Floor Levelling over WBP Ply

26 Nov 2007
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United Kingdom

I've pulled up the chipboard tongue and groove in my upstairs bathroom, and laid an 18mm WBP Ply sub-floor (solid noggined), ready for ceramic tiles.

The joists are not quite level, so there's a slope from the left to the right of the bathroom of about 4mm, with a deeper dip of about 6mm in the centre of the floor. This needs to be sorted so the tiles lay flat and don't crack.

Can I cure this with floor levelling compound - I'm going to lay ceramic tiles over the Ply - or do I need to pull up the ply and level the joists and noggins, then re-lay the ply? (I really don't want to do that!)

If a levelling compound will do it - any suggestions? (I got the ply from Wickes, and it seems a bit more flexible than I'd have expected - so maybe avoid a wickes compound?)
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It might have been better to level the joists with firing strips before laying the ply. You can probably use a form of self leveller but it will have to be flexible. Also. You say the ply is a bit flexi so it may have been better to lay in some 18mm tongue and groove floor sheets such as weyroc and seal this over. Much more robust

When you come to lay the tiles get a top quality floor tile adhesive dedicated to the job in hand skimping on price here could lead to problems later. Maybe one of the tiling guys will pick this up and give you better advice than myself :D
lift the old flooring find the highest point of the floor and level a line all way around now nail timber to side of old joists at each edge only infact use srews itl be easier to ajust if needed ok then run to string lines accross the joists put them a quarter of the way in from fixed edge then bring each joist up till it just touches the line and fix it work away wont take long then fix 22mm mr chipboard flooring ontop make sure to glue the joints people dont but its not correct hope it works out remember screws are alot easier to remove and adjust good luck :D
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if you haven't don it already you can use the following product made by MAPEI,its called fibreplan,
just make sure you prime floor first and make sure its (screwed down)not nailed!!!!.heres the jargon.
Water-bored ultra-fast hardening self levelling fibre reinforced smoothing compound.
Fiberplan is used for smoothing and levelling from 3 to 10 mm over adequately anchored wood substrates and wooden boarding where good resistance to loads and traffic is required; Fiberplan is suitable for wheeled chair traffic and for heated floors.
Fiberplan can only be used internally.
Smoothing of old and new timber floors: wooden boarding, chip-board panels, plywood, parquet.
Smoothing cement, terrazzo, old ceramic tile, natural stone substrates. Coverage
1.6 kg/m2 per mm of thickness. Packaging
25 kg bags.
ive used it heaps as under amtico its the bee's knees...
good luck

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