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I’m definitely interested, Simon!

I saw you mention MEK, so I’m guessing that’s the solvent you’re using for Luthierthane. What is the catalyst?


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I'm not sure if the isolante sealer is as bad as the urethane -- but I do know the urethane hardener has isocyantes. Some people react very badly to isocynates and others are just fine ... but I'm not interested in taking any risks.

One appeal for me with the Cardinal product or catalyzed urethane in general -- is that it will be around for a good long while. Products like Royal Lac scare me a bit because it is a small operation. I always remember the varnish guys complaining about how frustrating it was to find a replacement for the Rockhard Varnish. I'd like to find a product that works for me and that will be readily available in the future so that I will benefit from increased experience with working with the finish material.

I will definitely keep you all posted and for nothing else, maybe various aspects of my experience will be useful or informative.

I wonder if Sutherland-Welles is not tweaking the formula on the Murdoch's varnish a bit. I've noticed that I'm having fewer witness line issues with the last few cans I've gotten; they may have found a way to get it to burn in a bit better. I'll note that I always scuff sand pretty thoroughly with dry #400 between coats, to get the surface energy up, and I try to not go more than 24 hours between coats. I always do the last two coats on the same day. Also, avoid the blueish stearated papers; and don't recoat after wet sanding. If I sand through wet I do a very complete dry sand before re-coating. Something in the water that reacts with the surface? Who can say.

The intermittent issue with it not hardening on some tropical woods is the main problem now. The only thing I've found that works to stop it out is CA; shellac, which is usually a good sealer for that sort of thing just doesn't cut it. The biggest issue is that there's no way I've found to predict when this will happen. Some woods, like morado and macassar ebony, do it all the time, or nearly so, while others that I'd expect to be problems, such as BRW, don't seem to be, and I get it sometimes with IRW but usually not. I've noticed that using Super Soft 2 to bend the wood can bring this out, and even with out it sides or bindings of wood that comes from the same plank as the back can cause problems, where the back doesn't. With any oil varnish, don't try to re-coat until the first coat has cured. I've had the first coat on the Murdoch's take several days to get to 'dust' when sanded, but after that it's fine. Finally (for now) UV light really helps, with any oil varnish.

Which Murdoch’s product are you using


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Luke,
I'm fairly certain Al is using the varnish that I used, Murdoch Uralkyd 500.

Expensive stuff at 50 dollars a quart


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Agree with the above suggestion of trying some buttonlac, esp for backs, sides, and necks. Real good stuff; *way* more durable than the lighter, bleached shellac.

Yes, the 'Ure-Alkyd 500' floor finish.

I get about three guitars out of a quart, so it's not so bad. You have to keep the stuff from hardening up in the can; 1/3 of a can of air will gel it all. I tried various things, and ended up with 'Al's Marinated Marbles'. Just put enough marbles into the can to keep the varnish level up to just below the rim. When I get two cans with enough marbles in them to make it hard to use the varnish I consolidate them into one can, and clean off the marbles for re-use. One of me students found a source for new empty pint pain cans on line, and got me some a few years back which makes it really easy. I hardly ever throw any out because it's gelled.

As with all varnishes, it's quite a lot cheaper in larger cans; about $75 for the gallon, iirc. The problem is that the state of New Hampshire won't allow them to ship the larger cans, so I have to get quarts. If I order a gallon they send quarts and give a bit of a discount.

I've been using button lac for decades. Never did think much of the more processed types. If I want a clear sealer I tend to use sandarac, which can be almost water clear. I don't dewax the button lac, I use as is. I'm in the UK but I import pretty much all my shellac from shellac.net. They have some specialist button lacs that are much lighter in colour, the lightest being like a blonde. In over 40 years of making I've never seen those types of button lacs in the UK or Europe, we just get the more usual Kusmi.
I only make classicals, so I'm not going to join in on whether it's suitable for steel strings. If I played SS I wouldn't have an issue with it at all, that's me though.

I’m watching this closely because I’m going thru the same thought process with my shop.

My question of the day is this: Would you rather step into the booth and spray nitro a dozen times for one guitar, or cat urethane twice?

Is exposure to urethane a six times more toxic than nitro?

Michael, This is certainly borne out by my experiments. I prepared test panels with waxed and dewaxed (coffee filter method) buttonlac. I then subjected the finish to all sorts of tortures and could not discern any difference between the two in terms of durability. I prefer to dewax since the finish becomes a little clearer and it also removes the residual bark and insect bits at the same time.

_________________
Stay with the happy people.
--Reynolds Large

The best way to dissolve shellac is the 'tea bag' method. Tie up the shellac you want to use in a cloth bag; old T-shirt material is good. Avoid dyed cloth, as some of the dyes can be soluble in alcohol: DAMHIKT. Suspend the bag near the top of a tall jar and put in enough alcohol to come up to the bottom of the bag. The dissolved shellac will settle to the bottom of the jar, forcing the clear alcohol to the top. You don't have to stir it; it does it's own mixing. The dirt and bug parts will stay in the bag, as will the wax in some cases, particularly with seedlac, so long as you don't squeeze the bag. It's the no mess and no fuss way to go, and quick too.

Take one of the buttons, scratch it with your fingernail. Not exactly a scientific test but gives a rough indication of how hard waxy shellac is. Of course the button itself is hugely thick and it doesn't have the underlying soft wood.
I load the filling of the pad rather than applying the shellac to the outer covering. It does act as a filter and probably removes a small amount of the wax too.

Have you considered using Tru-oil to French polish? I am in the process of finishing my fifth guitar, four previous have Tru-oil finishes, and it is a pleasure to work with. Tru-oil is self leveling, coats can be applied every 30 minutes or so and emits little odor. If you mess up, sand the area and keep going. The only possible downside is that Tru-oil has a amber hue once it dries. I personally like the color as it give the guitar a vintage look.

In these pictures, I have approximately 30 coats on

Wow, that looks great, Patrick. Do you do any sanding between coats or polishing after the last coat?

I do if I get trash in the finish. I have learned, the thinner I apply it the less trash grabs the finish. I let the finish cure for two weeks. Then I use the 3M sanding pad 1800-12000, not necessarily all of them, to do a final sand before hand rubbing a scratch removal polish followed by a ultra finishing polish.

Quick Update:

I got the last coat of urethane applied last night. I'll wait about 2 weeks to level and buff and then report back on my experience.


A couple thoughts thus far:

1). My spray booth is managing the fumes very well and I'm getting practically zero overspray in my shop. Almost no smell in the house during and after I spray. What I am smelling is a bit of MEK but it is very faint. Absolutely no smell in the house about 6 hours after spraying and also very little smell in my shop either. After I've finished spraying, I hop back in the shop and run the booth fan for a few minutes -- and I'll do that every few hours or so. After a few times, there's no smell except that coming from the guitars. As mentioned, my home has terrible air sealing -- put a cup of acetone outside and you can easily detect the scent inside. In short, I feel very comfortable about the safety of spraying urethane in my attached shop. The urethane is high solids and in combination with my HVLP turbine - almost all the material is getting on my guitars.

No overspray is reaching my shop -- just a bit on the floor and table in the area directly in front of my spray booth.


2). I'm using a FUJI Mini-Mite 4 HVLP Turbine. I've had a hell of a time getting this Cardinal Luthierthane product to level out. 2k Urethane is obviously a lot more challenging to spray than lacquer or varnish, which flow like glass. Ultimately, I've figured out a way to apply thin coats (1 mil dry) that level enough to be suitable for my purposes. I'd love to get it to lay even smoother but the texture is subtle enough that it will work for my needs. I've spent a lot of time experimenting on test panels and have probably wasted about $75 of materials but it was necessary. Tried slow reducer and medium reducer in varying amounts and percentages. Tried different air cap/needle sets as well. Each product is different - so what is working for me with the Cardinal product will likely need adjusting for a different 2k urethane. Feel free contacting me if you are using a turbine and a urethane clear - I might be able to offer some tips that worked well for me.


3). I believe I managed to get a fairly thin coating on the top -- hoping to have 3mil maximum by the time I've leveled and buff. We'll see.

I'm tellin ya, you can use regular shellac to repair Royal Lac. I just did it last week and it looks fine. I guess if they come back in a year and tell me it's awful then it will prove otherwise. I use shellac to repair simple finish problems on any finish and it seems to stick to anything and using the FP technique it's so thin you don't get any lines. No need to sand an buff if your FP technique is down.

Speaking of Royal Lac. I'm finishing one now with a can I bought last year and had already opened and used, seems to have good shelf life. But I was doing some reading about it, apparently there is now a post cat Royal Lac option that is supposed to be a very tough finish, still very thin and acoustically transparent.

Has anyone tried that?

BTW for the aforementioned tea bag method of dissolving shellac I like to use a coffee filter to make the back. With button lac, or any shellac, I pulverize it to powder in a coffee grinder (dedicated to this job) and the shellac is almost ready to use in a few hours. The coffee filter actually holds in most of the wax too but if you want it truly dewaxed then let it sit for a day and decant it.

I sprayed a guitar with PC RL and it turned out mostly fine. I used a Preval sprayer and it went on horribly, runs and drips everywhere. I did 4 coats and sanded back with 400, then 2 more topcoats.

I believe if I had sanded back the first 4 coats with 800 and up, the last 2 coats wouldn’t have been needed. Overall film was 3-3.5, which still had a damping affect on the tone.

I’ve a friend who pads it on and gets a consistent 1.5 coat, which seems ideal...