What size trowel should I use? As a technical representative for MAPEI, I often get this question.
Obviously, the first response to this question is: What type of flooring are you installing? We will start by discussing tile and then move on to resilients, carpet and wood.
With all the industry standards and norms, there is no trowel standard; there is, however, a coverage requirement. The tile industry requires 80% mortar coverage in dry interior areas and 95% coverage for exterior wet and natural-stone installations – after you have placed your tile in the notched mortar and pressed down, you should be achieving the coverages that are required for the installation.
The way to check for appropriate coverage is to remove a tile after it has been bedded into the mortar; the back should be covered with mortar at 80% or 95%, accordingly.
One method that helps in achieving coverage is to back-butter the tiles. To back-butter, you spread a bond coat to the backs of your tiles – typically using the flat side of your trowel – before placing the tile in the mortar notches on your substrate.
Standard-size trowels for tile flooring
1/4″ x 1/4″ x 1/4″ (6 x 6 x 6 mm)
For tiles up to 8″ x 8″ (20 x 20 cm)
1/4″ x 3/8″ x 1/4″ (6 x 10 x 6 mm)
For tiles 10″ x 10″ (25 x 25 cm) up to 17″ x 17″ (43.2 x 43.2 cm)
1/2″ x 1/2″ x 1/2″ (12 x 12 x 12 mm)
For tiles 18″ x 18″ (46 x 46 cm) up to 12″ x 36″ (30 x 91 cm)
3/4″ x 9/16″ x 3/8″ (19 x 14 x 10 mm)
For tiles 24″ x 24″ (61 x 61 cm) and larger
The tile sizes above are suggestions – what matters is making sure that you get the proper coverage.
Resilient and carpet flooring
A trowel is simply a measuring tool to meter out the correct amount of adhesive for the finished flooring that is chosen; there is no one-size-fits-all trowel. Thus, trowel selection for resilient and carpet flooring is determined by the flooring manufacturer. Site conditions, the backing of the flooring material and the surface of the substrate are a few of the factors that are considered when a trowel is chosen.
Trowels for resilient and carpet flooring are often misused in the industry. Using too much or too little adhesive on these trowels will likely compromise your installation. For example, too much adhesive can cause indentations from rolling loads, adhesive ridges to telegraph through the flooring and adhesive to come up through the seams, among other unsightly conditions.
Adhesive manufacturers suggest common trowel sizes for resilient and carpet flooring; however, the flooring manufacturer’s recommendation should be followed.
Standard-size trowels for resilient and carpet flooring
1/32″ x 1/16 x 1/32″ (1 x 1.5 x 1 mm)
For flat-backed vinyl and carpet tiles
Average spread rate: 185 to 245 sq. ft. per U.S. gal. (4.53 to 6.0 m2 per L)
1/16″ x 1/16″ x 1/16″ (1.5 x 1.5 x 1.5 mm)
For vinyl-backed, carpet tiles, felt/mineral-backed, sheet goods, vinyl composition tile
(VCT), luxury vinyl tile/luxury vinyl plank (LVT/LVP) and rubber flooring
Average spread rate: 125 to 185 sq. ft. per U.S. gal. (3.06 to 4.53 m2 per L)
1/8″ x 1/8″ x 1/8″ (3 x 3 x 3 mm)
For jute, polypropylene (ActionBac®), needle punch/wall carpet and outdoor artificial turf
Average spread rate is 85 to 95 sq. ft. per U.S. gal. (2.08 to 2.33 m2 per L)
As with resilient and carpet flooring installations, using the correct amount of adhesive when installing a wood floor is critical. Failing to choose the correct trowel can result in costly remediation expenses. The general rule is the thicker the wood, the larger the trowel that should be used.
Standard-size trowels for wood flooring
3/16″ x 5/32″ (4.5 x 4 mm)
For wood flooring < 1/2″ (12 mm) thickness
Average spread rate: 45 to 55 sq. ft. per U.S. gal. (1.10 to 1.35 m2 per L)
1/8″ x 1/4″ x 1/4″ (3 x 6 x 6 mm)
For wood flooring 1/2″ to 5/8″ (12 to 16 mm) thickness
Average spread rate: 40 to 50 sq. ft. per U.S. gal. (0.98 to 1.22 m2 per L)
1/4″ x 1/4″ x 1/4″ (6 x 6 x 6 mm)
For wood flooring > 5/8″ (16 mm) thickness
Average spread rate: 30 to 40 sq. ft. per U.S. gal. (0.73 to 0.98 m2 per L)
Keep in mind that the spread rate can vary depending on the adhesive for all the flooring types that have been mentioned in this blog, so always check the manufacturer’s technical data sheet for detailed information.
If you are unsure of which trowel size to use for any flooring type, or if you have any questions, do not hesitate to reach out to one of our MAPEI Product Support specialists at (800) 992-6273.