Why is Cement Backer Board So Great? (And What to Use it For!)

Cement back bathroom renovation
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Cement board is one of those neat home remodeling inventions of the 20th century that makes your tiling project go faster and look better in the end.  Why is cement board so great for some remodel projects?  Where and how do you install it?

What Is It?

Cement board is now commonly called a cementious backer unit (CBU),  CBUs are 100% inorganic, meaning that, unlike wood-based materials such as drywall, greenboard, or plywood, there is no organic matter that will promote mold, rot, shrinkage, or decomposition.

Cement Board vs. Drywall

To understand cement backer board, you should first look at its cousin--drywall. For years, interior walls were finished with lath (wood strips) and plaster laid over the studs. Plasterers used hundreds of pounds of plaster, trowel by laborious trowel.

Then someone got the brilliant idea of pressing all of that plaster, plus the structural qualities of the lath, ahead of time in a factory--in the form of sheets of drywall.

This is the basic idea behind cement backer board. Instead of laying beds of mortar on the job site, or using inferior backing boards such as greenboard, you can simply screw in these pre-formed and already-set sheets of concrete board. Pretty neat.

Applications

The great value of cement board does not rot, warp, grow mold, or deteriorate when subjected to water.

Wood obviously is not a great material to use in wet applications, and even green board, a more hardy type of drywall, is not recommended for places with constant water usage, such as showers.

Cement backer board is mainly used as a sub-surface for tiling.

Cement board on concrete as a sub-floor is usually not recommended or needed.  in most cases, you can apply tile directly to the concrete.

Manufactured veneer stone is another use for cement board, though not a common one.  Veneer stone cannot be applied directly to drywall or other materials that will draw in moisture from the mortar.

 Not only that, drywall is not a strong enough material to support veneer stone's considerable weight.  One solution is to nail cement board CBUs over the drywall, tape the seams, and then grout over the cement board.

Manufacturers

There are three main cement board products available to the home remodel DIYer.  All are found at major home improvement stores at 1/4" and 1/2" thicknesses.  They can be nailed or screwed into studs or into cinderblock, brick mortar, or concrete.  All can be easily cut with a hand saw, circular saw, jigsaw, or multi-tool.

Durock Brand Cement Board

Made by USG, Durock vies with HardieBacker as being a favored cement board for tile workers and tradespeople.  Durock tends to be slightly lighter than similarly sized HardieBacker.

HardieBacker

Made by James Hardie Industries. HardieBacker is 90% Portland cement and sand, with a patented MoldBlock additive.

WonderBoard and EasyBoard

Made by Custom Building Products, WonderBoard is markedly different from Durock and HardieBacker in that it has a looser, more crumbly composition.

How to Install

If you have any obstructions to work around, before laying down the boards you can easily (but messily) cut the cement board with a SkilSaw with a carbide blade.



First, you apply thinset mortar on the surface, and "comb" it out with your trowel. Keep the cement boards about 1/4" apart.

After pressing the boards into the mortar, screw them in with screws made especially for cement board installation. Just as you would with drywall, make sure the screwheads are slightly depressed below the cement board surface. Cover and mortar the seams with fiberglass seam tape. Please see our complete cement backer board installation guide.

Can You Tile Directly on Drywall In the Shower?

One common question that homeowners have is whether they should install tile directly to drywall greenboard, or cement board when tiling a shower.

In the past, tiling guides recommended installing the surrounding tile directly to drywall,

Tile, with its seams and numerous avenues for moisture infiltration, can eventually lead to the drywall being soaked.

Once the drywall is soaked, the studs begin to dampen. Mold, mildew, and rot result.  In short, tile and grout are not inherently waterproof.

Opt for a more effective method of backing your shower/tub tile.