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.

Oh yeah I know and it wasn't directed at you, if that wasn't clear. But more to the point of, we use all that material and waste so much to get a flush/glass surface.

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Originally Posted by RocknRolf

Oh yeah I know and it wasn't directed at you, if that wasn't clear. But more to the point of, we use all that material and waste so much to get a flush/glass surface.

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Yeah sorry, didn't think you were having a go. Just meant to reiterate the sanding part.

And, yes, I wouldn't be surprised if more poly ended up in the rag each time than what goes on the timber!
I know we try and balance a thick enough coat to protect the timber and a thin enough one that it's not "too thick", but literally paper-thin is thin!

IMO, the whole "thin finish is better" debate is just more internet BS when it comes to electric solid body guitars.
Acoustics and maybe semi-acoustics, yeah, but that's a whole other kettle of fish...

I just use Cabots water base poly. Its not a wipe on but you can spray it on as well as use a brush but I found it was easier to use a wipe on approach as I dont get any runs and its easier to control the amount you apply to the surface. Plus if you need to thin it or clean up you just use tap water which is much cheaper than using some form of turps/metho. Trust me it took quite awhile to perfect my technique to get to the place where I am now but it was well worth it.

The main reason I use a water base was due to the lack of smell and how fast it dries compared to oil base. When it is a little bit too cold to use oil base I can apply it on in my house and let it dry in my spare room and there is no complaints about smell from the missus, unlike when I used oil based poly. I have sprayed in the past but you have to have a reasonable clean area with no wind but when you wipe on I can do that anywhere.

I have used Tru-oil on 2 guitars, one I sanded back and put on poly and the other I sanded with a Scotchbrite as I wanted a satin finish as I found when it was gloss my hand would not slide once I got some sweat on my hand. I had experience using Tru-oil on my gun stocks and on my stocks I only ever used 2 coats and always sanded to a satin/matt finish as I didn't want anything that reflects the sun. On my guitar I only used 3 coats as that was enough but again I made sure when I applied enough per coat and I achieved a gloss finish normally within 2 coats, sometimes with only a single coat but I needed enough to flatten and polish hence I used 2 good coats and then followed that by a thin flat coat. Plus poly is easier to obtain and cheaper and doesn't go off and is another reason why I use poly. I have used oil based poly in the past but was restricted to where I was allowed to hang it to dry.

So how many coats of poly are too many? I wood burned/painted/clear coated a 20$ ukelele kit to practice and test my products, put on 8 coats of wipe-on, water based polyurethane, wetsanded- and accidentally relic-ed it! I had to touch up and apply a couple more coats of poly. With this telecaster, I'm aiming for between 25-30 coats of wipe on, water based poly before I wet sand. But is there a point where there's too many? When it gets cloudy?

This is the thing I am worst at, but I gather that it depends quite a bit on the product you are using and how it's applied. You may want to say exactly the product you are using, so that anyone who has used it can chime in. There are a lot of differences even between polys

I use a water based poly from General Finishes called "High Performance." You can apply it with a synthetic bristle brush, a foam brush, an applicator pad or a roller. I use a 2" Wooster sash brush or a 2" foam brush, and usually both. The mfg recommends no more than 3 coats. I use 6-10. I find that both bristle and foam brushes leave brushstrokes, and for me 3 coats risks sanding through. With 6 or more I can usually sand out streaks and other imperfections to get the finish pretty flat. There are at least two downsides with this finish. It takes a good 3-4 weeks to cure. It also takes a lot of careful sanding to get it flat. On the upside it has very little odor and very low VOCs. Also water based polys have the lowest propensity to yellow.

I think you can get quicker curing times and flatter finishes with solvent/oil based polys, but others here have more experience with these than I do.

I am using minwax water-based wipe-on polyurethane in clear gloss. At 9 coats, it's pretty shiny, and remarkably flat. That's why I stopped here with the ukelele - it seems done. But when I wet-sanded it, I sanded through in places, even though I felt like I was barely touching the surface. That's why I was figuring on double the coats of the ukelele. But I don't know what the signs are that you're done, since I obviously stopped too early the first time. The ukelele polished very nicely, but it's a 20$ kit going to a 6 yr old, not quite the same as guitar that's hopefully going to be used and treasured for years. I really want the finish to hold up.

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Originally Posted by ElleBrooke

So how many coats of poly are too many? I wood burned/painted/clear coated a 20$ ukelele kit to practice and test my products, put on 8 coats of wipe-on, water based polyurethane, wetsanded- and accidentally relic-ed it! I had to touch up and apply a couple more coats of poly. With this telecaster, I'm aiming for between 25-30 coats of wipe on, water based poly before I wet sand. But is there a point where there's too many? When it gets cloudy?

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FWIW: I have not used a wipe-on water-based poly, and I'm not a fan of wet sanding! I'm also not great at finishes!

For Tru-oil I would typically aim for 2/3 brushed on (thick) coats, then 20+ wiped-on coats. I generally lightly (denib) sand (with 600 or 1200 g) along the way, being very carefully around edges. And gently sand to smooth surface every 5 (or so) coats with increasing grits from 600 to 2000g.

I'm not sure about too many coats, or if it goes cloudy! If it starts going cloudy the wet sand should bring it back a bit.

Oh yes, thanks, TD, forgot about scuff sanding between coats. I use a 3m maroon sanding pad between coats to ligthly scuff sand. I typically don't scuff sand between the first two or three coats over artwork or decals.