What is a good product to use to cover removed/missing solder mask on PCB's?

[hydrogen maser]

Looking for opinions on what product to use, I have had several cases recently where the solder mask has been removed from a board, due to capacitor or battery corrosion or other reasons so after you clean all the up and neutralize the board and you have bare copper traces or other components that you wish to be protected what do you like to use? I have heard various things, everything from clear nail varnish to just lacquer. Any commercial products that anyone thinks are particularly good? Or just something cheap intended for other uses? 

[KL27x]

I have used laquer in a spray can. But evermore I just use MG Chemicals conformal coating in a little bottle. It goes on with a brush and it dries fast. You can shoot it with a heat gun if you want to speed it up; a small spot can be heat-dried in like a minute. I happen to use the silicone variant.

Even on a 4-5 square inch toner transfer pcb, I find the brush to be great. No matter how thick and sloppy you apply it, it seems to look pretty good when it's done, and one coat will generally be all I need. I am sure there is something on the hardware store shelf that will work just as good at a 10th the cost, but the MG stuff works and the one bottle has lasted me for several years.

[hydrogen maser]

It is a little pricey at $19 for 55ml but I bet I could go years with just the 55ml. It says you can solder right through it and it is good to 200C, so sound oks to me. Ordering it, thanks for the suggestion!

[tautech]

As KL27x said PCB lacquer in an aerosol is the simple solution, cheap, solder through and lasts for years

[hydrogen maser]

I don't like the idea of overspray, my lab is not huge and the fewer contaminates the better, but I am sure spray lacquer would work.

[elecman14]

At work I typically CHEMTRONICS CW3300G conformal coat pens for solder mask touch-up. At home I typically use clear nail polish. Not 100% sure that I would use the nail polish in a production environment without doing some serious electromigration studies but it works well if you want to prevent oxidation on the cheap.

[wraper]

There is UV curable liquid solder mask on ebay. http://www.ebay.com/itm/331823958823

[KL27x]

As KL27x said PCB lacquer in an aerosol is the simple solution, cheap, solder through and lasts for years

Actually, I decidedly prefer the MG in the brush bottle, and I'm a cheap bastard.

My experience with (a random) acrylic lacquer spray from the hardware store is that it's a pain to go outside to apply it. If you spray it on too thick, it runs around and doesn't look good. If you spray it too thin, it doesn't protect/last. And it takes a relatively long time to dry. And a can is only 8 bucks, but it doesn't actually last very long, particularly if you want to keep the nozzle clean and end each use by blowing it out, upside down. I think my can lasted about 4 years. I have been using a 55mL bottle of MG for a year or two, and it's over 90% full, still.

The best part is MG silicone 422B or w/e can be applied thick and still dries crazy fast and smooth and can even stand heat-drying (actually recommended for strongest finish) without bubbling.