Remodeling Tips and Reviews

Installing Cement Backer Board on a subfloor

Installing Cement Backer Board on a subfloor

Jan 28, 2012

Installing Hardibacker or Durock Cement Panels are a pretty easy and straight forward

Nailing down the staggered Cement Board

process. I have installed both materials several times and prefer durock over hardibacker because hardi seems to come apart in layers much too easy for my taste, so I use Durock. Installing over a wooden sub floor ( i.e. a pier and beam or second floor) means laying the sheets long ways with the room, making sure to stagger the sheets like bricks so no seams line up on the short side. I usually lay out the entire room with whole sheets and then cut the perimeter pieces as needed. Make sure and leave around an 1/8″ gap between each sheet and the walls for expansion. Durock also has a smooth side and a rough side. Make sure and use the smooth side for finer tile and the rough side for larger tile.

Trim and Doors

If this is a remodel you need to keep in mind that you will likely be raising the floor around 3/4″ from its current level if there was no tile there before. You may need to cut 1/2″ or more of the bottom of any doors in the room prior to installing the tile.

Trim may have to be taken off and reset to the new height if it is a short trim style. If you have to remove the trim, make sure and take a utility knife and score the top edge where it meets the wall and is caulked, this will help prevent tear out when you are pulling off the trim. Use a flat crow bar and carefully work the trim off from one end to the other.

If the space was an old bathroom, you likely demoed up a thick bed of mortar and will need to take a minute to calculate the new floor thickness so you meet the old floor at the door. This usually means adding a 1/4″ or 1/8″ sheet of plywood after the subfloor is down but before the cement backer is installed.

Mudding the Cement backerboard Base to the Subfloor
Once the floor has been laid out you will need to use a 3/16 square notched trowel to

Taped Seams ready for tile

install mortar on the floor below each row of cement board. I used modified Versabond when doing this. It is a few dollars more per bag but has a stronger bond. You will need to lift each row up and trowel a layer of mortar down and then relay the cement board. Once it is down you will need to use roofing nails that are 1 1/2″ or cement backer board screws. A common question I am asked is do I need the base layer of mortar under the cement board. This is a judgement call in my opinion. If the joist are stout and the floor is very stable and level there likely is no problem with putting down the cement backer without a base of mud. But, each project is different and requires some analysis. If in doubt, take the extra hour or 2 to lay the mortar then you don’t have to worry about it later.

Once the backer is installed, you may need to tape the seams with special fiberglass tape and mortar. This is a quick process then you are ready to lay tile.

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2 comments

  1. susan /

    thanks so much.I have a water soluabe, i believe asbestos glue on my subfloor which is very solid. Just wanted to know if i can put durarock over it with just nails. dont want to remove the glue cause it smells so bad when water hits it. bviously i cant sand it. thanks for the info

  2. montytx /

    Sure Susan,
    You will want to use roof nails or cement backer screws and nail/screw about every 6″. I have done several floors like this with no problems.