Guys

I've had some great advice on here on how to tile a new bathroom floor (suspended wooden floor, 7 inch joists, noggins, etc, pretty solid). I've also contacted various companies (Mapei, Ditra, etc) and now have a plan to move forward with. Before I go out there and spend lots of money, I just wanted one final sense check - all advice gratefully received!

1). Fix 22mm WPB ply to joists (although I have been told 18mm would be plenty???)
2). Lay my 150W Devi floor mat directly on my unprimed ply wood (Was told by someone that I really ought to use insulated boards if using more than 100W mat system???)
3). Prime the top of the Devi mat with Mapei Eco Prim C (this surprised me but was told to do this by Mapei as it helps the Fibreplan bond- what do you reckon???)
4). Use Mapei FibrePlan on top of Devi mat as SLC layer - leave to set (Mapei advice again)
5). Layer of Mapei Keriquick mixed with Laytex Plus (1/6 to 20kg bag).
6). Bed / attached Ditra mat in above adhesive / Laytex Plus mix.
7). Another layer of Mapei Keriquick mixed with Laytex Plus (1/6 to 20kg bag) as adhesive for tiles.
8). Tiles - Limestone / natural stone.
9). Grout with Mapei's Ultracolour Plus.

What do you think guys? Probably overkill no doubt, but any serious issues? (such as do i need to insulate UFH on a plywood base, is it OK to use the Laytex Plus for the tile adhesive mix, Should I prime the plywood, if so, with what?, etc).

Also would someone be kind enough to tell me layer by layer the thicknesses involved as I need to keep this to a minimum e.g. 22/18mm ply, 3mm slc, 2mm adhesive, etc?

Thanks!!!!!!!!!

All seems fine to me...a bit over kill from mapei but OK to go i say..

Good to know u approve Dave!

Unfortunately I have ended up with 18mm marine plywood instead of the 22mm WBP recommended (don't ask why or how - please!!!!). Given that my joists are so stable and I intend to use noggins to stregthen it even further do you think I'll be ok with the 18mm? Also can you confirm what I should use to seal it please? (could I get away with the ECO Prim T for that as well?)

Thanks!

would have went with the 22mm but the 18mm should be ok as long as as there is almost no movement in the floor

18mm will suffice if the floor is solid just prime the substrate with sbr primer and use a flexible adhesive

you need sealer for your limestone mate

you could always overboard the 18mm plywood with another layer of 6mm plywood which would of course go across the joins in the first layer.
IMO - Devi reccommend 100w mats maximum for timber substrates - so your someone may be correct with insulation boards!
Fibre plan is good and it should just cover the top of the UFH cables.
Your Flexible fast set adhesive should be WHITE for Limestone.
IMO - Stone seal/impregnate the limestone surface before you fix.

Timeless John.

i didnt think you were supposed to use latex addative for putting the ditra down ?

what makes you say that chris..?

Thanks guys!

You're right about the 100W Devimat for plywood, so i'll go for that as opposed to the 150W with insulation boards.

The laytex additive with the adhesive was a recommendation by Mapei - so I assume this is correct?

I need to prime the plywood under and sides (and maybe the untiled top under the shower tray i was thinking?) and really don't want to spend £30 odd on an expensive primer. Can someone confirm if the ECO Prim T that I am using anyway ontop of the Devimat as recommended by Mapei would do the job for the plywood too? If not what are my options?

yes that will be fine..

honestly i cant remember why but it was in my mind so there must be a reason or somethink i have read somewhere

just cant remember where ?

Personally chris.. i would not use a latex admixture to stick it down....the membrane is designed to un-couple and not combat deflection, so the need for a highly flexible isn,t needed IMHO..

The membrane is for lateral stress...thats why i said mapei's advice was a bit over kill...

So S1 adhesives will be fine if the floor is solid to start with , as it should be anyway..

it might of been schluter when i went to one of their training days

im waking up slowly

OK guys so what if I just don't mix the laytex additive into the adhesive ontop of the SLC/Fibrepaln layer to bed in the Ditra? Is that better?

Also can someone please tell me why it is that the plywood is never sealed / primed on top and only on the sides and underneath? And what should i use to seal it with?

Thanks

Guys

A new issue that I need some advice on...

One of the bathroom walls that the shower will be against is a solid wall that has been plastered (pretty badly). The wall is made of thermal blocks and has a long crack along it covering an expansion gap. Someone has suggested removing the plaster completely, using a metal mesh over the expansion gap and using a Sika sand and cement product with waterproofer to re-plaster the wall. Maybe even tank that for extra cover once it has dried. How does this sound to you guys?

Thanks

I would hack off the plaster and dot and dab the wall, then tank. Light weight blocks are a pain to do for solid plaster, so much cracking.

Been checking this out and 'sticking' aqua panel to a solid wall / blockwork is a no-no.

My choices then are dot n dabbing regular pb to the wall and tanking it or rendering it with snad and cement and tanking that. What do you guys favour and do you se any issues with cracking/movement with the render option?

The trouble with light wieght blocks is there is so much movement on the joints, if you render and it cracks it will follow through to the tiles. Dry linning will not crack if there is any movement in the block work,