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I recent bought a house with a detached garage, made of old concrete (high aggregate content) reinforced with steel rods and set into a hill. Built in 1938 or so; no waterproofing.

Now that Boston has turned into a rain-forest, water is seeping / leeching through the walls of the garage, making the whole thing very damp and smelly. There are no obvious drips, but the bottom 3-4 feet of concrete is discolored and damp, and there are patches of dampness on the (newer) floor.

The concrete is degrading, and I was thinking of parging over it with new concrete to smooth the walls, but I want to address the leaking first. Or would a parge coat help? What else can I do to seal up the concrete, short of digging up the foundation (15' of dirt with a garden on top!) and painting the outside surface?

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I'd suggest a french drain around the sides of the garage. This requires that you have somewhere to output the drain, and it also involves a lot of digging. But it will work much better than waterproof paint.

Short of that, check the grading of the land around the garage and make sure everything slopes away.

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  • No, the land is a big funnel directing the water at the garage...
    – Alex Feinman
    Jun 28, 2011 at 17:43
  • While a french drain should help, I'm not sure it will be a silver bullet in this case. The structure is so far below grade, ground water may still find it's way against the wall. Adding a drain tile system inside the garage, would allow any additional water to escape.
    – Tester101
    Jun 28, 2011 at 17:48
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    With the land sloping into the garage, and no where else for the water to go, I'm not sure you're going to find a good solution to this one. Good luck!
    – BMitch ♦
    Jun 28, 2011 at 18:32
  • I misspoke. The funnel is only on the uphill side; I can divert the water around the garage and on down the hill...
    – Alex Feinman
    Jun 29, 2011 at 14:06
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It sounds like your garage is the low spot in the landscape and making a drain system difficult or impossible. If you are sure that drains aren't possible, the only other possible solution may be treating the interior wall surfaces with an epoxy wall treatment like "Dry Loc". Dry Loc will withstand hydrolic pressure of about 3psi, which is usually enough for walls and floors effected only during times of heavy rain etc. The trick of making this stuff work well is to be sure the concrete is dry and any loose, flaking or effluence is removed. Obvious cracks and foundation form pins must be "keyed" and filled with hydrolic cement such as "rocktite" before painting the Dry Loc on. The Oil based Dry loc is much easier to use than the latex based version, but lots of ventilation is needed, which should not be a problem with a garage. you will probably need two coats and be sure to work it into all the tiny holes etc, 100% coverage is important. Good Luck.

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  • This feels like the easiest option to implement, so I'll start here and see what happens...Now to move everything back out of the garage!
    – Alex Feinman
    Jun 29, 2011 at 18:00
  • I really enjoyed listening to you on the podcast. Lots of great advice!!! Keep up the great work. If I ever get my own home and need some advice, I hope I run across some of your answers on this site. :)
    – jjnguy
    Jun 30, 2011 at 6:02
  • Alex, did you end up implementing this? If so, how did it turn out?
    – Shimon Rura
    Mar 25, 2012 at 14:16
  • I didn't. For now it's just a dehumidifier in there. We changed the landscape drainage, which helped a bit.
    – Alex Feinman
    Dec 5, 2012 at 17:37
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You can try an interior weeping tile system, similar to a house basement. First, you jackhammer out about two feet around the edges of the garage, down to earth. Then, you put in your weeping tile, which nowadays isn't clay tile but a perforated plastic pipe with a mesh sock over it (to keep out dirt). That weeping tile will collect water that leeches into the house, and run it into a drain line (which must obviously run downhill from the garage floor to a storm sewer or cistern). Then, you need a waterproof wall liner; it doesn't stop water leaching through the walls, but it catches that water behind the liner and directs it down to earth, where it will seep into the weeping tile, while keeping the liner's interior surface dry. That goes all the way down to the dirt next to the weeping tile, and you will back-fill over it before cementing. I would recommend a center drain, with the garage floor sloped slightly (1-1.5 degrees) towards the drain; worst case scenario, you can sweep or squeegee standing puddles into the drain. Patch the concrete you jackhammered out, possibly with a parge coat to set the grade over the whole floor, and your garage should be much drier. If this sounds expensive, it is, if you have a contractor do it for you. But, it's not an impossible DIY project if you have access to the jackhammer and concrete mixing/pouring tools.

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  • Would you recommend drilling weep holes in the wall (below the floor level) to allow water trapped behind the wall to drain into the weeping tile system, or is this only done with cinder block walls?
    – Tester101
    Jun 28, 2011 at 22:46
  • How might this affect the stability of the walls? I got the impression they were tied together with the floor.
    – Alex Feinman
    Jun 29, 2011 at 14:09
  • @Tester: I don't think weeping holes should be drilled into a concrete wall, but I may be wrong. It seems to me that if water is "trapped" behind that wall, it should eventually sink down under the entire garage and find the weeping tile that way. The interior treatment is simply to direct water that weeps through the wall naturally to the tile, keeping the inside drier.
    – KeithS
    Jun 29, 2011 at 14:21
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    @Alex: The walls and ceiling of the garage, assuming they're structurally sound, should remain rigid. However, there is a good chance that your floor is tied into the walls using rebar or other reinforcing hardware. If so, you can either try and work around the rebar, or remove it temporarily and then drill into what you didn't jackhammer and replace it before re-pouring the concrete. Either way, as long as the job doesn't take months between jackhammering and repouring/patching, there should be no troubles. However, you might consult a structural engineer or building inspector.
    – KeithS
    Jun 29, 2011 at 14:25
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We had this same problem in a part of our garage, and it was water from the hill coming into the garage, as well, as the rain that fell on the house/garage roof. Once we added gutters to the roof, and ran a long gutter away from the house and the garage, the water situation improved. It can be really easy to add gutters, and really hard to add drain tile. We ended up doing both, and the drain tile or weep holes is in the inside of the foundation line. It is attached to a sump basket and a pump. Water problems are gone!

we hired this out, and did it all for around $2000. No more water problems for us, as long as the gutters and pump keep up with the water.

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