Bathroom floor tiles

[pnburdon]

Just ripped up smelly old floorboards in bathroom and replaced with 18mm chipboard T&G flooring (the type suitable for bathrooms). I now want to tile - do I have to put ply on top or can I tile onto chipboard with some treatment? If ply - how thick?

Thanks

 

[tictic]

either overboard with 6mm cement based backer board..follow m.i..for fixing..or
12mm -18mm wbp ply, primed underside and edges with acrylic primer.

screwed down every 150mm-200mm.

or lift the lot and put 22mm-25mm wbp ply down onto joists and tile..

 

[Richard C]

What on earth possessed you to lay new chip (crap) board as a tile base, it’s probably the worst thing you could have done! Your going to have to overboard it anyway so I’d take it up & lay new WBP ply, 18-25mm depending on floor construction; you can tile straight onto that.

 

[skitzee2k]

Just ripped up smelly old floorboards in bathroom and replaced with 18mm chipboard T&G flooring (the type suitable for bathrooms). I now want to tile - do I have to put ply on top or can I tile onto chipboard with some treatment? If ply - how thick?

Thanks

You can do as the other guys have said...or you can use a Highly deformable adhesive of an S2 grade.

I'd go with the ply overlay idea.

 

[tictic]

You can do as the other guys have said...or you can use a Highly deformable adhesive of an S2 grade.


skitz..dont want to have a fall out here mate...

but you know and i know and others will know what a S2 grade addy is..

but a lot of poster wont know...so can you not give posters a few names..i.e weber/ardex/mapei/bal..etc..and the name of the adhesive..

 

[pnburdon]

Richard - Nothing possessed me - I never inteded to tile straight onto the chipboard but I am not a pro and thought that it was standard to lay chipboard and overboard it. I didnt even know until yesterday that you could buy 25mm ply to use as flooring - although looking at it it's not cheap!

I havent actually laid the chipboard yet - I have a floorless bathroom and 3 sheets of chipboard in the garage - but am leaning towards tictic suggestion of using 6mm hardie backerboard 250 to overboard the chipboard......

 

[Richard C]

I’m not a lover of over-boarding & if you don’t get it right, you will have problems; have a read through the archive posts where you will find at least one recent thread regarding tile failure where backer boards were used over chipboard. Personally I would never trust a chipboard floor as a base, far better to start again with a well supported, single board thickness floor; overlaid floors will never be as rigid unless they are bonded as well as screwed. If you’ve not laid the chip board yet, I would advise you seriously consider going with WBP ply, which tictic also suggests. It’s not as cheap as chipboard for sure but it’s the best base you will get & you won’t need the backer boards which will work out more expensive. The ply thickness you need will depend on joist span/size/pitch & the aim is to reduce flexing in the floor as far as possible, it's flexing which causes tile failure. Each floor needs to be assessed but for the average bath/shower room, 18mm will be sufficient; the most your likely to need is 22mm; 25mm would normally only be required in heavy traffic/use areas such as kitchens, halls etc.

 

[pnburdon]

So I took Richard's advice and took the chipboard back to the shop and boughth some 18mm WBP plywood which I have laid on the joists. So next question is (not really a tiling question mind..) what size/type screws are best to fix ply to joists and what distance between?

Also do I need to do anything special where there are joints between 2 bits of ply?

Thanks

 

[Richard C]

Minimum twice the thickness of what you’re screwing so 38-40mm but longer won’t matter. Screw @ 150-200mm crs max. Seal the underside & edges of the ply with an SBR primer/sealer before laying. Lay the largest boards you can physically get into the room, with longest edge down the centre line of a joist if possible; avoid cross joist joints in the centre of the room if possible; any cross joist joints must have minimum 100 x 50mm noggins fixed between the joists to support the edge of the ply; only exception is around the edge of the room where you can leave out noggins if it’s unlikely it will ever be walked on or is not subject to any load worth mentioning. Butt the ply as close as possible, immediately before tiling, skim the joints with tile adhesive & stick 3 layers of 40mm overlapping glass fibre reinforcing tape over the join so it ends up about 80mm wide. Most cement powder addy’s don’t require a primer but always follow the MI’s & never use PVA.

 

[pnburdon]

Thats pretty comprehensive! Thanks

 

[pnburdon]

Two more ?s about the sealer primer...can you suggest a couple of names for sbr primers? Screwfix do a mapei primer g - is this the same?

Also you say seal the underside and edges - so I should paint primer on the entire underside of the ply? WHat is the purpose of this?

Thanks

 

[Richard C]

As I exclusively use BAL products I use this;
http://www.bal-adhesives.co.uk/products/bond-sbr
In reality, any SBR primer/sealer will probably do & the reason for priming the underside & edges of the ply is to reduce the risk of moisture or water getting in; if this happens, the ply can expand/warp & crack the tiles. BAL doesn’t recommend priming the tile surface but always check your chosen tile adhesive manufacturer’s recommendations.

The only Mapei primer I could find on Screwfix was “Primer G” which is for priming bare Gypsum plaster or Gypsum based screeds prior to using cement based adhesive (to avoid a chemical reaction). If you want to use Mapie, “Primer S” may be more suitable;
http://www.mapei.it/Referenze/Multimedia/538_Primer S_gb.PDF