What kind of caulking can I use to seal knots in pressure treated lumber (decking)?
Answer Bob, When you say “seal” knots I’m not sure what you are asking. The entire board is pressure treated, including the knots so they are already sealed relative to rot. If you are asking how to seal the knots from absorbing water you would need to apply a water repellent product. But it wouldn’t make much sense to protect the knots but not the boards themselves. If you are trying to fill gaps, or absence of wood around or within the knots, then you could use any of a number of caulks or caulk type products, however, your deck might look like polka dotted quilt. Whatever you use will undoubtedly be a different color and will stick out like a sore thumb. Aside from that it is likely the caulk would prematurely fail because of the conditions it is being subjected to–horizontal boards in full weather, sun, snow, ice and rain, and abrasive foot traffic, and constant deflection from walking on the surface. If you have large gaps where knots, or parts of knots have fallen out, the only
