Newbeee - Woodworking Talk

c_james_10 · 12-01-2008, 02:05 PM

Hi and thanks for taking my question. Can anyone tell me what happens to my polyurethane to make the finish go from semi-gloss to dull from the same can? I have been putting the minwax on some new Oak trim and I have noticed that as I get to the end of the can the final boards I do are dull not glossy like the rest? Is the poly seperating? Evaporating, contaminated ? What?? Thanks for your reply and P.S. What are some solutions to the problem that i described? Thanks!

cabinetman · 12-01-2008, 03:04 PM

Stir, stir, stir, whenever you use, and don't shake. If you are using out of the same can with long open times, you may have some evaporation, which may affect the glossing agents, by the time you get to the end of the can.

bradnailer · 12-01-2008, 03:29 PM

Probably not stirred enough. If you have the can open for a while, pour some out into another container and seal the original can.

Streamwinner · 12-01-2008, 05:09 PM

And be sure you're stirring from the bottom of the can to the top (not just in circles).

mainzy · 12-01-2008, 05:09 PM

Hey Newbee;

Most finish has some sort of dulling agent in them that usually sinks to the bottom of the can. high gloss would have very little and dull quite a bit more.
What the dulling agent does is cause a chemical reaction so that the outer surface of your finish wrinkles and forms lots of microscopic bumps. The bumps cause reflected light to be scatterd so that it looks dull.
If you took a can of dull finish and poured some out without stiring it what you poured out would be more like a high gloss. And what was left in the can would be extra dull once stirred.
It is only the outer layer affected.so if sprayed dull onto a surface and then did your next coat with satin it would leave a satin sheen.

Your last coat is what determines your sheen. I'm sure you could coat the dull stuff with a new can of finish and get your desired sheen.

God Bless;Mainzy

c_james_10 · 12-02-2008, 08:18 AM

I see stirring must be the key ingredient that I failed on. I did recoat the dull boards and they came out fine.!

mainzy · 12-03-2008, 05:58 PM

Hey james;

There is a great book called understanding wood finishing written by Bob Flexner. It is a great investment and an awesome reference book. I got one on amazon for about 20 bucks.

He explains finishing in a detailed but understandable way.

God Bless;Mainzy