Hi guys, I'm about to tile my bathtub surround and have some questions regarding moisture barriers. I already have the 1/2 durock cement board and 6 mil plastic sheeting. Before I put up the plastic sheeting on the studs, I wanted to double check to see what people thought was a better moisture barrier... Redgard painted directly onto the cement board or the 6 mil heavy duty plastic sheeting attached to the studs? If you pick one over the other, can you tell me why? Is there a difference in how well each one will protect from long term moisture problems? It would be nice to hear the pros/cons to Redgard vs the plastic sheeting. I don't know if this makes a difference, but the long side of the tub will be up against an exterior wall and I believe this can impact the difference between using plastic and redgard.
I'm debating whether or not I should just go buy some Redgard and leave my plastic sheeting for another purpose. But if they both offer the same long term protection, then I'm happy just sticking with my plastic sheeting since it will save me a trip to the store. I'm actually leaning towards the plastic sheeting since I already have it but I wanted to see if it really was important to do the RedGard.
And I do have another question, this one is more about the technical aspects of each moisture protection method. I understand how RedGard works. You just paint it on and the painted surface is impenetrable to water so long as all areas are actually covered with RedGard properly. That way, water doesn't penetrate through your cement board and it just drips down back into the tub. However, with plastic sheeting, you are supposed to attach the bottom of the sheeting to the inside face of the flange of the tub, so water drips down into the flange area and supposedly into the tub. But my question about this is where can the water go once it drips down into the inside face of the tub flange? It can't directly seep into the tub because in between the flange and the tub will be silicone tub caulking. So won't the water just sit there in between the flange and the caulking, creating long-term moisture problems? I know I must be missing something here because I believe people have been using plastic and/or felt for moisture barriers in bathtub tile surrounds and somehow they get the water to drip back down into the tub or something. If you're curious about the installation of the moisture barrier, whether it be felt or plastic, here is a youtube video of it. The moisture barrier installation starts at abou 39 seconds.