Suspended Timber Floor Tile Prep

[Deyna]

Wait a minute. Where do you have Wet UFH?

Dont worry, adjacent room! Its just the pipes run under this room and over the sleeper wall near the opening.

 

[acaciaguy]

Ok.

 

[Deyna]

All it means is that it limits where I can put joists on that section of the sleeper as the pipes are in the way, but at 12" OC its fine.

 

[Waluigi]

It does have an impact if you are overboarding the ply and need to build up the height of joining floors. For example, a Foam tile backer board would be unsuitable and instead a cement board like Hardiebacker would be OK on top of wet UFH

 

[acaciaguy]

Are you tiling the wet ufc area too as part of the same tiling

 

[Deyna]

It does have an impact if you are overboarding the ply and need to build up the height of joining floors. For example, a Foam tile backer board would be unsuitable and instead a cement board like Hardiebacker would be OK on top of wet UFH

Ofc, its a problem for the other room. Thats not being tiled until the extension is built. Either way the ply will need another layer of something so I'll end up with a height difference. Can't lower this floor without rebuilding the sleepers.

 

[Andy Rhodes]

Dense concrete blocks would work, you could place them under every second beam from the middle beam on the picture but you would have to put a piece of slate under the block or DPM to stop damp, may also cheaper & quicker

 

[Deyna]

Eventually yes. I mentioned it in the OP these rooms will be joined so there will be a substrate difference and will need to be factored in. Thankfully the tiles will run with the join so at most its one tile that will straddle the two floors although I suppose you could just end of a full tile at the edges.

 

[acaciaguy]

Ofc, its a problem for the other room. Thats not being tiled until the extension is built. Either way the ply will need another layer of something so I'll end up with a height difference. Can't lower this floor without rebuilding the sleepers.

Or take ply up and put a thicker cement / structural board down. Double up joists and maybe even block and you should be sound as a pound

 

[Andy Rhodes]

You can fix mechanical expansion joint to bridge where the 2 floors meet,& by cutting up to the joint continue it with the off cut & it still gives the impression that the floor runs through

 

[Deyna]

Thanks guys, this stuff is good.

I've got spare timber, so I will go ahead and double up the spans showing deflection and re-test. I think this will solve any lingering deflection problems and shouldnt take a great deal of my time.

I'll look into Blanke Permat for this subfloor. The extra expense might be worth it (12m2), but Ditra would be more suitable for the adjacent room with screen/WUFH and more cost effective. Both add the same height so would work.

 

[acaciaguy]

I live in Warwick if you would like to pm me. I can come have a look.

 

[Deyna]

I live in Warwick if you would like to pm me. I can come have a look.

Cheers buddy, I'll be working on it this weekend so will report back after bolting some more 4x2's together. A second opinion would be much welcomed.

I should have gone gone 6x2 really and just cut back at the ends. Wouldn't have got anything bigger than that in though.

 

[Deyna]

I've given it a bit more testing, and I've come to the conclusion that bolting more timber together will not reduce vertical movement to an acceptable level to be considered for tiling. However given the sleepers are 2 courses, I'm going to basically add another 2 walls mid span either side so the max clear span is 1m. I've got aload of spare blue engineering bricks here from the previous owners. A quick test of deflection over that span with some offcuts shows it will not move.

 

[acaciaguy]

I agree. The thing with bolting them together is that you aren’t increasing the x4 part. They do need support underneath. You are doing the right thing.

 

[Deyna]

I agree. The thing with bolting them together is that you aren’t increasing the x4 part. They do need support underneath. You are doing the right thing.

Ye, the strenght comes from the depth not the width. I can leave the existing frame "as is" then (the extra support for board joins isnt a bad thing plus it'll still be where foot traffic is).

Realistically its about 50 bricks and I'll just have to make do with workaround around the existing frame. I will feel a helluva lot more comfortable with it then!

 

[Andy Rhodes]

Blue engineering bricks good shout you've no need to use slate or DPM with them bad boys

 

[Deyna]

Ye for sure! I'll do the first two and consider rebuilding the others if thats the case to take up some of the slack underneath (upto 20mm shims in places). Feels like an extra weekend on it will be worth it in the long run.

 

[Andy Rhodes]

Preparation the key word always

 

[acaciaguy]

Couldn’t agree more Andy

 

[Andy Rhodes]

If you've got 50 bricks you could support most of your beams shown in your orginal pictures ,this would hopefully stop any bounce what so ever

 

[Deyna]

If you've got 50 bricks you could support most of your beams shown in your orginal pictures ,this would hopefully stop any bounce what so ever

Thats the plan! Max span will about around 1m then. Just need to decide on appropriate underlayment but I think Ditra would be OK to keep the height down to a minimum.

 

[acaciaguy]

Get everything flat and level now too. Will make the tiling easier.

 

[Andy Rhodes]

Denya are you using fast set or standard set adhesive

 

[Deyna]

Denya are you using fast set or standard set adhesive

I was going to ask for recommendation on that. Assume thinset for Ditra mat and then S2 adhesive for tiles?

 

[Andy Rhodes]

instead of Ditra how about backer boards or are you really tight on height

 

[Deyna]

Morning @Andy Rhodes !

I'm a little tight on height yes! The new subfloor is flush with the adjacent screed and the wood floor. Both substrates need a decoupling layer so Ditra would be the best bet from herein.

I built a couple more sleepers over the weekend, went back around and packed out with slate and plastic shims for small adjustments. Blocked in the frame at opposite corners. The max clear span now is approx 800m at any point. Ply joints have a small expansion gap.

Probably give it a more rigorous test this evening as I left the mortar to go off but on first showing it was much improved the missus did a bit of jumping mid span on a few joists and the laser was moving at most 1mm and nothing at all if you're walking around normally.

The length of the tiles are 1200mm, so when you run them perpendicular to the joists you're actually spreading the load along 4 lengths so I'm not worried about any interstitial deflection between them due to the ply thickness.

 

[Deyna]

I'm still torn on Ditra or 6mm hardie though. I can accept the extra height to strengthen the subfloor a little more for belt and braces

Would someone be able to recommend me suitable adhesive/grout for such large format tiles. Something thats got a bit of "flex" in it.

 

[Perry]

A little trick I found is cut strips of 3/4 ply the size of the joists and glue and screw to side of joists, it can make quite a bit of difference sometimes.

 

[Deyna]

To be honest I've spent the last couple of nights poking and prodding and even with the extra walls its just not good enough...

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Even with overboarding again I don't think this can be eliminated or at least reduced to an acceptable level.

 

[Deyna]

Back again...the things you do for love 🙂

I did a slightly more visual test by running some building line over a specific joist and put a 3mm shim for reference. The building line was 2mm at most.

So while the the movement looks bad to me (I really have no point of reference though), the visible deflection cannot be more than 1.5mm as at no point does the building line rise above the shim but you can see clear air underneath.

So if the allowable deflection over a 3ft span is 2.5mm (36/360) then the L value is more like L/720 observed.

If someone were tiling a standard bathroom i.e. 8x2 joists, 10ft span and 16"OC then the allowable deflection is 120/360 which is about 8mm. I cannot imagine doing the same jump test on this setup would yield zero movement.

I'm still feel like some extra noggins or doubling up with the left over timber would provide some more assurances though I just dont feel like it would further reduce what I'm observing.

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