Waterproofing shower stall

The contractor for our remodel prepared the shower stall base and curb with an Oatey 40 mil membrane and then some kind of hard material with a mesh below the surface. To secure that material to to the curb and the low part of the shower walls the workmen used nails. A couple of guys who came to do quotes to do the tilework (they came while I was at the house, the contractor was not here) both said that the method used was not good (the nails would have punctured the membrane) and both suggested repair - one even said to replace the shower pan at a cost of $800. The contractor says that is not necessary. Who is right? The shower will only be used by my husband and myself and we wouldn't be letting water get up to the curb height.

From your description, I'm not sure. Nails anywhere that puncture the membrane are not good unless they are higher than the curb (it's okay to nail something on the outside of the curb). But, it sounds like they put down the liner on the floor THEN put down a sloped mud bed. If that is the case, then it was installed incorrectly, and you will have other problems. A correctly installed mortar bed shower pan (based on the Tile Council of America and many plumbing codes) calls for a water proof membrane ON TOP of a sloped bed, followed by another layer of mud (sand mix cement) that you then apply tile to. If the liner is on the flat floor, then any water that makes its way through the grout lines (and it will, a little at a time), has no incentive to flow out the drain and will sit there and grow mildew and othernasty things. So, if the liner is on the floor, make them tear it out and put it in by the book. If there are nails anywhere below the top of the curb, then it should probably be done over as well. My unprofessional opinon. For a site that specializes only in tiled things, check out www.johnbridge.com

Did they put cement backer board on top of the liner? If they did that in the shower itself it makes no sense because you cannot slope backerboard. As others have mentioned, if you do not have preslope, liner on top, then sloped mud base on top of liner, the shower will not perform well. There will be problems.

Now, if the base is OK, and what you mean is that they put cement board on the walls, that is OK. There should be no nails close to the floor, but some nails 4 to 6" up the wall is OK . These nail heads should be covered with waterproof joint compound, as should all the fibreglas taped joints.