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BTn5qsc2zB93ztGN9vJP 08-21-2008 07:10 PM

Concrete Walkway with Exposed Aggregate
At my condominium complex, we have a few hundred feet of of concrete walkways. The surface of the walkway shows exposed aggregate. It looks good.

Over the years, sections of the walkway have been replaced by various contractors. In every case, the new walkway is poorer quality that the original walkway. After only 2-5 years, new sections start to become pitted as the aggregate comes loose. The original walkway, in comparison, is 22-years old and shows almost no pitting.

I'd like to know how to create a concrete walkway with exposed aggregate that doesn't start pitting after only a few years. Our contractors obviously don't know.

Can anyone offer specific suggestions about materials and techniques?


concretemasonry 08-21-2008 08:10 PM

Order a exposed concrete mix from a ready mix supplier if you find a way to justify the cost for a smaller volume. Ready mix will be good and consistant. Around here, when I told the contractor I wanted exposed aggregate for a 20x12 patio, he said "No problem, I will just order the standard McDonalds mix (as in Big Mac)". This mix is common to many different uses and is a standard mix for 4500 psi and 5% air entrainment from different suppliers.

When you have small quantities and are concerned with cost, you can easily end up with site mixed or hand cast/embedded aggregate in a normal mix. Both are subject to more variation and differences from contractor to contractor. You will never get air entrainment with a site mix.

Tscarborough 08-21-2008 09:52 PM

The most reliable way to create quality exposed aggregate finish is with proper mix design and accurate finishing, including a chemical retarder. This is not practical for small repairs.

BTn5qsc2zB93ztGN9vJP 08-21-2008 11:41 PM

Thank you for the advice. Before now, I was not aware of a difference in quality between site mix and ready mix. I think that explains the situation, since all our patch jobs have used site mix. Ironically, we have a lot of area to cover, but we've been giving our contractors small jobs on the theory that until they prove they can do a 10' section competently, we don't want them doing the full job.

Your comments about ready mix have raised a number of questions. If I order a standard recipe of ready mix from a supplier, will they be able to provide me with a matching site mix recipe? I ask because, even if we do a big repair job once every ten years or so, we will still need to do dozens of small patches in-between, and those will inevitably use site mix. I now know that the site mix won't have the same quality, but it would be nice at least to have a recipe that produces something consistent and similar in appearance to the rest of the walkway.

Also, Tscarborough, can you be more specific about what I should demand regarding finishing and a chemical retarder? Is there a specific product I should ask for?


Tscarborough 08-22-2008 07:49 AM

The retarder is surface applied after finishing and is then washed away after a certain amount of time to expose the aggregate.

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