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Ask the Builder: Miscommunication to blame for concrete problems

Here’s a close-up shot of the sandy texture. The workmanship is expert, but the surface could be rough on tender feet. (Tim Carter)
Here’s a close-up shot of the sandy texture. The workmanship is expert, but the surface could be rough on tender feet. (Tim Carter)

DEAR TIM: I’ve got a big problem. Concrete was poured around my new swimming pool. I wanted a colored, sanded finish that resembled cobblestones. It’s been four weeks now and the concrete has a milky, splotchy appearance and the finish is really rough to walk on with bare feet. What, if anything, can be done to salvage this job? How could the mistake have been prevented? What’s causing the milky appearance? The contractor has said all will be well in a few months. – Tom H., San Jose, Calif.

DEAR TOM: Oh my! The photos you sent me are excellent and tell the tale. Believe it or not, from what I can see, the concrete finishers did a remarkable job. They used the correct sand in the mix to produce a nice, sandy texture, and they washed just enough cement paste out to produce a gorgeous exposed aggregate finish.

But I realize this is not what you had envisioned for the final product. I’ve got granite cobblestones in my own yard that actually look quite similar to the color of the exposed coarse sand in your new concrete! If you hired me as an expert witness – I’ve done this type of work for many years – I’d testify that you got a sanded finish that has a cobblestone coloration.

Can you see the problem? What you picture in your mind and what another person envisions based on your verbal description can be miles apart. You may have wanted a stamped concrete look that resembles actual cobblestones. For all you know, the contractor may have never seen a cobblestone alley, street or sidewalk.

To achieve a stamped cobblestone look, concrete finishers broadcast dry pigments into the wet concrete, mix these into the top layer of the concrete and then lay rubber mats onto the concrete that have the cobblestone texture and outline.

These mats are tamped into the wet concrete and then peeled off. The concrete then looks just like cobblestone. Based on your email to me, I don’t know that this is exactly what you wanted. It’s a classic case of miscommunication.

You could have prevented this situation by doing any number of things. You could have given the contractor a few excellent photographs of what you wanted. If the exact concrete finish you wanted was at some local business, park or other place, you could have taken the contractor there to show him exactly what you wanted. There are countless videos on YouTube that show patterned and textured concrete. You could have found one or two and shown them to the contractor to communicate what you wanted.

If you want actual stamped concrete as I described above, you have to start over. You need to tear out all the concrete and replace it.

If you just want a different colored finish that’s not as rough, you might be able to produce the finish you want with a very thin cement stucco overlay that’s no more than 1/8-inch thick.

Your big challenge is that you can’t add much thickness where the concrete slab touches up against the cast border of the swimming pool. You need positive drainage away from the pool.

You can create a unique cobblestone finish using the thin overlay, stencil templates and some dry pigments. I’ve seen it done and the look is stunning. You can also create the look of flagstone, tile or even brick. Shaded coloration is very possible so it’s not just one uniform color when complete.

An expert concrete mason can make up the thin overlay cement stucco and can colorize it. He would apply this over your new concrete, smooth it and then overlay heavy paper templates that might resemble brick or the cobblestone outline.

These are lightly pressed into the wet stucco and then an additional dry pigment is broadcast onto the stucco. The paper template prevents the second color from touching all the stucco. The concrete mason floats the pigment into the stucco and then may use a few special rollers to create a unique texture to the overlay. After all this is complete, the mason peels up the paper templates, revealing the gorgeous workmanship.

The surface’s current milky, splotchy appearance looks to me like too much curing compound was applied to the wet concrete. Curing compound is an excellent product and it prevents the concrete from releasing too much water into the atmosphere. Water is needed inside the concrete slab for many, many weeks after the concrete gets hard so it achieves its design strength.

The curing compound could have been defective, or perhaps far too much was applied. Over time, sunlight will remove the milky appearance, but it can sometimes take a very long time.

The contractor should not be penalized for this mistake. The photos tell me he did a great job and the final finish you wanted didn’t happen because you failed to clearly communicate what you wanted.

Before you tear up the existing concrete, do a small test to see if the stenciled overlay will produce the finish, texture and coloration you want. I think it’s possible to get very close, and the work could be done in just one or two days.

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