Another waterproofing question: our basement has a walkout door that is leaking from where the metal doors meet the concrete base. Three pictures from inside and one from outside are attached below. The metal doors extend beyond the small stop at the top of the stairs, so rain is draining (correctly) to the outside perimeter. However water is able to weep inside. There was old, probably latex-based caulk on both sides of the door stop, which apparently failed.

How do I repair this? Do I have to clean out the existing caulk and start fresh? Or is it possible to clean it and add a compatible latex-based caulk?

If I have to start from scratch, what should I use? I found several suggestions for caulking concrete (similar to this question plus hydraulic cement):

Walkout door inside 1 Walkout door 1 Walkout door inside 2 Walkout door 2 Walkout door inside 3 Walkout door 3 Walkout door outside 1 Walkout door 4 Walkout door outside 2 Walkout door 5 Walkout door outside 3 Walkout door 6


3 Answers 3


This does not look to me like something that can be fixed with caulking.

The entire door assembly is sloped away from the opening (good) but it seems as though water running down the doors is dripping off the end on to the concrete curb, then pooling and/or running back into the opening (bad). If it were me, I would:

  • use an angle grinder to smooth and further slope the curb edge away from the opening, just past where the doors "land" at the bottom.
  • wire brush, then prime and paint the entire bottom curb area, with a glossy polyurethane concrete paint. This will facilitate water runoff from the newly smoothed and sloped curb.
  • fasten a sheet metal strip to the bottom of the doors that is bent such that water running down the doors drips off beyond the top of the curb (a "drip edge", if you will...)
  • These definitely sound like more solid solutions. Fastening a drip edge is especially interesting and feels to me should solve my problem on its own? On the other hand, what are the problems you see with caulking? The concrete curb has rough texture but does slope away, so the caulk will not be against large water pressure.
    – P. B.
    Commented Dec 26, 2020 at 17:51
  • Several problems with caulk: 1) it is designed to seal cracks and crevices, bonding to both surfaces; you are essentially meaning to build up a dam of caulk and I don't think that will work. 2) the labor required to properly ensure the surface is clean and dry is significant and I don't think it will stick well 3) That is a stair-step/high traffic area and putting a caulk dam down where people step is bound to present problems, as in it will not last. Commented Dec 26, 2020 at 21:06
  • I saw what you mean now! There is actually a metal rail on the top stair step (sort of like a door stop). The excessive, existing caulk is not meant to build a dam on its own but to seal the (small) gap between the concrete step and the metal rail. This is why I wanted to repair the caulking, but completely cleaning the existing caulk turns out messy and difficult. I think I'll take your suggestion to smooth the end step with patching concrete and paint, and try my best to repair the damaged caulk. Then in the future, getting a drip edge will be nice.
    – P. B.
    Commented Dec 28, 2020 at 21:26

It's hard to prescribe an exact product, but I ran into similar issues recently myself and here is what I learned. Some of this may be helpful in making a decision...

There used to be two main options for caulk: silicone and latex. These days there are 'siliconized' latex caulks that perform well and are easier to use than 100% silicone. Silicone is hard to clean up, and nothing much sticks to it. Latex (a.k.a. acrylic) caulk, whether siliconized or not, can be cleaned up with water, and other things can be applied on top such as paint or additional layers of caulk. So there is less reason to go with 100% silicone anymore.

If the sealant needs to accommodate expansion and contraction, a caulk advertised as window/trim may be a good choice as these are designed to be flexible.

DAP DYNAFLEX 230 is one such siliconized flexible caulk that is generally considered to be of high quality.

If the existing base is well adhered and non-silicone, you can probably clean it and apply latex on top. If there's any doubt, it's better to remove it and start from a known sturdy substrate.

You can probably narrow the field by eliminating caulks advertised as 'non-shrinking', 'paintable', 'quick drying', as those don't matter so much in this case. Adhesion, water-sealing, and possibly elasticity, are the things I would prioritize. Good luck!


I would avoid using a flashing/drip edge type of solution unless it was cemented down to the concrete somehow with no loose edges. You don’t want to have something to catch your foot on, especially when going down the stairs. My screen porch has this treatment on the thresholds and I wish it had been done differently because I can’t count how many times we’ve pulled it up with out feet, scraping the top of our shoes on the flashing.

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