Rough hewn wood for porch construction

Question

My front porch was constructed using rough hewn wood as an architectural choice, with knot holes, cracks and crevices. The wood is painted white. Although it looks great, after just a few months the brown knotholes are showing through the white paint. We’ve tried repainting the knot holes with a Kilz product but in a few more months they are back.

Also, we are seeing a significant amount of mold on the various wood pieces, especially those that do not get a lot of sun. What can we do to remedy these two post-construction issues while still under the 1-year construction warranty?

Answer 1

Regular primer is not good enough for knot holes. What you need is a shellac based primer to seal those trouble spots. At this point, it might be best to sand/scrape down most of the existing paint so the primer can make the best bond. An example of this type of primer is Zinsser BIN primer:

For the mold issue... They do sell mold resistant paints and paint additives. Once the surface is properly primed for stain blocking, get a mold resistant paint.

Answer 2

Sand all the knot holes back to the wood, then hit that area and the area around it with multiple coats of stain sealer and repaint. Some products are better than others, and you'll need to go around the knot a bit.

You can wash the mold off with a power washer using a mild bleach solution. You can also try to put copper wires or flashing and hope that the copper ions will inhibit the grown of mold, but there isn't a ton of stuff you can really do.