OSB Prep options - self levelling compounds?

[Daveyd]

I know I know OSB3 board is ***** for tiling onto. If only I'd known at the time! Ah well its now pretty well impossible to rip it up and start again SO.....

How would I best prep my bathroom floor before laying my ceramic tiles?
I've got some good quality flexible adhesive and also some membrane matting (thin material type)

The OSB is 18mm and has only a very tiny amount of visible flex with the fat man test. Another concern is that there is a bit of a ridge where it is higher than the rest maybe 20mm higher.

One thought is to use self levelling compound straight onto the OSB then stick the membrane using PVA. Then tile.

OR Lay plyboard, prime then membrane and tile (but the ridge might still be a problem)

My favourite option is to use SLC to get a nice even flat floor but what are peoples experience of using this stuff straight onto OSB? Would the small amount of flex pose a problem?

What do I do!?!?

Any help or advice much appreciated!

Dave in Cornwall

 

[J Sid]

over board with a cement board, glued and screwed and then tile. Screw down obs first being careful not to hit pipes

 

[Flintstone]

I agree with Julian. When you say step, do you mean the bathroom floor is lower or higher then the hallway etc ?
Throw that pva in the black bin!

 

[Bathfix Bob]

It sounds like you have a 20mm high spot, thats worrying. 5-10mm you could loose but 20mm??!!

 

[hmtiling]

Overboarded as above then latex

 

[J K Tiling Cornwall]

Hi Dave
Not much else to add as all sound advice so far. Would overboard using a 6mm cement backer board either bedded down with a flexible rapid set adhesive (I personally tend to mix slightly runnier to keep the bed depth as low as possible and to compensate for the boards drawing in the moisture from the adhesive) or a polyurethane glue. Then screw down once set with 4x20mm screws so as not to risk pipes and wires. Then good to tile. Avoid Pva like the plague anything dusty or porous just use a quality primer. I tend to use dilute SBR. Is the ridge at the door threshold? From your post I get the feeling you may have over boarded originally with the 18mm OSB?

Hope the weather in North Cornwall is a bit better than here.

James

 

[Daveyd]

OK just looking at the ridge - where 2 of the OSB boards meet it gets higher in a long line or ridge (Not a step as if compared to bedroom floor level)
The difference in height over the bathroom floor is about 20mm or perhaps even more however the difference in height is actually spread out as the floor slopes slightly both ways. Its as if one of the joists is higher than the rest. The ridge itself is not actually that pronounced as the slope gradually makes the height difference. Hope that makes sense? Its more like 2 slopes meeting rather than a ridge. But as you can imagine this does form a slight ridge.

I guess laying the tiles so the joins are aligned with this ridge might help prevent them cracking I suppose

OK so screw down the OSB as much as possible. Then glue and screw down 6mm cement backer board followed by a latex based primer presumably so the tile adhesive has something to cling to?

Any need for the thin material membrane I already have?
Would 12mm be better?

Cheers

Dave

 

[Daveyd]

No the weather is horrible here too - proper wet rain and so muggy! Its a cabin I built from scratch - I used 18mm OSB straight onto 400m spaced joists

 

[J K Tiling Cornwall]

6mm should be fine have never had any issues, it's alot easier to cut and screw. The material membrane sounds like a anti fracture matting? More for lateral movement but wouldn't hurt to use it (usually bedded on flexible adhesive and troweled over).

Cheers

 

[J K Tiling Cornwall]

In that case would definitely recommend using the matting if all new built. Might prevent any problems should the wood expand and contract.
Try to bridge the join in the OSB boards with the backer boards. Hopefully that all helps. I've been working in Falmouth, just as miserable weather wise. Good luck

 

[Daveyd]

Cool thanks everyone for the help. Gonna rasp and rough sand down the ridge, overlay with 6mm cement board then glue down membrane with PVA before tiling with flexible adhesive.

I can't see any reason not to glue the membrane with PVA. Is there any reason?

 

[Flintstone]

Don't use pva Dave it has no place in tiling. Stick the membrane down with tile adhesive providing it's actually a suitable membrane..

 

[J Sid]

Cool thanks everyone for the help. Gonna rasp and rough sand down the ridge, overlay with 6mm cement board then glue down membrane with PVA before tiling with flexible adhesive.

I can't see any reason not to glue the membrane with PVA. Is there any reason?

what make of membrane are you using and what is this pva product you want to stick it down with ?