Painting my garage..

July 9, 2007 7:56 PM

Garage-floor repainting.. After etching the old surface, how do I rid of the fine powder?

This is my first time painting my garage floor. My old car leaked a lot of oil and now that I have a new car, I'd like to get the garage looking new again.

What I have

Degreaser/Cleaner
Concrete Etcher/Acid.
Primer
Paint

They go on in that order. However, after etching the concrete, there is a fine powdery residue. The instructions say if there is powder, re-etch with a diluted solution. I've done that ... three times now. I've tried my best while it is wet to scrub the solution out while spraying with the hose. (The 3rd time I rinsed for 30 minutes straight).

Every time there is a fine powder left. How do I get rid of it so I can prime the surface? I've tried sweeping it, vacuuming it, its still there.

Please help.. I want to get this done right, and I am left without my garage.

posted by mphuie to home & garden (7 answers total)

Do you have access to a power washer?
posted by jkaczor at 8:10 PM on July 9, 2007

What's wrong with using the hose?
posted by Steven C. Den Beste at 8:15 PM on July 9, 2007

I don't have a pressure washer but I do have a hose with a fairly strong nozzle. I've tried spraying while scrubbing for around 30 minutes (for a small 2 car garage...) . It seems excessive as well as unproductive.
posted by mphuie at 8:23 PM on July 9, 2007

It sounds as if your still using the Etcher in the solution you are attempting to remove the dust with. At this point use just plain water, there should be no dust after a good plain rinse.
posted by crewshell at 8:33 PM on July 9, 2007

I guess you could rent a compressor and blow all the dust away. Be sure to use a mask to avoid breathing the most likely toxic dust. Then you can use the compressor with a paint gun to paint the floor.
posted by JJ86 at 8:43 PM on July 9, 2007

Some concrete will never stop dusting on its own, no matter how much you wash it. In fact, washing it simply exposes additional fresh surface to dust, which will happen simply as a matter of water drying on the surface. This is because concrete made without latex or polymer additives, and a high proportion of portland cement to sand or aggregate (which is a common mix for smooth surface work such as residential garage floors) has excess water of hydration at the crystalline interface of the portland cement. When new surface is exposed, the excess water of hydration can be easily driven off, freeing new silica crystals in the reacted mix to mechanical loss.

In these situations, you will never get rid of the last bit of concrete dust by continuing to etch and wash, or even rinse, repeatedly. The concrete actually makes new dust, simply by drying out. But you need not get rid of all the dust. Penetrating sealer will absorb and bond a thin uniform layer of dust as it penetrates the concrete and increases the density of the concrete. Essentially, sealer prevents new cement crystals from being exposed to loss of water of hydration, at the same time it fills micro-voids in the concrete, created by initial drying. The result is a substantially harder and denser surface, and improved crack resistance, since the sealer typically penetrates and bonds the concrete matrix from 2 to 4 inches depth.

If anything, you've probably over-etched your garage floor substantially. Give it a few days to dry, and stay off it. Then apply your primer/sealer liberally, according to directions. Stay on the heavy end of package recommendations. Apply a second coat, if the appearance seems uneven. Paint over, if you like, but many people stop with just the sealer. In future, as wear occurs, it is much easier to get a fresh uniform appearance by just washing and resealing, than by repainting.
posted by paulsc at 9:34 PM on July 9, 2007

Concrete and general masonry treatment (from wikipedia)

Concrete treated with a Sodium Silicate solution helps to significantly reduce porosity in most masonry products such as concrete, stucco, plasters. A chemical reaction occurs with the excess Ca(OH)2 in the concrete that permanently binds the silicates with the surface making them far more wearable and water repellent. It is generally advised to apply only after initial cure has taken place (7 days or so depending on conditions). These coatings are known as silicate mineral paint.
posted by hortense at 11:04 PM on July 9, 2007