Subfloor prep for tiling

gluppers

Hi. I removed old tiles from a small kitchen, which revealed a wooden floor with remains of adhesive and possibly an old primer. I plan to put down new tiles. There is a general smell of dampness from previous washing machine leaks, but obvious signs of rot.

Unfortunately my budget is tight, but I suspect I should at least clean and level the subfloor the best I can and apply some sort of primer. Perhaps use a dehumidifier too?Any advise is very much welcomed, thanks

20241007_184046.jpg

10-10-20

Hi, that looks bad enough. If that's a suspended floor, can you check if the subfloor vents are sufficient and open? It might be that the damp is being trapped having risen from the subfloor.

Normally in this situation plywood is fitted onto the floor to strengthen it, screwed in every foot or so, but this will add cost and you might be safe enough with tiling directly, it all depends on how the previous floor failed, really. You need to test how strong the floor is - there should be no deflection (movement) when walking at all, but the best advice would be to lay probably >12mm ply perpendicular to the floorboards.

Finally, SBR is the primer/bonding agent that you need here, it's available from builder's providers in various brands, one from Evostick (technik primer 918) is specifically for tiling, but it's just SBR in a pre-diluted form. Just dilute standard SBR by 50% (1:1) and apply it over the wood with a roller and let it go tacky (1hr in good drying conditions).

gluppers

https://www.boards.ie/discussion/comment/122696142#Comment_122696142

Thanks a mil! Fantastic info. The floor is sturdy on foot. The previous tiles took a fit of force to pull up in general, not bad condition. They had been there for 20 years and only had damage in a small section near the washing machine. I suspect fractural damage from the previous renter, though not ruling out loosening of the tiles in this area from washing machine leakage. Thanks for the tip on the SBR

GreeBo

If the floor has any movement (and it will!)

The you should install some sort of decoupler membrane to prevent the tiles/grout from cracking. The older approach is to stick 9/12 mm of ply over the existing floor, but thats likely to cause havoc with levels.

Schluter Ditra would be a well known product for this
https://www.instructables.com/Install-DITRA-on-a-Wood-Subfloor-stop-Cracked-Tile/

gluppers

https://www.boards.ie/discussion/comment/122697402#Comment_122697402

Thank you, nice info. What is that thin set being laid under the ditra in that video? I already bought the SBR primer, can that be used in conjunction with your suggestion?

10-10-20

Thin set is just a name for tile adhesive. Yes, SBR is used as I said.

gluppers

Just wondering...if I go for putting down the ditra, couldn't I leave the remaining harden bits of adhesive and grout on the sub floor as I'll be covering it anyway. Correct me if wrong

10-10-20

https://www.boards.ie/discussion/comment/122698834#Comment_122698834

Only if it's perfectly level. Ditra will have a spec for the level of levelness - check that and go by it.

GreeBo

https://www.boards.ie/discussion/comment/122698937#Comment_122698937

Ditra et al are installed with a notched trowel so if you cant get all of the existing adhesive off, you might be better off pouring a thin self leveling compound to give a flat surface.

There goes the budget! :)

gluppers

https://www.boards.ie/discussion/comment/122703831#Comment_122703831

I think I might go with that option, thanks. Doesn't seem too dear for a bag. I might just invest in a good mixing paddle too