Retiling an MDF false floor - the old tiles are cracking off

[Wilbur111]

Hi.

Our house had bad subsidence so we levelled the kitchen floor by building a frame and sitting 10mm (or maybe 12mm) MDF on top. We tiled it but since then the tiles have popped up in places and we're about to retile it.

I'm reckoning the tiles popping up could be for a number of reasons.

1. It was MDF instead of Plyboard.
2. There's "bounce" in the boards.
3. The downstairs shop did a lot of structural work which caused new subsidence.
4. All the above.

What solution would you recommend that wouldn't involve taking the floor up entirely?

Would a couple of millimetres of plyboard stuck on top make a difference?
Would I need to take it up and make a stronger frame?
Would better adhesive make a difference (apparently flexible adhesive wasn't used)?
Or will it likely be all right just to blast right ahead?

The bounce is there but not massive. Will any give in the floor be a problem in the long run or can it be overcome?

Thanks so much for any help. It's much appreciated.

 

[Richard C]

4. All the above.

I’d go along with that one; what you’ve done is completely inadequate to tile over.

What solution would you recommend that wouldn't involve taking the floor up entirely?

None

Would a couple of millimetres of plyboard stuck on top make a difference?

No

Would I need to take it up and make a stronger frame?

Yes

Would better adhesive make a difference (apparently flexible adhesive wasn't used)?
Or will it likely be all right just to blast right ahead?

It should have been flexible but it almost certainly wouldn’t have made any difference in this case.

The bounce is there but not massive. Will any give in the floor be a problem in the long run or can it be overcome?

A suspended floor will always flex but you cant have an bounce at all; you should not be able to feel any degree of flexing in the floor at all ; if it flexes the tiles will crack & even the very expensive 2 part epoxy adhesives wont help with that.

 

[Wilbur111]

Thanks for your help.

A suspended floor will always flex but you cant have an bounce at all

Clearly it is inadequate, but just to be clear, I only feel movement if I bounce up and down on it to see if it moves. In normal walking I don't feel a movement at all.

I’d go along with that one; what you’ve done is completely inadequate to tile over.

So in terms of making a stronger frame, what would you recommend? When we did it, I was sure there was a lot of framing involved. It certainly felt solid at the time.

Is there a certain minimum distance you'd recommend for the distance between slats?
How about the "horizontals" between the main pieces of timber?
And we didn't make all the main slats touch the ground, instead they were raised up on periodic "pillars". Was this a mistake? It's what was advised. Should the pillars be a certain minimum distance apart?

Any kind of details would be handy, really?


Finally, I'm sure I'm going to have a hell of a job getting out the screws. Any advice on that?


Thanks very much again. This is very helpful.

 

[Richard C]

Couple of questions; you are over a shop, how old is the property? Is the original floor which you’re supporting from already a suspended timber floor or is it concrete slab? If timber, what condition are the original joists in? Do you have any financial interest in the property as I think this will largely dictate what you do!