Redgard waterproofing membrane is one of the most popular products used when tiling a shower. Because of its availability at Home Depot and ease of use, Redgard is the waterproof membrane of choice for many DIY'ers and Contractors. Because Redgard is a roll-on or paint brush applied product it is easier to use than Schluter Kerdi or Oatey pan liners.
I did this test because I see so many people use it at the wrong rate of application and I wanted to see how it performs when applied to the rate as specified in the technical data sheet (TDS). In order to meet IAMPO standards for a shower pan, Redgard must be applied in two coats at a rate of 80 square feet per gallon for each coat. One gallon of Redgard will cover 40 square feet at this rate.
My test module had an area of 2.88 square feet, so I divided 2.88/80 to get the ratio of the test module to the 80 square feet rate as specified. The ratio was .036 or 3.6%. To calculate the amount of Redgard to be applied, I multiplied the ratio (.036) to the gallon in fluid Ounces (128). The amount equaled approximately 4.6 fluid ounces per coat.
The first coat was applied over the dry pack mortar bed in the test module that had cured for 24 hrs. The mortar bed looked dry (light gray in color) and had hardened properly. The surface of the mortar bed was clean, smooth, and free of contaminants. The first coat dried for 24 hrs before applying the the second coat. It was noted that the first coat dried nicely and evenly without any visible cracking.
The second coat was applied in the same manner as the first and allowed to dry for 48 hours. Upon inspection the second coat had cracked significantly in the changes of plane of the test module, notably where the bottom and sides of the test module intersected.
A third coat was applied in the corners to cover the cracks that had formed and allowed to dry for 24 hours after which the water was poured into the test module and allowed to soak under intermittent observation and time lapse video.
Time lapse video showed almost immediate change in color from the dark red (dry) color to the light pink (wet) color of the Redgard. Also, a leak formed in the lower right corner of the module after approximately 60 minutes.
After eight hours, the water was removed from the module and the membrane was inspected. Upon inspection, a small crack was observed in the lower right corner that had leaked. It was noted that this crack had been covered by the third coat previously applied over the cracking that happened after the second coat had dried. Also observed were small bubbles that were filled with water in the surface of the Redgard that covered the mortar bed. The surface of the Redgard that covered the mortar bed was also soft and broke apart easily.
My conclusion is that the Redgard was applied over the mortar bed too soon (24 hours). Even though it is common practice for installers to apply Redgard the next day after the dry pack is installed, this time frame may need to be extended.
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