Concrete board installation

Old 04-12-07, 12:24 PM
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Concrete board installation

Going to start installing concrete board for tile this evening and just wanted to see if I'm missing anything with the installation.

It's new construction, so the concrete board will be installed over 3/4" Advantech. Prior to anything, we'll use a shop vac on the Advantech to get the drywall dust off it.

From what I have been told, use a layer of Thinset between the Advantech and concrete board. I've heard to use both a 1/4" and 3/8" square notch trowel. Does it make a difference? (I'm using 1/2" concrete board and the tile thickness is ~1/4". The tile will mate up with 3/4" thick hardwood floors and we'd like it to come out as level as possible.

For cutting the concrete boad, is it just a utility knife to score the surface, then break it similar to sheetrock?

I'll use a nail gun to attach the concrete board to the floor. How often to nail? I think I recall every 8-10". Also, do the concrete board pieces have to be staggered when placed?

What else am I missing?

I was thinking of having someone else lay the tile, but after getting another bid today, it might also be a do-it-myself job.
Old 04-12-07, 03:10 PM
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First off I will say I know nothing about Advantech so if there are any special requirements for working with this board they would supercede what I am about to say.

Use a 1/4" square notch trowel for the thinset under the board. The thinset is not there for bonding or coupling the CBU to the subfloor, it is meant to fill in gaps and voids between the CBU and the plywood.

Nail it at 6" intervals around the perimeter and 8" in the body. Use galvanized roofing nails 1 & 1/4" long.

Depending on the type of CBU, different scoring tools are used. If it is DensShield then a utility knife can be used. For all other cement boards like Hardibacker, Wonderboard, Durock and Permabase, a special scoring tool is used and sold at the big box stores in the tile tools area. All manual scoring tools are knucklebusters. If you have a 4.5" right angle grinder you can get a continuous rim diamond tipped cutting blade for about $35 and is well worth it. Makes a ton of dust so cut outside and wear a mask, but quick and clean cuts.Some people also use a jig saw with carbide blades or a circular saw with a larger continuous rim blade. A cheap masonry blade might work, dont know for sure. If you want to be the test pilot on that post back with results.

After the boards are installed, tape all seams with fiberglass mesh tape and a thin coating of modified thinset. What size tile are you using?

Last edited by Tileguybob; 04-12-07 at 03:13 PM. Reason: forgot some additional info

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