I want to build up a short dam of maybe half an inch in height, to control where water is flowing. The water flows as a small, steady trickle. Right now it fans across a large-ish area. I'd like to concentrate its flow to a specific area.

What kind of cement or mortar should I use to direct the flow? I was thinking of hydraulic cement, but I wanted to check first. The area is wet. I want to make sure the new cement sticks to the existing thin cement floor in the cellar.

I also have some quick set mortar powder on hand, as well as some resurfacing cement. If none of the products I have on hand is the right thing, I can buy something new.

I don't care about the aesthetics in this case.

  • why not just slope the floor gently?
    – Solar Mike
    May 13, 2019 at 5:08
  • @SolarMike - There's already a slope. // I don't want to tear up the floor and reconfigure the whole contour, and I don't want to resurface the whole thing. (I'm not sure if that's what you were suggesting.) May 13, 2019 at 5:11
  • I usually find new cement sticks well where it is not wanted, but otherwise does not stick... IMHO adding a 1/2" ridge is just a trip hazard, but your choice, which is why I suggested a slope as that detail was lacking in your question.
    – Solar Mike
    May 13, 2019 at 5:16
  • @SolarMike - Sorry I didn't mention the slope. At any rate, the location would not create a tripping hazard. It's under some stairs. What do you think about the hydraulic cement? I watched videos about it, and read the instructions. The standard way to use it is to plug up a hole. My situation is different. May 13, 2019 at 5:18

1 Answer 1


Hydraulic cement sticks to wet fine, but you may need to abrade the surface to get to clean concrete, as it won't like a greasy, dirty or otherwise befouled surface.

However, what I would actually do (and have actually done) to direct water on a concrete floor is to use a diamond saw to cut a small channel into the surface - much neater and tidier - also easier to walk or roll over. And much less wet area.

  • Thank you, I'll try putting some leftover siding cleaner on it and scrubbing, and then rinse well. Unfortunately I don't have a diamond saw. May 13, 2019 at 14:09
  • You might be surprised how affordable a one-day rental is, if you don't get the absurdly large one. Depends on your local tool rental outlet, but they are not hard to come by.
    – Ecnerwal
    May 13, 2019 at 14:14
  • Thanks for the encouragement. If my first primitive attempt doesn't turn out, I'll try the diamond saw rental idea. May 13, 2019 at 14:17

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