Gloss stripes in my satin poly finish

[Cesar Vega]

I'm applying satin polyurethane on a desk with a brush, and I'm getting some gloss stripes on the larger top area when it had to be all dull finish.

They look, like if I took a can of gloss finish and did some random strokes ranging from 1" to 2" wide and 10" to 16" long, the surface is about 20" by 32". The legs does not appear to have this, neither the base of top, between each legs.

I applied one coat like 6-7 days ago, with a brush, the top had just 2 of these stripes. Initially I saw it was just taking longer to dry, but next day I realized it was already dried, and it dried gloss. I had no idea why that happened.

Last friday, I sanded all down with 220 grit, dry, cleaned up with mineral spirits and decided to apply with a rag, mixed 50/50.
Now, more bright strokes appeared on the top, covering like 30% of the the surface.

On Saturday, I prepared some mix and made some tests of apply this mix with a brush, and also with applicator to some 6" by 6" pieces from the same wood, that were previously finished with the same dye, sealer, etc. In this areas, I didn't get the bright stripes.
I was about to blame the 1qt bottle, which I opened 3 weeks ago (though perfectly closed again). But it seems it wasn't, was it?


Yesterday, Sunday, I applied the same mix, same method to a small piece, the keyboard tray, and I got gloss stripes in my satin wannabe finish.
I decided to blame the applicator. So, I took a brush and did another coat to the top, (prior sanding with 220, clean, etc) and for my surprise (or not), the same stripes appeared again. So, it's not the application method.... is it?

I somehow suspected that the flattener agents were "running out of flattening power", so to say. Or the poly was getting stale. But my tests on saturday proved to not be so.

I also somehow thought the the mix in my working bottle was acting weird because may be the flatteners were going to the bottom, but in that case, my finish would be all gloss in the beginning and all dull at the end, but that was not the case, the gloss strokes were all over the surface.

Actually, in the last try, I was stiring the mix after very often during the brushing, and it happened the same.

Any idea? really.... any idea, please.

Thanks in advance.

[Joe Chritz]

I also somehow thought the the mix in my working bottle was acting weird because may be the flatteners were going to the bottom, but in that case, my finish would be all gloss in the beginning and all dull at the end, but that was not the case, the gloss strokes were all over the surface.


That isn't always the case. The flatteners have to be suspended evenly in the mix to get consistent results. The only thing I can think of is that you are getting some mix without any flatener in it when applying.

Try to mix the main batch very very well. I use a power mixer and a cordless drill for almost everything since it seems I can never stir it well enough by hand.

Joe

[John Keeton]

In my experience, this usually happens by trying to "rework" the already applied finish. May or may not be the answer here.

[Cesar Vega]

In my experience, this usually happens by trying to "rework" the already applied finish. May or may not be the answer here.

Thanks for your answer.

Do you mean to rework the current finish being applied, still wet? or a previous dried coat, which might not be totally cured?

[Prashun Patel]

I bet it's inadequate mixing. You need to mix thoroughly before, and you need to keep mixing after every couple brush strokes.

[Lee Schierer]

+1 on the incomplete mixing. The flatteners don't stay suspended forever. The gloss streaks are from mix without flatteners. Most semi-gloss or satin finishes will appear clear until they are stirred because the flatteners settle to the bottom of the can.

[Howard Acheson]

As has been said, your problem is a classic case of the flatteners not being stirred into suspension. Always stir 100 strokes in one direction and then 100 strokes in the other direction keeping your stirrer in contact with the bottom of the can. Re-stir every 10-15 minutes as you use the finish.

You can even out the gloss by buying a new can of finish, stirring it thoroughly as above, scuff sanding the existing coat and applying a new coat. The final coat determines the final gloss.

Let me add that thinning the poly will cause the flatteners to fall out of suspension faster. More frequent stirring is necessary. It you are attempting a wipe-on finish where the poly has been heavily thinned you can have a problem. Any thinning approaching 50% will almost always create the sort of gray, clouding areas. Best to use a gloss finish for all but the final coat. For the final coat, use the satin but thin is only about 25% and stir frequently.