Finish thickness FYI

I just thought I'd share this...

Whilst currently undergoing a refinish on my 2018 TLA-1, which I had originally applied a wipe-on poly finish to (longer story in another post) I was able to remove a "piece" poly by scraping it off with a razor blade.

Just out of curiosity, I measured it's thickness with my digital callipers. Now, these are not a highly calibrated instrument, but they are pretty close for 40 bucks (tested with feeler gauges).

Anyway, my point being that this flake of poly was the result of 28+ coats of homebrew wipe on poly (mixed 50/50 - poly/turps) then wet sanded and polished. as you can see the coating left on the timber is only 0.11 mm! (same as a single sheet of 80 GSM copy paper) That is sweet bugger-all!

I know it is difficult, if not impossible, to quantify what is "a coat" especially with a wipe-on finish, but I think this still illustrates what slim margins we're dealing with in our finishing pursuits.

So when we read about "sand-throughs" (we've all been there!) it's not hard to understand just how easily they can happen.

FWIW, I took samples from various areas of the body and they consistently measured between .009-.011mm.

Wow, thanks for sharing this McCreed!
Though thin finishes are what we are after, it just goes to show how slim our margins are!

How are you going to re-finish?

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Originally Posted by RocknRolf

Wow, thanks for sharing this McCreed!
Though thin finishes are what we are after, it just goes to show how slim our margins are!

How are you going to re-finish?

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Just started grain filling today. Colour will alcohol based dye (still debating colour) then I'll spray gloss poly with a gun.

I might try spraying the dye just because I've never done it before, and toying with the idea of some kind of burst.

Do you need to put a sealer onto of the dye before spraying the poly? I'm doing a dye finish at the moment and trying to understand what i have to put onto (if anything) before i do the finish...which is either TruOil, wipe on poly or spray can.

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Originally Posted by a_novice

Do you need to put a sealer onto of the dye before spraying the poly? I'm doing a dye finish at the moment and trying to understand what i have to put onto (if anything) before i do the finish...which is either TruOil, wipe on poly or spray can.

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The short answer is no, if the clear coat is being applied by spray (can or gun).

If you're going to do a wipe-on finish, there will be colour "transfer" of the dye. There are steps you can take to minimise smudging etc.
The most effective is to spray a couple of light coats of shellac (or polyurethane) to lock in the dye/stain and then start your wipe-on.
But many people choose a wipe-on finish simply because they can't spray anything due to workspace etc, so that may not work for everyone. Also, my feeling is if you're able to spray (even with a spray can) you might as well do the whole job that way.

If wipe-on is your only option, the first few coats can be applied using a rag and a blotting or dabbing approach rather than wiping.
You'll still want to change your rag or at least refold it often to prevent smearing any dye.
Once there is enough poly or tru oil to set the colour, you can start with the wiping process. Levelling can be addressed after subsequent coats as needed.

I've heard of people using foam brushes to apply the initial coats, but I have no experience with that. I presume you would need to use a really light touch so the colour(s) don't run.

I've got room to spray, but was looking for an option to replace my tru oil as i want to remove the amber colour but retain the fast, smooth feeling of tru oil.

I heard wipe on poly was a good option so was looking to see if it was worth it.

Might have to stick with tru oil....or spray on.

I think your decimal point should be moved one step to the right as my paper measures roughly 0.1mm and most digital calipers only read to the second decimal point.

I normally use wipe on poly and have changed to water based just recently as it dries much quicker than oil base. I sand to 240grit, apply some Feast Watson sanding sealer and finish sand to 320-400. Depending on the wood I normally get by with a single coat.

I then stain and apply normally 2 coats of poly before I sand with a Scothbrite to flatten then apply one more coat and finish sand and polish. I always use a piece of Chux lint free cloth and I make sure the finish looks wet. If it looks dry then you havent used enough finish on the cloth.

Sometimes I stain then sand to the desired amount of stain to highlight the grain. Then I apply sanding sealer and finish my process. Since using this process I have used much less finish and I still get a finish that looks like glass. Plus I have now moved over to using a cloth and sponge rubber buff in a electric drill to give my final polish.

I came to this way of finishing my guitars after about 10 years of building and having some less than satisfactory finishes. Since using this I haven't had any sand throughs, touch wood. Also went away from using sand paper once I start to apply the poly and only use Scotchbrites. There is no way you can sand through with a Scotchbrite as it removes minimal finish but unless you have a totally flat surface to begin with you end up using more finish to hide the rough wood base.

@ Dikkybee007:

D'oh!!! You're right. And I forgot to post this in my OP

Attachment 42984

Have edited OP...

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Originally Posted by Dikkybee007

I think your decimal point should be moved one step to the right as my paper measures roughly 0.1mm and most digital calipers only read to the second decimal point.

I normally use wipe on poly and have changed to water based just recently as it dries much quicker than oil base. I sand to 240grit, apply some Feast Watson sanding sealer and finish sand to 320-400. Depending on the wood I normally get by with a single coat.

I then stain and apply normally 2 coats of poly before I sand with a Scothbrite to flatten then apply one more coat and finish sand and polish. I always use a piece of Chux lint free cloth and I make sure the finish looks wet. If it looks dry then you havent used enough finish on the cloth.

Sometimes I stain then sand to the desired amount of stain to highlight the grain. Then I apply sanding sealer and finish my process. Since using this process I have used much less finish and I still get a finish that looks like glass. Plus I have now moved over to using a cloth and sponge rubber buff in a electric drill to give my final polish.

I came to this way of finishing my guitars after about 10 years of building and having some less than satisfactory finishes. Since using this I haven't had any sand throughs, touch wood. Also went away from using sand paper once I start to apply the poly and only use Scotchbrites. There is no way you can sand through with a Scotchbrite as it removes minimal finish but unless you have a totally flat surface to begin with you end up using more finish to hide the rough wood base.

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Great to hear about your success with finishings. Much of it has to do with how meticulous you are in your previous steps, and I think you have just nailed that.

What water based poly do you use, and is that still wipe on?

Something I find hard to understand is how 20+ wet coats only equate to 0.11mm finish, yet than again 1mm would be a lot!



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Something I find hard to understand is how 20+ wet coats only equate to 0.11mm finish, yet than again 1mm would be a lot

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FWIW, I did make it a point to say the finish that was removed and measured was after wet sanding and polishing, so that would likely have decreased the original thickness.