Kerdi membrane is hydrophobic...it repels water. So, if you have it embedded properly in thinset, and overlap the seams at least 2", per the manufactuer's instructions, it won't leak, so no, it does not matter if you apply it like 'shingles' so it overlaps in one direction. I took a class on the stuff, given at the TCNA headquarters training facility. They had a cardboard box covered inside with Kerdi and thinset they used as a drink cooler. Every morning, they filled it with drinks and ice. By afternoon, the drinks were swimming in icewater. The box had been in constant use for about 6-months...never showed signs of seepage. the stuff works. If you take a square of the stuff, wrap it into a cone, and fill it with water, water won't escape out the pointed end if you have the cone reasonably tight. What you want is shown on this chart: http://www.schluter.com/print/8_2_kerdi_drain_3963.aspx The Residential floor drain adaptor kit with stainless steel integrated bonding flange. You may have to call them to find out where to buy it. this would screw into your clamping drain assembly, and provide a surface that will accept Kerdi directly via thinset.