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I have a an exterior concrete wall that had some loose paint and started scraping away. The paint in some sections was so loose that I went all the way to the bare concrete, peeling away over 6 layers of paint. I'm worried that If I paint the wall, it will still show the deep areas.

What should I do to cover this properly and what paint should I use?
Should I use some heavy primer coats on the bare concrete areas first then paint as normal or just use paint with included primer and paint it?

This is a portion of the exterior wall scraped to the bare cement.

enter image description here More Pics

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Whatever you do, be sure to use a proper, breathable, masonry exterior paint. The reason a lot of paint flakes off of concrete and stucco is that the wrong paint was used in the past. –  DA01 Nov 19 '12 at 16:42
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How big of a wall is it? How much work is involved in scraping the entire wall down to the bare concrete? –  Steven Nov 19 '12 at 16:46
    
The wall is pretty big, about 10 feet tall by 13 feet. It is an old (50+ year-old) reinforced concrete house. I started scraping about 3 square feet of the wall and stopped. Some parts the paint is stuck very well and won't come off as easily with my metal scraper. –  Rick Nov 19 '12 at 20:35
    
I just saw your edit where you uploaded the photos. To be honest it doesn't look as bad as you described it. If you scrape the loose stuff off, and sand the edges with sandpaper then you should be able to paint it and have it look seemless. –  maple_shaft Nov 20 '12 at 12:01
    
I have been trying to sand the edges where the paint meets the bare concrete with a rubbing brick. Is sanding paper better? If so what grit? –  Rick Jul 11 '13 at 14:08
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3 Answers 3

If there is six or seven layers of paint over the concrete then it will be sufficiently thick to be noticeable if you attempt to just scrape a single area and paint. It sounds as if a number of different people over the years have been putting off the dreaded inevitable conclusion that you should completely scrape and remove paint from the entire surface and repaint it with a proper exterior enamel approved for concrete.

When scraping paint always make sure to wear a dust mask as one of those layers may be lead based paint and it would be extraordinarily bad to breathe this in. When scraping keep children, animals and pregnant women away as they are particularly susceptible to ill effects from lead exposure.

Most hardware stores sell lead testing kits that will let you know if any of this scraped paint dust contains lead. A word of caution though that if you happen to verify and know that lead is in the paint then if you ever go to sell the place that you would be legally obliged to add this information to the sellers disclosure. Sometimes it is better to just treat the paint dust as if it contains lead and not know for your own sake.

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I have been using a metal spatula like metal tool. What is the recommended tool? The wall is pretty big and some parts the paint comes off easily, others not so much (please see added comment above). –  Rick Nov 19 '12 at 20:37
    
I would use a standard wire brush for the loose areas and get as much of that as you can. You can try the power washer too but I doubt it will peel the paint. For the stubborn areas that are not coming off try using some thinner or chemical based solvent at your local hardware store, and then it should scrub off with a wire brush fairly easy but it will make a mess. When using solvents make sure to wear non-reactive PVC gloves and take care to not inhale the fumes. Keep children and animals away. –  maple_shaft Nov 20 '12 at 3:33
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Since this is exterior, I would be tempted to use a power washer (you can rent one if you don't already own it):

power washer example

Just be careful around cracks since you can make them worse or force water into the wall. It's also important that you pay attention to the pressure and the distance from the surface so that you just barely flake off the paint without damaging the concrete below.

Then, you'll want to repair any cracks or damage (hydraulic cement is useful for this task) and apply an exterior grade primer that's designed for masonry. The wall needs to be able to breath so that moisture can't get trapped inside, freeze, and cause flaking or cracking.

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I have an electric power washer that runs at about 1,900 PSI. Not sure if that's enough. –  Rick Nov 19 '12 at 23:46
    
@Rick: With a red nozzle, no problem. –  staticx Nov 20 '12 at 13:46
    
@0A0D: I have this Power washer. I don't think I can change the nozzle that easily. –  Rick Jul 11 '13 at 13:55
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The right way, is the hard way, as always.

  1. Remove all the paint off the wall, using a scraper, or a heat torch, or a paint remover.
  2. Sand paper all the wall.
  3. Remove all the dust from the wall and wipe it clean.
  4. Do many layers of sealer or primer. Let it dry for 24 hours.
  5. Do many layers of good quality paint. Let it dry for 24 hours.
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What grit of sandpaper would you recommend for the concrete wall? –  Rick Apr 10 at 14:19
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