I have a 1960s concrete foundation. There are some small cracks in the floor. During the last [epic] rainfall, they started to seep water. I'd like to seal them. Also, the seam where the concrete floor and concrete walls meet is letting water in. I'd like to seal this, too. I do recognize that an external drainage issue is the problem. I am looking for a now/before the next storm solution.

I know there are many DIY concrete sealer solutions available, but here is my question. Do i need to wait until the concrete is dry to seal it?

  • It shouldn't be a problem, as long as there is no running water, and the surface is clean. Usually, before applying new patching, the old concrete should be kept in a moist but surface-dry condition. You can also adjust the amount of mixing water for the sealing material if cement-based material is used.
    – r13
    Jul 12, 2023 at 21:08
  • You're trying to make a bathtub out of your foundation. That won't work. Water will always find a way. Instead, look into a sump drain or other means of removing the water. You need to eliminate the static pressure under the slab.
    – isherwood
    Jul 13, 2023 at 12:58

2 Answers 2


Depends on the sealer/repair.

I know hydraulic cement is suppose to work with running water/water coming in, but I imagine dry clean cement/concrete will work the best for most of them.

Hydraulic cement you are suppose to make an inverted V shape, small at the surface and wider deeper in, into the crack.

Repairing from the outside is the best long term(forever) repair.


If it's coming through the floor, that means you have water under your slab. Since you say it comes through the joint between slab and walls, it means the water table comes up higher than your floor. It is very hard to seal water leaks from the inside. Your best bet here is to prevent the water from getting into the soil near your house in the first place (assuming you don't have a naturally high water table).

  • Gutters and downspouts; any downspouts should daylight as far from the house as possible, at least 10'.

  • French drain around your foundation.

If you have a high water table, it's likely your only hope is to install a sump pit in your floor—basically dig a hole, insert a perforated bucket, and an electric pump. You might need an interior french drain too, connected to the sump pit.

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