VARNISH differences - between "spirit" & "polyurethane"

[zcorsez]

Hi to all

As I am considering buying one of Strunal basses 1 simple (for someone who knwos the answer...) question comes to my mind: what's the difference between spirit and polyurethane varnishes ???

All series of basses offered by Strunal are avaiable in both finishes, so I am nor sure which to choose.

I've searched talkbass forum about that but have not really found the answer...

Any help please ?

[mje]

Spirit varnishes are made from a mixture of organic oils and resins dissolved in an organic solvents. Polyurethane varnishes are a long-chain polymer- a plastic- that cures on the surface of the instrument.

You don't want a polyurethane varnish. Fine for cabinetry, bad for instruments. It's heavier than a spirit varnish, and difficult to touch up. It has different acoustic properties. Maybe some day a poly varish will be developed that challanges the spirit varnishes, but that hasn't happened yet.

(Some guitar makers are using water borne polys to cope with clean air requirements, but that's because they spray on finishes.)

[John Sprague]

I've got to think that they're using the poly to make the instruments more resistant to abuse, since their target market is primarily school systems. You shouldn't need that. Spirit also looks sexier when it ages.

[zcorsez]

Thanks guys

So spirit is the choice - I just wait for the cash and get one of them ...

Some more :
- what's the difference= "Laminated quilted maple" and "Laminated flamed maple" ? ? ?

- and which is better - flat or swelled back?

I don't know if this is right place to ask these questions

Thx in advance

[christ andronis]

Is there any advantage to re-finishing a polyurethane bass with a spirit varnish? Is it cost effective to do so on a, say, Strunal?

[John Sprague]

If you visit www.thetalkbasses.com, the first bass shown, Ahnold's Montagnana, is quilted. Jeff Bollbach's is flamed.

[nicklloyd]

Spirit varnish is shellac flakes in alcohol. Oil varnish is a blend of oils and resins, usually in turpentine.

If you are going to be playing outside, as well as clubs and strange venues spirit varnish might give you troubles. It softens at much lower temperature than polyurethane. An extended period of direct sunlight/leaving the bass in a hot car can affect the finish dramatically. If the applications of poly were thin, it could be a usable finish for basses. However, Strunal lays it on very thick.

For refinishing, a poly oil blend or drying oil (tru oil, danish oil, waterlox) would work quite well and not be susceptible to the problems of spirit.

[Brent Norton]

Remember, spirit, oil, lacquer, poly -- they're ALL films. Folks tend to forget (largely because info is often contradictory and labels are next to worthless) that straight polyurethane IS a type of modified oil varnish. Still not ideal for instruments, but acceptable when applied judiciously.

[mje]

Originally Posted by Brent Norton

...polyurethane IS a type of modified oil varnish...

There is the oil-modified polyurethane varnish at the local store, which is alkyd varnish with polyurethane added, and then there is pure polyurethane. Someone working alone would use an oil modified alkyd, but a factory with a production line may well use a pure polyurethane. Although it has to be mixed just before it's sprayed, it will cure very quickly, whcih is a great advantage in a production line.

A lot of the inexpensive Pacific rim factory guitars I've seen use what's obviously a two-part poly resin. If you see an instrument with a very thick film finish, it's probably a two-part polyurethane since an oil-modified poly won't set up well if applied that thick.