Wood – Polyurethane Curing – will blue tape or dropcloths damage it

What you will want to do is to get a polyurethane stripper with brush, a pair of rubber gloves, a scraping tool, fine grit sandpaper (200), a clean cloth, and a well ventilated room.

Start by applying the polyurethane stripper liberally and evenly over the wood using the brush. Let it stand for about 5 minutes or whatever the directions instruct you to do.

Using the scraping tool, gently scrape off the polyurethane in the direction of the wood grain, taking care to remove the scrapings as you go along using a clean cloth.

Once the scraping is completed, lightly sand the wood in the direction of the grains until the surface is smooth.

You're now ready to apply the finish of your choice, whether it be polyurethane, a stain, or paint. :)

I add 20% thinner to my polyurethane to promote even coats, prevent bubbles(they pop more easily on their own when thin), and speed up drying time. You can alternatively use lacquer thinner and this will dry even more quickly due to it's lower flash point -- but in high temperatures it might dry too quickly.

As far as methodology for mixing, I have a "mixing can" that I bought at a big box store -- they sell empty paint cans -- and I add 20% thinner and the rest poly. I use a plastic can attachment that acts as a spout to prevent poly from filling the lid gap when pouring. Stir with a stir stick. I don't get too many bubbles but I don't worry about them either because they pop on their own. Pour onto the side of the can to prevent bubbles (think of pouring beer from a bottle into a glass).