I've been following this guide from Family Handyman on installing a fiberglass tub surround, and am to the point where I need to tile over the nailing flange. They say to put 1/4" tile backer over the flange to bring it out to the same depth as the 1/2" green board, as shown in this picture:

diagram of shower flange

However I had to shim behind the surround, so the difference in depth between the green board and the flange varies from almost nothing to a little more than 1/4", which you might be able to discern in the below pictures:

overview photo of shower flange

The question

How do I fill the uneven gaps in depth between the flange and the green board? The 1/4" tile backer can fill the bigger gaps, but I'm not sure about the smaller ones.

Do you see anything else wrong with what I'm doing?

  • 1
    Nooooooo not greenboard! Showers need cementboard, full stop!
    – iLikeDirt
    Commented Nov 1, 2016 at 13:40

2 Answers 2


You just want a stable platform for your tile. It depends on the size of the tile.. If you are cantilevering 10-15% of a larger tile, just fill the thinner areas with more mud and put backer where it will fit.

It looks like you needed some blocking behind the green board (where the rear curve comes in) to be able to fill in. Perhaps some fiberglass mesh tape would let you land some thinset to bridge the gap.


Why tile over the nailing fin? Fill the gaps with drywall an tape and float. You can use liquid nails if you prefer--to attach the drywall green board. Caulk the edge from the tub unit to the newly finished drywall. Once it is all finished you can add a border of tiles around the tub for decoration...i did that once using the same tile as the vanity backsplash. If your vanity countertop has an integral backsplash you can add a row on top...it is stylish to have a tall bath backsplash, especially with vessle sinks.

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