tile question - backerboard seam hump

[unc27932]

Bathroom redo, with ceramic tile.....

Following all the DIY sites & friends' advice, I put down thinset on my bathroom subfloor, then my backerboard, then I put thinset in the seams of the backerboard, pressed fiberglass tape down in the seam/ thinset, then put some more thinset over the tape. I thought while doing it it was pretty level. But now that everything's in place, I put a test tile down on the seam & it rocks back & forth a bit.

Should I go to the trouble of grinding down the seams to get the seam perfectly flat? Or will the thinset that goes under the tile handle this minor hump?

[Paul Franklin]

You did it right. The thinset will handle the bump unless it is really bad. How bad is really bad? Depends on the tile size and thickness, (and hence, on the trowel notch size and thickness of thinset). If you're really worried about, lay a couple of test tiles using the proper notched trowel. You can always pick them up and scrape off the thinset if you don't like what you see. If it's a problem, just skim coat all the backerboard with thinset rather than trying to grind down the seams.

HTH,

Paul

[unc27932]

[Joe]

You can grind a seam flat with a $20 Harbor Freight angle grinder in far less time than skim coating more of the area. But then there's a dust issue, so choose your method keeping in mind the old pro's adage, "The flatter the substrate (wall, ceiling) the better the job". HTH

Joe