I recently installed an exterior double door. On the one side, the concrete floor slopes down, so I raised that side with shims. The bottom plate is level. I can cut and replace these shims with pressure treated wood, but I'd like to fill that gap if possible. I was thinking of forcing quickcrete or rocktite into the gap, and a neighbor suggested that liquid nail would probably work just as well.

To summarize I'm looking to:

  1. Fill the gap between the metal plate and con. 21" x 4" area, starting at 0 and sloping to 1/2".
  2. Provide support for the plate. Existing shims are not weather proof and will encounter moisture, and possibly direct contact with water.

Most other questions I've seen have to do with the threshold.

bottom door plate

2 Answers 2


Personally, I would use plastic shims and simply caulk the front with a solid color to hide the gap.

  • I didn't know they made plastic shims. Will check that out.
    – ytjohn
    Mar 17, 2019 at 16:40
  • I did indeed end up going with plastic shims, then filled as much as I could under the threshhold with wood glue. After accidentally bumping the threshold with a pallet put two tapcons through in order to keep it from moving much. It turned out great.
    – ytjohn
    May 17, 2019 at 15:56

I would consider an epoxy or resin type of material that can be injected through a small nozzle to fill up the space. It should prevent water/moisture from accumulating in the hidden spaces. In my opinion, using shims and just running a bead of your average polymer will not 'solidify' the plate. Movement from expansion/contraction or from foot traffic will cause the softer 'glue' to fail in time. With a solid - once cured - material, it will provide a rigid contact throughout the plate and be far less likely to fail, while also providing a moisture barrier if done correctly. Also, if you can work a quickset mortar into the gap it would be better than shims. But if you've never worked with a fast setting mortar type material, I wouldn't experiment with it on the first go round in this application.

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