Rough cut cedar siding is a durable building material. The non-milled wood surface creates a rustic appearance, but it can present some challenges when it comes to finishing. Because it tends not to be as absorbent as a more traditional, milled siding, stains can have trouble penetrating. Painting is a possibility, but then you sacrifice the unique look of the rough cut siding. Finishing rough cut cedar siding involves preparing the surface properly, selecting the right type of finish and performing regular maintenance.
To prepare the surface of rough cut cedar siding, wash the siding down with a good wood cleaner, and follow that up with an application of wood brightener. The wood cleaner will remove dirt, gunk and grime that could be contaminating the surface of the wood. It also helps to open up the pores of the wood so that the coating you decide to use has a better chance of penetrating. After applying the wood cleaner, let it sit for 15 to 30 minutes and then scrub it down with a nylon scrub brush. Then rinse it thoroughly.
The oxalic acid in the wood brightener neutralizes the wood's tannins, a natural preservative in cedar that can bleed to the surface of the wood during the cleaning process. You can apply the wood brightener as soon as you rinse away the cleaner, and it is recommended to apply brightener to wet wood. There is no scrubbing involved with the brightener; just apply it to the wood, let it sit for about 45 minutes and then hose it off.
Assuming you want to keep the wood looking natural, you have a couple of choices when it comes to finishing rough cut cedar. You can use a penetrating type of oil-based stain or a hard-drying, film-forming urethane. There are pros and cons to both products.
The penetrating stains are nice because they soak into the wood completely. There is no film formed, and, as a result, there is no coating to peel or lift. An issue with rough cut cedar, though, is that the product may not absorb very well into the wood. As a result, the initial application of penetrating stain typically doesn't hold up very long. You may end up having to re-coat in as little as six months until the siding has a chance to season.
Over time, the pores in the wood open up, and more stain will absorb. You really have to keep up on it at first, though, in order to prevent the sun's ultra-violet (UV) rays from damaging the siding.
A film-forming urethane can give your cedar a longer lifespan. Also, many people prefer the glossier look you get with that type of product. The main drawback of the film-forming products is that over time they lift and peel. The maintenance may not be as frequent, but it is more involved than is anticipated with a penetrating type of stain. Re-coating with urethane usually involves some sanding in areas where the coating is badly deteriorated.
With either the penetrating stain or the urethane, the UV protection comes from the pigment in the product. Generally, the darker you go, the longer you can expect the product to last.
Regardless of the finish you choose, performing routine maintenance will increase the lifespan of the finish and keep your siding looking good. Wash the siding down with a mild solution of wood cleaner at least once a year. This will keep dirt off of the finish and prolong its longevity.
Tannins can be drawn out of the wood even after it has been finished. So if the siding turns dark, go ahead and use the wood brightener on it.
With a penetrating stain, expect to re-finish the siding once or twice a year for the first couple of years. As the siding seasons, it should begin to accept more stain and hold a stain longer as a result.