Official Luthiers Forum!

Hey all,

Need a hand figuring out how to get Rock Hard varnish brushed without flecks/bubbles..

Brush is clean, no chips or sand. Using a Purdy China bristle brush... while not "expensive", also not a Cheap $4.00 special.

I figured out that I was pulling little flecks off of the rim of the Rockhard can -- so I strained it and changed cans.
I am using Marbles to take up excess air space, and it doesn't appear to be polymerizing in the can.

I thinned it out some with Rockhard reducer, and that seems to have helped some, but I am still getting bubbles in the finish
that look like itty bitty gritty bits when it cures out.

I will post a pic when I get home today.... but this is driving me nuts. That rockhard finish is absolutely beautiful......
except for the little rough spots all over the place. I think if I could get it bubble free.... I would be done with the finish on this guitar.

Thanks

John

Halfway down this link there is a tutorial by Alan on rock hard may be of some use

_________________
Formerly JJH

I learn more from my mistakes than my successes

I used oil varnish on my first four guitars and learned a few things. Bubbles can be present in the varnish if stirred too hard, or they can be created during application. I would transfer the varnish to a clean glass jar and run it through a filter to remove any grit or dried chunks. The glass jar makes it easier to inspect for bubbles and provides a better seal than a paint can.

When brushing the varnish, make sure you only dip the brush into the varnish about halfway. You do not want the hilt of the brush to get saturated as that seems to churn up fine bubbles. Touch the brush tip to the inside of the glass jar to remove the excess and then apply the brush to the surface in a gentle stroke. Don't go over the same area more than once, except for a final leveling stroke with just the tip of the brush.

If you are still getting bubbles, you may want to look at getting a better brush. I have a boar bristle brush that has very soft and fine bristles, like mink fur.

John, I think you forgot to add the link.

_________________
Bill Hodge


One does not simply, own enough guitars!

I'm having trouble myself. I've read the tutorial too. While it's very helpful, I wish it included a trouble-shooting portion. I get bubbles too, but the mostly seem to clear as the varnish self-levels. My main problem is that the varnish seems to want to gather at the edges and form ridges there that need to be sanded down. Alan, anyone...help, please?

There was a good article maybe a couple of years ago in FWW mag. The guy used a foam brush. The main points other than the usual brushing techniques were to make a mark on the wood handle and only use the brush in one direction. The mark shows you which side of the brush to use or not to use. He also never wiped on the side of the can. I used his techniques with very good results. If you really want to know how to lay on varnish with a brush go to a boat yard and watch some of those guys who do wooden boats. Unbelievable how good they are. Hang out, buy beer and ask questions. Varnishing is a skill that takes time and practice to get good at. I might add I am not good at it.
Link

_________________
Cut to size.....Beat to fit.....Paint to match.

Forget the brush and try wiping. Use a good quality paper towel that is plain, no embossing. It sounds like you might need to thin it a little. Some like to add a couple of drops of kerosene to help level it out.

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

I don't think it's possible to get a 'guitar grade' finish using varnish without leveling and rubbing out. It's hard to obtain as shiny a surface as you get right off the brush, but shiny and not level is not good either.

The way to minimise the aount of leveling you will need to do is to keep the coats as thin as possible. There is just less room for problems in a thinner coat. Good surface prep, leveling reasonably well between, and a lot of care with the last two coats, will save a bunch of effort in the end. But I don't think you can eliminate that final step.

Anyway, here is what I am seeing... (Ignore the flash/shine from the lamp.... the finish doesn't have big white spots in it.) This is the back -- which is dry. Fingerprints are just from oily fingers and wipe off, not mushed into the wet finish

As you can see -- its not brush marks or puckers or drips -- those are easier to control. The extra thinner made a big difference with stray brush marks, but I think technique makes the bigger difference. "Laying" on a coat, then wiping the brush back over the entire thing 1 time only seems to take care of those problems... and a paper towel dampened with paint thinner seems to help wipe off drips nicely... no sticky gummy mess.

What is driving me crazy is these little pips or bubbles or dust spots or whatever. Once the current coat dries well enough, I will get out the Loupe to see what they are -- whether they are dust or bubbles or whatever should be obvious.



Maybe it is normal. I think it is aggravating.

Thanks

John

what I'm seeing almost looks like hardened pieces of varnish that were in your brush....

from dim memory (from like 35 years ago) I remember my father used to keep his varnish brushes supported by a hole in a screw on top for a glass jar filled with spirits....he didn't do the same for any brushes used for Aero-Gloss (a model airplane paint resistant to fuels), which makes me think the concept is specifically for varnishes...Aero-Gloss is very similar to lacquer if I remember correctly in that it completely burns into prior coats, whereas varnish does not, which indicates there is an issue with keeping your brush clean as old materials left in the brush will not melt, which could result in what you are experiencing...

I go through gallons and gallons of varnish for my canoe building, so you could say that I'm one of those guys in the boatyard...

I gave up on bristle brushes a long time ago, especially when doing small jobs. Its just not worth the effort and cost to risk ruing a good brush, or to clean and prepare it properly. I use a good grade foam brush, the 2" size, and I buy them by the box.

First, ensure that the surface is dust free! Think of dust as the enemy. Surface dust, peripheral dust, floor dust, air borne dust, reduce or eliminate all of it as best you can.

Second, use a fresh can, or filter some varnish into a fresh container. Never shake the can. If you have to stir, do it slowly to avoid mixing in air. Plastic beer cups are great for this, always clean and cheap.

Dip the foam brush into the varnish maybe 1/4", hold of a few seconds till the air in the foam is displaced. Apply to your work in a systemic fashion, let the varnish flow, don't overwork it or work it dry. Apply it as flat as possible.

Hang to dry and ensure that dust does not accumulate on the fresh finish.

Good luck!

_________________
Expectation is the source of all misery; comparison the thief of joy.
http://redrivercanoe.ca/

I feel like I can post an update to this....

Success in part...

What I found out:
A. Al's suggested Rockhard recipe brushes and levels great (25% rockhard reducer, 5-10% Acetone, 1-2 drops Kerosene)
B. There were many hairs and dust left in my finish that were sticking up after sanding/levelling. These were ruining the next coat.
C. Too much ambient dust and hair floating around.

Solution.....
#1 Wet sand, then "Shave" the hairs with a straight razor. Sounds kinda weird... but shaving your back works... Mmmm smooth....

#2 Need a good dustfree area for a coat. I took a cue from a guy who does auto body work on the side -- wet down the room real good..... That means the bathroom is perfect. I ran a hot shower for ~15 min to get it good and humid. Then spritzed water all over the bathroom to pull down the dust. Used the hair dryer to pre-warm the guitar so it wouldn't condense on the finish....

Results:
Beautiful.
No dust, no brush marks, no streaks or smears or runs.....

Thanks

John

Thanks Doug & John for the tips. I had a bad experience with Rockhard last year (due to my own ignorance) and ended up sanding a complete guitar back to bare wood and then refinishing with French polish. I'm game to try it again based upon the tips you have given. Perhaps this time I'll practice on a few pieces of scrap first before I commit to an instrument....

_________________
Peter