How to fill voids in exterior siding

It's all about the caulk, baby

By Inman News Feed
Add Comment Add Comment | Comments: 0 | Posted Mar. 16, 2011

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It's all about the caulk, baby

Bill and Kevin Burnett
Inman News™

Q: I am trying to maintain a small house built in the 1930s. It has lapped redwood siding that is less than 1/2 inch thick with a 6-inch exposure. The siding runs under vertical boards butt-joined at each corner. Because the siding is tapered, there are triangular voids where each piece is covered by a corner board. Should these voids be filled -- and if so, with what?

A: Caulk till you drop. Although this extra step isn't always taken, a first-class job requires that all voids should be filled to prevent water infiltration, critter infiltration and to help keep the cold air out.

The siding could be beveled clapboards, rabbeted clapboards or shiplap siding. We've seen all of these siding styles with narrow exposures at the edge where the boards overlap on the horizontal plane of the wall. Corner boards are part and parcel of each installation.

Beveled clapboards are milled to taper from a thin edge to a thicker edge -- usually from about 1/4 inch to 3/4 inch. Rabbeted clapboards are milled with a notched cutout at the thicker edge to fit over the thinner edge of the board below it. When the beveled boards are installed they form an angle allowing the siding to shed water.

Shiplap siding is milled with the notch of the rabbeted clapboard siding but the rest of the board is straight except for a cutout to create the thinner edge for the notch to fit over.

All of these siding styles have the corner boards and the corresponding gaps between the corner boards and the siding.

Based on what you say about your triangular voids, we're guessing your siding is a rabbeted clapboard about 6 1/2 inches wide. Half an inch is too narrow for standard clapboard siding, unless it was really cheap material. We don't think this is the case because the boards have lasted 80 years. Six inches exposed to the weather also leads us to believe the boards are thicker.

We presume you're contemplating painting, hence the question about preparation. Check all the nail heads on the siding. If any are compromised these should be part of the repair.

As to the material, we suggest a top-of-the-line acrylic caulk. Shop where the painters shop and let the salesperson guide you. Plan on making two or three passes at each void where the siding and the corner boards meet. The caulk will shrink some. Making more than one pass will minimize the craters.

Finally, plan to get on a regular maintenance schedule of painting every seven to 10 years. Do this and the siding will last another 80 years.

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