When I introduce Scott Tarr, I tell the audience that he wrote the book on concrete slabs—literally, since he is co-author of the Portland Cement Association publication, Concrete Slabs on Ground. Now I will be able to also say he wrote the book on concrete toppings as the American Society of Concrete Contractors prepares to publish his new book, Guide to the Design and Construction of Concrete Toppings for Buildings.
After graduating with a master’s degree in civil engineering from the University of New Hampshire, Tarr went to work at Construction Technologies Laboratories (CTL), which was a subsidiary of the Portland Cement Association. For many years, CTL was the world’s leading concrete research lab, so he learned from the best and became one of the nation’s leading forensic engineers, solving problems with slabs and structural concrete.
In 2007, he left CTL to work in a partnership with several other concrete industry experts, but things changed and he soon set off on his own, founding North S.Tarr Concrete Consulting with his partner, Ron Kozikowski. “The first 15 years of my career was all back-end troubleshooting, but today I do more front-end work,” he says. “A lot of design reviews, mix design reviews, preconstruction meetings, construction monitoring.” These services are often performed for the developers of new buildings—warehouses and distribution centers—who have begun to realize that avoiding the problems in the first place is better than fixing them later. “But I think when the economy goes bad there won’t be so many new floors and I’ll pop back over to troubleshooting,” he laughs.
Tarr sees different owner expectations for slabs today, such as flatness requirements that are unreasonable without some grinding and slabs with extended joints. “I think the concept of these extended joint systems is good,” he says. “It’s going in the direction everybody wants but we’re not quite there yet. I expect to see more of these extended joints systems and improvements in that technology over the next few years.”
Proper curing is another issue Tarr focuses on with contractors. Some may think curing is not necessary in some situations or with certain slab systems. “I don’t care what kind of concrete you have you still have to cure it. Let’s get back to the basics. It costs the owner more money but it’s necessary. If you put a trowel finish on concrete, it may retain the moisture but you’re not really curing, it’s just a densified surface, but you’re not curing the exposed surface layer.” This issue will be discussed further at the Quality in Concrete Slabs luncheon at the 2020 World of Concrete where Tarr will be a panelist.
Increasing the quality of toppings may be the next big trend in concrete slabs, especially once the new book begins to get more use. Tarr has seen many failures with toppings that were simply due to a lack of knowledge or to the responsibility for topping design being put onto the contractor. “Toppings are overlooked in many project plans and specifications,” he writes in the book. “All too often, the project design documents simply require the contractor to ‘install a topping in areas as designated to bring the floor elevation to that shown.’ ” He advises contractors with a topping project to “insist, however, that it is the engineer’s responsibility to provide the design requirements of the topping.”