Q. My concrete driveway has eight large slabs. The driveway slopes down from my garage to the street. The straight-line gaps between the slabs has enlarged, and some cracks are as wide as 2 inches now. I patch them and they open up again. Is there a guaranteed way to repair these cracks so I don't have to do it every other year?

A. Concrete cracks of any type are the bane of many a homeowner. They can be in flat slabs, retaining walls, foundation walls and steps. Concrete has fantastic compressive strength, but usually only 10 percent of that in tension when you try to pull or stretch it apart. This lack of tensile strength explains, for the most part, why concrete cracks.

It’s impossible to cover this topic completely in this tiny column. I’ll just focus on your situation and give you an interesting option.

First, your driveway looks to be in great shape, other than the gaps between the slabs. That makes a repair job much easier and more likely to be aesthetically pleasing. It’s important that the repair be functional while not detracting from the overall look of your driveway.

If you try to fill the cracks with a hard material, such as more concrete that contains small aggregate like pea gravel or very coarse sand, it eventually will crack as well. The gaps you have are far too wide for most institutional and commercial caulks designed for filling concrete cracks.

Doing a specialized and exhaustive search on the Internet, you may discover some product used by airports, state departments of transportation or other owners of massive amounts of concrete pavement that will fill those massive cracks. But the look of the repair may not be in your best interest.

I recommend that you repair the cracks with wood. I know that may sound nonsensical, but wood and concrete have been used for years together. It was a fad in the 1950s and 1960s to install redwood slats in between concrete slabs and sidewalks in the modernist homes that were popular in that period. I’ve inspected houses with this combination, and the redwood appeared to have lasted for well over 25 years.

Because of the natural water repellents that are in redwood, it would last for decades, even though it was exposed to moisture in a slab on the ground. Using some new water repellents and drainage aids, I believe you can get strips of wood to last at least 30 or 40 years, if not more.

The first thing you need to do is clean out the gaps between the slabs to the thickness of the slabs. Scrape off any old patching tar with a stiff putty knife and remove residual tar or asphalt compounds with mineral spirits and gentle scrubbing with a wire brush.

Dig a 4-inch wide trench along the sides of the slabs from the crack or gap closest to the house all the way down to the street or sidewalk. This trench should be as deep as the slabs are thick.

Fill the trenches on either side of the driveway with small, rounded pea gravel (the size of marbles or peas). Do the same for the gaps between the concrete slabs, but stop filling the gaps about 2 inches from the top of the slabs.

Buy some redwood or other fine-grained lumber, like teak, that is naturally resistant to rot. Cut the strips of wood to fit each of the gaps, making sure the shape of the strips is wider at the top than at the bottom. This tapered shape will allow you to tap the pieces of wood into the gaps between the slabs with little effort.

Each strip should be cut so that it’s 1¾ inches from top to bottom. This dimension allows the wood to be recessed below the top of the slabs about ¼ inch.

Before you install the wood, completely coat all the sides, edges and ends with three coats of a high-quality synthetic resin water repellent. It’s very important that the ends are well coated. In fact, I would dip the end of each piece of wood into the can of the sealant for at least two minutes allowing the water repellent to be drawn deeply into the end grain.

Once the wood strips are in place, fill any small gaps between the wood and the concrete slabs with medium sand. The sand will be natural looking and it will finish off the job nicely.

The pea gravel under the wood strips and on the sides of the driveway acts as an interconnected series of drainage channels that will remove any standing water from around the wood. This will significantly extend the life of the wood strips.

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