Flooring question (installing Durock 1/2" concrete board)

Richard · Oct 24, 2015

Finishing out an upstairs bathroom. 2x10 floor joists and 3/4" subfloor.

I have a couple questions.

Room is roughly 6' 3" x (doesn't matter)

The Durrock is three feet wide. I understand I should leave a little gap between the two pieces and between the edge of the room to prevent crowding (or whatever the word is)

We will have a 1x6 as our baseboard so the baseboard will be 3/4" thick.

The tile she's planning on using is 24"x24"

Question #1: Can I leave say, a 1/4" gap between the two pieces of Durrock and have a 1 1/2" gap at the edge of the room? Normally I would not like this much of a gap but, 3/4" of that gap will be covered by the 1x6 and it will have a 24" piece of tile on it. I don't really see where the very edge of the tile is going to be needing that support (???)

Question #2 regarding installing the Durrock itself: I have read that I should fit the Durrock to the floor. Pull up one piece at a time and lay a bed of mortar down to adhere it to the 3/4" plywood and help even it out.

I have also been told that since it's going over 3/4" plywood that I do NOT need to mortar it down.

The floor doesn't have any appreciable bounce to it unless you maybe (literally) jump up/down.

We did the prior two bathrooms (in same house) and I did NOT lay any mortar down. So far, 14 years later, they seem to be doing fine.

I'm not against the mortar and I'm not 'for' it. I want to do it 'right' and I don't care about speed.

(I think the flooring guy who said I didn't have to use the mortar was saying that "HE" would not use it.....as it would presumably then allow him to get to the tile sooner and finish the job sooner which is something I'm not concerned with)

Thoughts?

If I DO use the mortar.... what would I use? I was at the box store today and to be frank, received little help.

Richard · Oct 24, 2015

(I have a box of screws so I can screw the Durrock down irrespective of using mortar or not)

bamboozled · Oct 24, 2015

Unless cost is a concern there are better systems. For example:

Schluter-DITRA - Schluter-Systems

https://www.youtube.com/watch?v=CdNkzhnfioA

EddieWalker · Oct 24, 2015

I prefer Hardie over Durrock for tile. They have a quarter inch thick product that is designed for floors that you just screw down to the wood. I'm not a fan at all of Schluter products. It's all plastic and styrofoam that is very expensive, overrated and getting more and more negative reviews from failure. None of the pros I know of use it, it seems to be more for the home handyman who watches a lot of HGTV.

Barnbuilder · Oct 24, 2015

I'd put the ditra down. That's how my tile guy does it. Backer board is crap. And you can add the heated floor to the ditra.

jeff9366 · Oct 24, 2015

When I worked as a plumber's apprentice, we used 3/4" Durarock secured with 2" (sometimes 2-1/2") Phillpp's Head screws, screwed in til fraction below surface. No mortar. We did not leave a gap where the sheets meet, nor did we try to make the joints tight.

We laid tile over the Durarock, Mastic used to hold tile in place. Mastik varied as necessary to produce flat tile surface. It is difficult to get large tiles to lay flat but it can be done. Sanded grout was the final step.

ch1ch2 · Oct 24, 2015

I have a pier and beam house and I had ceramic tile installed 15 years ago. It was explained to me that a concrete board, Hardy or Durarock had to be laid down first to prevent the tiles from cracking. We used Hardy. We screwed it down. I do not remember if we used mastic or mortar to attach the tiles. We have not had any problems.
As far as the edges...I do not see any reason you could not fill that 1.5 inches on the edges with mastic or mortar.

downsizingnow48 · Oct 24, 2015

I recently used this backer board on a bathroom remodel. It is not as light as the foam boards, but is much lighter than the cement type boards and can be cut easily, like sheetrock, to fit your space. Comes in 1/4" and 1/2" sizes.

http://www.certainteed.com/resources/CTG-2506_Diamondback_DSS_Eng.pdf

SJay · Oct 24, 2015

Definelty put mortar under the backer board and screw it down. Also, mortar and tape your joints with fiberglass tape. Just replaced my son's bathroom tile because all the tiles where coming loose because of improper backer board installation. I wouldn't leave a gap of more than a 1/2" around the room. Remember to back butter the tiles, especially a tile 24x24

FredH · Oct 24, 2015

I am with Eddie . We used Hardie on both Bathroom floor's and on the floor and wall of Our Fireplace install . Also used it on the Wall's in My Mom's New Walk in tub install . There was No mortar under or Behind the Hardie , Joints were not tight , but no gaps either . Bathroom floor's have 12" tiles , Fireplace was 16" tiles on floor and wall and Mom's Tub walls are 6" tiles . Disdain the cement board stuff as if You have to cut it , the cut netting lets it chip and chunks fall out . If Floor is Sound to begin with without flex , The only issue's that may come up would be with Actual tile install , mortar used and Grout used .

The only tile jobs I have seen were there has been a issue is the Grout was not sealed after install . So many people bypass that step since it is so time consuming .

Fred H.