I have my shower room down to the studs. It has an old terrazzo shower pan which I hope to reuse. It had an inch high metal (lead?) edging around it. It was fairly decayed so most of it has broken off or been removed.

I have Wonderboard lite and Redguard ready to go up, but I'm not sure if I need something to further waterproof the section between the shower pan and the backerboard? I had a drywall guy in and he mentions that there is usually a rubber strip on new shower pans that prevents water ingress.

Is there something I should do before putting on the wonderboard / tile?

Shower pan Above Profile Corner

  • The terrazzo will let water pass through, the lead pan contained the water and sent it to the drain. A PVC liner should be used again, although I do not know how to tie the drain and the terrazzo pan in.
    – Jack
    Commented Dec 28, 2018 at 22:40

1 Answer 1


Nothing but caulk (100% Silicone), is the hands-down best I've found.

The Wonderboard would sit (actually stand-on and rest-on before screwing down) on the Terrazzo's top and back lip in a squished-out caulking bed for drain backup flood waterproofing.

You really don't want any firmer type of gap-creating "gasket". Then, your Redguard, Thinset & Tile overlap that seam. They are all that really makes everything actually waterproof.

You can then chose to either rest your tile down to & on the inner and lower secondary Terrazzo lip above the pan floor or you can raise it slightly to grout a larger joint. Neither is any different in waterproofing, but not grouting means no ugly possible breakaway crack later.

  • This seems to be if you're building from scratch vs trying to save an old pan? I don't think this answer is relevant to the question
    – Gribbler
    Commented Dec 28, 2018 at 18:23
  • Thanks. I think I misunderstood your re-use idea. I'll correct my answer to going with my first option and considering the Terrazzo as your shower base.
    – Iggy
    Commented Dec 28, 2018 at 18:47

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