If your concrete patio is in good condition except for gray, tattered and splintering wood dividers then wood replacement may be in order. This is a repair that is relatively inexpensive, and although somewhat time-consuming, fairly easy.

If you were present when your patio was being poured, you may have noticed that there were evenly spaced rows of nails partially driven into both sides of the wood dividers. The nails are used to “key” into the concrete to hold the dividers in place. Don’t worry about the nails though. Once a divider has rotted enough to need replacement the nails are probably rusted and rotted away as well.

During divider replacement the nail keying technique cannot be used. You might assume that once you have removed the old wood from the concrete there won't be anything to hold the new wood in place. Not so. The new wood strips are held by the irregular shape of the recess in the concrete.

Wood divider replacement is rather easy. You'll need a hammer, a wood chisel and a hand saw, maybe a pair of side-cutters, a small vacuum and an electric sander or an electric planer or a small table saw (these can be rented) and a small block of soft scrap wood about 12 inches long.

First, use the hammer and chisel to remove the wood strips. No special technique is required. Just get the wood out as best you can. Be careful not to dull the chisel by driving the sharpened end into the concrete. You might consider using knee pads for comfort. Oh, and don’t forget eye protection.

Once the wood is removed, use the side-cutters to shorten any nails that may remain in the concrete. Don't cut them completely away. Leave about one-quarter inch of the nail sticking out of the concrete. Again, if the wood is rotten enough to need replacement there probably won’t be any nails. Next, vacuum the cavity removing scraps of wood, concrete and small debris.

Use the electric sander (or an electric planer or a small table saw) to mill the replacement dividers so that they are approximately one-sixteenth to three thirty-seconds of an inch wider than the average width of the divider cavity.

Cut the wood to length, and starting at one end begin driving the strip into the crevice using a wood block between the divider strip and the hammer. We don’t want hammer marks on our brand new divider strip now do we!

Simple physics holds it all in place. As the wood is driven into the concrete cavity the sides of the strip adjacent to the concrete are torn upward. Between the compression created by installing a slightly oversized piece of wood and the upward angle of the torn sides of the wood you'll have a tight fit. Clear, dry redwood should be used. Not just clear, but clear and dry. If green wood is used (green referring to moisture content, not color) it will shrink as it dries out and in very short order two to three months it will be loose and in need of replacement.

To make the wood dividers will last as long as possible, be sure to rub a couple of coats of clear wood preservative onto all six sides of every strip. Once in place the dividers will be fully protected. Every year or two pour oil onto the divider strip and let it trickle down the sides and ends. Wipe off the excess to prevent a sticky mess. Follow this process and your new replacement dividers will outlast the originals. And that’s all there is to it!