Basement waterproofing
Boston2022
| Posted in General Questions on
Looking to finish off our 50% below grade basement. We’ve been here 12 years and the worst we’ve had is occasional seepage from a wall during heavy heavy rains. Call it 2 small puddles per year.
slab is being broken up and repoured, interior drain with sump, and wall waterproofing on the granite block walls. Once contractor recommends full wall wrap, the other just uses a dimple mat a foot or so up from the slab. Is there really that much of a difference if it’s an occasional drip?
anything else I should be considering?
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Two big things you should be doing are grading the exterior ground so that it slopes away from the house, and putting up gutters and a drain system to direct the runoff from those gutters away from the house. Gutters can make a huge difference here. If you think about things conceptually, all of the rain falling on your roof ends up getting concentrated along the edges where it runs off. This means the localized area of the exterior foundation wall in those locations sees a LOT more rainwater than it would if the roof wasn't concentrating the "rain" in that area. A gutter system carries that excess water away and often will solve these basement water problems with little else being needed.
If you're stucking doing interior work only, then a sump pump, perimeter drain, and dimple mat are probably your best way to go. I would run the dimple mat all the way up the wall if you've had issues with seepage through the walls. It doesn't cost much to add more dimple mat, and with the entire wall covered, ANY leaks will get captured by the drainage system. I would seal the top of the dimple mat to the wall with polyurethane sealant too.
Remember that all water management is best done on the EXTERIOR of the house whenever possible.
Bill
To put a finer tip on Bill's points, you want to do what you can to keep water out of the basement in the first place, and if it gets in anyway you have to deal with it. Dealing with it means you can't just let it disappear into your finished walls, you have to give it a path to go someplace where it can be safely dispersed. Usually that means either allowing to drain to daylight if the topography allows, or pumping it someplace with a sump pump.
Wouldn't closed cell down to the dimple mat, to a full interior perimeter drain to sump pump, accomplish that?
Hi Boston2022! Tackling that basement seepage is a smart move for a dry, finished space. Both full wall wraps and partial dimple mats can work, but they differ in coverage. A full wrap offers a complete moisture barrier, great for granite block walls where water might sneak through joints. A partial dimple mat channels water to your new drain and sump pump but may leave upper walls exposed. Since you’re already upgrading the slab and drainage, you’re off to a great start!
Consider ensuring exterior water flows away with proper grading and maybe adding a dehumidifier for air quality. Got details on the basement’s size or how you’ll use it? Share more, and we can suggest tips to keep it dry and ready!
We are planning on full interior perimeter drain (with new slab), with partial dimple mat to closed cell on the granite block walls. Exterior downspouts drain away, and the rear portion of roof dumps in to a drywell.
Basement is 1100sf, finished area about 600. General playspace and kids area.
With 14mil plastic under a new slab, is it safe to use an underlayment to soften the floors? Or is condensation still a problem. Boston area.
I’d go with a Partial Dimple Mat—it’s a solid option, especially if you’re looking for something practical and easy to use. They offer good grip and comfort, which makes a real difference depending on how you plan to use it. I might even check MorningSave to see if they have them or any similar alternatives. I came across this review page: https://morningsave.pissedconsumer.com/review.html —worth a look to see what others are saying and maybe find a good deal too
Given how minor your seepage has been—just a couple small puddles a year—I’d lean toward the dimple mat option. It’s usually sufficient for occasional moisture and still gives that drainage layer behind the finished walls. A full wall wrap might be overkill unless you’re seeing widespread or high-up seepage.
That said, since you’re already going all-in with a new slab, interior drain, and sump, it could be worth the extra peace of mind if you ever plan to finish the basement and want to protect insulation or drywall long-term. One thing I'd also consider is addressing exterior grading and gutters if you haven’t already—sometimes the cheapest fix is outside, not in.
We are finishing the basement now, installer mentioned spraying closed cell on plastic wrap isn't recommended.