Q. My driveway has many unsightly cracks, which detracts from the appearance of the front of my house. This is important because I am preparing to sell the house soon.
I don't want to pay for a new driveway. How successful would it be to repair the surface? I do not like the appearance of the tiny pebbles embedded in plastic resin. I would prefer the appearance of a concrete topcoat.
A. You should be able to repair and resurface your driveway if you follow some important guidelines. Major cracks and holes must be repaired before resurfacing. Before patching any surface, all loose particles or deteriorated concrete must be removed.
If you have major breaks in the existing concrete, these need to be undercut before repair. This means chiseling out all loose and weak concrete with a cold chisel and hammer. Undercut the side of the repair area (cutting under the solid concrete at an angle) to "lock" the patch in place.
Use compressed air or hand bellows to blow all loose material out of cracks. Apply a sand-cement grout or bonding compound to the old surface, then fill the crack with patching mortar or concrete and use a trowel to smooth it.
Usually the easiest way to patch holes and other surface defects in concrete is to use commercially available patching compounds. These are premixed and are either wet (resin-based) or dry. Because of their convenience, you can use them to effect most any repair with ease. Be sure to follow manufacturer's instructions carefully.
Once major cracks and holes have been repaired, you are ready for resurfacing. Concrete surfaces to which concrete or mortar is to be bonded should be rough, clean (all oil and dirt residue removed) and dry before applying the new material.
Some bonded concrete overlays call for overnight prewetting of the newly cleaned surface before resurfacing, while other processes are successful on dry surfaces.
A fully bonded overlay is placed on a clean, prepared surface. A sand-cement grout is used to develop a strong bond between the slabs so that the overlay becomes an integral part of the slab.
Bonding is necessary for resurfacing less than two inches thick. The surface should be roughed up before placing the overlay.
Methods of cleaning and roughing the surface include dry removal by machine, such as grit blasters, shot blasters or planters. Wet cleaning methods, advisable in cases where oil has penetrated the concrete surface, include acid cleaning and etching.
Immediately before a fully bonded overlay is placed, a thin coat of bonding grout should be scrubbed into the clean, damp (but not wet) surface if it has been prewetted overnight.
Hand methods can be used to place and finish the topping, but machine methods usually are recommended.
Proper and adequate curing is even more important in bonded resurfacing than in ordinary concrete work because of the potential for rapid, early drying of the thin concrete overlay.
Protect against rapid drying by using coverings such as wet burlap, plastic sheets or waterproof paper as soon as it is possible to do so without marring the surface. Keep the concrete covered and damp for at least seven days when using normal portland cement in temperatures above 50 degrees Fahrenheit, and at least four days in warm temperatures or when using high-early-strength portland cement.
If you tackle resurfacing as a do-it-yourself project, I suggest that you write the Portland Cement Association, 5420 Old Orchard Rd., Skokie, Ill. 60077. Request the pamphlet "Resurfacing Concrete Floors," and enclose a check or money order for $5.
Q. How can I remove automobile oil from my concrete driveway? I have used several commercially prepared products without much success.
A.The Portland Cement Association recommends these methods:
First try saturating the stain with mineral spirits or paint thinner. Then cover the area with an absorbent material such as dry portland cement, talc, cat litter, fuller's earth, cornmeal or cornstarch.
Let stand overnight, then sweep away the cover. Repeat if necessary.
For more resistant stains, scrub with a solution of half cup trisodium phosphate and half cup household bleach mixed in a gallon of water.
If the stain remains, try a poultice of powdered whiting mixed with benzol. Leave this paste on the stain for an hour after the benzol has evaporated. This may also need to be repeated.
Concrete is a porous material, and it may be impossible to completely remove serious stains.
Send inquiries to Here's How, Copley News Service, P.O. Box 190, San Diego, Calif. 92112-0190. Only questions of general interest can be answered in the column.