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DIY: Waterproof a Cement Block Wall

Whether you are looking to brighten up that dank dark garage or you are considering adding value to your home by expanding the amount of living area into the basement, waterproofing the cement block should be your first step to ensure a dry and hospitable climate for years to come. When homeowners are faced with the moist and damp environment that often accompanies a cement or “cinder block” basement they often balk at the option of having a professional come in to do the job because of the high cost. To some this may seem to be a daunting or challenging task but with the proper preparation and possibly a few friends to help out, you can easily complete the job yourself and save some money in the process even after you pay off your work crew with all of the pizza that they can eat. To complete the job and insure that it’s done correctly, you will need a few basic items to get you started.

§ Paint (we will discuss this at great length later in the article)

§. He helped me select the right brushes, rollers, roller grate, and paint and gave me several helpful tips as well. These guys know what they’re talking about because they’ve probably done the job themselves so ask them any questions you might have. They’ve probably heard the question before.

The Paint

There are a wide variety of paints, colors, finishes and brands to choose from. The representative at the hardware store will help find a product that best suits your needs. I chose a flat finish white paint as I will be finishing the basement with drywall (look for that article coming soon) from Drylock. It was $99.00 for a 5 gallon bucket which promised to cover 1,000 square feet but I found that the cement blocks really soaked up the paint so I had to get three buckets to cover an area of approximately 900 square feet with to coats of paint (recommended). You can calculate the area that you will be painting by multiplying the total length of the walls by the height of the wall. This will give you a good idea of how much paint to buy so bring those numbers with you to the hardware store. The product is also available in 1 gallon containers if you end up with an odd amount of square footage but having a little extra on hand isn’t a bad idea. Plan on two coats and don’t worry too much, the second coat goes on much faster and lighter than the first.

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Before you break out the brushes and slather on the paint, you need to prepare the cement block surface so that the paint adheres properly and provides you with a waterproof seal. I was dealing with new construction so I simply used a course broom and “swept” the walls vigorously to remove some dirt, dust, cobwebs and some of the excess mortar mix that was left. USE A PARTICLE MASK – you will be kicking up silicate dust and this stuff can be bad news for your lungs. If the surface you are painting is aged or has stains or a white chalky buildup from moisture, you will need to treat the area first. The bucket of paint actually has recommendations for surface preparation on it but this is also another area that the representative at the hardware store can help you with.

If you have any evident cracks or gaps between the cement blocks or gaps between the floor and the cement block walls, purchase an expanding mastic which will hold up to the expansion and contraction of the wall due to changes in temperature. Follow the directions for applying the mastic and it’s usually as easy as using a trowel to apply. Let this dry thoroughly before painting.

Mask off each corner or area that you don’t want painted including a line of masking tape along the seam in the floor and lay down your drop cloth. I used plastic drop cloths as this makes clean up much easier. Spots of dropped paint and the little balls of paint that form when you use the roller are a pain to clean up and unsightly if just left there…I know, I didn’t use a drop cloth in one corner and spent the better part of an afternoon trying to clean it up. Trust me, drop cloths are only a few dollars, can be reused for other painting jobs and are well worth the effort.

Try to paint after a few rainless, dry days as you don’t want to apply the paint over a damp surface because it may not adhere properly and may take longer to dry.

Call up your friends and you can even try the “Tom Sawyer” approach and tell them how much fun it will be. My friends didn’t believe me and there probably wasn’t enough pizza in the world to get them to help (some of them had obviously already done this task to their own home) so I had to go it alone. Any help is better than no help so you might even try a local high school or college for some cheap labor for hire.

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Finally, crack open some windows and use the fans to move as much air as possible through your workspace. This stuff stinks pretty bad so you want some good air movement and it will help to decrease your dry time as well.


The bad news is that you should apply the first coat of paint with a brush. The good news is that if you can survive that, the second coat can be applied with a roller. When it comes to painting with this stuff, I would liken it more to “smearing” than I would actually painting. This task definitely conjured up images of “white washing” a picket fence because the brushes are long bristled and you just sort of swap the wall with it. I found it easiest to dip the brush, spread all of the paint from one side of the brush with an upward stroke on a single brick and then turn the brush over and smear the paint on the other side of the brush with a single downward stroke. I then used side to side strokes to spread the paint and even it out. I’m sure that Mr. Miagi would have been proud. You can usually cover about two cement bricks with a dip of the brush. I also found that when painting the bottom course of bricks, it made it neater and wasted less paint if I dragged the bottom edge of the brush on the rim of the bucket after loading it with paint to get all of the excess paint off and then let the cleaned bottom of the brush ride along the masking tape and drop cloth.

As you progress through the first coat, you may look back and see that there are little pin holes forming in your drying paint. This is fine, it’s just the paint absorbing into the cement block and this will be corrected with the second coat. Once you have finished painting your first coat, clean up is as simple as a bucket of warm water as this stuff is water soluble. Define irony…waterproofing paint that is water soluble…go figure. The instructions on the bucket indicated that I only needed to wait for three hours to let the first coat dry before applying the second coat. Obviously the person that wrote the instructions didn’t have to paint a 900 square foot area in one day by himself. I let mine dry for an entire day.

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The Second Coat

After a good night’s rest, two bottles of Tiger Balm, a dose of Bayer Back and Body, and an hour of stretching muscles that I forgot that I had, I returned to paint the second coat. This went much faster than the first coat as I used the ¾ inch nap roller. Place the roller grate directly into the paint bucket and use it to roll the excess paint off of the roller so as not to drip it all over your shoes. I found that a few downward pushes on the grate worked best as upward strokes seemed to spray and splatter the paint outside the bucket. Then it is just a simple matter of repainting the surface and applying a second coat. As you progress, pay attention to the finished parts to insure that you are applying a thick enough coat to seal all of the pin holes that developed after the first coat dried. If a few start to develop here and there, I found that a small brush finished them off nicely. If you start to get too many holes and perforations, you may need to apply a third coat.

After sufficient drying, peel your masking tape, fold up your drop cloths and tidy up your newly painted and waterproofed living area. This project can easily be finished in one weekend by a single person and is a rewarding feeling knowing that you reclaimed some of your house from the elements. Good luck with your project and happy painting!