Q.: We have had an increasing number of requests to replace factory woodblock floors with concrete floors. There might actually be enough of this kind of business to keep us occupied full time. One thing that makes us hesitate is that we aren't sure about whether there is a good way to clean up the base slab effectively enough to bond the new concrete topping to the concrete base slab. What can you tell us?
A.: This subject has recently been getting attention in the Indiana area. The June/July 1984 issue of the Indiana Concrete Council's Concrete Columns reports that in Marion, Indiana a contractor investigated this problem. He learned from the manufacturer of the wood blocks that a scarifying machine is effective for removing the mastic that bonds the blocks to the floor and cleaning the base slab. The old, brittle mastic is said to come off easily, although they say that newer mastic should be blotted with silica sand before trying to remove it this way. Both walking model and riding model scarifiers have been used successfully. Machines with widths of cut up to about 20 inches can be obtained from local rental yards.
The Indiana Concrete Council also suggests that blasting with water might be effective and they refer to the June 1984 issue of the Portland Cement Association Concrete Technology Today, which reports on removing old floor tile adhesive but not specifically on removing the mastic used to hold woodblock flooring. That article says that a water blaster with a pressure pump that provides pressure from 800 to 2000 psi produces excellent results. Using hot water at about 180 degrees F improves the efficiency. Then the water and refuse are picked up with a wet vacuum system.