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Basement walls: Any idea what this is and how to treat it?

I have already fixed the outside issues to prevent, as best possible, water from coming in.  Now, I'm left with these.  FYI -- it is a 1925 home, and the basement walls have been previously painted with Drylok about 6-8 years ago.


Any solutions to fix and then what paint to use?



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Posted 2012-08-24T20:02:21+0000  by gwenk gwenk

 Hello and welcome to the community - we are glad you stopped by.


   Concrete block uses mortar as the adhesive to hold them in place.  Mortar is a mixture of Portland cement and sand. Over a period of time the mortar can deteriorate and its porosity will increase allowing water to penetrate through weak areas.  The visible areas on your wall are called a “honeycomb” and are caused by weakening mortar or aggregate materials.


   If the water source has been addressed and you are confident no moisture is coming through, then lightly scrape off any loose material and coat with a water proofing paint DRYLOK EXTREME  You will have to apply two coats to insure long lasting protection.  Then simply paint over the wall with quality paint.





Hope this helps.  paiintpro.JPG


Posted 2012-08-26T15:06:18+0000  by Kevin_HD_ATL

Your walls look like they've already been painted. That limits what you can put on them. Products like Drylok and Behr's basement waterproofing paint want to penetrate the wall. If it's already got a coat of paint on it, they can't penetrate. Either company might be able to give you possible solutions (call their customer support number) that would allow you to use their products on a previously painted surface.


Here's a decent write up on waterproofing basements (from


If you’re trying to figure out how to cure a wet or musty basement, you’re almost certain to have come across advertisements for products that claim to be able to waterproof basement walls. So you wonder: Is it really possible to dry out a basement simply by sealing the walls?


Unfortunately, it’s not that simple. You need to figure out if you have a drainage problem and fix it through permanent solutions, such as directing gutter water away from your house, and making sure the soil around your foundation slopes away from your house.


Where’s the moisture coming from?

Walls still damp? Check if the moisture is coming from the outside, or if it’s actually high humidity that’s condensing on the cool walls of your basement.


Tape a 1-foot-square piece of aluminum foil to the inside of your basement walls, and leave it in place for 24 hours.


If there’s condensation on the outside of the foil, you have high humidity in your basement. Fix it with a portable room dehumidifier ($200-$300) or a whole house system.


If the foil has condensation on the inside surface (next to the wall), it may be the soils around your house are naturally damp from a high water table or poor soil drainage. In that case, waterproofing your basement walls can be useful. 


Interior waterproofing for basement walls

There are four basic kinds of interior waterproofing products — three types of coatings, plus plastic sheets and panels. None of the products will work, however, unless cracks and gaps are properly sealed.


Fill cracks and gaps less than 1/8-inch-wide with polyurethane caulk made for masonry ($5/10-oz. tube). Patch wider cracks with epoxy filler.


Concrete waterproofing coatings: These thick coatings are cement-like; once dry, they adhere permanently to concrete and masonry walls. You apply the coating with a heavy brush made with tampico bristles — a natural fiber. Swirl the brush at the final stage of application to give the wall an attractive, finished look.


Concrete waterproof coatings can’t be applied to previously painted surfaces; check the label. A 5-gallon bucket (you add water to the dry mix) is $30-$40 and covers 100 sq. ft.


Silicate-based concrete sealers, also known as densifiers, are also suitable only for walls that haven’t been painted or sealed. The sealers soak in and chemically react with ingredients in the concrete or brick, forming a hard, waterproof surface. 


Because these are penetrating sealers, they can’t flake off or peel and you can paint over them (but check the label first). Applying a silicate-based sealer with a brush, roller, or sprayer is easy enough for a DIY project. A 1-gallon can is $40-$50 and covers 200 sq. ft., but you’ll need at least two coats.


Waterproofing paint is an acrylic formula, not all that different from ordinary wall paint. But you brush, roll, or spray it on much more thickly — one gallon covers just 75 square feet, not the 300 square feet typical with standard paint. 


Waterproof paint is fine for DIY application. You can apply it over painted surfaces, and paint over it once it’s cured (1-gal./$35).


Plastic sheets and panels are suitable as wall waterproofing only in combination with interior basement drainage systems. They don’t stop water from getting through the wall, but they do stop it from ruining things in the basement. 


Water that gets through the wall runs down the back of the plastic, into a drainage system in the floor. A sump pump moves water out of your basement. The entire system is $3,000-$5,000 for a 20-by-20-foot basement room.


Exterior waterproofing of basement walls

The surest way to waterproof your basement walls is a full-scale exterior waterproofing solution. It’s also the most expensive — often $15,000 to $30,000.


Exterior waterproofing involves excavating all around the house to the full depth of the foundation walls, then installing a waterproof coating or membrane topped by drainage panels. The panels provide an easy path for water to flow down to an exterior French drain at the bottom of your foundation.


From there, water flows by gravity — or with the aid of a sump pump — away from your foundation to another part of your property, or into a storm drain.

Read more:

Posted 2012-08-26T16:55:18+0000  by Paul

Thanks for the input, Paul.


Two follow-up questions:


1.) Some of the black stuff is mold, what's the best way to treat that before painting?

2.) I have already used the Drylok acrylic paint about 8 years ago, so is the Drylok Extreme OK to over that in these spots? Or, do I paint the entire surface wth teh Extreme?



Posted 2012-08-26T18:04:22+0000  by gwenk

Great, tips and article...thanks so much!  The walls are painted, but with Drylok.  According to its website, I can Drylok over it or simply paint over it.  Of course, I'll need to treat the trouble areas first.


Thanks again!

Posted 2012-08-26T18:05:56+0000  by gwenk

You may want to treat the mildewed areas with a bleach/water mixture to kill the mold and mildew.  You should be fine with just "spot coating" those specific areas - but be sure to apply two coats.


Thank you once again for stopping by the community.

Posted 2012-08-26T19:04:18+0000  by Kevin_HD_ATL
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