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.Originally Posted by HandyHarry
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.