Waterproofing and crack isolation membranes are widely used in the tile industry as part of substrate preparation prior to the installation of ceramic tiles or similar rigid materials. Membranes that deliver crack isolation performance are intended to maintain their integrity during movement of the substrate and thus prevent tile cracking, which minimizes costly repairs. Ensuring the integrity of these membranes is essential for guaranteeing the efficacy and longevity of any tile project, making this an essential consideration for the industry and tile professionals.
Naturally, testing is a key determinant of membrane performance that influences market-available membranes, in addition to ongoing research and development for this product. Currently, crack isolation testing of these membranes is based upon the industry standard: the American National Standards Institute (ANSI) 118.12, Section 5.4: System Crack Resistance Test method. Although widely recognized as a proven, reliable test, there are some notable drawbacks to this test method.
The ANSI crack isolation test method is a large, heavy set-up composed of cement pavers, a membrane, tiles and grout mounted on steel plates. Because the ANSI 118.12 test apparatus is custom-designed, large in size and requires large quantities of testing materials, the test is impractical for a typical lab. In fact, only a few laboratories in the nation have this scale of testing capability. Subsequently, the cost and size of this custom test equipment limits the number of tests that can be performed.
Furthermore, the ANSI 118.12 method provides standards of performance with a pass/fail result, with crack distance at failure as the only test result (this relates to the crack-bridging performance of the membrane compound). While this is certainly valuable information, there is an industry desire to obtain additional information on the elastic behavior of the latex polymer and membrane as stress is applied during the test. In particular, there is a need to generate information on how the membrane responds to testing stresses, which could aid in latex polymer and formulation development.
The ANSI method also uses a wet thickness gauge to measure the wet thickness of a troweled or rolled-on membrane, but fails to measure the dry thickness. Given potential variables in the volume of solids between batches and brands of membranes, it is valuable to have insight into the dry film thickness to ensure similarity between test samples.
Given these drawbacks, the team at Trinseo developed the Crack Isolation Simulation Test.
ANSI 118.12 vs. Trinseo Crack Isolation Simulation Test
The Crack Isolation Simulation Test method was designed to generate supplemental information useful to the development of polymer latexes and compounds primarily used in waterproofing and crack isolation membranes. It is not intended to replace the ANSI 118.12 method, but rather to augment.
One of the benefits of this new test method is that test specimens are smaller, allowing for the use of less materials. Since test specimens do not need to be mounted on a large test apparatus, many specimens can be assembled and tested in a given period of time, which supports reproducibility and repeatability data generation. Furthermore, the test set-up allows for the use of a common tensile tester (in this case, an Instron) and is designed using readily available materials. Altogether, these features and the easy set-up enable test performance in most standard lab settings.
The test design also allows for the measurement of the actual tested dried membrane thickness by difference — formula: (wood + membrane) – wood = membrane thickness. Alternatively, dry membrane thickness can be measured by casting a blank membrane on a Teflon-coated stick, then removing and measuring when dry.
Notably, the Crack Isolation Simulation Test includes measurements of the maximum tensile force applied to the tile/membrane assembly prior to failure. This is important, as there can be significant differences in quarry tile tensile strength (see Table 1 for a range of tile tensile strengths). Additionally, the stress reduction portions of the curves in Figures 1 to 4 provide valuable insight into the mechanism of stress-energy absorption of the crack isolation membrane. This stress-reduction data is of particular importance because it can be used to predict performance, even in specimens that fail due to cohesive membrane failure or thin set mortar failure.
Requisite Materials
The following is a list of materials required for the Crack Isolation Simulation Test:
• Test membrane compound
• Clear-grain red oak wood strips that measure 1 1/2- x 6- x 1/4-inch
• Mastercraft 104-2203, Solid Oak 1/4 inch x 2 inches x 4 feet, Select Grade Sanded Smooth (actual size 1/4 inch x 1 1/2 inches x 4 feet);
Cut to 6-inch lengths
• At the point of re-assembly of the strips, ensure matching cuts are kept together
• Lightly sand assembled strips to remove rough edges and splinters, clear of dust
• Masking tape
• Finishing sandpaper
• Metal frame – 0.045-inch-thick
• Assembly instructions:
The metal frame is made from a 4- x 12-inch cold-rolled steel (or aluminum) flat sheet
A 1 1/2- x 8-inch rectangle is cut from the center of the steel plate
On either long side of the hole, a 1- x 12- x 1/4-inch flat metal is adhered with epoxy, super glue or Gorilla Glue
The wood strip will snugly fit into this slot
The top surface is buffed to remove cutting burs
1- x 4- x 1/4-inch strips are adhered along the top ends of the flat metal to prevent flexing in the width direction
Applying self-adhering Teflon film to an uncut test oak strip is recommended to check applied membrane thickness
• The thickness of the sheet is chosen to target the desired membrane test thickness when dried
A frame thickness of 0.045-inch will generate an approximately 0.032-inch dry film thickness; A thinner frame (0.035-inch) will provide an approximate membrane thickness of 0.027-inch
An approximate calculation is (desired dry thickness)/(compound solids fraction)
For example, with a 68% solids compound and 31 mil. desired thickness: 0.031-inch/0.68 = 0.0456-inch sheet metal thickness
• Unglazed quarry tiles – 4- x 6- x 1/2-inch
• Cleaned, rinsed and dried prior to testing
• Can purchase as 6- x 6-inch square, cut to 4 x 6 inches, keeping the grooves running the short length
• Commercial two-component, polymer-modified thinset mortar
• A 3:1 powder to liquid ratio was used, as directed in the product instructions
• Optionally, a one-component, polymer-modified thinset mortar may be used
• 5-lb. weights
• Drill press with 1/4-inch bit
• Tensile Tester with cyclical testing software
• Instron with Bluehill 3 software
Note: Dimensions of test materials were selected to remain within the capability of the available Instron (1,000 lb. maximum force and 7/16 inch maximum grip opening)
Specimen Preparation
Steps for specimen set-up and specimen testing preparation:
1. Align the grain pattern of two matching red oak strips and adjoin together length-wise, taping the full 12-inch length on the backside with masking tape to hold the two pieces in place. Lightly sand the top surface to remove splinters and burrs. Use air or vacuum to remove wood dust from the strip.
2. Select and place a metal frame with a 1 1/2- x 8-inch rectangular opening over the wood strips. Ensure the frame is flat against the wood strip on the ends and load the necessary amount of compound at one end of the frame (Figure 5). Work a small amount of compound across the joining crack in the wood. Use the rigid, straight-edge drawdown piece to pull the compound across the frame opening, evenly coating the wood strip. Remove the frame (Figure 6) and allow the coated strip to dry under ambient conditions.
3. After the membrane has dried for 24 hours, prepare and mix the components of the thinset mortar system.
4. Using a 1/4- x 1/4-inch square notched trowel, spread the thinset on the coated strip, making sure to leave three rows of thin set (Figure 7). Set the 4- x 6-inch quarry tile length-wise onto the strip, centering the tile over the strip seam (if the tile needs to be cut to 4 x 6 inches size, ensure cut allows for tile backside ridges to run perpendicular to thin set ridges when set). Once the tile is in place, place a 5-lb. weight on the center of the tile (Figure 8). Leave the weight in place a minimum of one hour. Do not handle the assembled test strip until the next day.
5. Allow the tiled specimens to cure for 28 days before testing.
6. After the curing period, use a drill press to drill 1/4-inch diameter holes centered in the exposed ends of the wood strips 3/4 inch from the long edge (Figure 9). Remove the masking tape from the backside of the specimen and insert 1/4- x 1/2-inch dowels through the 1/4-inch holes in the wood strips. The metal dowels are to stop the wood strips from slipping in the tensile tester grips (Figure 10). If the wood splits from the pulling force, cable ties can be securely attached around the width of the wood strips between the dowel and the end of the wood strip.
7. Provide ample jaw space and load the top of the test assembly into the grips. Allow the dowel to rest on the top edge of the upper grip face (Figure 11). Adjust jaw height accordingly to set lower dowel on the bottom edge of the lower grip face. A slight force reading will indicate the dowel is snug to the grip face. Zero the gauge distance and balance the load. Figure 12 shows the assembly ready for the test sequence. Select and run the Instron method written for this test called “Crack Bridge Simulation Method.”
Crack Bridge Simulation Method
The “Crack Bridge Simulation Method” is a cyclic test, cycling between a pulling phase (also referred to as a crank) and a resting (or recovery) phase. Time 0 is a pulling phase. Each pull phase increases the jaw gap by 0.015 inches at a speed of 0.015 inches per second. Each rest phase is 10 minutes. The recovery time is adjustable and could be moved to 60 minutes, as required in the ANSI method. If the specimen reaches pull phase 8 (or crank 8), corresponding to 0.12 inch, without a tile break or thinset mortar adhesion failure, the specimen has passed the test by the ANSI 118.12 method (0.125 inch).
The test may continue past pull phase 8 for further specimen evaluation. If the tile breaks at or before crank 8, the specimen has failed (Figure 13). If poor mortar adhesion causes the tile to pop loose, the test is not a valid measure of latex polymer membrane performance (Figure 14).
The test generates plots that show the stress relaxation curve during the time the membrane polymer is absorbing and redistributing the stress forces (Figures 1 to 4). This will continue until the polymer can absorb no more stress, and the stress is transferred to the tile, and it cracks (usually between 500 to 600 lbf) or the membrane fails internally.
Conclusion
Given the various limitations of the ANSI 118.12 test method, there is a noted need for supplemental testing insights into the performance of crack isolation membranes for tile application. The Trinseo Crack Isolation Simulation Test is a viable test option to augment the ANSI 118.12 test method, which can provide additional insights into membrane response to test stresses in a less costly test assembly that can be performed in most standard lab settings.
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