Tiling onto a suspended floor

[Crofter]

My bathroom floor is built up using 300mm JJI joists at 600 centres, over a 16ft span. 22mm T&G P5 chipboard on top. There is definitely a degree of deflection going on with this buildup.

The bathroom itself is at one side of the span, taking up 1.6m, so coming to about a third of the span.

Can I just stick tiles directly down onto this using an appropriate flexible adhesive?

If not, would a layer of ply provide sufficient additional stiffness? I know that is the default procedure, but tbh I'd be surprised if e.g. an extra 12mm of ply would be able to change the degree of deflection by any measurable amount. Perhaps my intuition is way off on this.

 

The other option is to give up on tiling, and just stick vinyl down, which would be OK, I guess. It would have the advantage of the bathroom floor being lower than the rest of the house, so less chance of water running out.

[ProDave]

I am never happy with a floor that has detectable deflection. Can you not get underneath and add an additional beam underneath to give extra support directly under the bathroom wall (i.e at 1/3 span as you describe)

 

I find there is slight deflection noticable on my JJI ground floor but not on my posi joisted first floor (same spans)

 

 

[Temp]

+1

 

You really need to make the floor as rigid as possible to minimise the risk. I'd lift the chipboard and install noggins (got any JJI joists left?) then replace the chipboard with two layers of 18mm plywood with staggered joints all screwed down on 200 mm centers. Drill clearance holes for the screws so they don't pry the ply layers apart. 

 

 

 

[Crofter]

I could certainly put props underneath, at key points. Nothing fancy, just a length of wood and a wedge. I might do that under the stove actually, because I've ended up building the hearth up using three stacked paving slabs, and it's a lot of weight concentrated close to mid-span. If the joists deflect permanently it could open up an air gap somewhere.

 

I'm a little surprised how much bounce there is in the floor- I used the online calculator on the JJI website to spec it. It's possible to get a miniature Millenium-bridge style resonance going if you walk around at the right speed.

[Crofter]

1 minute ago, Temp said:

+1

 

You really need to make the floor as rigid as possible to minimise the risk. I'd lift the chipboard and install noggins (got any JJI joists left?) then replace the chipboard with two layers of 18mm plywood with staggered joints all screwed down on 200 mm centers. Drill clearance holes for the screws so they don't pry the ply layers apart. 

 

 

 

 

That's the strongest argument yet in favour of vinyl flooring

[bassanclan]

Given where you are at the minute I would try and get a few more noggins in if you have access and then go for vinyl or (robust) tile effect laminate.

[Ferdinand]

4 hours ago, Crofter said:

 

That's the strongest argument yet in favour of vinyl flooring

 

If you want to look posher than vinyl, in case Hyacinth Bucket or Lady Nugee stay , then vinyl tiles are a more-perceived-upmarket option.

 

OTOH Roll Vinyl is effective nearly-tanking if in one piece and siliconed round the edge if somebody washes their souvenir rocks in your whb and it leaks.

 

F

 

Edited July 17, 2017 by Ferdinand