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I'm interested in trying to spray shellac as a full finish. Internet reading has shown that checking or crazing can occur, and that it's too soft, hence the invention of u beaut. But U beaut's horrendously expensive. It would seem that sandarac, a hardener, and gum mastic, a de brittlizer (whuh?) are common additives available. It seems one could make their own version of a suitable shellac finish for guitars for a non FP application. Does anyone have any experience with this, or can anyone recommend a good source if info to learn more?

Thanks

The mastic is supposed to add some flexibility to the film, the Sandarac some hardness.
I'm unsure just how much these things really add. I've done a number of Spirit Varnishes and to be honest it's very difficult to tell which is hard, which is soft and which is durable. You probably wouldn't find out until years down the line anyway. Most of these finishes change properties over long time periods. It's often reported that certain Shellacs become impervious to alcohol after many decades.
If you want to play it safe I suggest the 1704 recipe. At least it's very tried and very tested. Most people seem to omit the boiling stage.
No idea how it sprays though. I've only brushed.

Thanks!

Adding Sandarac to Shellac is supposed to add hardness to the finish.
I think it does, but the danger is adding at too great a percentage will cause surface flaking or chipping at the edges.

My experience is to stick with straight shellac, Seedlac, the most basic form, and to do my own dewaxing by decanting & filtering.

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Yes probably wise to keep the percentage of Sandarac low. According to the Fiddle folk Varnishes that contain decent amounts of Sandarac tend to scratch white i.e they leave a very visible white mark if you scratch the finish. The problem with seedlac is that it isn't much good when you need a very light coloured finish.
Most of the knowledge on these types of finishes are to be found with the Violin makers.

I'm hoping for a spray able, ROS sand able, power buff able shellac finish that won't check or craze...too much to ask for? There's probably a reason everyone's not already doing it...

Straight shellac can be sprayed successfully. You need to keep an eye on dry film build, it's not lacquer. Final film builds should when cured and buffed should be under 6 mils. Proper drying and good level sanding between coats is also recommended, shellac does not flow anything like lacquer when sprayed. I spray shellac as a sealer quite a bit these days and a 1 lb cut seems to spray nicely. As always, spray test panels first to confirm the process before committing to a finish job. Sprayed shellac however will not be as hard or durable as that which is applied by FP, that is why violin guys add things. Actually shellac is an additive to the varnish in most cases.

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Would it be any worse that UV Poly?

can lacquer be apply on top of shellac ?

I believe so if it's dreaded shellac.

Ha ha auto spell, real funny. Sheesh.

Dewaxed shellac, dewaxed...

Here's a good website describing different resins used in violin making. There's a recipe for the 1704 at the bottom in case your interested.

http://www.leroydouglasviolins.com/varnish.htm

Short answer: yes

Not so short answer: Depends, I do it quite often with good results. Which in the world of wood finishing means that it works with the products and schedule that I use. I know others who have had serious de-lamination issues doing it. I can not speak for their materials or process. So the first thing I advise is doing a test panel using the products & schedule you intend to use and evaluate from there.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

Last git I made has a sprayed shellac finish.
1 lb cut, 320 quick level between coats.
A real pleasure to work with.
I don't care about durability.
Most people take good care of their guitars.
If they don't, well.....

Thanks, Lots of useful information on that site.

-jd

I will have to try and do some tests over this theory that brushed or sprayed Shellac is softer or less durable than French Polish. Essentially it's exactly the same stuff and once the alcohol has gone you are left with nothing but Shellac.
Some people point to the friction/heat caused by the pad or the pressure applied by the pad. Neither make much sense to me. I suspect that it's the additional film thickness that has some bearing on matters. It takes a lot longer for a thicker film of Shellac to get as hard as a thin film.
I've been playing a Guitar with a brushed on Shellac finish for the last 8 months, probably 2 to 3 hours daily. Not very long but I can't see any evidence that it's wearing faster than a French polished finish. Not one bit.

Michael, I am tending to the same understanding of shellac hardness, Polished vs sprayed or brushed. It is chemistry, and the method of applying it shouldn't change the chemistry, so shellac is shellac, no matter the application.

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I had wondered if perhaps the rubbing action melds the layers together a bit more? I have also read that the rubbing forces it into the wood a bit. That seems a bit more plausible...
I think the supposed advantage of FP is that you can get it so thin compared to a sprayed/power sanded finish. I'd be curious what a chemically educated person thought of that.
I could also believe that laying on enough shellac to be power sanded/buffed could make it more prone to checking.

But every finish has it's own special pitfall, just a matter of picking your poison I guess...

Yes the rubbing does 'join the layers' so to speak. So does brushing or spraying, otherwise we would be seeing witness lines as happens with oil finishes. I've never noticed separate layers with a brushed on spirit Varnish - and I've done a few.
The checking/cracking/chippy finish is certainly possible. To a certain extent that is also true of FP. but probably less so. There are an awful lot of variations under the term 'Spirit Varnish' though - you can practically tilt the properties from hard and chippy to soft and sticky if you really want.
Personally I think the difference between the two is in the film thickness, although I've started another side by side comparison to see if I can discern any real difference.

I'd like to hear more about your objectives and parameters.
Will you be using any additives such as sandarac or mastic?

I've tried a number of recipes over the years. For the most part I've just followed the instructions and not really tried to do any sort of testing other than to see if the finish takes a print.
This will be straight Shellac, one brushed and the other F.polished. Mostly it's being done to see how much of a visual difference there is (as some claim) but I will also try discern the respective hardness. Durability is much more difficult to assess, although I do have the experience of the Guitar that I play daily.
Here is a 'rough' test I did of the 1704 around 1 year ago. It's slightly modified in that I used less mastic and less spike oil. The Shellac content was seedlac. I was only really testing the colour pigments/dyes hence the wood wasn't scraped or sanded. However this piece seems to resist scratches as well (or as badly!) as any F.Polished surface.

I was thinking of doing a few test panels in various formulas, sanding and buffing them, and then throwing them from the fridge to the sun and back, using them as coasters/doorstops etc. to see what they do. It's really the crazing that worries me the most...

The act of French Polishing does by virtue of the process does pack the shellac tighter than spraying can. Sprayed shellac will amalgamate into one solid layer of coating but the pressure used to apply a FP will cause the finish to become denser and therefore tougher and allow it to be thinner and offer the same level of protection. Selection of shellac used will have a great influence as well, with buttons being the toughest and IMO the best suited to FP. Button Lac was after all used on virtually all gymnasium and Ballroom floors well into the 60's. Crazing of a coating is usually caused by excessive film builds. Occasionally it can be caused by using a coating that is to rigid for the application. Careful examination of the failure will often tell which was the case.

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Brian

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So, flake then if you want to spray?

Flake has been my choice of late for spraying sealer, but only because it is readily available locally. Any shellac should spray as long as the cut is right for your equipment. I have sprayed button lac with an airbrush for furniture repairs.

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Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/