Some marble tile advice, please!

[HandyHarry]

I will be installing marble tile in a new bath in a few weeks and have some questions. I am doing the floor and tub surround as well as a 6" trim around a fiberglass 1-piece shower. The floor has electric radiant heat mat. I have installed tile before, but only ceramic and porcelain. I have laid marble once as a hearth in front of a pellet stove, but did not grout (left no space's). So my questions:

Do I need a sealer on the tiles before I grout? (I heard this somewhere)
Is mortar better than thinset in this application? What about tub and shower?
Can I get away with stapling down (on mesh only, of course!) the heat or do I need to thinset 1st, let cure, then lay tile?
What size grout lines would you put in?

Thanks for all your help!

[geniescience]

... have installed tile before...

Seal marble before grouting? Yes, try this out on a spare piece of tile. It is impossible to remove grout haze from polished marble. Best is for youto choose what the marble will absorb first. Two different kinds of sealant, water and oil based.

If you back butter each tile with thinset and also thinset the floor, you'll have full contact and adhesion, and a thick enough setting bed in my opinion. Another option is buy a mediumset "mortar". Thinset is a mortar too, and brick mortar is a mortar too, so the word mortar is not specific enough.

The heat cables are thick, either 1/8" or 1/4" depending on what you bought. Whether to embed them in thinset the day before you tile, or to try to thinsit over them on the day you tile, I cannot say. But to be safe, you do it in two steps; no harm done to you as DIY; a professional might not want to take extra steps, and would have to rationalize; they might ask you to set the cable the night before the came in. Nothing to lose, everything to gain, even if the mat mesh appears to hold the cable together well, the big concern is how well the marble tiles line up and set in terms of height and levelness; that is going to be permanent so the fewer obstacles and constraints the better.

Use white thinset so that its color doesn't affect the grout later. If it is a light colored marble. Cost more, harder to get, but worth it really really worth it.

Size grout lines depends on the tile. Look for tiles that are not perfectly square, lay down ten in a row on the short length, measure total length; turn them all 90 degrees, measure length; compare two numbers. This helps you figure out how bad the grout lines will look if they are too thin to enable you to compensate as you go for the uneven squareness. If after tiles are laid down, you have corners that don't align well across all four tiles, you can slide a grinder blade in there to open the grout line spacing at the corner so that all four tiles appear to align.

David

[jadnashua]

Some things to consider:
1. A stone tile install requires twice the stiffness for both the joists and subflooring as does a ceramic install.
2. You need two layers of plywood for a good stone tile install
3. The deflection rating for the joists should be L/720 or better.
4. You need a decoupling layer somewhere under the tile, this could be cbu, or a membrane.
5. Thinset shouldn't be used over 1/4" thick. A medium bed mortar can be a lot thicker...some up to an inch thick.
6. You might want to consider using slc over the heating mats...it makes for a nice flat floor to tile on. It needs to be 1/2" higher than the highest point it is covering over a plywood floor, though. If on a slab, it can be thinner.
7. Use a joint 1/8" or less since you'll want to use unsanded grout. Using sanded on polished marble will likely lead to scratches and mean it couldn't be restored (i.e., polished in place at some later time).

[geniescience]

if you thinset to fill in between the cables (e.g a bit less than 1/4" thick), then later when you tile, you can still use thinset again because EACH new layer is what has to be 1/4" or less, for thinset to be thinset and to work as expected.

Did you try out the cement haze on a sample tile? With and without sealing first. If it is a polished not honed finish, think an oil-based sealer will make the polish look shinier.

Definitely non-sanded grout.

david

[claycarson@comcast.net]

Good advice above.

With radiant heating mats, I like the option of fully encasing it in self leveling cement or possibly thinset or medium set mortar and then letting it dry. That gives you a flat surface to lay tile on, which you definitely want with marble. Plus, no worries about clipping the wires with your trowel as you go.

Most SLC's don't need to be a full half inch, though, to work well. Many can be feathered almost down to nada and still stay intact.

Onliest thing is, this is a pretty advanced install for a DIY.....I would also weigh the cost of having a pro do it, just to see if it makes sense for you. If you get it wrong, the cost of all materials over again may make the project less fun financially.

But this is a DIY positive forum, so don't hesitate if you are up for it.

[PEW]

I have done it both ways, SLC and a two step thin set process.

Would strongly recommend you go the SLC route. Will give you a much better finished job.

[jadnashua]

SLC requirements for minimum thickness vary considerably brand to brand and also for the substrate. Using it over concrete slab is one thing, over plywood an entirely different thing. Different brands have different capabilities, as well as the changes in characteristics if you use their latex additive verses water alone. Best thing is to read the instructions carefully of the choices you have available to you and abide by the instructions and guidelines they specify. It is too expensive to take shortcuts.

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