Q&A: Caulking Cypress Paneling

From on May 20, 2009 in Tools and Tips


“We have put cypress walls in our home and I need to know what to put in between the boards to fill the cracks. We have been told that this wood breathes and to use something that stays elastic, otherwise it will crack. I hope you can help me.”



I do believe we can help. This question is not as difficult as it may seem. The main problem for most people is that we just don’t know that much about cypress. So first a bit on the wood itself.

Although typically grouped with hardwoods, cypress is actually a softwood, one of only two conifers that shed their leaves every year. It’s native to swampy areas from Delaware and follows the coastline through Florida to Texas’ gulf shores and the other wet regions of the South. If cypress is rare it is in large part because the swamps that it calls home can be very hard to get to.

Cypress is very durable and rot resistant thanks to oils in its heartwood, which make it a classic choice in exterior siding, shutters, shingles, trim, and fence posts. In addition to paneling, cypress’ interior applications include molding, cabinetry, flooring, and furniture. Cypress sapwood has a pale yellow color while the heartwood varies from light to dark brown. It typically comes from the lumberyard in 4” to 12” wide boards.

In terms of interior wall claddings, cypress panels are usually tongue-and-groove or shiplap design. Like other wood products, cypress paneling will certainly “breathe”, or expand and contract, as temperature and humidity change. In most cases, caulking shouldn’t be necessary for interior applications (unless painting) where temperature fluctuates much less than outside, especially if the wood is acclimated prior to installation.

However, as is the case for our reader, caulking may be necessary, especially if in a bathroom, kitchen, or other area where moisture is oft present. For cypress, on interior or exterior surfaces, you should use a high grade, non-hardening acrylic caulk or its equal. You can actually look at a tube of caulk on the hardware store shelf and look for a number, i.e. 10-year or 20-year. That number represents how long the caulk should hold before losing its elasticity. Do not expect the caulk to actually last that long but it does present an easy guide—the higher the number the better.

bayoucypress.jpgPhoto credit: Bayou Cypress

Colored caulks are also available that can closely match the color of the wood. Again, the most important factor is flexibility. Silicone caulks are highly flexible and weather resistant but are usually not paintable. Manufacturers however make “silicone-ized” caulk that sometimes may be painted with water or oil-based paints. A good and simple rule of thumb is to read the label on the caulk carefully to make sure that it fits your particular application. As rare and beautiful as cypress is, it does not act too differently than most other softwoods.