How to seal Paulwonia ?????

To truly seal it epoxy is best, but I'd recommend you use Bote-Coat, instead of WestSystem. It's cheaper, in country formulated and I've heard many good things about it too.

You can raise the grain, but I prefer to slice the grain with a scraper instead. This makes the ends of the exposed cells open, with a clean cut, unlike what sand paper does, which is fuzz up the ends of the cells and fill them with dust and debris. Epoxy penetrates much better on scraped stock than sanded. Apply the first coat with a bog applicator or putty knife, literally pressing it in as you spread it around. Once the surface has sucked up some goo, scrape excess pools of epoxy onto areas that have yet to get coated. Leave no areas with a pool of goo, which will eliminate out gassing. Do this only on raw wood. You'll want at least 2 more subsequent coatings, but this time your goal is a uniform coating thickness. Again the plastic applicator works well, so does a squeegee. A roller works good too, but you'll waste a little in the roller, which will make you feel guilty, given its cost. A brush is the worst way to apply epoxy evenly, though sometimes, it's the only thing that works well, such as inside tight corners.

After you have 3 coats on, all epoxies will need a topcoat of some sort. If looking for a bright (natural) finish, varnish or polyurethane are the usual choices. 3 coats (minimum) on this stuff too, with more offering more UV protection, but also more "color".

For more information about coating wood with epoxy, try this link: > PARyachts: Epoxy Tips & Tricks <
For additional information about other stuff, like painting, try this link > PARyachts <