bouncy floor

[Ajax123]

I have been assistng a customer who has used an anhydrite screed and placed 300x300mm porcelaine tiles on it. They have ALL popped off the top of the screed. Whilst my normal line of questioning would be was the prep done correctly was it damp was it primed etc etc this one seems slightly different in that the floor is bouncing which I beleive is the primeary cause.

The substrate is Timber joists and a timber osb deck with screed on top. Now I know all about the design criteria for the joists and the floor and I am not convinced it has been built correctly. Which is bad enough in it's own right.

My question is what level of bounce/deflection would a tiled floor using a flexible adhesive stand before the tiles begin to fail. I know the theoretical answer is "zero" but this cannot be absolute (I don't think) as beam and block floors and pre cast concrete floors and timber floors etc would then not be available for tiling. I cannot find the answer in the tiling standards and wondered if anyone on here might be able to answer it.........

 

[DHTiling]

It is in BS Alan.. and if i recall right it is 2mm over a certain length etc... but will need to read through BS to check.

 

[Ajax123]

Thanks Dave - will have another scan. Do you know which part it is in?

 

[doug boardley]

I thought it was 3mm over a 2metre span, but I'd be happy to be corrected if wrong.

 

[DHTiling]

That is deviation doug, this is deflection for timber floor joists and is calculated over a slightly longer length... same basicly for timber floors Alan.. same stress issues really

 

[Ajax123]

Hi doug.Thanks mate.I need it precise and absolute in this instance - could cost well in excess of £200k to out right cos the whole first floor of a house might need to come out......aaaarrrrgh!

 

[DHTiling]

Alan, check the timber floor ratio's.. it will be the same..

 

[Rob Z]

Alan,

The tile industry here in the US and Canada uses deflection maximums of L/360 for tile and L/720 for stone. That's measured both along the length of the joist, as well as the span between the joists. I-joists are typically designed to hit L/480 along the length.

I might be able to help you with some of this but I don't know anything about how framing is done in the UK. But I could at least talk to you about what is done here and then you might be able to apply it to your situation?

 

[Ajax123]

Where we put screed on timber we design for a maximum deflection of L/300 or 5mm which ever is the smaller (usually 5mm) This project is not actually in timber frame but is screeded timber floors in masonry construction so racking stresses do not come into play. This means that the screeded floor should not "bounce" perceptibly.