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I had to add tread height, to make an old stair come out even when adding an insulated floor below (see How can I deal with a short bottom step on a stairwell? ). Now I've got a gap on the top tread's sill nosing. What type of product might work? "Bondo" is often used for such things, but it may be too stiff and crack over time:

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What might be both structural, and form a neat enough edge? The stairs will be painted, then have carpet runners. Note that each stair from here down was raised by 1/4" more than the prior one, averaging out the short bottom step.

Bryce
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  • A heavy bead of architectural sub-floor adhesive will prevail any squeaks but not stiffen it. I use PL400 $7 in a large tube. Use more but apply like silicone caulking . It takes a few days to harden since they are now low VOC. It is not brittle but an inside corner spreading tool or latex gloves and your finger may achieve a smooth finish it is paintable polyurethane. – Tony Stewart EE75 May 15 '18 at 20:36
  • Answers go down there, Tony. I considered construction adhesive also, but it shrinks quite a bit. You won't be able to reliably achieve a rounded bullnose shape with one application. – isherwood May 16 '18 at 11:23

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Here's what I'd do to avoid hacky patch solutions that will probably fail:

  1. Carefully remove the cove molding from under the original nosing.

  2. Cut the original nosing and the overlay flush with the riser to create a flat vertical plane. Use a circular saw, jigsaw, and a belt sander, if available.

  3. Screw and glue down the overlay if it isn't already, so it's solid.

  4. Glue and screw a replacement nosing in place, matching the original size and profile, flush on top.

  5. Reinstall the cove molding under the new nosing.

  6. Fill fastener holes, sand, prime, paint.

This will leave you with a result indistinguishable from the original and just as solid.

isherwood
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