I'm building a concrete shower curb and pan. I built the curb and when I removed the 2x8 forms I notice that I didn't pack the cement all the way to the bottom in some parts:

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A bit crumbled and fell out when my wife touched it, but the rest seems very solid. (There is a lot of dust near the curb left over from the install.)

I'm a little north of 200 lbs and I stomped on it and there was no movement or anything.


  • Is this a failure? Is failure of the curb imminent (within 5/10/20/etc. years)?
  • If it will not fail then how should I fill the gaps? Fill it in?

Next time, tamp the cement into the corners (using a putty knife, large screwdriver, gloved finger, etc.) after a couple inches is set down. If you wait until the form is almost full, it forms stronger bubbles and they are harder to coax out.

Structurally, the curb is more than strong enough unless you anticipate automobiles driving over it. The major issue is adequate structural support for the finishing material.

If you will be tiling the curb, the thinset is plenty strong enough to support the tile if worked into the gap and corner well. So there would be nothing more to do.

If you will be putting vinyl, etc. over it, the mastic would not be strong enough, so the curb should be smoothed out with concrete filler.

  • Tiling. Thanks a lot of the tip. Really helped me out :) I'm going to be doing the actual shower pan tonight so I could use the same type of cement? Just to fill the gaps and let it all cure together or is the filler the better option? – cbrulak Aug 20 '13 at 20:51
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    The thinset is much 'stickier' but won't build thickly in one 'go'. Pan (deck) mud should be a bit crumbly and coarse. I'd actually patch with repair mortar (sand mix concrete with latex , no stone), if I needed more than 1/4 inch. – HerrBag Aug 20 '13 at 21:50
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    100% agree with @HerrBag. I use thinset to make my curbs look nice. With the thinset then tile there should be relatively little force put on the concrete. – DMoore Aug 21 '13 at 18:19

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