PDA

View Full Version : White spots after varnishing



Ron Stohr
06-03-2014, 11:35 PM
Does anyone know what would cause white spots on walnut after it has been varnished? I put 2 coats of varnish on workbench and the underside of the tool tray developed whites spots after the second coat. I used SW quick dry varnish as it is what I have on hand right now. I had another spot that showed up on the top of the leg vise chop so I know it is easy to get rid of the spots. Just curious what may have caused them?

There is another white spot to the right but I know how that one happened. paper towel too close to the work. The other picture is the finished project. Time for some shop cleanup and more organizing. :)
290564290563

Jim Rimmer
06-04-2014, 1:54 PM
Just wanted to leave a reply to let you know folks are looking but are apprently stumped. Hopefully the finishing gurus will see this post soon.
Nice looking work table, though.

Rich Engelhardt
06-07-2014, 7:03 AM
It looks like either unmixed flatting agent or moisture somehow got trapped under the varnish.

I highly doubt it's either of those though since neither would be easy to remove.

Having had both happen to me - the only way I got rid of the white spots was to sand them out. & sand & sand & sand...

Ethan Melad
06-07-2014, 7:47 AM
I'm no guru, but i'd agree that the first coat was not 100% dry before the second coat went on or some other moisture was trapped. I've had this issue more than once with Target's EM2000 varnish - however for some reason the fogging only appeared at a glue line. I sanded, waited, recoated, sanded, waited, etc until the fog disappeared. In one case, it went away almost entirely just by letting the piece dry longer.

steven taggart
06-20-2014, 5:10 PM
I suggest putting the piece in the sun, and seeing if the additional cure will lessen or remove the spot. I also concur with other posters that it looks like water trapped under the finish.

David Macfee
06-21-2014, 2:23 PM
I'm unclear you mention it was easy to get rid of the spots but I didn't catch how you did it. Also you said you had the varnish "on hand" so I wonder if it is a partial can that has been on the shelf a few years. Using varnish left overs is always a risk. Its usually best to go with fresh material. If it is a dull sheen varnish you need to stir it gently and for a long time to make sure the flatting agent in the can is totally dispersed. Then I would run it through a fine strainer and that would catch any bits of flatting agent that didn't get into solution. Never-ever use varnish that has begun to gel or skinned over.

Howard Acheson
06-22-2014, 11:39 AM
When it's all said and done, a varnish is a poor choice for coating a work bench. Here is an article I wrote a few years ago that may be helpful.

A film finish (lacquer, shellac, varnish, poly varnish) is not the way to finish a workbench top. A workbench is going to get dinged and film finishes will crack or craze or be otherwise damaged. Once a film finish is penetrated, it looses its effectiveness and adjacent areas begin to fail. No treatment is going to make a soft wood benchtop harder. I much favor an "in the wood finish". Here are two that lots of folks find effective.

First, is an boiled linseed oil and wax finish. Sand the surface to 180 grit. Mix paraffin or bees wax into heated boiled linseed oil. USE A DOUBLE BOILER TO HEAT THE OIL. The ratio is not critical but about 5-6 parts of boiled linseed oil in a double boiler with one part paraffin or beeswax shaved in. Take it off the stove. Thin this mixture about 50/50 with mineral spirits to make a heavy cream like liquid. Apply this mixture to the benchtop liberally and allow to set overnight. Do it again the next day and again the following day if the top continues to absorb it. After a final overnight, lightly scrape off any excess wax and buff. This finish will minimize the absorbsion of any water and you can use a damp rag to wipe up any glue excess. Dried glue will pop right off the surface. Renewal or repair is easy. Just use a scraper to remove and hardened stuff, wipe down with mineral spirits using a 3/0 steel wool pad (a non-woven green or gray abrasive pad is better), wipe off the gunk and apply another coat of boiled linseed oil/wax mixture.

My personal preference is for an oil/varnish mixture treatment. Either use Minwax Tung Oil Finish, Minwax Antique oil or a homebrew of equal parts of boiled linseed oil, your favorite varnish or poly varnish and mineral spirits. Sand the benchtop up to 180 grit. Apply the mixture heavily and keep it wet for 15-30 minutes. Wipe off any excess completely. Let it dry overnight and the next day, apply another coat using a gray non-woven abrasive pad. Let it set and then wipe off any excess. Let this dry 48-72 hours. To prevent glue from sticking apply a coat of furniture paste wax and you're done. This treatment is somewhat more protective than the wax and mineral oil as the varnish component adds some protection from not only water both some other chemicals also. The waxing makes the surface a little more impervious to water so you can wipe up any liquid adhesive. It also allows hardened adhesive to be scraped off. Repair and renewal is easy. Just go throught the same scraping, wiping down with mineral spirits and reapplication of the BLO/varnish/mineral spirits mixture and an application of paste wax.

Both of the above treatments are quite protective but are easy to maintain and renew. They do not fail when the surface takes a ding.