Q.: We have recently had stringent inspections of architectural concrete with a sandblasted finish. Many of the defects relate to honeycomb revealed by the sandblasting. Please send any literature you have about tolerances for percent defective area allowable.
A.: We do not know of any established tolerances. In architectural concrete work it is usually best to first do some panels before actual construction begins and then to finish the surface by the technique proposed for the job. Sometimes more than one technique may be used. The amount of honeycomb showing will be influenced by the placing and vibrating techniques as well as the amount of sandblasting done.
By conferring with the architect about the results it is possible to agree on what visual effect is expected by the architect and possible to execute. It is then a good idea to do a mockup to be sure the effect can be accomplished on the same scale as the final job. This procedure is usually more satisfactory than adopting someone else's tolerances, which possibly neither the architect nor the contractor will be happy with.