Tiling question

[cidley69]

Tiling question for you. Planning to install natural slate tile over ditra heat.

We removed the old lino and 3/8" k3 partical board, and there is 5/8" plywood subfloor left. Can the Ditra heat go directly on plywood, or is another layer of plywood required?

[mr2mike]

I believe you can tile over top no problem with this. Next floor surface would have to tile over the tile which is possible too.

Just make sure no soft spots in the wood from water damage.
Soft foundation would leave room for tile and bonding to crack.

Easy to cut out soft spots. Cut from center of floor joists so you have a place to anchor to on edges of new plywood.
Particle board is garbage. Swells, shifts and glad you took it up.

[?????]

Yes - it's stated in the installation guide.

[cidley69]

Found the installation handbook: https://resources.schluter.com/media/DITRA-HEAT-InstallationGuide.pdf

Limitations
requires double layer wood floor regardless
of joist spacing
minimum 2" x 2" (50 mm x 50 mm) tile
Requirements
maximum spacing of joists, I-joists, or floor
trusses is 24" (610 mm) o.c.
double layer wood floor consisting of:
• minimum subfloor thickness – 23/32",
3/4" nom. (19 mm) tongue-and-groove
• minimum underlayment thickness –
11/32", 3/8" nom. (10 mm)

Sounds like a second layer required.

Anyone have experience with this? is it actually required?

[Tik-Tok]

Personal opinion, I would still do it with single. Instructions are made for the lowest common denominator, which is a high humidity coastal area where plywood sags easily, and has a lot of seismic activity. You should be ok. Especially if this isn't your "forever home"*

I'm not a tilist though.

*those don't exist

[bjstare]

Unless the bathroom is 1200sqft, the cost and effort to do a second layer will be negligible. And if the bathroom is 1200sqft, you likely have enough money that the incremental cost won't be a consideration.

Just do the second layer.

[Tik-Tok]

Unless the bathroom is 1200sqft, the cost and effort to do a second layer will be negligible. And if the bathroom is 1200sqft, you likely have enough money that the incremental cost won't be a consideration.

Just do the second layer.

If he's like me, he doesn't want a massive floor height difference between two rooms. I, very painstakingly, ripped up my subfloor in the kitchen just to avoid this.

[mr2mike]

Sounds like you're buying 3/8 plywood by the install guide.

Where is this going? Small bathroom or an entire main floor kitchen?
House build year?

They tell you why it's required in the manual.
"In some applications referenced in this Handbook, adding a layer of plywood or OSB before installing Schluter®-DITRA-HEAT
and the ceramic or stone tile covering is required to reduce deflection and curvature of the sheathing between the joists."

So this is why I ask, small floor span or large?

[suntan]

How far apart are the joists?

[JRSC00LUDE]

Do you want to risk replacing your tile? Do things right the first time.

[mr2mike]

If he's like me, he doesn't want a massive floor height difference between two rooms. I, very painstakingly, ripped up my subfloor in the kitchen just to avoid this.

I've done something similar in a main entrance way. Removed the current small, crap tile over hardwood job.
Carefully cut out the hardwood down to the subfloor and laid a nice, larger tile floor flush with the hardwood. Looked 100% better although only people that would notice would be Tik-Tok apparently.

[bjstare]

If he's like me, he doesn't want a massive floor height difference between two rooms. I, very painstakingly, ripped up my subfloor in the kitchen just to avoid this.

That's a good point, I saw that he ripped out a layer of garbage wood over the plywood, but glossed over the fact that it was lino previously. I'd be having second thoughts as well adding that much floor thickness between rooms.