How rigid should my subfloor be?

[Lindav01]

Hi, we are overboarding an old wooden floor. We found evidence of woodworm which we have been led to believe has been treated, although I have poured on some more shop bought treatment just to be sure. Some of the old boards are in a sorry state due to this, and there is some movement through the edges of the ply, in a high traffic area.
We are going to use ceramic tiles with a flexible adhesive - how much flex can we get away with underfoot? We have screwed floorboards and ply as much as possible, and need to be fully tiled by the weekend. As we are both working full-time, you can see this leaves not much time to redo it the way we should (new boards).
We also have a concrete section of floor in the corner by this dodgy bit, can we just use self-levelling to bring it up level with the ply?
Thanks for any advice,
Linda x

 

[gcol]

Hi and welcome Linda!

Some of the old boards are in a sorry state due to this, and there is some movement through the edges of the ply, in a high traffic area.

Any visible movement is too much I'm afraid.

We are going to use ceramic tiles with a flexible adhesive - how much flex can we get away with underfoot?

Virtually none - the flexibility of adhesive is more to deal with the expansion of the timber rather than the bounce level of the floor.

We also have a concrete section of floor in the corner by this dodgy bit, can we just use self-levelling to bring it up level with the ply?

As long as you use suitable self levelling comound then this is ok. But as I've hinted above, you need to sort out the floor before you tile or you're just wasting your time.

 

[Lindav01]

Thanks for the advice, I have taken the ply up and put 100s (slight exageration) more screws into the floor boards where they meet the joist. I only have 2 small areas left that I am worried about, but I wonder if maybe I am being a bit paranoid as the movement is maybe only noticeable to me. We have used one layer of self-levelling, but need to put a second layer to build it up, to a thickness of 10 mm although I see this is not ideal either!
So, as we are adamant (hubbie not budging) that we are to lay floor tiles, they will be laid up to most of the cupboards, not underneath as planned, and I'm keeping a spare box in the garage for the first couple of repair jobs!
Now I just have to find out how I can lay tiles to a unit that is not yet there? I guess we could just measure where we think it will come to and hope for the best. And pray that the new tiles don't get damaged in installation!
But thanks again for the advice, with all the snippets I have read on here, I have learnt so much!
Linda x