on Mapei through a mate, but would go for the Ardex if essential.

As far as i know there isn’t any other than the AF200.

 

[J Sid]

Mapei vinyl adhesive is what was used for years.

 

[muppetman74]

Thanks all, I'll search for some of the Ardex.

Just so I don't make any further mistakes(!) please critique my plan:

1. Clean plywood thoroughly.
2. 3mm V notch Ardex down to secure matting.
3. Lay down matting.
4 10mm square notch Mapei rapidflex for 600x600 Porcelain.

Do I need to SBR the ply before the Ardex (Ive got some Mapei Pimer-G which I think is the same thing as SBR?

Thanks!

 

[Dave]

Thanks all, I'll search for some of the Ardex.

Just so I don't make any further mistakes(!) please critique my plan:

1. Clean plywood thoroughly.
2. 3mm V notch Ardex down to secure matting.
3. Lay down matting.
4 10mm square notch Mapei rapidflex for 600x600 Porcelain.

Do I need to SBR the ply before the Ardex (Ive got some Mapei Pimer-G which I think is the same thing as SBR?

Thanks!

Info required ..

ARDEX AF 200 PLUS - Ready Mixed Uncoupling Matting Adhesive

ardex.co.uk

 

[muppetman74]

Thanks for all your help. Must say, this is the first trade forum I've been on where I've received good advice without the "get a man in" brigade, so thanks.

 

[J Sid]

Good luck and keep us posted oon progress

 

[Dave]

Thanks for all your help. Must say, this is the first trade forum I've been on where I've received good advice without the "get a man in" brigade, so thanks.

Good luck and let us know how you get on. 👍

 

[Andy Allen]

I would get a man in....

 

[LM]

Thanks for your reply - that's the bit I wasn't getting...lack of deflection is one thing but I hadn't considered the uncoupling element.

I haven't chosen the tiles yet so no issue with size.

As regards the Ardex adhesive, is there a Mapei equivalent? I can get a good deal on Mapei through a mate, but would go for the Ardex if essential.

Yes Mapei Ultrabond Eco VS90 is also approved and use a B1 or 2 x 6mm V notched trowel.
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Also you don’t prime the plywood with these adhesives just make sure they’re clean and dry.
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Personally the smallest square notch trowel I’d used for 600’s would be a 12mm also back buttering the back of the tile with a flat skim of adhesive.

 

[Tony_C]

Another option you have is Nicobonds plastic ply which is self adhesive and only 2mm thick If I remember right. It is a product for tiling onto timber substrates.

I have never used it and I also know nothing much on on it apart from that it exists as I've never understood it really to be honest but it's an option for you if you wished to look into it further with less of a step up.

 

[muppetman74]

Thanks again, all - I'll tap my mate up for the Mapei Ultrabond and I'll invest in a new trowel - I've got two other bathrooms to do after this one so I don't mind splashing out as I'll use the tools again.

I'll also check out the plastic ply - self adhesive sound like it may save some effort.

 

[Boggs]

Another option you have is Nicobonds plastic ply which is self adhesive and only 2mm thick If I remember right. It is a product for tiling onto timber substrates.

I have never used it and I also know nothing much on on it apart from that it exists as I've never understood it really to be honest but it's an option for you if you wished to look into it further with less of a step up.

Just watched the grainy installation video on YouTube, don’t think I will risk a floor with it.