By Gregory Mowat, Forensic Tile Consultants
After inspecting thousands of tile countertops and evaluation failures, the following recommendations are made for successful tile countertops:
Cabinets are to be set level within 1/4” in 10 feet. Cabinets are to be securely anchored to studs in the wall assembly through the top back rail. Island cabinets are to be securely fastened. The best fasteners are commonly 3″ #14 truss screws in each stud. If wedges are present underneath the cabinet for leveling, then the wedges must not protrude into the floor space in front of the cabinet. The cabinet side’s adjacent walls should be fastened to the studs in the wall. Where an overhang is planned, proper support of the corbels should already be in place and secured.
The wood rough top should use 1″x6″ boards spaced with 1/4” gaps between the boards. Where 3/4” exterior glue plywood is used, verify or add dot-and-dash saw cuts 6″-8″ on the center, staggered, but not within 2″ of cut edges including plywood edge at sink cutout. Note that Oriented Strand Board (OSB), composite panels, non-veneer panels, softwood plywood, and particle board are not suitable rough tops due to their expansion and contraction with change in moisture content. Further, do not bond tile directly to OSB, particle board, plywood or plastic laminate unless specific directions are given and warranted by a manufacturer, which may include a fully waterproof adhesive for installation of tile.
Further, the tile surrounding the sink should be securely supported. Top-set sinks following tile installation may be set by plumbing or another trade with the understanding that the caulking meets ASTM 920, and it is to be installed between the sink flange and the tile assembly.
Where tile is to be installed over backer board, follow backer board installation instructions explicitly, including v-cap installation.
Tile choice for countertop use is important. Thick, glazed tiles or high strength bisque tiles have fewer problems with errors in installation and long-term maintenance. That being said, the choice of tile should also take apron installation into consideration. Manufacturer’s v-cap should meet a minimum 100-lb. load expansion and 170 lb. for compression. The tile should also be warranted by its manufacturer as suitable for a countertop apron installation.
Mortar bed, lath and cleavage membrane to follow ANSI A108.1 requirements:
The installation of a membrane, such as 15-lb. felt, should be set and wrapped into perimeter assemblies including splash, underneath sinks, and sinks, and lapped at least 2″ at joints. The cleavage membrane should be recommended by manufacturer and free from holes or breaks.
Wire reinforcing should be 2.5 lbs. per square yard, or 3.4 lbs. per square yard. Utilize lap reinforcing at least one full mesh and support so that reinforcing shall be suspended in the mortar bed. Reinforcing on a horizontal surface shall not abut adjacent vertical surfaces; reinforcing on vertical surfaces (splash) shall not abut adjacent horizontal surfaces.
Place, tamp firmly, and screed the mortar bed. Mortar bed thickness should be 1″ and not exceed 11/2“. Tile does not need to be soaked when it is installed with thin-set or modified thin-set over a cured mortar bed. Soaked tile may be set over a workable mortar bed with a Portland cement paste.
All mortar bed surfaces shall be plumb, level and true with square corners. Maximum variation from plane shall be 1/4″ in 10 feet for both horizontal and vertical surfaces.
The installation of tile also includes planning for trim. V-cap tile is to be bonded both on top and on the apron without voids. The finished bottom edge of the tile on apron is set at 34 5/8” above the finished floor, with +/- of 1/8“. In order to have an adequate bond on the apron, install a punched metal strip and attach it to the front edge of the cabinet. Then fill the punched metal strip with wall mortar. It’s important to verify the installation of a dish washer, compactor, etc., which can still be completed and serviced following the tile installation.
A pencil rod can be installed in large tile deck assemblies, and in the mortar in front of the kitchen sink.
Installation of #16 galvanized wire or 8d nail reinforcement is ideal where butterfly sink corners are installed to prevent cracking of the butterfly sink corner.
Embed the tile in the mortar by beating-in, pushing in a direction perpendicular to the combed ridges, or other means to obtain the best installation and contact possible. The method used should produce maximum coverage with the corners and edges fully supported. Periodically, remove and check a tile to assure proper coverage is being attained. Lugs on tile determine the joint between tiles. Spacers, string or rope may be used to space tile that have no lugs. Install all tile to a true plane at the proper position or elevation. Remember that the uneven edges of V-cap, quarter round and surface bullnose are susceptible to chipping and uneven wearing of the exposed higher edges.
There is no question that the grouting of tile should be uniform. Grout manufacturers have made tremendous improvements with grout, including pre-mixed versions. Install grout following the manufacturer’s installation instructions explicitly. Cure the tile and grout assembly if required.
For lavatory countertops, chemical-resistant epoxy, chemical-resistant furan grout or modified emulsion grout may be installed. Again, follow manufacturer installation instructions explicitly.
Although finish plumbing is usually completed by other parties, ensure that is properly supported and sealed to the tile assembly. Use caution to not to overtighten the finish plumbing installation.
It’s important to note that modifications to the above procedures may be done as long as you take full responsibility for the finished installation.
Lastly, where possible, owners should be told to clean tile assemblies with a neutral soap.