overboard timbers with 3mm plywood?

[budeman]

Hi,

First post here after months of reading....

I want to tile our kitchen/breakfast room - kitchen floor is screed and the breakfast room is floorboards (quite new as it is an extension). I know I need to ply the breakfast room but I was wondering what the thinnest mm I can get away with so that the kitchen floor isn't too much lower than the breakfast room? The timbers in the breakfast room are quite solid, not any bounce in them that I can see so I was going to see if I could put down 3mm ply (think it is actually 3.7mm) and just use extra adhesive when tiling the kitchen. Does this sound acceptable?

Other issue that I have is that the kitchen floor slopes v slightly downwards away from where it joins the breakfast room - I am not sure how many mm it is but rather than putting self levelling compound down (looks quite tricky) could I just build up the adhesive a bit more? What mm difference would it be ok to do this?

Also regarding the adhesive are there any recommendations of makes to use/avoid

Thanks,

Mark.

 

[lancenotalot]

If your worried about height use backer boards min is 6mm 3mm ply wont do anything.You can bed up with powdered adhesive up to about 10mm.A floor needs to be flat rather than level.Being out a few mm over a few meters is nothing to worry about.

 

[tpt]

you'll need to use a backer board such as no more ply as prev. suggested over the wood floor, on that you'll need a flexi adhesive and grout, use the same grout all over, and you can use the same adhesive or switch to a normal cement based adhesive on the screed.

one thing to be careful of though, if the two floors meet (sounds like they do) you will get a difference in movement between the two and this is a prime cause of cracking across the 'divide', you can use a decoupling mebrane, an expansion joint or a few other methods but be aware of it.

also be aware that 6mm is still a lot to make up with adhesive - may be worth using some self leveller to help first

 

[Richard C]

“Not any bounce” is not a reliable test & 3mm ply overboard is a joke & of absolutely no use whatsoever; your tiles will most likely fail. A kitchen/breakfast room is also a heavy use/load area which will need a very, very good base if it’s going to last. If it’s proper T&G timber floorboards in good condition then, maybe, a decent 6mm tile backer board will cope but I would go for 12mm; it depends on the joist size/pitch/span.

A solid floor meeting a suspended timber floor will most likely need an expansion joint. A decoupling membrane is not sufficient & even over boarding the lot with backer overboard may not work due to the differential movement that will occur between the two floors; you will most likely end up with an almighty crack where the two meet.

A decent cement adhesive will give you 4-6mm & you can use it to fill voids up to 10mm or so but it would be foolish to attempt to level an entire floor with tile adhesive, that would be a challenge for even an experienced tiller; by comparison laying an SLC is a doddle but it will still not provide a solution the your dissimilar floor substrates.

I would advise you read the tiling forum sticky & archive posts before doing any more work, it could prevent you making disastrous & potentially expensive mistakes. Use only quality trade tiling materials of the correct type for your tiles & tile base, cheap own brand & DIY products are mostly crap; an archive search will give you good product advice.