The proper installation of backer board in a tile assembly is the foundation for success. Without a solid base, the balance of the installation could be in jeopardy.

The question has been raised. How difficult can it be to properly install backer board (panels) for a tile installation? The manufacturers of this product category provide written instructions, maintains a website full of “How to Install’ guidelines, and ultimately, the instruction label is glued either on the face or back of the board. How can a conscientious installer miss three opportunities to get it right? Unfortunately, it happens way too often.

The basis of backer board installation is found in the ANSI A108.11, Interior Installation of Cementitious Backer Units document. This standard provides all the requirements necessary for a successful installation. 

This manufacturer’s installation requirements are almost identical to the ANSI standard. The subfloor must be a minimum of 19/32” (5/8”). Stagger the backer board end joints a minimum of 16” so that four corners do not meet as well as offsetting the board joints a minimum of 8” from the subfloor intersections. Spread the adhesive, (thin-set mortar) in a straight line, placing the panel into the mortar fitting the edges of the panels closely, but not forced together. Fasten while still wet, securing the board with 1-1/2” (38 mm) 11-gauge hot-dipped galvanized roofing nails or 1-1/4” (32 mm) corrosion-resistant screws at 8” (203 mm) on center around the perimeter and in the field of the board. Fill the joints with modified dry-set mortar and immediately embed alkali-resistant, fiberglass mesh joint tape. 

The job did get off to a good start. The plywood subfloor was the required thickness and thin-set mortar was applied on the subfloor just before the board was set in place. But, these two requirements are where the good part ends and the hybrid tricks begin.

As you can see in the photo, the board is butted tightly together in some areas while widely gapped in others and there is no mesh tape on the seams. The fasteners should be 8” on center, but along the edge of the board, they are 10” to 14” apart. However, the really big fail is that there are NO screws in the field. Notice too, that the tile installation has already begun, but it probably will not enjoy a long life. One last thing: the instruction label must be removed. 

With the well-established ANSI standards in place along with the instructions from the manufacturer, which if followed, provides a warranty, why would the installer create his or her own hybrid system? Remember that in doing so, the installer is completely responsible for the failure.