New ply bathroom floor for Karndean

12 Apr 2012
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United Kingdom
Hi all,

We're redoing our bathroom at the moment and as the floorboards are in poor condition I'll be pulling them all up and replacing with 25mm ply which will then have a Karndean floor professionally installed.

I can't get full 8x4 sheets of ply up the stairs so will have to rip them down to either: 600x2400 or 900x2400. I'm in two minds which way to go, 600x2400 will result in less waste but more joins in the floor, 900x2400 would mean I waste more as I probably wont use the 300x2400 offcuts but it might make for a better floor.

What do people think?
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I think that you should post a pic of the floor - it would show the condition of the boards and the position of any fixtures. Its unusual for bathroom boards to be in such a delapidated condition that they must be replaced.

Karndean more often appears to go over a SLC than a ply underlayment.

Raising the FFL height will have to be taken into consideration no matter what underlayment is used.
Thanks for your reply Ree.

The floor boards are in poor condition, they are 130 years old and have been butchered so many times in the past through wiring, rewiring, heating, new heating, water damage etc that it is best to start from scratch.

The joists underneath are fine generally and my Karndean fitter has sais 25mm ply will be a great base to work from. The floor level is not an issue.

I think I'll go for 900x2400 lengths of ply, it means more waste but less joints which can only be a good thing.
You be better using 18mm plywood then 6mm rather then 25mm. You shouldn't be laying Karmdean straight to 25mm unless your having a fibre smoothing compound screed ontop of the plywood.
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Thanks Daz, I'll speak to the fitter and see if he thinks it would be better to go 18mm then 6mm. I can get full sheets of 6mm up the stairs as they have a bit more give in them.
The number of joins won't matter too much as the fitter will be planning on feather edging the ply anyway in preperation for the Karndean.

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