I'd like to fill a gap between the bottom of my tiles and the bottom of my shower pan. The shower pan is fiberglass.

Diagram of shower base

I'm considering using an epoxy to fill this void, and I want to put tiles on top, flush with existing tiles, to make it look nice.

Will (cement-based) tile grout adhere to a set epoxy such as Marine Grade Epoxy Adhesive Paste?

An alternative is to use the epoxy to bind a piece of concrete board, and then grout the tiles to that.

Suggestions / implications?

  • How big is the gap?
    – Sean
    Apr 26, 2017 at 13:56
  • @Sean The gap is ~1.5" high, and ~1" deep.
    – CJBS
    Apr 26, 2017 at 17:02

1 Answer 1


Just as a matter of terminology, grout is not used to adhere tiles. Thin-set mortar is used to adhere tiles to floors and walls, and mastic adhesive is used to adhere tiles to walls. Grout is similar to Portland cement and goes between the tiles. I only bring this up because if you go to a hardware store and ask for grout, they'll probably give you grout, which is not what you want.

Your best bet would probably be to use epoxy thin-set or epoxy bonding mortar. Being an epoxy, it should stick much better to the fiberglass and is suitable for use as a mortar. Personally, I'd use it to adhere some cement board in that gap (pending a description of how wide the gap is) and then the rest to adhere the tile to the cement board. Let it set, and then you can grout.

  • You're right; I confused my terminology - grout's the coloured stuff for between the tiles after it's been mortared in place. The gap is ~1.5" high, and ~1" deep. Would you mind commenting on whether the linked product (marine epoxy paste) would work to bind the concrete backer board, or would you mind suggesting another product (with link)? Thanks.
    – CJBS
    Apr 26, 2017 at 17:01
  • 1
    I can't say for certain. It claims to adhere to concrete and fiberglass, which is functionally what you are bonding, but I've never tried to adhere backer board to just fiberglass. In my non-professional opinion, it seems like it would work.
    – Chris M.
    Apr 26, 2017 at 17:26
  • I haven't actually done this, but having had success with adhesion of epoxy-based grout elsewhere, I agree that using epoxy, possibly in conjunction with a filler (e.g. cement board) is probably the way to go. Thanks.
    – CJBS
    Dec 9, 2020 at 0:01

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