The shower corners should not require reinforcement if installed properly. If using a concrete board such as hardiebacker on the shower walls, make sure there is solid backing (2x4) at the corner to firmly attach the concrete board so it will not flex at the seam. Use the appropriate seam tape and thinset just like any other hardiebacker seams. If the corner is done right and if the RedGard is applied properly, it should stay waterproof. If the materials forming the corner can flex independently, adding this flexible seam tape is not the best answer. Make the corners solid first.
To better have your question answered, please call Custom Building Products at 800-272-8786.
RedGard Uncoupling Mat Membrane is available in both Canada and US. If your local Home Depot does not stock this product, it will require a special order. For further assistance please contact us at 1 800 282 8786 option 2.
I did it the other way around. I used redguard and then placed it on the seams. Then redguard it so that it sticks. You’ll have to do both side to make this seam tape stick. Fiber mesh tape works just as well but easier to manipulate
To better have your question answered, please call Custom Building Products at 800-282-8786.