Varnish Bubbles

[Dan Cavins]

Hi, sorry if this has been beaten silly before but it's driving me nuts. I'm varnishing my hatchs. They are a solid on the sides and a piece of mohogany ply with a slight arc over the top. No matter what I do I get these mini bubbles. At first I thought it was grit but... I don't get this on the solid sides. I'm guessing it is tiny gaps in the ply sort of outgassing if you will. I've sanded down, tried Cetol, brush, foamie... just to get the same. Rather not rebuild them. Read about using a hair dryer to pop the things in the search section. Just throwing it out for ideas. Thanks, Dan.

[TimH]

You arent stirring or straining your vranish are you?

[mic]

Have you tried realy thinnig out the varnish heaps, and applying the first coat on super thin. You can thicken up the next few coates, hopfully without bubbles. :D

[Bob Smalser]

You can get bubbles from using improper brushes, too...make sure yours are for varnish.

[Wild Wassa]

Some thoughts, distil what fits your situation. I'm only adding a bit of detail.

Bubbles, could be outgasing as you have stated. Outgasing will occur, until the varnish has a firm set. This takes a lot longer than touch dry.

Standing the wood grain, this will happen on all occasions, I find. You may have roughened up the wood grain with too course a grit. This is dependent on the timber not so much on what one expects to be the grit needed. Try a finer grit.

The hairdryer, should be used on cold setting only, and with a gentle stream not on full blast, to reduce the bubbles that are formed as the varnish leaves the brush. With fine bubbles it sort of works, this technique suits the larger bubbles only.

Mic is spot-on when he wrote thin the medium. Then progressively reduce the solvent quantity, per layer, as you paint your way to the top. This technique is called thick over thin or fat over lean. The same result can be achieved by increasing the binder level, the oil, as you paint your way to the top. Adding binder increases the drying time.

Only consider each layer as a part of the total process. Sand well between coats, you will notice that things will improve at a greater rate than just one coat plus one coat. After 7-9 coats it should be as good as a poly, ;) . I don't think paint is worth 'a look at' until at least 4 coats are applied. Sand well between coats.

Foam brushes are crap, totally crap, and should be banned. If you use foam you are a cultural vandal. Unless you want to scumble a bottom layer of course, ... that's the quality. Finger painting gives a better finished film quality than using foam.

The quality of the brush is truely shocking and affecting, I totally agree with Bob. I would favour a fine mono, over a finest bristle, for varnish. Don't under estimate the brush.

Be uniform with your brush strokes, and stroke the medium back into the wet. Do not consciously lift the brush off the paint, just let it happen, as the stroke extends to your limit, ... otherwise you will get bubbles.

One other thing that can impact greatly is glue residue from dry sanding. Could I suggest using a quality paper like a Norton's Champaign. This caught me out two boats ago, when I changed papers.

Did we mention humidity? ... keep it low Brother. Especially if you use a gas heater which you switch off at night.

Finally, don't over stroke the varnish, as this will draw the binder to the top, give uneven gloss levels and also create, ... bubbles.

Warren.

[ 12-31-2003, 11:59 PM: Message edited by: Wild Wassa ]

[Steve Miller]

Try adding a bit of Penetrol to the varnish instead of thinner. It will increase the flow time of the varnisha and give the bubbles time to exit. Try just an ounce or two for a quart of varnish.