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Polyurethane or Varnish?

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Forum topic by Steve Kreins posted 01-23-2014 11:44 PM 1152 views 0 times favorited 5 replies Add to Favorites Watch
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Steve Kreins

358 posts in 1091 days


01-23-2014 11:44 PM

Topic tags/keywords: polyurethane varnish food safe question

Marc on Wood Whisperer uses a mixture 50% mineral spirits with his food safe salad bowl varnish.to finish his end grain cutting boards.

Q 1. What is the difference between polyurethane and varnish? Or is there a difference?

Q 2. How do I know if it’s food safe?

-- I thank God for everything, especially all of you!


5 replies so far

View Gene Howe's profile

Gene Howe

8239 posts in 2889 days


#1 posted 01-23-2014 11:56 PM

Poly is virtually plastic. Varnish is a mixture of oils and a thinner.
Both are food safe once FULLY cured.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

View alohafromberkeley's profile

alohafromberkeley

257 posts in 1865 days


#2 posted 01-24-2014 12:22 AM

One thing to keep in mind- varnish and poly harden on the surface of the wood. I don’t relish the idea of eating plastic in my salad. They both will chip if you use ‘em on cutting boards….maybe it’ll add that extra flavor that will make people ask you- “What’s the secret ingredient, Steve?”(LOL) I think Marc is basically making a thin wiping varnish. I prefer to use mineral oil or coconut oil as a wipe-on for my cutting boards. Both are food safe and don’t go rancid…..........Wes

-- "After a year of doing general farmwork, it was quite clear to me that chickens and I were not compatible"-George Nakashima

View OggieOglethorpe's profile

OggieOglethorpe

1211 posts in 1571 days


#3 posted 01-24-2014 12:41 AM

“Polyurethane” can be a varnish… ...or it can be lacquer, or water-base…

“Varnish” usually simply means it’s some sort of cross-linking oil-based clear film finish. Cross-linking means that it chemically cures, vs. drying due to solvent evaporation. The big cue is what happens if you wipe the dry film with it’s own solvent. Varnishes wiped with mineral spirits suffer no damage. Shellac and nitrocellulose lacquer, which are both evaporative finishes, will dissolve over and over again when wiped with the correct thinner.

The words polyurethane or urethane refer to the resin suspended in the clear varnish binder. There are also phenolic varnishes, like Pratt and Lambert 38, that use a phenolic resin in place of urethane. Other varnishes may include natural oils that polymerize as they combine with air, solidifying the resins.

Most varnishes are non-toxic when fully cured, but those claimed as “food grade” have undergone more testing, and have a legal department to answer questions. Think of it this way… Writing “food grade” on the can means a certain small percentage of sales will be added for food contact uses, but the manufacturer may be open to new legal actions based on the label. Not writing “food grade” on a label means you aren’t guaranteeing anything, even if the product is known to you to be non-toxic when cured.

View Fred Hargis's profile

Fred Hargis

3928 posts in 1954 days


#4 posted 01-24-2014 03:09 PM

Just a slight difference with what Barry said, P&L 38 isn’t a phenolic varnish, it’s actually an alkyd resin/soya oil formula. Waterlox original is a phenolic varnish, the only one I know of.

To make varnish you cook resins with a drying oil. The reins are usually a urethane, or an alkyd, or a phenolic; though there are others. The drying oil is typically linseed oil, but can be soya oil, or tung oil; again there are others less common. There are numerous other finishes labeled “polyurethane”, the manufacturers believe that magic word will sell more stuff, even if it’s wrong. Water borne finishes, for example, are mostly an acrylic resin coalescing finish, yet add a very small amount of urethane and put that on the label, viola! you have a winner (at least in theri deceitful minds). As a rule, if someones refer to “poly”, I’m assuming they are referencing the oil based varnish…something that is getting more and more less likely.

-- Our village hasn't lost it's idiot, he was elected to congress.

View Clint Searl's profile

Clint Searl

1533 posts in 1822 days


#5 posted 01-24-2014 05:48 PM

1. No difference; they’re meaningless marketing terms for a film finish.
2. Any commercially available film finish is “food-safe” once cured. The same goes for BLO and tung oil.

-- Clint Searl....Ya can no more do what ya don't know how than ya can git back from where ya ain't been

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