Can I Tile this Floor?

enduringNovember 10, 2011

Hi, I would like to put down slate tile, over an electrical floor heating system in my bathroom.

I want to know what I need to look for, prep for, and consider alternatives for, with my situation.

I have confidence that I can do this on my own and with my DH's brawn & brains.

Here is under my bath. the joists are 8x2 (but not quite, is that called nominal?). Unfortunately the joist are 21" on center. The diagonal flooring boards are 6" or so in width, and I presume 3/4"-1" thick as I estimate the thickness looking at a knot hole. These boards have a slight gap between them:

Top side - with the toilet removed it appears that there is 3/4" fir tongue & groove flooring over the diagonal boards. Then over the T&G there is an old linoleum floor. I don't want to add more than 1-1/2" to the height of my floor from the T&G fir flooring, preferably 1".

1) Will this floor situation be stiff enough for tile, as is, with the subfloor and fir flooring?

2) Is it recommended that 4 more joist go in between the 5 that are there. Currently there is 1 at each edge and 3 filling the middle, at 21" on center.

3) Do I add plywood atop the T&G to add more rigidity?

4) What is the depth of a slate tile + prep + electric underfloor heating?

5) When does the floor go in place? I will be relocating toilet, sink, putting in new tub, taking out plaster to insulate exterior walls, new electrical, etc.

Thanks for your consideration.

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My BR is 10' x 6'8". Tub will stay at the far end of the room along the short wall. This short wall is an exterior wall. One of the long walls is an exterior wall too.

    Bookmark   November 10, 2011 at 4:48PM
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Your picture is not showing up

    Bookmark   November 10, 2011 at 10:06PM
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Thanks lazygardens
here's the pic:

Its not pretty under there;)

    Bookmark   November 10, 2011 at 11:24PM
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Your floor will be stiff enough, but you still need to add a layer of plywood over the planking before anything else. Being that you already have the beef in the planking, you only need 3/8" ply (exterior grade). On top of that, you can put your heating system, and bury the wires in self leveling compound (make sure you use the bonding agent the manufacturer makes for this condition), and then go over that with Ditra, and you're then ready to tile. Figure 3/8" ply, 1/4" heating system and SLC, 1/8" Ditra, and 3/8" tile= 1 1/8". As for the joisting, what's the size of those joists, the on center spacing, and the span?

    Bookmark   November 11, 2011 at 7:26AM
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Thanks Bill V. Very helpful.

The spacing of the joist is 21" OC. The length of the joist are about 10', free span, but possibly 12' total taking into account the ends that sit on the plate.

I had meant to ask on my post if there would be a tile size limitation such as 12x12 or 16x16. I was thinking of doing a small Versailles pattern where the largest is probably around 16x16.

As I mentioned, this part of the house is joisted differently than the rest of the house, I think they where saving some lumber;) My DIA (dear inlaw ancestors) had this bathroom addition put on over the crawl space after they moved this small house from town and onto the farm. The rest of the house is sitting over a regular basement. My late DFIL and his sister hand dug the basement when they were teens. They used the horse team and a slip. DH remembers his dad talking about how hard the soil was. His DD said when the slip hit the hard soil and bucked, he'd end up on the backs of the horses. He must have been standing on the slip.

    Bookmark   November 11, 2011 at 9:35AM
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They look to be 2x8's in the picture. If that's the case, then yes, you want to add another joist in between each of them. As for size limitation, you add those joists and build the subfloor as I described above, and your floor will be rock solid enough to use whatever size tile you like.

    Bookmark   November 11, 2011 at 3:37PM
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Yes, these are 2x8s so I will talk to DH about adding joist. Thanks so much Bill V, you are always so helpful and courteous:)

    Bookmark   November 11, 2011 at 8:18PM
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