Return to the Flooring Forum | Post a Follow-Up

 o
1 3/4' subfloor under tile??? Is this necessary?

Posted by deedles (My Page) on
Mon, Jul 9, 12 at 10:02

Hello,

Hoping I can get a quick coupla answers to this. We're being told conflicting info.

We want to install a pebble tile floor with a heat tape mat underneath in our bathroom. We have 3/4 inch plywood subfloor thus far.

One installer said we should prime the subfloor, lay the tape mat and he'll pour a subfloor to encapsulate the heat mat. Then the tile can go on that poured subfloor.

Another installer said we need cement board, THEN pour the stuff to encapsulate the heat mat, then the tile goes on that for a thickness of 2 inches to 2 1/4" total. This installer says you need 1 3/4" of sub-flooring under tile, esp. in our part of the country (wisconsin) or we'll have movement and cracking of the tile or grout.

This amount of flooring seems extreme to me but the guy said anything less is substandard and we'll have problems down the road?

A 2 + inch flooring difference? WTHeck?


Follow-Up Postings:

 o
RE: 1 3/4' subfloor under tile??? Is this necessary?

Add a 1/2" BC sanded or plugged ply or 3/8" for that matter. Get the heat mat that's a waterproof membrane as well set in thinset bed and tile over the mat.. Make shore your 2nd ply layer is staggered correctly on joists.


 o
RE: 1 3/4' subfloor under tile??? Is this necessary?

Joist span?

Tile and stone floors do not tolerate the normal movement allowed in a wood floor.

Look around the John Bridge forum for guidance on floor substrate thickness.

Cement board does NOT increase floor stiffness.


 o
RE: 1 3/4' subfloor under tile??? Is this necessary?

It's a bathroom so most likly is 16oc the question is are the joists 2x8, 2x12? Ect... Need at least 1" of wood for any tile install. 1/2" & 3/4" of ply is plenty. Can actually install heat lines over the backer board here is how.

http://floorelf.com/how-to-install-suntouch-warmwire-in-floor-heating-part-1


 o
RE: 1 3/4' subfloor under tile??? Is this necessary?

The actual joist span and height are more important than the joist spacing.

the joist spacing does drive the required subfloor stiffness, with 24 inch spacing needing even more thickness than 16 inch spacing.

If the joists are at the limit of span, no amount of thickness from the subfloor is likely to eliminate joist flex adequately for tile.


 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!


Return to the Flooring Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.


Learn more about in-text links on this page here