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I am still finishing my guitar ( first time with my new spraygun ).
All is going great up until 400grit dry sanding.
Thenas I enter wetsanding, all looks well at first, but then a few huers after the lacuer ahd began to harden I see scratchmarks !! long scratchmarks. I had it before as I came to wetsanding, So I went back to drysand with 400g again. and now after 2 days dried I wet sanded with 800grit, and there it is again Scratches ! long freaking scratches . This time I even used real thin lacuer 75% thinning and 25 lacuer or so. as was suggested in the Erlewine book. (step by step) . not in the best mood right now .
I am using oilvarnish ! epifanes 24 huer drytime.
need a solution so I can fix it tomorrow.

As for the sandpaper I am wery careful and I take away all on the paper as I see anything that might clog it up etc. also. I am using water for wetsanding.

Lars.

Yo, Lars,

Sorry is happening to you... happens to me too.

Don't think you done did nothin wrong...shift happens...a lot with lacquers and water born stuff...is why me much prefer oil or french polish.

One speck on a sheet of paper and theres that infernal scratch...sorta like them emotional scars and scratches we all carry.

I am sure someone else gonna post on how they do it without scratches.

I know, not much help...but at least we cried in our beer together.


blessings

Padma

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ain that the truth . Good to kmow I am not alone making mistakes hmm .

So where are you others to chime in and help me on this matter to make a perfect wet sanding procedure...

lars

Lars, I'm no expert so I ask this question trying to learn myself.

When you say, "All is going great up until 400grit dry sanding.", does that mean that you started with less than 400g for your final sanding? I've read that some start with 400g and others state that 400g will leave scratches so they now start final sanding at 600g.

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Formerly known as Adaboy.......

You sure the scratches aren't below the finish surface? Either in the seal coat or on the wood?

I start my level sanding with 600 dry, then go to 800 dry. I try to avoid wet sanding at all honestly....but that's just me.

Personally I like to build at least 6 coats before I start level sanding......9 is better too. Once level, I'll shoot 3 more thin coats let that cure for (insert adaquate cure time here) then sand with 800, and go to wet sanding with 1000, 1500 and 2000 then go to buffing.

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I Started at 220 lightly after having put on a thick coat. then 320. then 400. all looks great so far, shiny and nice no scratches as of what my eyes can pick up anyway. then next day wet sand at 800g then next day when I look at an angle to the light scratches here and there. So I go back to 400 and level, then spray a nice coat all looks great again. So then 2 days later 800g wet tehn spray thin coat, next day (this morning) scratches here and there again. !!!

Lars.

bumb

bumb? Do you mean bump? If so here is another one...

bump

I second that opinion. Start with 600. 400 is so coarse that it takes a million years with 600 to get rid of the scratches, possibly longer. 600g takes a little longer to level but over all, you'll have a shorter finishing experience.

220g? That's just crazy coarse. I'll use 320 if I feel the need to rough sand between coats, but never anything so coarse on final coats.

I also go dry the whole time.

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I'm with Andy, except I wet sand the final leveling. I do at times knock off the tops of orange peel with 400 but that's it and I use a small ebony block to make sure the surface is really flat.

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Lars,
Just a quick possibility.
If you make some coarse scratches, then spray a very thinned down coat to fill them in, It my look level off the gun but then you sand relatively soon and the finish shrinks back into the scratch. I'm having a hard time articulating this.
In affect, it looks good initially but you have a scratch that is a valley of relatively moist finish. waiting longer before sanding for the shine or not tying to fill such coarse scratches or both might be the cure.
Does this make sense?

By the way, what is your sanding block?
Is that sucker perfect?

Thanks for the bump hesh

The 220 was for the first coat ! not final level. and I have 2 coats of shellac underneath that.

might be different kinds of papers , as my 400 is really smooth. But I will change to 600 for the future as you´ll suggested.
I am using a 3 by 3 cm MDF block U cut out. and did round the corners and edges on it first. is it to small ?

You are all telling me what grits to use "good info" but I need to know how to get the scratches out the easiest way possible - now as they are already there. will try what David suggested today.

Lars

The OP is a bit misleading. Lars, you are referring to oil varnish finish -the Epifanes-, not lacquer, right?
Or am I missing something?
The procedure for oil varnish is totally different than for lacquer. A light scuff with 220 is OK on the first couple of coats to create a mechanical bond.
As been stated before it is very possible that the scratches are below the finish surface, and only appear when the last coat is cured and reflective enough.
Another possibility is that, as I tried to warn you, the finish below the surface is too soft and marks easily. Do a test: how deep can your thumbnail leave a mark in your finish? You mentionned in your other post that you sprayed a few coats of shellac as sealer, how long did you let those dry before shooting the 1st varnish coat? Shellac will remain forever soft under other finishes if it hasn't gassed out.
2 questions: what sandpaper are you using? What blocks are you using - you use sanding blocks, right?
The best sandpaper for varnish is IMHO either the Norton or 3M open coat (yellow), the Norton 275 (Champagne) is more expensive but well worth it. Any other sandpaper will bring aggravation, frustration and a large amount of waste. I use 1/2" thick acrylic blocks, and cork lined dowel lengths (of various sizes) for waist and cutaways. I go through sandpaper fast, as sanding with a raggy piece is asking for trouble, and is a waste of time.
You may have to scrape your finish off and start over.

EDIT: I see we posted at the same time. Use some kind of lubricant in your water, a drop of soap or a drop of kerosene. I get the sense that you may think lacquer and varnish are the same, they're not. I do not know if the Erlewine book covers oil varnish (I'd be surprised), but the methods are very, very different.

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Laurent Brondel
West Paris, Maine - USA
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Acutally the more I think about it, the more I think the shellac underneath continues shrinking. Sanding the varnish flat will make the marks invisible, until the next day when shellac and varnish have shrunk a bit more and the marks show again. I bet that if you scrape your varnish off you'll discover your shellac underneath is still somewhat "wet".

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

This won't help get rid of the scratches that are there but is and additional attempt to avoid them in the first place. When wet sanding, use a spray bottle with water and a drop of soap for a lubricant. When you rinse your block, if you dip it in a bucket with those particulates, you may just be reintroducing them to your finish.

Using the spray bottle insures that you're not putting any of the grit from the previous coats or the sanded residue back onto the surface.

Good luck.

Darrin

Sorry guys, I saw lacquer in the first post but not the oil/ varnish part. I have no experience in that realm.
there are a few grit sizing systems. P graded and C graded are the most common. They overlap in the coarser grits. but then diverge. If you mix and match you can unwittingly go backwards.
3x3 is plenty big enough, but MDF can sometimes shed small granular partials.
Some softer layer on the bottom of your block (cork, rubber, etc.) will make it much more forgiving. Especially with dry paper.
Also, the lubricant on the paper serves to soften the paper backing. Completely dry paper can occasionally causes a scratch where it is creased at the corner of the block. I sometimes soak sandpaper in water to make it pliable but blot it dry before using it this leaves the paper soft but not wet. this will work with other lubes as well.

Laurent, David, Darrin. Thanks amillion for your help mr friends.

I just got back up after having been downstairs sanding. then a while later I Sprayed again ( didn´t read your post before this ). Still, I Seem to have gotten the scratches away, we will see tomorrow once the varnish has sunk back a bit. But I think so anyway. BUT Now in some freaking way at 2 places the varnish is separated from the top in like0 .2mm lika a miniature crater ! grrrrrrrr. man this is soooo frustrating. This is the guitar I sold a while back ( for those who read about it) and in some way the string height had gone down, so after lots of thinking and trying, I did a neckreset on it - went great. also took the bridge of as the guy had put a few scratches on on the surface and I felt I could fix it, askt him if he wanted me to spray the top instead of tru-oil. felt this to be a good chance to train the spray technique. . So now he calls me asks me how things are going eeehh. I answered him that she´s done soon. but now all is going the wrong way it seems. Atleast I get some good training both for spraying and patience hahaha.
Tomorrow I´ll get some great papers I bought from stewmac. hopefully they will help my work. Laurent, I will give it another try. then if the same result I will do what you said and start over. (but with Nitro. !!!!!!)

Lars

Just make sure you tell your customer EXACTLY where things are at. As they say, Bad news travels fast and you don't want your young reputation to be starting out on a bad note.

If you find yourself chasing the scratch ghosts, stripping and starting again is probably the best way to go.

Good luck Lars. We've all been there with the finishing. It's honestly the hardest part of building guitars, unless you live in the US and can send it to Joe White

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"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

I haven't read all the post, only skimmed them................but, 220 grit is too course. I also suspect you may be using too much pressure when sanding. Let the sandpaper, and sanding block do the work. Light, or even no pressure is needed.

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Lars-
Finishing is my least-favorite part of building.
I've been in a situation like yours- trying to fix a problem , adding more finish, sanding, polishing, etc....
I've used varnish a couple of times and found that it takes weeks in a warm area with good air circulation to get 'hard' enough to go to the final finishing (wet-sand and polish) steps. Trying to work on too-soft finish is an exercise in frustration for me- varnish, nitro or FP.
My advice is to either-
a) Take a deep breath and just hang the guitar up for a few weeks, or
b) Let the customer take the guitar away and bring it back in a month for final finish (Bream played his Romanillos for a couple of years with only a sealer coat of shellac before bringing it back for FP, so the story goes...)
or
c) Strip off the finish and start again

Any way you choose- I don't see a quick result.

Cheers
John

Thank you all so much for helping me. I have spoken the the guy who´s getting the guitar. and he said it was not problem to wait ! felt good to hear.
I also spoke to an autopainting shop, then guy I spoke with said that with a 99 % certainty, is was the gun that was not perfectly cleaned, that it was old laquer/ paint spitting out. he showed me a newly painted car front and askt me if it lookt like this- he poited at a speck on the hood and yes It lookt just like it. therefor he said clean your gun, take it all apart and clean carefully. So not I am on my waydown to fix my gun. I also bought a better moitfilter, and I will change the position of it to where it is supposed to be. so I have some stuff to fix .hopefully this will fix my problem.

Lars

Cleaned the gun all through. bought me 2 water filters and new hose. connected them, 1 at begiunning compressor and one middle of hose. Used a tackcloth on the top to get all the dust off. sprayed. No change !!!!!! same darn specs are there. like a a hundred tiny specs. what the %&"€&#/%&#€. man this is soo enoying. might it be the varnish that is old or the gun thats busted or what ??? . Got info from Iwata how to set the gun right. and did thats so thats not the issue I guess.

Lars.

Lars, I tried explaining to you that your shellac underneath is probably too thick and shrinks at a different rate than the varnish coats, hence the lines. Besides, I get the feeling that the 1st varnish coats have not cured properly either.
What you're experiencing is typical of mixing two different finishes, the shellac wants to evaporate, shrinks faster than the varnish and pulls it.
My advice would be stop wasting your time, scrape off your finish and start over, this time with proper cure time. I bet you'll find your shellac base soft, perhaps almost wet.
A wax-free shellac sealer works great under oil varnish, however you need to thin it considerably, like water-thin, and spray a very thin coat. Let dry at least a few hours, best overnight, and scuff lightly with 320 grit or maroon 3M pads before spraying the varnish. The sealer is there to prevent the wood from absorbing finish, especially spruce (or worse WRC or redwood), and to act as a base coat for adhesion.
For a fast varnish build thin your 1st coat 1:1 with solvent, the second half of this, and so on. Spray full strength at the 3rd or 4th coat. This will improve adhesion and cure time. This is also recommended in Epifanes literature, which I urge you to read for a better understanding of oil varnishes.
Finish work is difficult and maddening at times, and with oil varnish you've increased the difficulty a couple of notches.

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Laurent Brondel
West Paris, Maine - USA
http://www.laurentbrondel.com/

Thanks Laurent. I will scrape it off and start over. cant find a smiley with tears hahaha. thanks for your advice my friend.
will also read up on varnish. Perhaps I should just wait until middle next week and then spray Nitro instead. hmm not sure yet.

Lars