10

I'm having trouble with polyurethane (Helmsman semi-gloss) drying much glossier than it should - like an extra-gloss instead of a semi-gloss. I'm using it on stained wood moulding, and when I did the majority of it in the winter, I got the expected semi-gloss sheen. But now It's coming out extremely glossy and does not match the rest (which is already installed). It's the exact same product (although a new can) and I even tried buying another can in case the can was defective, but I'm getting the same result. The only thing that seems to be different is the weather and possibly the conditions (heat) in which the cans were stored. Can exposure to heat in the can or while drying affect the sheen of polyurethane? Is there anything I can do to compensate?

Some pics:

enter image description here enter image description here

R.. GitHub STOP HELPING ICE
  • 1,101
  • 2
  • 12
  • 23

4 Answers4

6

The gloss in clear finishes is reduced by flatting agents which are suspended in the clear finish. Flatting agents are tiny particles that reflect some of the light back, thereby reducing the sheen of the finish. If they settle out or are not mixed well, then the finish will be more glossy, so it's possible you did not mix the finish as well the second time.

Finishers often start with full gloss for the first coats, and then finish with the lower-gloss levels desired, so you may be able to fix the problem simply by applying properly mixed finish over the existing finish.

Another way to reduce the gloss level is to essentially scuffing the surface with fine scratches. This is sometimes called 'rubbing out' the finish. You can do it using various powdered abrasives, fine sandpaper, or scotch-brite pads and sanding with the grain of the wood. The advantage to the mechanical scuffing is that it gives you complete control over the degree you reduce the gloss. However this treatment can be much more time consuming and this would be more typical for fine furniture rather than for trim.

You can read more on adjusting sheen of a finish in this article written by Bob Flexner, a very well known wood finishing expert.

JayL
  • 3,408
  • 1
  • 20
  • 21
5

Can exposure to heat in the can or while drying affect the sheen of polyurethane?

No.

Is there anything I can do to compensate?

Yes...

As a hardwood flooring installer for 4 years, I often recommended against any kind of gloss finish (It looks great at first, then it looks horrible for awhile, then it looks okay - but isn't glossy anymore). I often recommended a satin finish, which would avoid your problem... The reason you are likely getting different results are:

  • Different finish batch numbers
  • Inconsistent can mixing
  • Delayed application times

The 'glossy' look is actually an additive to the finish, and it settles in the can, and it can settle in your pail while trying to apply the finish if you are not right on top of keeping it mixed. Options to correct your issue:

  1. You can go to your local hardware store, get a 180-220 grit sanding screen.
  2. Lightly buff and sand your trim.
  3. Apply another coat of finish, making sure your can is large enough to do the whole project (or cans have same batch number).
  4. Make sure to get the finish well mixed, and keep it mixed as you go...
ShoeMaker
  • 633
  • 4
  • 13
2

I have had the same result from improper mixing and weather combination. I have been able to "knock it down" by first applying lemon oil to the piece and then using a fine sanding sponge pad or fine scotchbrite pad and working all of the way down the piece in 1 - 2 foot increments. You don't need to "grind" the finish just apply enough pressure and make a few up and down swipes with the grain. The oil will lubricate the piece and melt the residue you are making. Then just wipe off the piece afterwards. The sanding sponge works good for me because it fits into all of the nooks and crannies of the piece. You can always go back over some shiny spots in the piece afterwards if needed.

Mike A.
  • 21
  • 1
2

Using the same product produced the same result shown - high gloss finish. After letting initial coat set up for 3 hrs, stirring the can well before and during application resulted in the desired semi-gloss finish. Just need to stir the heck out of it.

Denton Fender
  • 21
  • 1