Uneven backerboard [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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07-25-2001, 11:45 AM
I've installed concrete backerboard (thin set & screws) in my bathroom and when I started to layout the (marble) tiles, I noticed that one of the pieces of the backerboard sits higher (about 1/16th of an inch) than the adjacent piece (and all the others, for that matter, since the rest are level). I guess I got a little careless there. The bathroom is about 80 square feet, and very oddly shaped and the offending board is along one wall, but unfortunately also right in the entranceway. My question is should I rip up that piece and reset it, or can I rely on the layer of thin set (or apply a thicker layer of thinset on the lower boards, which is most of the bathroom) to even out the tile on top?

I have a similar question about the taping of the joints. I taped them when I put in the wonderboard so they are now dry. When I lay a piece of tile over a joint, the thin layer of thin set used to secure the tape acts as a fulcrum and produces a see-saw effect on the tile. Is this also something that the layer of thinset will "cure" when I actually lay the tile?

I hope I haven't screwed this up too bad.

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07-25-2001, 03:42 PM
Well...you can't rip up wonderboard..it will just fall apart..but you don't have to anyway. Use the flat side of your trowel to skim the offending area with thin set, to level it out...1/16 is nothing really...besides you should be using a notched trowel with 3/8 or 1/2 notch in it to help you level the marble as you lay it. Marble ain't easy..so take your time.

07-25-2001, 05:06 PM
You're right -- I meant replace the wonderboard. I will definitely take my time with the tile. What in particular should I be on guard for with marble that I wouldn't have to face with ceramic? This site has done a wonderful job educating me on tiling in general -- any suggestions unique to marble? Thanks for the response.

07-25-2001, 05:25 PM
Marble...hmmm..there's a good chance it's not all the same thickness...and since marble is set with a small joint(1/16 to 1/8) you'll have to be careful you don't get any edges sticking up..it has a square edge, so ther's not much room for error...ceramic has a cushion edge(a bit rounded) and has a bigger joint, so it gives you some breathing room. I don't know what your marble is..but you'll have to decide on the graining also..ie: which way you want it to run. You should open every carton to see what your dealing with..if you have some strange looking ones, you can use them for cutting,or in the closet, or even behind the toilet. Plus you'll need a water saw to cut every peice...a tile cutter won't work....what am i forgetting guys?


Bud Cline
07-25-2001, 06:19 PM

I would try hand grinding (with a floor stone) that high spot before I would fill & feather it. With marble a high spot will really cause some teetors and some serious lippage.

When I set marble tile over CBU's I always rent a 350 rpm floor machine and either screen or sand the CBU's just a little. This gets rid of the unseen and thus far indetected highs and flattens the floor satisfactorily.

This should be done before running the seems though. To do it now would destroy most of the tape but I would highly recommend it anyway.

After the floor is planed (flattened) then the tape and thinset used to tape with just kinda disappears into the combed thinset during the tile setting process.

07-25-2001, 06:27 PM
Use a white modified thinset, the gray can show through on some lighter colors and veins. (Assuming your not using an epoxy to set the marble) A 1/8" grout joint will help leveling the marble in relation to neighboring tiles and reduce the effect of any lippage, but a 1/16" joint is probably closer to a "visual standard" with marble.

Here lately, I've been "butt-jionting" alot of marble and travertine installations at customer request. These tiles often have a slightly beveled edge so even butted together, there is still a small joint for the non-sanded grout to grab.

Like Brian said, if there is a noticable variation in the thickness of the tiles, you might want to use a larger notch trowel (1/4 x 1/2 u-notch) to reduce any necessary back-buttering to keep the field level.

07-25-2001, 08:00 PM
When you bought the marble did any one say any thing about the marble being suseptable to warping?

Some are. What color is it?

Just a safety precaution.