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I've just leveled the finish on the back of a mahogany 000 that I've been working on for a loooong time. Not sure it's relevant, but, ZPoxy filler, then KTM 9, sprayed. I'm thinking I got to about 14 coats over a couple of days.

The issue is this - While levelling - 400, wetsanded, then 600 once I got close, (then the plan was to go to 1000, 1200, then buff) I cut through the finish on the edge of the lower bout, this was before I got through the "sparkles" that always seem to be a feature of my sprayed water- based finishes. While levelling through the orange peel it looks like 1) flatter orange peel, 2) sparkles, then 3) smooth.

I'd assume that I didn't spray enough KTM 9 on the spot in question. The other factor is that I seem to feel a very subtle upward ramp on the edge of the binding - maybe while sanding prior to finishing, the ebony binding sanded less than the mahogany back due to differences in hardness? Have I got a problem with technique here?

Thoughts welcome. Thanks.

This has happened to me on more occasions then I care to talk about. FWIW it's one of the reasons why I gave up on KTM. I find 400 way to coarse and start off with the process using 1200 and finish with 1500.

Thanks. What do you use instead of KTM?

I switched to the water base stuff Stew Mac sells. I found it to be a bit more tougher but still have issues. I wanted desperately to use water base finishes for health and environmental reasons and did so for the last ten years but I've given up. The guitar I am finishing now is with lacquer and it's easy and looks very beautiful. I've just ordered some shellac and all the necessary materials to do a french polish on the flemenco and Selmer guitar that I am building now.

It's always been a never ending battle for me. One thing I've found is that if you open up a can of water base it's only good for one use, that is you know over the course of days to finish. If you have half a can and then go to use it months later it's not the same and I've seen it actually peal off!

i don't like spraying laquer for the same reasons you stated. I've done two instruments so far with sprayed shellac. I absolutely LOVE working with spraying shellac. Obviously, it wears quite easily. but dry times between coats is so fast.

I want to do some more testing and fine tune my finishing schedule with sprayed shellac and see if i can find a way to increase its hardness/durability. i ain't no chemist though....we shall see

b

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brendan 3.0 new and improved, with better interpersonal subroutines

Bren ;
I love shellac also.
I spray mine also;besides some French polish.
www.shellac.net is a great place to get it with great prices.

I use allot of the Stew mac stuff.
I use 1000 for my wet sanding to start with.
I make sure the finish is level before the last few coats go on
so that I do NOT need to start with a quik cutting paper.
That may be why you went through the finish.

Mike

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Mike Collins

I have found that the biggest source of sand through problems is preparing the surface before finishing. The top and back should be sanded with a somewhat large very stiff and hard sanding block. I like to use a 4x6 piece of corian with stick on sandpaper. You really need to level the surface. I you use a hard foam block or start with too find a grit, you will just make the surface smooth but not level. You don't want those nearly invisible shallow and wide valleys in the wood. Since the top and back are domed, you can't get it actually level but the surface should always be convex.

As you pointed out, it is easy to get a slight re-curve near the edges because the binding is harder than the other wood. If there is a spot that seems to fill up with sanding dust, you probably have a valley.

Going to higher grits than 220 seems to just make the surface smooth and not level so it may look like it is well prepared. I stop at 220.

I think sanding the finish is best done with a hard foam or cork block. These will deform to follow the surface. Even so, if you have a wide valley in the surface, you can still sand through near the rim of the valley while the finish at the bottom of the valley is still shiny. I've stripped and re-sanded the surface on instruments where I sanded through in the same spot a couple of times.

I'm not a particularly good finisher but lately, I've been spending much more time on surface prep and my results are improving.

All - thanks for your comments. Appreciate your feedback.
Mike - this seems like some very good common sense - I'll give it a try

2 Disclaimers, 1. I don't used waterbornes, but I assume the technique is the same. 2. I'm not pretending that I never get a sand through.


I'd say it's technique, with spraying, and/or sanding. Spray off the edge of the guitar. Pretend the guitar is 6" wider/longer than it is. Concentrate on consistant distance, speed and angle with your spray gun, and BE SURE you continue spraying PAST the edge of the guitar. Don't tilt the gun near the edge. Also be consistant with your sanding. If you have "sprakles" in one are that area has a problem. More sanding in a specific area is only going to give you inconsistant film thickness.

Orange peel? Try thinning the finish some, moving your gun slower, or adjusting your gun for more fluid to help with orange peel. Adding some retarder will help the finish flow out better too. These suggestions may not work with waterbornes, but they work with most finishes.

Measure your film thickness. Obviously you need to be consistant with application, and sanding, but measuring the thickness will help insure you're not trying to get a .001" finish, or ending up with .010" either.

Mike's points about prep are good too.

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