Installation Guide

24 TESTING
Evaluation of mortar types used with Schluter
®
-DITRA
TESTING
As stated previously in this Handbook, Schluter-Systems recommends the use of unmodified thin-set mortar between DITRA and the
ceramic or porcelain tile covering. In this section, we will address concerns regarding the use of unmodified mortar over DITRA and provide
insight into the overall function of the tile assembly using experimental data. The Tile Council of North America was contracted to perform
independent testing of all experimental setups described hereafter.
A popular misconception in the tile industry is that porcelain tile cannot be bonded using unmodified mortar. To show that
unmodified mortar will provide the necessary performance in DITRA installation systems, the following tests were performed.
First, unmodified mortars from two different manufacturers were used to bond porcelain tile to DITRA over a single layer of 3/4" plywood
with joists spaced at 19.2" o.c. The two installations were tested according to the ASTM C627 “Standard Test Method for Evaluating
Ceramic Floor Tile Installation Systems Using the Robinson Type Floor Tester” and produced ratings of heavy and light. Heavy indicates
a performance level acceptable for shopping malls, stores, commercial kitchens, work areas, laboratories, auto showrooms and service
areas, shipping/receiving, and exterior decks, while light indicates a performance level acceptable for light commercial use in office space,
reception areas, kitchens, and bathrooms. Given that the test assemblies only utilized a single layer of plywood, these high-performance
ratings demonstrate that unmodified mortar can provide a secure bond even over a bending and deflecting substrate. Tiles were removed
from each of the ASTM C627 specimens after the Robinson test was complete, and then used to evaluate shear bond strength between
the unmodified mortar and the tile. Test results are summarized in the table below.
*Test Setup:
1. 2" x 2" joists spaced 19.2” o.c.
2. APA-rated “Exposure 1” tongue-and-groove plywood subfloor; 3/4" thickness
3. Spray-dried latex-modified mortar in Test TCA-046-03 and liquid-emulsion latex-modified mortar in Test TCA-126-03 (ANSI A118.4)
4. Schluter
®
-DITRA mat
5. Unmodified mortar, as indicated in table above (ANSI A118.1)
6. 12" x 12" porcelain tile; 3/8" nominal thickness
7. Sanded, spray-dried latex-modified portland cement grout (ANSI A118.7)
† Tile samples removed from ASTM C627 test specimens and evaluated for shear bond strength between mortar and tile
Given concern over freeze/thaw performance of unmodified mortar, the next set of tests included shear bond tests of porcelain
tile bonded to concrete with and without DITRA after exposure to freeze-thaw cycles in accordance with ANSI A118.4 (F5.2.6).
An unmodified mortar was used in one installation, while a liquid-emulsion latex-modified mortar from the same manufacturer was used in
the other. It should be noted that when used between two impervious materials, such as porcelain tile and DITRA, latex-modified mortars
must be afforded extended drying times. According to the TCNA Handbook for Ceramic, Glass, and Stone Tile Installation, the necessary
drying period can fluctuate from 14 days to over 60 days when using latex-modified mortar. Since unmodified mortars do not require a
drying period (and actually benefit from continued water presence), they allow for normal use of the tile installation in a fraction of the time
and, as shown in the test data in the table below, provide more than adequate performance.
‡ All specimens subjected to freeze/thaw cycles in accordance with ANSI A118.4 (F5.2.6)
_
ANSI A118.4 requires minimum shear bond strength of 175 psi
° ANSI A118.10 requires minimum shear bond strength of 50 psi
Tests were also performed on DITRA assemblies using unmodified thin-set mortar over concrete according to ASTM C627. The two
assemblies produced ratings of Extra Heavy, indicating a performance level acceptable for extra heavy and high impact use in food plants,
dairies, breweries, and kitchens, and Light, indicating a performance level suitable for light commercial use in office space, reception areas,
kitchens, and bathrooms. Variation in the performance levels achieved is attributable to the different tile used. Test results are summarized
in the table below.
Mortar Type
(Applicable ANSI Standard)
Test Report Number ASTM C627 Test Rating* Test Report Number
Shear Test Results
†
(psi)
Manufacturer 1
Unmodified (A118.1)
TCA-046-03 (B) Heavy (13 cycles) TCA-073-03
Specimens: 327, 267, 267, 246
Average: 277
Manufacturer 2
Unmodified (A118.1)
TCA-126-03 (A) Light (9 cycles) TCA-186-03
Specimens: 425, 381, 275, 377
Average: 365
Substrate
Mortar Type (Applicable
ANSI Standard)
Tile
Grout (Applicable
ANSI Standard)
ASTM C627 Test Rating Test Report Number
Concrete Unmodified (A118.1)
12" x 12" porcelain;
5/16" nominal thickness
Polymer Modified
Cement Grout (A118.7)
Extra Heavy (14 cycles) TCNA-039-06
Concrete Unmodified (A118.1)
2" x 2" porcelain;
1/4" nominal thickness
Polymer Modified
Cement Grout (A118.7)
Light (6 cycles) TCNA-057-06
Mortar Type
(Applicable ANSI Standard)
Shear Test Results
‡
(psi) Test Report TCA-145-03
Tile Bonded to Concrete (ANSI A118.4)
—
Tile and DITRA Bonded to Concrete (ANSI A118.10)°
Manufacturer 1
Unmodified (A118.1)
208
Specimens: 66, 61, 70, 62
Average: 65
Manufacturer 1 Liquid-Emulsion
Latex-modified (A118.4)
199
Specimens: 53, 57, 58, 75
Average: 61