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10-06-2017, 07:26 AM
Ok, I can hear the moans all the way here....

I have a kitchen floor 3.0 by 4.0m, (10' x 13'), that has a border of old tiles about 2' wide. There's a section of wooden planked subfloor in the middle that's sunk below the tiles by about 3 - 4mm, (1/8th ").
The subfloor has 100 mm by 50 mm joists, (4" x 2") about 300 to 320 mm apart, (12"), with 20 mm thick planks, (just over 3/4 ").
Using the deflecto macro I get a trampolining L/205, however the joists are supported every 4' by a concrete and brick pad, giving a deflection better than L/1023, (calc only goes down to 4.5' ). I've done the glass/spillage test and there's hardly a ripple across the surface.

My question is that I want to tile over with travertine/limestone tiles, (12mm), and want to minimise height increase. I don't want to rip up the floorboards and replace with 1" ply because they're in pretty good condition and I can think of better uses for the money/time.

I'm planning on ripping up the tiles, creating an expansion joint between the concrete subfloor here and the planks with foam strip, and levelling the floor out with self leveller, (concrete section only). All the subfloor planks will be screwed into the joists every 150 mm to secure

Once this has set, I was hoping to get away with either using a 6 mm hardibacker board with a modified latex thinset, (back buttered since I don't want the stuff to pour between the plank gaps), straight onto the boards.

Failing that, using a Ditra heated decoupling membrane and then tiling onto that for a full floor coverage.

Ideally I want to keep the level rise to about 15 mm, (just over 1/2"), otherwise I have to raise the adjoining floors to the same height, (major price and hassle).

Are either these options suitable or should I just go the route of levelling the screed to the existing boards and then plyboarding, (3/8 or 1/2") the entire lower floor, (I hate transitions after breaking a toe on one in a previous abode :cry:).

Will the potential expansion differences be taken up by the expansion joint?
Also would using 3.5 mm stainless steel single thread, double self countersinking screws be ok instead of the hardibackers screws, (because I have a job lot from a previous job)? In my head, the stainless would be better, (no corrosion potential).

I can post some photos later if that helps, but I hope my words paint a thousand pictures :)

Thanks for your patience and your help.

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10-06-2017, 03:27 PM
I got lost in all of that...what I did see was you're wanting to use a natural stone. If thats the case I would make a strong case for a double layer of ply.

I would get rid of the planks if height is a concern.

Concrete subfloor has me confused, is it a mud bed or actually concrete?

Pouring self leveler over planks is a no go.

Hardi directly over planks is a no go.

If there is a change in substrate like concrete to ply subfloor you'll need to honor that expansion joint all the way up through the install. That means a joint in the actual tile install as well filled with a flexible sealant.

I would use CBU screws not because I don't think the stainless wouldn't work (I don't know if they would or not) but because the appropriate screw have a larger head preventing them from pulling through when fastening.

I'll be honest, from the sounds of it tile may not be the best option for what you have going.

10-06-2017, 05:10 PM
The specs for tiling something in North America are in the TCNA handbook. Don't know, but expect there is a similar handbook for the Euro zone which has different specifications on many things. But, none of the methods in the TCNA handbook allow applying much of any tile or tileable substrates directly onto planks...they all require a layer of plywood first. The manufacturers' instructions for all of the products that I'm aware of available here do not allow their products to be installed directly onto dimensional lumber (planks) without a layer of plywood, generally a minimum of 3/8" or about 9mm, but more is usually available that lays flat.

10-07-2017, 04:30 AM
Cheers for this,
The house is old and has been "extended" in a variety of ways over the years. What used to be an old large fireplace is now a window, (hence the concrete, screed and tiles), and the back door of the kitchen that looks onto the garden has a sub-base, concrete and screed again. So the wooden floor is like a small archipelago :rolleyes:

The floor is level, (although slopes sightly towards the back door, 1 in 180), there are a couple of high spots in the planks but I'll sand/plane these down. I'm not worried about deflection in the wood floor, my only concern is differing expansion rates between the different sub floors.

To keep the height down i'm now thinking 3/8th ply then ditra on top of this, then 10 - 12 mm travertine tiles, (lighter than stone/slate etc.).

My question is do I thinset/mastic adhesive the sections of concrete before I ply over them or just rely on screws. I was intending to lay the ply over the boards and just screw into the planks below with no adhesive, then ditra over this.

Would I still need to fit expansion joints or could I rely on the decoupling of the plywood and ditra? Could i go thinner plywood as the floor is really rock solid?

Maybe the previous torn/stained vinyl floor/3mm hardboard wasn't so bad?

10-07-2017, 01:51 PM
Still wouldn't go with travertine over a single layer of ply, I would suggest looking at a porcelain that mimics travertine.

Some pics would help envision what's going on

10-07-2017, 01:59 PM
At least in the USA version of the Ditra installation manual, the planks with a layer of ply over it is sufficient for natural stone tile. The issue is supporting the ends and edges of the ply acting like little levers, and the planks provide the support and act like that second layer of ply.

I don't think the ply onto the cement is a good idea!

The Ditra installation manual calls for a minimum of 3/8" ply as a second layer, and unless you have access to better stuff than is available here, most 3/8" stuff tends to be warped, and doesn't lay flat easily. More is actually better and often easier. The added height can be an issue.

I'm not a pro at this, but I don't see plywood bonded to the concrete as working as a tile layer. There are materials that could be put on the concrete to bring the two areas even in height, but the differing materials would still dictate a soft joint in the tile over them.

10-08-2017, 07:44 AM
Photos attached.

I spoke with a coupe of different pro's over the last few days, all with differing approaches.

One suggested I have the whole lot excavated and a new floating floor installed throughout the kitchen and adjoining rooms, (way way too much money).

The others were more along the line of removing tiles and self levelling compound. Waterproof barrier and then overboard with 3/8ths as a minimum, (all were surprised at how there was almost zero deflection until they saw the concrete pads under the joists). Since the wooden floor is suspended and already vented and there's no sign of rot in the timbers, a waterproof membrane should be fine, (not a vapour barrier though).

With the ditra fitted they don't see an issue with the travertine but recommend a high polymer modified thinset for the tiles.

Either way, there's going to be a step difference so I'm also going to have to look at fitting an engineered floor throughout the rest of the ground floor to keep levels equal :crap:

Does anyone have any experience of working on a floor composed of different subfloors? I have a feeling that whatever I do will be something that wil have to be redone after 10 - 15 years, (unless I go the nuclear option and remove/replace it all).