Recently, a local storeowner phoned our dispatcher to complain about the poor concrete he recently purchased for his exterior sidewalk. His complaint was that the surface was unduly rough and blotchy.
When we investigated the complaint, we determined that the storeowner had purchased the concrete through the concrete contractor as part of an "add-on" project to a large city curb-and-gutter improvement project.
Since we really didn't sell the concrete to the storeowner, what information can we show the storeowner to prove that their claim should be directed toward the contractor's poor workmanship? I've enclosed photos of the job.
We've shown the photos of the problem to several producers. They all agree that the problems are caused by the contractor. One related that in a similar circumstance, the storeowner contacted the city's engineering office to solicit help. It turned out that the project was placed on the city's right-of-way, and in an effort to make the local storeowner happy, the engineer refused to accept the product due to the surface blemishes. The contractor subsequently tore out the poorly finished concrete and replaced it with higher quality work.
The photos you submitted are textbook examples of common surface defects for which producers must have an explanation.
From photo A, it appears that the concrete may have been placed just before it rained, with the plastic cover still on the ground near the new concrete. Many of the defects may be due to the finisher's haste to quickly complete the job.
Several of the blemishes in photos Band C suggest that someone walked on the plastic cover just after the broom finish. Or perhaps the weight of gathered rainwater put the cover in direct contact with the just finished concrete surface, and some of the paste adhered to the plastic and was removed with the cover.
The blotches found along the lower control joint in photo D may have been caused by a finisher walking along the next pour segment, or from splatter that occurred during concrete placement.
In this circumstance, it's apparent that the contractor should accept the responsibility of a poorly finished slab and find a way to settle with the storeowner.
Several good references help in describing surface problems to contractors and contractors' customers.
Chapter 11 of ACI 302, "Guide for Concrete Floor and Slab Construction," explains the causes of floor and slab surface imperfections.
Surface Defects in Concrete (3910) and Placing, Finishing & Curing Concrete (1030) are both Hanley-Wood, LLC, publications that use collections of articles from Concrete Construction magazine to explain how to prevent these types of surface defects. Both of these publications can be found at the Hanley-Wood Bookstore by logging on to www.hwbookstore.com