Varnish problems

[ruby@magpage.com]

Finishing my Nick Lucas Special. I am using fresh Pratt and Lambert #38 - first time with varnish. I had no problems with flow out or with the length of time for working it. I did 4 coats with a real light leveling after 2 and then an 80% leveling after 4. Now I am doing the serious leveling after 4 more coats. I have been varnishing for about 5 weeks and it has been a full week since the last coat.

I noticed this on the leveling after 4 coats and it is showing up again - the scratch pattern looks just right, but a topographical map of the layers of varnish has shown up. It moves around as I sand. I started with 320, then 400, then 600 - the shot below is as good as I can photograph it. It appears to be the layers that are giving me a variable sheen.

I did a small section through 8000 grit micromesh and noticed two things - first the pattern does not go away, and second, the shine is no where near what shellac was at the same stage. Any ideas?

[B. Howard]

What you are seeing are witness lines. They are the lines formed by the different layers of coating. While I have never used this particular product and it says "varnish" on the can, by the manufactures description it sounds like s basic poly urethane type finish. They describe it as an alkyd. Alkyd's don't melt together like lacquer or shellac to form one continuous layer of coating, instead they build in layers. That is what you are seeing. This will continue to be a problem if you try to level sand and buff at the end. The best thing to do may be to level sand and then apply a flow coat for the final coat and then lightly buff without sanding. I would try cutting the varnish with 20% thinner to get good flow out on that last coat.

[ruby@magpage.com]

Brian
thanks for that. P+L make a couple of varnishes - their polyurinate is called Valmor while the #38 is their standard alkyd varnish. I have spoken to 2 makers who have usde it, but they tend to spray and therefore have to level less. One told me when he gets the "witness lines " (thanks for the terminology) when he levels, he just sprays another coat and starts with 1500 so he does not go through the last coat. Another told me he will put FP shellac over the varnish.

Not sure what I will do

Ed Minch

[B. Howard]

Ed, the term alkyd is generally used to refer to a coating based on polyester resins. Traditional varnish is made from natural resins like copal, sandarac, even shellac and it's based on a drying oil like linseed or walnut oil. So to me the P&L 38 is still a polyurethane rather than a true varnish because it is based on plastic. The witness lines do not happen with a true varnish as the layers melt together. This does not happen with most plastic type coatings. Various manufacturers like to put a happy marketing spin on products by calling them varnish or lacquer when they really are not and do not behave anything like the original product they are named after.

[Alan Carruth]

My understanding is that 'polyester' usually refers to a styrene resin, where 'polyurethane' is made from urea; a different monomer. Both are synthetics, and I doubt you'll find many 'modern' varnishes made from natural resins any more. Darn.

[B. Howard]

Alkyd's are polyester modified by the addition of an acid. They are the base of a whole family of coatings that used to be known as enamels. They are routinely modified by the addition of things like vinyl, urethane, and styrene to name a few. They are still the base for most synthetic coatings. Modern conversion varnish is an amino-alkyd where the acids are amino acids. The other synthetics in use today I believe are urethane modified poly-amines but I am not sure of that.

You can always make your own varnish , we used to when I was young. And what we didn't make came in a tin like paste wax and you cut it with gum turpentine by the pound much like shellac.