Sanding Varnish: is this a bad sign ?

[Patrick McCarthy]

I am doing 3 exterior doors with Epifanes, laying flat on saw horses. About 4 coats in, and have let the initial coats dry several days/week each before recoating. On one of the doors, while sanding with 220 or 280, rather than getting the usual dust I started to get little rollies like from a white eraser. The finish feels dry and the sanded surface feels okay, but I am wondering if this means I have adhesion problems between the top coat being sanded and the next deeper coat.

Please tell me I am okay and just overthinking things . . . .

Also, where do all the dust nibs come from? Yesterday i vacuumed the sanding dust, then wiped them with paint thinner, and i closed my shop doors and windows. This morning I used a hand squirter water bottle to mist the floor (my neighbor has a new definition for crazy), moved slowly so as not to stir up any lingering dust on the floor, dry wiped the doors again, applied the varnish, tipped it off with the brush vertical and slow . . . . . . . . and by the time i finished the third door I noticed the nibs had come to town.

[robert raess]

As to the dust nibs, it's possible that these are bubbles from overworking the finish.During a long open time they will almost work out of the finish and can look like a nib.

[robert raess]

Question: I am experiencing air bubbles drying in my varnish.
Answer: We will bet that what you are experiencing is dust. Dust and/or lint particles that dry in the varnish can form tiny craters that can certainly look like air bubbles. It is very rare for air to dry in a coat of varnish. Let's try to figure out where this dust might be coming from. If the coat looks great upon completion but several hours’ later looks as if someone has taken a saltshaker to your boat, then the dust problem is most likely airborne. If the dust occurs right away, brushes and the initial cleanliness of the surface are more likely to be the culprits. Here are a few, sometimes overlooked, sources of dust; • Although your brush may appear clean, try flicking the bristles in front of a bright lamp. You will be amazed at what comes out of it. Turn on the TV and be patient. It can take an hour. Do not assume that a new brush is clean, new brushes are particularly dusty. • Be aware of what is happening overhead, it may be that your basement ceiling is shedding dust each time someone crosses the room upstairs. • Fluorescent lights will act as a dust magnet until the moment you turn them off. • Check your clothing. Wear dampened Tyvek coveralls. • Mask or temporarily seal all screw holes. Your brush will certainly pull out whatever is hiding in those holes. We know a painter that varnishes in the nude listening to Vivaldi. Hey, whatever works.

[Howard Acheson]

What you are seeing is called "corning". The corn is finish dust and soft, still sticky finish. Hopefully you are not using a power sander. Between coat sanding should be done by hand sanding in the direction of the grain. It happens when the finish is not cured enough before you begin sanding. Let the finish dry a couple of more days. When applying many coats of an oil based finish, subsequent coat interfere with the oxygen getting to the lower coats of varnish. They cure much more slowly.

Just moving around in your finishing area can stir up dust. In addition, dust falls off the finisher's clothing. It's best to change into freshly laundered clothes.

BTW, as I recall from my boat painting days, Epifanes requires 6-8 coats to build up a thick enough film for the UV protection. You really only need to do a careful sanding just before the final coat. You're going to sand then so sanding nibs and such are only an issue just before the final coat. Also, the number one benefit to an air cleaner is to clean the air after you leave the finishing area. That way it will remove most of the dust within a couple of hours. Wiping with a mineral spirits lightly dampened rag is best performed just before you apply the finish. Otherwise and dust on the surface will rise into the air if wiped with a dry rag.

[Patrick McCarthy]

Howie, thank you. I will be extra careful on the clean clothes too.

Sanding is by hand, Klingspor paper wrapped around a hard maple block, and with the grain, careful at the edges. Initially i thought four coats all together, but then re-read the instructions. I may never get this finished (time wise).

Instructions on Epifanes can recommends three thinned coats (50-50, 75-25, and then 85-15) and then FOUR MORE coats . . . .or 6 more if in direct sun, which they won't be.

[Prashun Patel]

Dry sanding a film finish can lead to corning. Wetsanding with ms or even water can alleviate that.

An easy way to avoid dust in the final coat is to sand with 600 and wipe on 2-3 more coats thinned just to fix the sheen. Done this way the thin finish will dry quickly enough to not allow much dust to settle. You shld still take precautions to be reasonably dust free, but no reason to go Bubble Boy clean.

[Scott Holmes]

Are you using satin?

[Rich Engelhardt]

Are you using satin?

That was my first thought too- satin or semi gloss w/"lumps" of flatting agent.
The OP didn't mention anything about streaks in the finish or uneven sheen though.

Give me six hours to chop down a tree and I will spend the first four sharpening the axe - Abraham Lincoln

To paraphrase somewhat on that sig line...

Give me two hours to varnish a door and I'll spend the first hour cleaning the brush....

[Kent A Bathurst]

Howie, thank you. I will be extra careful on the clean clothes too.

Sanding is by hand, Klingspor paper wrapped around a hard maple block, and with the grain, careful at the edges. Initially i thought four coats all together, but then re-read the instructions. I may never get this finished (time wise).

Instructions on Epifanes can recommends three thinned coats (50-50, 75-25, and then 85-15) and then FOUR MORE coats . . . .or 6 more if in direct sun, which they won't be.

Used Epifanes on a pair of WRC entrance gates that get direct sun, but for only perhaps half the day.

It seemed like it would never end, and that was after coat three. After coat seven, and 2-1/2 years, the gates look as they did when they left the shop. My conclusion - you get what you "pay" for.

FWIW - Coat seven was satin, on top of six gloss. I sanded very lightly after each coat (1-6), by hand - no sanding block, with Norton 3X P320.

[Patrick McCarthy]

Scott, no I am not. It is the gloss varnish.

No streaking and finish looks even . . exept for the dust nibs, which are both random and rather consistent throughout the 3 doors. I mention this re the new brush theory; I used a new Omega brush on htis coats but flicked it several times before using. I ASSUME that if it was dust in the brush i would see more on door one, less on door 2 and even less on door 3 . . . or exactly the reverse, but i can't say one is much better or worse than the other 2.

Since I have them horizontal on sawhorses, I am viewing them with a raking light when i enter the shop and that certainly accentuates perception . . . . but i can feel the little buggers too.

I love the clear depth and gloss that is developing but am frustrated that "perfection" is so darn elusive despite my attempts to prevent any surface contaminants. As i said, my neighbor thinks i am nuts for misting the floor and moving slowly . . . . and probably for a lot of other things he is too polite to mention.

Prashun, silly question but serious on my part, Can i wipe on varnish after brushing the other coats? I assumed the wipe on was more for the "in the wood" look whereas this is the more traditional varnish film finish. If i do wipe on the final topcoat, what dilution do you recommend so it , effectively, flashes off? 50-50 thinner/varnish??

Gentlemen, please know that i appreciate you thoughts and help, Patrick

[Prashun Patel]

You can wipe on varnish over brushed layers. The only diff is that to wipe you have to thin.
In the wood finishes are a whole nuther conversation. 50 50 is fine.

[Howard Acheson]

>>>> Can i wipe on varnish after brushing the other coats?

Yes.....

[Patrick McCarthy]

Gentlemen, as always, thank you kindly. Patrick