"Dry" Spots in Finish?

[Russ Filtz]

It seems like I've been getting "dry" spots in several finishes lately. Kind of like the finish got absorbed or pooled around it. Re-addding a coat doesn't seem to help much. Not sure what I'm doing wrong. I normally use pure tung/mineral spirits with a poly top coat. Here's my typical finish routine:

1- Sand to at least 220 to 320,
2 - Wipe down "wet" with MS,
3 - Rub in pure tung/MS, wipe off excess after awhile (start with 1/2 tung or less), let dry a day or more
4 - De-nub with sand paper or scotch pad, wipe down with MS
5 - Repeat 3 & 4 until it looks done, (maybe 3-5 coats without "building")
6 - After a few coats I start adding a little poly to the mix,
7 - Give a finish coat or two with thinned poly only, de-nubbing between.

Any thoughts? Can the tung get "waxy"? Should I stop with it after a few coats and then poly? I've noticed this problem a lot with the Cherry I've been using lately, but I think I had it happen on Walnut as well.

[Lee Schierer]

It sounds like the surface is contaminated with something. If you use an aftershave, that could be the culprit. Many aftershaves contain silicone which will stay on your hands and then get on the wood when you handle it. Also if you used automotive wax on any of your cast iron, most automotive waxes contain silicone. Silicone will create "fish eyes" in your finishes where the finish won't absorb. The only cure is to sand the wood down until you get rid of the contamination.

[Russ Filtz]

Can't figure what that would be. No aftershave etc. Use only Slip-it on the TS surface. Use clean shop paper towels (blue kind) to clean dust with MS. The spots are irregular and can be larger areas maybe a square inch or more, not fish eyes.

[Chris Padilla]

Some areas will absorb your finish better or more than others but it sure sounds like surface contamination. What kind of wood are we talking about here?

[Russ Filtz]

Cherry, but I think some walnut had some problems too, but not as bad.

[Tim Sproul]

If, by "dry" you mean more of a satin finish versus a "wet" gloss look....it is almost for certain a difference in the thickness of the final poly topcoat. Gloss finishes need to build up to a certain thickness prior to becoming "glossy." If too thin, a gloss finish appears satin or "dry."

YMMV

How are you applying the last coat or two of thinned poly and how much are you thinning? If wiping on a 50/50 thinned coat, it is too thin. 5-6 coats of that....or thin 10 - 20% only and brush on or spray. Personally, I'd avoid the poly altogether :).

[Russ Filtz]

It's pretty thin, probably 50/50 as I don't want a thick build, just a little more sheen and protection. I put on maybe 2-4 coats of the 50/50. The dry spot aren't just "less" shiny, they look like nothing was put on after the tung. I'm guessing it's some kind of waxy contamination. Just can't figure out how.

Could it be my Klingspor pre-cut hook/loop sandpaper for the PC 1/4 sheet palm sander? This sand paper has that white look, which I think means it's stearated to minimize loading. Could that be the waxy problem? I'd hate to have to give up the kilngspor.

[Chris Padilla]

Stearated sandpaper could be the culprit, Russ! I think you found it but a little experimentation is called for now.

[Tim Sproul]

I'm telling you from experience.....when you put gloss finishes on in very thin coats, it starts just like you're describing. Once a thick enough coat is on, the entire surface will take on the wet, gloss appearance. I typically don't build the finish up to such a thick layer than you could easily see the thickness with your naked eye....so you shouldn't be able to "see" the thickness of the poly. Caveat - I hate poly and avoid it like the plague....this is my experience with other gloss finishes.

IF it were the sandpaper, it seems extremely unlikely that there would be spots of dry appearance....you do sand the entire surface, no? At best, I could see a gradation occuring with the worst of it starting where you started to sand.....and you're supposed to be wiping down the surface post sanding to remove any dust.

[Russ Filtz]

Note I do wipe down with MS after sanding. Maybe the problem is where I start with a fresh sheet, before the stearate coat wears down?

[Tim Sproul]

My money is still on too thin of a film.

If the stearate coating were this much of an issue, you'd think pro finishers would swear everyone off of using such abrasives during finishing....yet most highly recommend the use of stearate coated abrasives when knocking down coats of film finish.

[Sam Blasco]

I use stearate all the time. love its no clog abilities and have never had a problem with finishing. With a 50/50 solution, you'll need 6 thin coats before even thinking about abrading to your final sheen. But it sounds like you are mixing alot of different finishes. Tung oil is almost never pure, no matter what the label says. If you wanted to end up with poly, start with thinned for sealer coat and continue with stronger solutions for all subsequent coats until it is time to wax (if you go there). The wood definitely is contaminated with something from somewhere. I doubt it is the sandpaper, but stranger things have happened. I knew a shop that was next door to a car detailing place and they had fits in their finishing process if the wind was blowing the wrong way that day.

[Russ Filtz]

Don't you need to scuff up any poly coat to get it to stick, even a thinned one? I've been scuffing pretty good between all coats. Not to the point of sanding it off, but pretty even scratching all around. Do you apply the 6 coats before even hitting it with anything, or maybe just a light de-nub?

I'm using the pure Tung from Rockler, so it's probably as pure as you can get along with odorless MS, Ace brand. The Poly, I also got from Rockler, but forget the brand.

[Sam Blasco]

sand between coats. 320 grit after the sealer coat, and 400 between the subsequent coats. If I'm looking for high gloss sheen in the final i will use 600 on the last two coats. don't be afraid to sand after the 1st sealer coat. for the others just a de-nibbing should be fine