Mortar Smooths Out the Rough Edges of Tiling

The big problem with installing tile--even with the small jobs--is the unevenness of the surface (counter top, wall, ceiling or floor) to which the tile is going to be applied. Tile seems to exacerbate waviness in a surface. Most uneven surfaces look worse after tile is applied.

In a home, most surfaces are wavy to some extent. Mortar is used to correct this kind of problem. Mortar is a substrate that can be made to be smooth no matter how wavy the surface. In short, troweled-in-place mortar is a backing that adds strength and smoothness for tile.

A mortar bed can be built to work over a waterproof layer, such as in a shower. First, a waterproof membrane is installed, then the mortar bed, and finally the tile and grout. When the grout fails and water gets behind the tile and mortar, the waterproof membrane protects the framing. All of these layers make tile in mortar very expensive.

Thirty years ago, builders decided to try a new technique--tiling directly to wallboard. No mortar. At first everything looked great and tile showers in modern subdivision homes were the rage. Soon after the warranties ran out, however, unlucky homeowners were spending big bucks repairing those tiled showers.

Discovering that tile-on-wallboard wasn’t a good application, better building departments started to outlaw the technique. But before long it was apparent that another alternative had to be found. Wallboard wasn’t the answer and mortar-in-place installations were too difficult and expensive.

Finally, a material was developed to replace wallboard for wet-tile installations. It’s known generically as “cement-backer board” or “mortarboard.” Mortarboard can be installed over a waterproof barrier and has the same water-stopping qualities of tile in mortar installation.

Mortarboard is very different from the old-fashioned and far-too-flimsy tile-on-wallboard. Once the grout starts to leak, the surface below doesn’t fall apart.

Even though mortarboard resists moisture better than does wallboard, it doesn’t smooth the surface. If the studs are crooked, the mortarboard will telescope the problem through. If you want good results, you have to make sure the wall studs are perfectly straight and that the face of each stud perfectly aligns with the face of each adjacent stud before applying the waterproof plastic and the mortarboard. Shimming and planing the studs as needed would be a smart thing to do.

Each manufacturer will recommend a different fastening method. Follow the manufacturer’s installation instructions to the letter. What you do with one product might not be recommended with another. Once the board is up, joints are taped and filled with joint compound--usually latex-fortified mortar. Latex-fortified mortar is a fancy way of saying mortar mixed with glue. Be sure to leave a 1/8-inch gap between sheets for expansion. Mortarboard expands and contracts just as wood does.

Some say that mortarboard is the answer as a base for tile floors. We don’t agree completely. Yes, mortarboard is an alternative to plywood. However, troweled-in-place mortar is still the finest way of doing any tile job.

With mortarboard, the floor that it will rest on must not vary in height more than 1/8-inch. This is a rather stringent tolerance. Most manufacturers recommended that a thin coat of mortar be used to level the floor before the mortarboard is applied.

If you are extremely careful with mortarboard, the job can look magnificent--without a lot of work, experience or cost.

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