Varnish over Shellac

[inecik38]

Hi, I need your recomments for refinishing on radio.I am using sprey varnish but I need 4-5 can sprey varnish for a radio and suıtable place and the weather will not hot or cold.alot of difficult.
I tried shellac varnish, it is easy and very nice but it is no strong on water so can I use sprey varnish over shellac.

[Bazz4CQJ]

I think that when Shellac dries, it does not change chemically but just loses its base solvent, so application of another solvent could dissolve it. If that is the case, it's possible the varnish could interact with it, which might or might not matter. Definitely one to try on a piece of scrap material I think.

B

[dseymo1]

The two finishes are likely to expand and contract at different rates as temperature and humidity vary, resulting in crazing (small cracks) over time.

[SurreyNick]

Why is water a problem? Surely the radio isn't going to be exposed to splashing water or rainfall is it? Atmospheric dampness, such as inside a boat, is unlikely to pose a problem to shellac as it's water resistant and you can always apply a wax polish over the surface for added protection.

To answer your question though, you can apply an oil-based varnish over shellac, and an oil-based varnish made from natural resins, such as linseed oil, can look great over shellac. But there is a problem. A varnish finish is only really good for ten years and unlike shellac it is not a restorable finish. So if the varnish gets damaged or worn you will have to strip back the varnish AND the shellac underneath completely and then apply a new protective finish from scratch.

If you do decide to varnish NEVER use a spirit-based varnish over shellac as it will dissolve the shellac layer and you will risk an ugly mess.

I hope this helps.

[inecik38]

I look a lot of page on the internet and all of them say that;the shellac is no strong to contact with water and the shellac is not original finish on the tube radios.
I want to say that; varnish over shellac, I want to add an acrylic spreyvarnish, no oil based varnish.

I have no idea what my A104 (Murphy baffle set) was sprayed with originally, I did give it a rub down and used car spray acrylic "varnish", worked a treat. As said before, try a bit first. Modern spray can stuff is 'green' and doesn't contain a lot of solvent to cause many problems.

[Bazz4CQJ]

For the first time ever, I've just tried a water-based varnish. It only has a satin finish, but I was really pleased with how easily it went on without streaking and dried to give a very nice even finish. Of course when it dries, it changes its chemical form, so it then becomes impervious to water. Probably not for use on our yachts, but fine for use at home.

B

[inecik38]

Hi, just now I added acyrilic sprey varnish over shellac and yet there is no a problem.

[David G4EBT]

Yes, that will be fine.

After sanding items turned on the lathe, most woodturners seal the wood with shellac sanding sealer. When the sanding sealer has been sanded, on smaller items the tendency is to use shellac friction polish, but you can't do that on larger items such as lager bowls because not enough heat can be generated by friction to melt the polish onto the wood. Hence, many turners these days use clear acrylic spray lacquer - either gloss or satin. The clear acrylic gloss lacquer as sold by motorists accessory shops (such as Halfords in England) doesn't react in any way adversely to shellac sanding sealer, which is basically, no different from French polish.

My other hobby is woodturning and to give an example of the finish obtained with acrylic lacquer, I've attached a picture of a bowl I turned, which was first treated with shellac sanding sealer, then sprayed with an aerosol (‘rattle can’) of water based acrylic clear gloss lacquer as used on cars. I've only attached it as an example of the finish obtained from spray acrylic lacquer - I've not had cause to use acrylic lacquer on a 'woodie' radio cabinet, but wouldn't hesitate to do so if need be.

As always, preparation is all important - as the saying goes - 'you can't put lipstick on a pig'!

Incidentally, though some radio restorers who are skilled at French polishing have done some wonderful cabinet restorations, I don't think shellac was ever used commercially on radio cabinets - it would be far too time consuming. Most would have been sprayed with nitro-cellulose lacquer until safer acrylic lacquers were developed in the 1950s. Such lacquers don't adhere well as they don't penetrate the surface of the wood, which is why it flakes off radio cabinets, (admittedly after several decades, and often not having been stored well).

There's a useful explanation of the various types of finish at the link below.

It makes the valid point that 'French Polish' is really a process rather than a product - it's simply a method of applying several thin layers of shellac. Worth reading the explanation as to why shellac is sold in flakes to be mixed with denatured alcohol (known as methylated spirits in the UK) at the time of use and not stored. (The flakes last indefinitely, but once mixed, the lacquer goes through a chemical process which limits its shelf life).

http://www.acousticmusic.org/Guitar-Finishes-sp-98.html

Hope that's of interest.

(No off topic posts about woodturning or guitars please).

[Panrock]

Acrylic spray clear lacquer, as obtainable from Halfords, is entirely satisfactory applied over cellulose and indeed today I do this in preference to using a cellulose top gloss coat. An example is attached: the flatting and toning coats were cellulose and the top coats acrylic.

Don't try applying it the other way round though - cellulose on top of acrylic!

Steve