Ist time granite tile installation on bathroom floor

[9design]

I'm a small-time contractor with ceramic experience only, and have been hired to install about 75 S.F. of polished granite bathroom floor tile. Underlayment is 1/4" cement board over 3/4" ply sub-floor, secured with 3/16" thinset & counter-sunk screws 8"OC. Tile (purchased previously by the client) is 12" X 12" x 1/2" thick light tan Chinese granite. They also purchased a 50 LB bag of Ultraflex 2 polymer-modified mortar in grey color for setting. (I think they were going to do this themselves originally and got cold feet). Anyway, I've never worked with granite before, and have gotten misleading "help" from other contractor friends. First, several say use an epoxy mortar rather than the Ultraflex?  Next, another said to seal it before laying, as the mortar can stain it during installation? He also recommended sealing top & bottom before laying, as the grey mortar could bleed into the tile? Should this be done, or will the sealant affect the tile adhesion? Does mortar color affect the finished look? What's the best sealant for a bathroom floor, Fluorocarbon or mineral based? Thanks for any help!

[Mark D.]

Use a latex thinset - the white stuff. The regular multipurpose thinset might bleed color through the stone, but the later thinset will bond much better.

When you butter the back of the tile, butter the whole thing, not just a dab in the corners. This will also give you a better bond and no hollow sounds.

Lay each piece so all of the tops will be on the same plane. That way the reflection doesn't jump when you walk across it and look down.

I would install it and seal if before grouting as the sealer will prevent the grout from staining the stone and will also act as a grout release.

I would not seal the bottom of the tiles. You want the thinset to bond well and the sealer may prevent this, plus there is no reason to seal the bottom. Sealing with an impregnating sealer fills the micropores in the stone to prevent it from staining.

Glad to be of service,
Mark