Concrete Board Installation

I’ve begun work on my guest bathroom. The floor tile and vanity were in bad shape and it was time to replace them both. A fresh coat of paint will go a long way too. I’ve removed the vanity, toilet and old tile (post coming) and now I’ve begun preparing the subfloor.

The old tile was laid right on the plywood. It was a poor job and no wonder we had lots of cracked tiles and some rotten wood. The better choice would be to put down concrete board overtop the plywood. Concrete board has some great properties that will ensure your tile-work stays beautiful for years to come.

Concrete Board

Concrete board, a.k.a. cement backer board, replaces the old plaster and lathe underlayment for tile. It’s a lot easier to work with preformed concrete board rather than laying a bed of mortar on the jobsite and it still carries the same great qualities. Concrete board protects against moisture and mold growth. It won’t rot or warp. Basically, it’s exactly what you want around a shower or tub.

There’s a few main manufacturers- Durock, HardieBacker and WonderBoard. I picked up some HardieBacker at HD this morning.

Cutting Concrete Board

If you plan on cutting lots of concrete board, you can use a circular saw and abrasive blade. This method creates a cloud of silica dust so make sure you are outside and/or wear a mask.

For smaller jobs, grab a utility knife. It’s recommended to have a carbide tip but a regular blade will work too. Score the backer board along a straight-edge. Make about 5 passes, pressing down firmly. Stand the board on edge and apply pressure on the opposite side. The cement board will break along the cut much like drywall. Use the knife to completely separate the two pieces and clean up the new edge.

There are tools available for creating cut-outs. I don’t know how well these work but they’re out there. Another option is to score around the perimeter and carefully punch out with a hammer.

Installing Concrete Board

Here’s how I laid my concrete board. This guidelines are not intended to replace manufacturers instructions.

• Prepare the subfloor
  This means making sure the subfloor is structurally sound- no loose, rotten, or uneven sections. Make sure all nails and screws are countersunk below the surface. Take a moment to sweep and vacuum the floor too.You also need to make sure the subfloor doesn’t bounce. A floor that moves will result in cracked tiles. Check that your floor meets minimum deflection criteria before continuing. Here’s a handy deflection calculator from John Bridge forums.
• Plan Cement Board Location
  There’s more thought required than just grabbing a board and putting it down. You need to stagger cement board joints and ensure they don’t align with subfloor joints. Fewer joints often means a more even subfloor. Leave a 1/8″ gap between boards that you’ll fill with thinset while laying tile.
• Laying Cement Board
  Traditional installations call for spreading a bed of mortar or modified thinset and raking with a 1/4″ square-notched trowel. Instead, I used liquid nail. I applied a generous bead in a zig-zag fashion before setting the concrete board in place. Next, I fastened the concrete board in place with screws using #10 x 1-1/4″ placed about 8″ apart. Make sure screw heads sink just below the surface.

What do you think? What tips can you add?

by: Ethan | February 16, 2010 | filed in: Projects
Related Tags: board, cement, concrete

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