Pressure treated lumber is not designed to withstand "the elements". But rather to resist the development of mold in moist environments, and therefore the resulting rot. Unfortunately, it is this very pressure treating process that seems to resist the absorption of almost any finish until enough time has passed that the surface begins to dry out some. This usually takes some months.
Agreed, the pressure treated material needs to weather-in for a few months before any additional treatment is applied.
Personally, I think anything Thompsons makes is really a waste of money. It won't make the wood last longer, that's for sure. You never see pros using it (or similar products like Behr) for good reason.
My advice would be to go with an oil-based penetrating stain/sealer. Penofin is a high quality product that will actually give you something worth paying for. Their 99% UV resistant stuff in the red can is about $40/gallon, and worth every penny in my experience. It'll help reduce the cracking, surface drying and checking that treated southern yellow pine is known to suffer. It comes in about a dozen shades including clear.
All of the above. If left unfinished, PT lumber will crack and check badly in a short time. It won't rot, it will just look bad. Consumers rates deck finishes fairly often, but they usually rate the solid stains as the best, because they cover up the wood. Some people like to see the wood grain, so clear or semitransparent finishes is what is needed there. They are often only good for 2-4 yrs.
A forum community dedicated to Do it yourself-ers and home improvement enthusiasts. Come join the discussion about tools, projects, builds, styles, scales, reviews, accessories, classifieds, and more! Helping You to Do It Yourself!