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We have a back patio with colored concrete that was poured last year. When the concrete was poured, it looked like the color was only picked up by the first half of the pour. The contractor poured the concrete mid-day when it was at least 110 and ended up not doing a proper finish because it was too hot for them to keep working. The result was the concrete ended up with slurry and trowel marks everywhere.

The contractor attempted to fix the concrete by putting some type of sealer over the top which ended up looking even worse.

What can we do (besides pulling everything up and re-pouring the concrete) to seal the concrete properly and get rid of the blemishes (see photos)?

From the photos, you can see the sealer splashes, improper broom marks, chipping everywhere, etc...

Click an image to see it full-sized.

Patio slabs, view 1 Patio slabs, view 2 Patio slabs, view 3 Patio slabs, view 4 Patio slabs, view 5 Patio slabs, view 6 Patio slabs, view 7

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I'm not a concrete expert, but if you don't mind a little extra height (which is often good for aesthetic and drainage reasons,anyway) you might try:

  1. Sandblast the crud off of the top layer of the slab. You want to leave the surface roughened too, and sandblasting accomplishes both.

  2. Was the old slab reinforced with mesh or rebar? If not, then maybe lay some reinforcing mesh down now. If it was me, I'd use concrete screws to fasten it, every couple of feet.

  3. Saturate the old concrete with water, so it doesn't "rob" the new concrete while it's curing.

  4. Pour at least an inch of "topping" or small-aggregate concrete.

  5. Finish to taste.

It's probably best to test everything on one slab first, to see how it goes. See this article for another take on it.

If you do mind the extra height, sandblast and wet, but just use a thin layer of proper topping or finishing cement. Don't be surprised if it doesn't hold-up as well, though.

Just about any hardware store carries "Topping" cement. A very common product is QUIKRETE® Topping Mix. Note that it requires an additional "Acrylic Fortifier" if you use it only in a thin layer.

For an even thinner overlay, there are "skim coat" products like "SonoSkim Concrete Surface Finishing". I've never seen one of these hold up in high traffic areas, but you can reapply it as needed.

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  • We'd prefer to avoid additional height. Given that, would you (or others) know of what type of topping we could use? (fwiw: The slab was reinforced; forget if it was mesh or rebar, though)
    – Metro Smurf
    Apr 23, 2012 at 14:06
  • See the updated answer. Almost any hardware store will have at least one topping/finishing product. Preparation is the key; Sandblasting works well.
    – Brock Adams
    Apr 23, 2012 at 22:14
  • Thanks for the follow up. It'll be a couple of weeks before I can attempt to re-finish. I'll post a follow up when I do.
    – Metro Smurf
    Apr 23, 2012 at 23:23
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I'd consider getting someone out with a grinder to see if the sealer can be ground off. If it can, then consider some sort of mottled concrete stain to even it all out.

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