Q.: We're having our driveway ground because of the large number of birdbaths produced in the surface during construction. I'm a little worried about what this will do to the durability. I'm pretty sure the air content is as high as it ought to be, but how will the ground pieces of aggregate survive freezing and thawing? Our northern winters are fierce.

A.: A report by William Perenchio, "Effect of Surface Grinding and Joint Sawing on the Durability of Paving Concrete," published in the Journal of the PCA Research and Development Laboratories, January 1964, pages 16 to 19, says that durability was not affected when thin layers were ground off. If the grinding goes deep and exposes large areas of the coarse aggregate it may affect the durability. If this describes your driveway you may wish to treat it with linseed oil to improve the durability. Dilute the first coat with an equal amount of mineral spirits and mop it on but don't leave puddles. Dilute the second coat somewhat less. It won't hurt to apply additional coats every year or so. The concrete will be darker in color but should last longer.