Moisture retardant for tile floors and walls?

britt_schaeffer · 09-28-2009, 02:09 PM

I'm about to tile my bathroom floor and walls. This will be my first tile job. for the floor, my plan is to lay cement hardie board on mastic over the subfloor. i was then planning in laying my slate tiles in thinset on top of the cement board. my question for the floor is this - should there be some sort of moisture-retardent material in the mix there? someone told me about a material that you spread, but I haven't read about that anywhere else.

Bud Cline · 09-28-2009, 06:23 PM

Waterproofing bathroom floors isn't unusual but it isn't done all that often. Why would you want to do it?

The cement board should be installed into a fresh mix of thinset NOT MASTIC and then screwed or nailed according to the manufacturer's recommendations. READ AND FOLLOW THE INSTRUCTIONS. Don't just settle for some crap you "hear" on the Internet.

There are liquid waterproofing membranes available such as Custom's "Redgard", Mapei's "HPG", Laticrete's "#9235" and Laticrete's "Floor and Wall Waterproofing". There are others.

JazMan · 09-28-2009, 11:15 PM

I agree there is no need to apply a membrane on the typical bath floor.

Why were you thinking of using mastic under the Hardie? Use thinset only.

I noticed you'd like to install slate tiles on this floor. Can I talk you out of it? In addition to the extra maintenance, your subfloor is probably not stiff enough for slate. Slate and other natural stone floors require a much stiffer subfloor system than ceramic or porcelain tiles do. Can you tell us how and with what the framing and subfloor are built.

Jaz

britt_schaeffer · 09-29-2009, 11:13 AM

I've heard that slate is quite a bit heavier and that much subflooring hasn't been constructed to withold it. i don't have the measurements offhand (am at work right now), but I'm not terribly concerned about it, primarily b/c in the renovation process i pulled out a 2.5 inch thick layer of cement, and then mortar on top of that, which was laid over some sort of wire mesh. then there was a heavy tile (the house was built in the early 50s, and i'm gathering this is the original material) on top of that. the space is incredibly small, i think about 25 sq feet and when i got to the dump, i had just under a half ton of material in my trailer. that being said, i feel fairly confident whatever ditra (or cement board), thinset, and slate I put on top of that will be assuredly lighter. you make a good point about being sure though - i'd hate to find myself in the basement one day after walking into the bathroom

Limit54 · 12-04-2009, 11:17 PM

I don't know where your from but if your from Toronto, Canada then like me you will have a hell of a time finding waterproofing material. I have found it though. The stuff id called Blue Seal and works amazing. Just make sure you go up at least about 1 inch where the floor meets the walls.

JazMan · 12-05-2009, 08:38 PM

Unfortunately Brit never came back with answers to the questions he was asked about how his subfloor was built. He thinks he knows more than he really knows about tile installations.

He thinks all he has to worry about is total weight of the tile installation. he should have been thinking about floor stiffness so there is very little vertical deflection. Too much deflection will ruin a tile job every time. If he only had one layer of plywood, the floor is not suitable for the slate he was thinking about.

He may be back asking why and how to repair his floor.

Jaz

Bud Cline · 12-05-2009, 10:44 PM

I'll add that the structure may have previously carried the additional weight of the cement installation but keep in mind that the cement was also adding rigidity to the floor. Removing the cement totally changes the dynamics of the floors performance ability. Just because the structure carried the weight doesn't mean the structure will support a slate installation without cracking grout and shaling tiles with the cement removed.

JazMan is exactly correct and I agree; Brit hasn't learned enough or answered enough questions to proceed with any real confidence.