How to Match, Patch and Repair Old House Clapboards or Lap Siding

Part of preparing an old house or outbuilding for painting is to repair and replace areas of damaged lap siding. When that old lap siding has suffered from either dry or damp rot, decay, or even cracks, it is no longer serving its purpose of protecting the house from the elements. Damaged siding that is not dealt with can lead to the decay spreading through the sheathing and adjacent clapboards.

Repairing old house lap siding is an easy DIY project for the weekend carpenter. Here's how it's done:

How to pry the clapboard away from the house

To remove damaged lap siding from your old house, you will need some wood wedges, a hammer, hacksaw, tee square, and pliers.

The first step is to drive the wedges beneath the damaged area of clapboard so that the board slightly lifts away from the house. In doing so, you should be able to locate the nails that held the board in place. These can be removed with the pliers or by cutting them behind the board using the tip of the hacksaw.

Once the bottom nails have been pulled, insert a second set of wedges beneath the clapboard that overlaps the damaged section. Remove the nails from top of the board, either by pulling them out or cutting them with the hacksaw as well. Remove the upper set of wedges, leaving the wedges beneath the damaged board in place.

At this point, draw a straight line on either side of the damaged area of the clapboard, using a tee square or level to make sure the cutting line is perfectly straight. Use the hacksaw to cut away the damaged clapboard on these lines, sawing through the damaged board but taking care not to saw down to the board beneath. Carefully pull the cut board out and save it as a guideline for a pattern match.

Matching the clapboards

When we restored our circa 1880 barn, we discovered that the old pattern had a slightly different profile than the clapboards being sold today at our local lumberyard. To find an identical piece, we paid a visit to a mill works yard.

Millwork is the decorative woodwork that is found on both the interior and exterior of homes and other structures. Most millwork lumberyards have many hundreds of blades in stock and should have a blade that matches the profile of your clapboards. If not, the mill works can create a custom blade to match the profile of your clapboard siding.

A custom blade can be expensive however and may not be worth the cost for a few pieces of board. A cheaper alternative for a single board replacement may be to pull off a section of clapboard from a less visible part of your home or barn and use that to repair the damaged area instead. The now-missing section of clapboard can be repaired with a similarly styled piece which won't be too noticeable when painted.

Once you have your replacement siding in hand, the final step is to install it.

Installing the replacement piece

Replacing the old siding with new is the easiest part of the project. It starts with cutting the replacement clapboard to fit the opening and sliding it into place, with the top neatly tucked beneath the upper board, and the bottom edge overlapping the bottom board. If the board is a little too snug, you may want to carefully sand the edges. Once the siding fits properly, paint all the exposed areas with primer paint, and let dry overnight. The following day, nail the clapboard into place and then finish up with an application of acrylic caulk in the seams between the patch and the old wood. Complete the repair by painting your new replacement siding to match the rest of your house or barn.

Replacing a piece of damaged lap or clapboard is an easy DIY project, though does involve a little running around as you search for a replacement piece. It's definitely worth the effort though for a professional looking repair job that will last .