Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 24 Page 25 Page 26 Page 27 Page 28 Page 29 Page 30 Page 31 Page 32 Page 33 Page 34 Page 35 Page 36 Page 37 Page 38 Page 39 Page 40 Page 41 Page 42 Page 43 Page 44 Page 45 Page 46 Page 47 Page 48 Page 49 Page 50 Page 51 Page 52 Page 53 Page 54 Page 55 Page 56 Page 57 Page 58 Page 59 Page 60 Page 61 Page 62 Page 63 Page 64 Page 65 Page 66 Page 67 Page 68 Page 69 Page 70 Page 71 Page 72 Page 73 Page 74 Page 75 Page 76 Page 77 Page 78 Page 79 Page 80 Page 81 Page 82 Page 83 Page 84 Page 85 Page 86 Page 87 Page 88 Page 89 Page 90 Page 91 Page 92 Page 93 Page 94 Page 95 Page 96 Page 97 Page 98 Page 99 Page 100 Page 101 Page 102 Page 103 Page 104 Page 105 Page 106 Page 107 Page 108 Page 109 Page 110 Page 111 Page 112 Page 113 Page 114 Page 115 Page 116 Page 117 Page 118 Page 119 Page 120 Page 121 Page 122 Page 123 Page 124 Page 125 Page 126 Page 127 Page 128Membranes that are applied wet and allowed to dry are everywhere in the tile world for waterproofing, crack isolation and more. But how do you know if you need one coat or two, or more? There are lots of rules of thumb – ‘If you can see through it you need another coat’ is a common one – but the only true way of know- ing for sure is to measure it. To determine if you have applied enough liquid membrane, you need to know how much the manufactur- er recommends. Almost all technical data sheets for liquid-applied mem- branes list a target film thickness. It will typically be listed in the form of “mils” of thickness; each mil is one one-thousandth of an inch (1/1000” or 0.001”). So, a 30 mil wet film thickness (you will often see this abbreviated WFT) means 0.030” of membrane. You will also see dry film thickness (DFT) referenced. To deter- mine the dry film thickness, multiply the wet film thickness by the per- centage of solids in the product (30 mils of a 50% solids membrane is .030” x 0.5 = 0.015” DFT). As manufacturers, when we mea- sure the properties of these mem- branes, we assume that you are using the correct amount. If we tell you that water will not penetrate the membrane, we mean water will not penetrate the specified thickness of the membrane. If it is extremely thin in some areas, or has holes in it from nails or pinholes during application, it will not be waterproof. Likewise, if we say that a crack isolation mem- brane can protect your floor from a 1/4” substrate crack, the size of crack the membrane protects against goes down as the thickness of the membrane goes down. This is particularly important in steam showers. The thicker the mem- brane, the more it resists high tem- perature/high pressure water from moving through it (the ‘permeance’ of the product). The TCNA Handbook for Ceramic, Glass and Stone Tile Installation requires no more than 0.5 perms from a membrane being used in a steam shower. The liquid products that meet this requirement typically do so at 30 mils or more, much thicker than you would apply with one or sometimes even two coats. If the steam shower fails – and you did not apply enough waterproof TECHNICAL FEATURE ––––––––––––––––– What is "Wet Film Thickness" and why should I care? By Eric Edelmayer, Business Development Product Line manager – Sheet Membranes, MAPEI Americas 58 TileLetter | February 2017