Our concrete sidewalks have buckled over the last eight years and sunk from one to three inches. I attribute this to the freeze-thaw cycles in this cold part of the country. Should I clean the existing surfaces and add more concrete on top? If this is the proper course, is there a bonding agent I should apply to the old surface first? R. Petty Stillwater, Minn.
You are on the right track. The heaving occurs when the ground freezes to the extent of its moisture content.
To reduce or eliminate the heaving, run drains along both sides of the walks and driveway to channel any water away from the concrete, thus cutting down on the amount of moisture that gets into the ground under the concrete.
Before adding a concrete overlay you should acid-clean the old concrete of anything that would inhibit the new concrete from adhering to it.
Carefully, add 1 part muriatic acid to 10 parts water. Then, to the rinsed surface, apply any one of the bonding agents available at your local supply company.Follow the labeled directions.
Ordinary concrete that is poured less than 3 1/2 or 4 inches thick on top of an old surface will likely crack and be unsightly.
For a thin concrete overlay, use one of the many products specially designed for such application, such as Sealwall Weld. Use airentrained cement, which weathers better.
Another product is V/SC, which is made by the Okun Company, West Haverstraw, NY 10993. The company makes a vinyl steel concrete that mates chemical, metallurgical, and structural properties compounded for "the chemistry of toughness." It is reinforced with steel, which contributes to the strength, adhesion, and stability of the product. Also, it is available in many colors and can be feathered to 1/16th of an inch.
Another overlay product is made by Hartline Products Company, 2186 Noble Road , Cleveland, OH 44112.
Whether or not a do-it-yourselfer can succeed with any of the above products depends upon his mechanical aptitude. Some homeowners may need to have this type of overlay done by a professional.