Measuring Lacquer thickness

[Taffy Evans]

In the recent post on French polishing Allen stated that he measures the masking tape covering the soundhole, and is covered in lacquer as the top is sprayed, and compares this to unused masking tape to get an indication of the finish thickness. This brought to mind the way I have always done this, and is as follows.

I cut a disc of plastic, from an ice cream container say, just a little larger than the soundhole and put this inside the guitar up against the top covering the opening. It is held in place by a block of foam put into the guitar first.

After spraying I remove the disc and bend it slightly and as the lacquer does not stick to the plastic it pops off in a fine sheet that I can then measure.

[seeaxe]

Thats interesting

On my acoustics, I use a balloon to hold the piece over the soundhole.

Is there any consensus on what is considered an acceptable thickness?

Cheers

Richard

[Alan Stassforth]

"They" say .005".
I say when it is polished, and you haven't gone through the finish.
Thin as possible.

[J.F. Custom]

If I'm correct, both of these methods measure the post spraying/curing thickness of the lacquer or given finish, so the "applied" thickness - not the "final" thickness.... or thinness for that matter.

It probably amounts to a ridiculously small (read - negligible) amount, but any idea of how much average material you might be removing during the cutting back and polishing process?

Does anyone measure the "final" thickness too or instead, say through/over the soundhole post buffing, with calipers or... ? Though of course, you would have needed to do this prior to any finish application too, in order to calculate the difference.

Personally, I haven't measured this before - having previously just worked by spraying the material, cutting and buffing by feel and experience learning as I went over the years. In the interest of facts and figures to aim/compare/refer to of my own work though, I will do this on the next build. I have a little set of engineers micrometers which should be accurate enough to get a clear idea of "finished" thickness.

Jeremy.

[TKAY]

"Painters All"!!
I once had the use (20 years ago), of an ultrasonic thickness meter used in the vehicle repair industry.Maybe this is an avenue to persue if you really want to know. Of course there is the finish which has penetrated the timber which could be nearly as relevant for protection as the "finish" on top!!!

[Puff]

Two initial questions.
1 Does it really matter?
2 What are you going to do about it? What's done is done.
From there:- who sets the optimum for what, and that is based on what. Are we talking nitro, poly, shellac, varnish, oil.....
Is the optimum on spruce the same as the optimum on redwood, red cedar or rosewood?

[Taffy Evans]

Hi Guys, I should have finished my post with ........"that I can measure if I wanted to."
I cant ever remember measuring the thickness of lacquer, I wouldn't understand the numbers anyway. I just flex the piece in my fingers and think shit thats thin. And compared to many of production guitars that I repair, it is thin. I do what you guys have mentioned above, experience and when it looks right its done, pretty much.

[Allen]

I only mentioned that I've measured it because I've been asked a few times. I don't worry about it at all as I know that I put it on bloody thin.

Like you Taffy, I've seen a few come across the work bench that have finish as thick as some of my uke tops. There's no way that can be good for tone.

[DarwinStrings]

Like you Taffy, I've seen a few come across the work bench that have finish as thick as some of my uke tops.

I wonder how they would sound if you got your hand in the hole with a scraper and removed the spruce(ply) and just left the couple of mill of two pack for the soundboard.

Jim

[Kim]

Like you Taffy, I've seen a few come across the work bench that have finish as thick as some of my uke tops.

I wonder how they would sound if you got your hand in the hole with a scraper and removed the spruce(ply) and just left the couple of mill of two pack for the soundboard.

Jim

Pick anything out of Asia back when they first started fooling with urethane and you have your answer Jimbo....thud!

[seeaxe]

Puff - It matters to me mate, or I wouldn't have asked the question!

The reason for the question was that I sense that using spray cans as I do, the finish goes on a lot thicker.
What can I do about it? I can take more off when finishinig and cutting.

Thanks Alan, that's a number at least.

Taffy, I'd be interested in the thickness you get at teh soundhole, because I can directly compare it to what I get, so if you remember next time you spray something, I'd be keen to know.

Cheers

[Nick]

2 What are you going to do about it? What's done is done.

That's why humans invented sandpaper, what's done can be undone with a bit of grit.
& is it important...yes, unless you are building electric guitars. Why spend all that time carefully tuning a top to then go covering/damping it with a lot of finish!

[Taffy Evans]

Hi Richard, Ok Ive got one ready for spraying, and another due soon. As soon as theres a gap in the weather I'll get them sprayed, don't hold your breath though. In the mean time Ill see if I have saved any of the samples from old builds, I save samples of every thing else.