Polyurethane is confusing me. 😉
I'm finishing a table top with polyurethane. I've sanded down the original finish to bare wood down to 220 grit paper.
I vacuumed and wiped it all down, then did a final wipe with a rag and some mineral spirits. After drying, I then put on the first coat.
It's been about 2 hours, and this is where I'm stumped.
The can says to re-apply coats after 2 hours, but doesn't say to sand. It does say that if you wait 24 hours, then you should sand.
Researching on the internet, the common advice appears to be sand between every coat.
So, the questions:
- should one sand between every single coat?
- how long should one wait before sanding?
My understanding of the can label is that multiple coats are fine after 2 hours WITHOUT sanding. They're also fine after 24 hours WITH sanding. Is that correct? Any thoughts on which method is better?
FWIW, this is a satin finish, as I'm purposefully trying to knock down any sheen to give it the barest-of-wood look I can, so super-smooth glossy isn't a priority on this project.
UPDATE: BONUS QUESTION!
What's everyone's opinion on 'with' vs. 'cross' grain bush application? Always go with the grain? Alternate between coats?
Best Answer
When you apply multiple coats of urethane, any dust or small flaws will be amplified with each new coat. If you want the smoothest finish possible, then wait until it is dry, very lightly sand with very fine paper (220 or finer) to remove any dust bumps, wipe it clean with a slightly damp cloth or tact rag, let it dry or buff it dry with a dry cloth, then apply the next coat. There is no reason to use mineral spirits, actually I would advise you not to use mineral spirits.
I see no advantage to applying successive coats with, then against the grain. As long as you apply an even coat with a good quality brush or foam brush and don't overwork it, any brush marks should disappear. The finished product should be so smooth that you couldn't tell which way you brushed the urethane on. Also, if you are using a satin finish urethane, be sure to mix it well, stirred, not shaken. The dulling agents tend to fall to the bottom, so it is important to mix it well. No matter how many coats you apply, it should not become "glossy".