Bubbles in my spar finish...any ideas?

[jonw]

I must disagree with the poster that says it should be thinned to "make the biggest difference in getting the best finish".
It may work great for them, and for spraying, but thinning each coat is not recommended.
Rob

Here are some woodworking sites that talk about thinning varnish, which is where I got the idea from:
http://thewoodwhisperer.com/a-better-way-to-apply-spar-urethane/
http://www.woodweb.com/knowledge_base/Avoiding_Bubbles_with_Spar_Varnish.html

Worked well for me. YMMV

Thanks.

[48Rob]

Rob..

I have to disagree with waiting 4 days to be sure the varnish is dry. From all I have read and in my personal experience, 24 hours is all that is needed. You don't want the varnish to be completely hard so successive coats will bond better. As far as sanding if you use the right dry sand paper or wet sand with silicone carbide paper, the varnish won't lump up on the paper. If your doing 6-12 coats of spar varnish, waiting more than a day is not going to work.

Hi Larry,

I agree that trying to do multiple coats while waiting days between is impractical.

The point I was trying to make was that at certain temperatures and humidity levels, it can take several days for varnish to dry enough for the next coat.
(Common in spring and fall when trying to varnish in a garage or open area that isn't climate controlled).
Varnish that is dry enough won't clog sand paper, but if the coat you applied is still sticky, sanding just won't work

Rob

[48Rob]

Here are some woodworking sites that talk about thinning varnish, which is where I got the idea from:
http://thewoodwhisperer.com/a-better-wa ... -urethane/
http://www.woodweb.com/knowledge_base/A ... rnish.html

Worked well for me. YMMV

Thanks.

Hi Jon,

I probably should have kept my opinion to myself...but...

I wasn't/am not trying to put you or your ideas down.
If it works for you that's great!

Thinning finishes slightly to get the best workability for the conditions in which you are applying a finish is common, and not a bad thing.

The point I was disagreeing with was the blanket statement that you have to thin heavily if you want the best job, period.

25%-50% thinner is great for the first coat or two, but if you practice with full strength, you can get a really fantastic result withough dumping large amounts of thinner in the mix "just to make it super easy".

Rob

[Wolffarmer]

At a old motorcycle show when I was active in vintage motorcycles. One of the best paint jobs had been done with a brush. He had thinned the paint with Coleman fuel and brushed it on and left the pieces hanging out side for them to dry. It was an impressive job. I think he used an automobile lacquer. He said he feared he would have bugs like crazy but it was early spring and he got away with it.

You never know

Randy

[driftwood]

Sounds like lots of ways to skin this cat, and obviously takes a certain skill level with spar. I am using Cabot satin spar varnish. I Let it dry 48 hrs between in basement at 55 degrees before second coat. Still felt a bit sticky but did not gum up when sanded. Waited a week before applying next coat, still and it has sat 4 days, and still has some Has some stickiness to it. Inside a finished room at 65 degrees. Will the sticky feel ever go away?

Also, any special brush I should use? And it sat in paint thinner between coats...is that a problem?

[Billy K]

We used Cabot...it says on the can to 'not thin' ...

It may be the culprit...?? Ours was done in/out of the garage and in August. The heat and humidity were rough!

The tacky cloth and spritzing ideas are all good. We wound up with a couple of "milky " spots where either dust or not drying were likely the culprit.

Good luck, it does drive you nuts...

Oh, we used natural bristled brushes.

[doug hodder]

So is it a true "bubble" with a ring around the base or a dust nib? Big difference....Epoxy will get true bubbles, like up to the size of a dime on the first coat as the wood will "outgas" and create them if the wood is still warming. I go around and touch them with a finger to get them to pop and lay down.

Humidity and temperature I'd say are your biggest concerns. Others may disagree. On a varnish...later coats will melt into the previous one, but if it's rough...all you are going to get is a "not so rough" 2nd coat. I'd let it cure completely and sand. You can pile on a load of coats, but if it's got problems, IE dust, fisheyes etc.......Your top coat will only be as good as what's under it. Your final coat will only be as good as the work that went into the previous coats. Just my opinion. Doug

[driftwood]

Doug, from your description of bubbles, that is not what I have, so must be dust "nibs" (unfamiliar with that term but will add to my vocabulary). I can srape them off with my finger nail. So must in fact be dust I coated over... will try to do next coat in more dust free environ (but wife already complaining about the smell wafting up from the basement!).

Regarding the slight "sticky" feel to the table, even a week later, any thoughts on that? It is not bad, and does not leave fingerprints or anything, but just seems like it should not be that way.

[Juneaudave]

Well...I'll take a shot on the sticky issue. Just my opinions...

Varnish dries by going from liquid, to tacky or sticky, to dry gummy, to "dry to the touch", to hard. The hard stage can take quite a bit of time...some canoe and kayak builders wll varnish in the winter with the thought that the varnish will be harder and more scratch resistant in the spring.

The best time to apply the second coat of varnish is once it is dry to the touch and can be lightly sanded or hit with steel wool or a synthetic (scotch) sanding pad. You can also recoat if it is dry gummy if you wet sand...I wet sand with 220 grit to avoid loading up the sandpaper and get good results.

If it is sticky...and you re-varnish...you might compound the problem and find successive coats never (or take forever) to get hard. In the worst case scenario, the finish will start to wrinkle and you have a gooey mess.

In the case of a sticky table top...I would try giving it some more time and make sure it has good air circulation and warm temps. It really should be "dry to the touch". I don't think I would add more coats if it is sticky. Just my thoughts.

[Moho]

Since your problem seems to be dust and particles, here is my 2 cents.

My family and myself own several motorcycles. I have always done paintwork myself in my garage which isn't the best environment for painting. Here is what I do when I am going to do a paint job in my garage and I avoid having any dust particles in the paint.

I have 4 plastic tarps which reach from the ceiling to the floor. I screw the eyelets into the ceiling and place bricks around the edges of the tarps. While I am mounting them I take a damp towel and wipe the ceiling surface of dust. All of the vertical corners get clamped together using small spring clamps.

One tarp I cut a hole in and duct tape a hepa furnace filter to the outside. In the oposite end I have another hole cut in the tarp and filter and fan setup in it venting the "home-made" booth.

The booth setup takes about 30 minutes and is large enough for a car to fit in. I painted my own car once in it, worked great.

Before I take the parts in, I wet the walls and floor with a hose. Turn on the fan system and I let the residual water mist drop to the floor. I turn the fan off and then take the item to be painted inside and fire the fan back up.

The item to be painted then gets cleaned of oils and tack clothed of all dust.

This may be overkill but to me the extra 30 minutes of setup is well worth not having to resand and repaint hoping that small airborn particles don't fall into the paint or finish. This has worked for several finishes without any blemishes for me

[Senior Ninja]

What he said!

[Juneaudave]

I saw this on the BearMountain Boats web site and thought I would share. I have heard of this before but never tired it...


[quote]Dust nibs, Final Varnish Coat and the Brown Paper Bag Trick

by HighPlainsDrifter » Fri Jul 29, 2011 10:25 pm

My final step (after applying 6 coats of varnish and fighting the ever present dust nib) was to go over the hull with a brown paper bag. I had a few small nibs and this trick worked for me and does not dull the finish.

I found this "Brown Paper Bag Trick" at "The Finishing Store.com". Their paper bag trick is as follows:

There’s almost always a little dust that settles onto the last coat of finish before it dries, even when you spray fast-drying lacquer. With slow drying varnish, there’s always dust stuck to the finish.

As long as the dust isn’t excessive and as long as the particles aren’t large, you can make the surface feel smooth by rubbing with a brown paper bag. Give the finish a couple of days to cure so you don’t scratch it.

A smooth feel is critical when judging the quality of a finish. It’s natural for people to run their hand over a finish. Feeling dust nibs says, “This is not a great finish.â€

[driftwood]

Interesting.

Now that I understand more about dust and spar, one thing I think went wrong is that I foolishly used a scrap half inch strip of birch plywood to stir the spar, and probably introduced particles into the liquid itself. Live and learn.

And the next problem: I sanded off the nibs last night using a vibrating sander, and am afraid I was not consistent because in certain light there appears to be light and dark spots.. ..wondering if I cut down into the stain. So now I am afraid if I put next coat of spar these spots will show. Does that mean I have to go back down to bare wood and restain and respar....geez.

Between the other coats I sanded by hand- is that what I should do instead of using hand sander?

[Larry C]

Interesting.

Now that I understand more about dust and spar, one thing I think went wrong is that I foolishly used a scrap half inch strip of birch plywood to stir the spar, and probably introduced particles into the liquid itself. Live and learn.

And the next problem: I sanded off the nibs last night using a vibrating sander, and am afraid I was not consistent because in certain light there appears to be light and dark spots.. ..wondering if I cut down into the stain. So now I am afraid if I put next coat of spar these spots will show. Does that mean I have to go back down to bare wood and restain and respar....geez.

Between the other coats I sanded by hand- is that what I should do instead of using hand sander?

As I mentioned earlier, always strain your varnish through a fine paint strainer. It makes a difference. I only lightly hand sand between coats, especially the first one. If you have sanded through the stain, you do have a quandary. It might be better to sand everything off and start over.
If you just add another coat of varnish, it may look blotchy from sanding into the stain in some areas.



Larry C

[driftwood]

makes me ill to think about having to sand all the way down the base wood and start over again. My wife wiped the wood with a wet cloth and it looked fine, could dnot really see where I sanded unevenly. She thought that was an indicator of how it would look when recoated with spar coats, and that it would be ok to add more coats now. Anyone have any thoughts on that?

Guess I could just test and area, let it dry, and see....