Bathroom Subfloor from Weyroc Chipboard to what ??

[LordBucketHead]

The bathroom has 20 y/o cork tiles 'welded' to 18mm t & g Weyroc chipboard and the boards are 'nailed' to the joists with some gun-nails. Understandably, it creaks and croaks. I'm currently ripping it out. My local DIY cuts plywood to size but it doesn't sell t&g. Does it matter if it's t&g ? Joists are 15 1/2 centres. Your thoughts about using cementitious boards straight onto the joists ready for tiling ?
One final point.. could I use a less-than-18mm subfloor (which was fine with the thin cork tiles because the bathroom and the landing were not noticeably out of level) to accomodate thicker tiles or will it not be stable enough ?

Thank you for sharing your expertise.

 

[Deleted member 174758]

My local DIY cuts plywood to size but it doesn't sell t&g. Does it matter if it's t&g ? Joists are 15 1/2 centres.

You say 15-1/2in, but it's much more likely to be 400mm as we did go metric in the 1970s, after all (so you'll need the cuts in multiples of 400mm whilst plywood is always in Imperial sizes). If you go plywood make sure that it's an appropriate grade for flooring (at the very least you need WBP hardwood plywood). Whilst T&G is desirable it isn't absolutely essential

Your thoughts about using cementitious boards straight onto the joists ready for tiling ?

Cement board has much lower impact resistance than plywood and is therefore not used as unsupported flooring. If you go that way you'll need 18mm ply with something like 6mm cement board on top

One final point.. could I use a less-than-18mm subfloor (which was fine with the thin cork tiles because the bathroom and the landing were not noticeably out of level) to accomodate thicker tiles or will it not be stable enough ?

I don't know why it is, but this question comes up repeatedly. In general 18mm is the thinnest flooring that you'd ever want to install because thinner boards will tend to flex and move under load - and when you think about it a full bath has quite a considerable weight when filled with water and an adult human.... (anything from 80 to 300kg for the water alone, depending on tub size)

 

[LordBucketHead]

aye.. I served my time at the National Coal Board and it was all gallons per minute, pounds per square inch, British Standard Pipe, British Standard Whitworth, yards, feet and inches, Hg pressure and so on and so forth and then on top of that, 30 years working for American engineers. I need to ditch that filthy imperial habit tbh. Your excellent point about the weight of water had my head in my hands. I almost have a hernia lifting six 2 litre (2.6 gallons) bottles of water at Tescos. I've put floor tiles on the back burner as I'm increasingly intrigued by 'luxury bathroom vinyl flooring'. 18mm ply it is. The bath will have to be raised to accommodate the trap and I'll fix more ply for the feet packers. Thank you for your reply. Much obliged.