Limestone tile floor on T&G floorboards - is the prep ok

[jesteh]

I am looking to tile with limestone tiles on top of existing T&G floorboards. I already had the brand new floorboards so didn't want to throw them away to replace with plywood.

Joists are 8x3 at 16" centres around 80 years old and sound/solid with no bowing or similar. Floorboards are standard 20mm t&g redwood boards.

First of all I've reinforced the floor by putting 3x2 noggins across joists (solid blocking). Noggins are also level with top of the joist so that each floorboard is supported by noggin (it was a lot of noggins). The idea of this is twofold - first of all tie the joists together and take out deflection in joists but secondly to take out any deflection in the floorboards as each board is reinforced/supported with noggin from underneath.

I've screwed the floorboards at 8" spacing - at joist and also midway through each noggin.

Next I was planning to put 10mm marmox/wedi or similar type of board on top followed by Ditra followed by UFH and finally tile adhesive/tiles. I know ideally UFH goes underneath the membrane with SLC but I am really trying to avoid raising the level too much. I have assumed that the only reason that UFH is done below with SLC is to avoid damaging it while tiling - I am happy to be careful & slow.

Does this sound about right or not?

Thanks.



The idea of this is to support
I've installed solid

Boards are sitting on top of 8x3 joists at 16" centers and all the boards are supported by

Floorboards are 20mm thick almost new and all screwed in thight

 

[DHTiling]

I would still slc the ufh to the cable height.. then install the Ditra.. then you do not get extra height.

 

[jesteh]

Thanks for the reply Dave. Regarding UFH & SLC - I was thinking it will add the extra height - cable is around 3mm thick so it will around 4-5mm. If on the other hand cable goes on top of Ditra, there would be no extra height as cable would be buried in 5-6mm tile adhesive thats being applied anyway.

Am I right in assuming that there is no structural reason for putting in UFH in SLC and main advantage is to prevent damaging the cable when tiling?

Finally, in terms of prep with noggins - is the method I've used good enough for stone tile or are there any potential issues that jump out?

 

[John Benton]

Thanks for the reply Dave. Regarding UFH & SLC - I was thinking it will add the extra height - cable is around 3mm thick so it will around 4-5mm. If on the other hand cable goes on top of Ditra, there would be no extra height as cable would be buried in 5-6mm tile adhesive thats being applied anyway.

Am I right in assuming that there is no structural reason for putting in UFH in SLC and main advantage is to prevent damaging the cable when tiling?

Finally, in terms of prep with noggins - is the method I've used good enough for stone tile or are there any potential issues that jump out?

Encasing mat with SLC also makes sure that you have no air pockets which may occur if you just apply adhesive with a notched trowel, as well as protecting cable

 

[DHTiling]

Thanks for the reply Dave. Regarding UFH & SLC - I was thinking it will add the extra height - cable is around 3mm thick so it will around 4-5mm. If on the other hand cable goes on top of Ditra, there would be no extra height as cable would be buried in 5-6mm tile adhesive thats being applied anyway.

Am I right in assuming that there is no structural reason for putting in UFH in SLC and main advantage is to prevent damaging the cable when tiling?

Finally, in terms of prep with noggins - is the method I've used good enough for stone tile or are there any potential issues that jump out?

The majority of UFH comps now advise that you encapsulate the ufh in slc now... yes for protection but as above 100% no voids, so better performance..

I cannot see 2 or 3 mm being a big deal... you only want to do this once, so do it the better way.

You could also do away with the Ditra IMO if height is deffo an issue. then the extra you think you might get with the slc will be lost by not using 3mm Ditra.

 

[jesteh]

Thanks guys. You've convinced me to use SLC. There is another reason I didn't want to use it - last time I did I got myself in a horrible sticky mess - I hated the stuff ever since.

In terms of the prep with noggins and floorboards - does what I described sound ok or likely to cause any problems longer term? I've read the general advice which is to use the 25mm plywood but I really didn't want to discard the nice new floorboards and they were already cut to size and paid for. My understanding of what the 25mm plywood does is tie the joists together to prevent deflection in joists and then provides a thick stable surface to prevent deflection between the joists. By adding noggins instead from underneath, I am hoping I have achieved both in a different way but this is theory and not practical experience. Any thoughts?

Dave, I am also surprised you suggested not to use Ditra mat? Schluter rep told me tiles on timber floor will always fail due to lateral movement - I wasn't entirely convinced as I expected Marmox type board must eliminate movement in wood. Would you say your unbiased opinion is that there is no real advantage to using Ditra in this case?

 

[DHTiling]

I only say this as you are using marmox type boards that will be taped at the joints.. Ditra yes will help with lateral movement but depends how OTT you want to go.. i would use the Ditra but i am not the one worried about 3mm :lol:

 

[Time's Ran Out]

You don't mention what the thickness of the limestone is, and what the scale of the project is in relation to the increased weight that you will be adding to your 8inch joists. I'd use the ditra with all stone jobs that have UFH and are there any other heavy items (ie granite worktops) that will cause the floor to have deflection.

 

[jesteh]

Thickness of limestone would be 12mm - I haven't ordered it yet but it really is nothing special - just plain limestone tiles 400x400x12.

Bathroom size is 3.15m x 1.8m so not big and rounded to 6sq m in total - joists run along the 3.15m length with 4 joists in total.

There is a bath in the corner which fully loaded has weight of around 250kg and takes around 1.5m2. This is equivalent to 0.16kN/m2 dead load.


The remainder of floor 5m2 is to be tiled. Weight of grout + adhesive + slc is around 10kg/m2. Add to that weight of tiles of around 30kg/m2. So 40 x 5 = 200kg. Also equivalent to 0.039kn/m2 dead load.


Overall full weight on the floor with tiles and full bath is 450kg. I didn't think this was a great deal across 4joists with length 3.15m, especially now they are joined together. Does that sound ok?