questionable backer board installation [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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12-22-2016, 03:32 PM
A contractor (who is not a tiler by trade) has installed a backer board around our bath tub surround for future tile installation. No shims or furring strips were used between the studs and the backer board to compensate for the thickness of the flange.

As a result:

1. On one of the three walls, the backer board ended up under the flange so the flange now rests on the surface of the backer board. The thickness of the flange is standard (around 1/4 inch). Tile is to go on top of the flange and onto the rest of the wall.

2. On the other two walls, the backer board (Densshield) was "shaved" at the bottom to land over the flange but some uneven surfaces and cuts in the corners of the boards were created as a result of this "hacking".

My question is whether these two issues are acceptable for future tile installation. I am the customer and new to tiling.

Thanks a lot in advance. I have tried to load some pictures, you may have to look horizontally.

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12-22-2016, 05:38 PM
Prep is key to a quality installation, so no that's not acceptable in my book. Walls should be flat and plumb before anything is installed on the walls. Tell the guy to come back and do it properly or get your money back and hire someone that knows what they're doing.

12-22-2016, 05:59 PM
Hi Elvira,

I can't tell where the problem is or why. It's possible that the situation has nothing to do with this installer but the way the surround was installed and/or the way the studs lineup. In other words, if this is an el cove, the space is usually ½" or so too long and if the surround isn't spaced just right, things don't lineup.

i.e. a tub cove might measure ½" more than the width of the tub surround.

The gaps should be easily caulked if that'l help. Were all the seams taped and thinset applied? Is the Denshield fairly flush with the wallboard it butts up to?


HooKooDoo Ku
12-23-2016, 11:53 AM
CBU, tub flange, and furring strips...

Sounds like you're talking about a situation where you mount the tub up against the studs, and then mount the CBU on furring strips so that the edge of the CBU overlaps the tub flange allowing any water that drips down the CBU to remain 'inside' the tub rather than leaking into the wall behind the tub.

But you're also talking about a tub surround... in which case, the CBU isn't really a part of your water containment system... it is above the tub surround at a height that building codes don't require a waterproof wall.

If that is the case, so long as tile mounted to the CBU such that it hides the tub flange, then "no harm - no foul"... you don't have to worry about a leak because you're talking about an area that is high enough that it shouldn't be getting hit with running water on a regular basis, only just a splash of water with painted drywall is acceptable.

or is there something I'm not understanding about this installation?

12-23-2016, 12:35 PM
If you check out her pics you can see that he has the flange under the dense shield (bowed out and wavy). And the other side the flange is mounted on the surface of the substrate. It looks like a hack job

12-23-2016, 08:21 PM
I guess the installer felt that it was okay to do it that way since you can't see both sides at the same time.:D

I'd tell the installer that the flange needs to go behind the Denshield on all the walls. Sorry to be so blunt but he shouldn't have taken on the job if he couldn't make that happen.

12-23-2016, 08:27 PM
Thank you very much for your replies.

As Ryan noted the substrate is NOT flush with the wall set in the flange area. The flange sticks out by about 1/4 inch.

What would be the approach to fix this to place the tiles properly?

12-23-2016, 08:45 PM
I have noticed Davy's comment after I had posted the previous reply. Is reinstalling the substrate the only way now?

Houston Remodeler
12-23-2016, 10:05 PM
Yes, along with furring out the wall to make the between-the-studs space the same measurement as the tub AND making the studs plumb (vertically) and flat (horizontally) with each other.