What are some suggestions on installing marble in a basement where the concrete floor is not really that level.

Deck mud?
SLC with Schluter?
Or just SLC?
??????????????????

How far out of level is the slab, and how level do you want to make it?

Hi Rob,
I thought to install marble the floor should be perfectly level. Does it not?
The floor slopes towards the drains, should I leave that slope?
And I can see that there are humps and holes all over.

Many basement slabs are poured and finished without any regards to the final finish that will be installed eventually.If you are planning to set polished 16" marble tiles ,for instance,the slab is probably not prepared flat enough.That is,if the marble floor has to be 100% flat.

A proper mortar bed is the best way to go.Schluter's Ditra membrane over that would also be a good idea.

The problem is trying to find the right people to do a mortar bed installation.It's just one part of the trade that has almost disappeared as a "standard" practice.Sadly.

Eliz

There are many setters that use a fat mud technique to set stone, and the flatness of the floor is of little concern to them. If you want to use a small notch trowel and thinset, then the floor should be as close to level as possible. It can a bit worse if you are using a medium bed material and a 3/4" U notch trowel.

The reason I asked how far out of level the slab is is because that will influence which method is likely the best to use. For example, a slab that is out 2" in 20 feet is a poor candidate for SLC.

Thanks Ron and Rob,

Can you explain to me what 'medium bed material' is?
And does it matter if you use 'fat mud' or 'deck mud?
And for those who know about the Ontario Code, can we level out a basement floor tht slopes towards drains?

Eliz

Medium bed setting material has much coarser aggregate than standard thinsets and can be piled up much thicker under the stone without sagging or shrinkage. Most medium beds can be applied up to 3/4" thick.

To really evaluate what you should do with your floor, we need to know its shape, or how far out of level it is over the distance the tile will be set on.

For example, over 15' the floor varies +/- 1/4" from level.