Nitro finish cracking

[Ed Perkins]

I completed a solid body electric guitar in December of last year. I noticed after five months old the finish is developing cracks ( one just over 2" long between the pickups at the top edge of them) . It so far appears to be just the finish cracking. The longest crack should not be in an area of high stress from the strings. Any causes ? The instrument has been maintained in a constant room temperature no extremes.

[Penql]

Just thinking out loud here, I am by no means an expert (or even close), I'm just real curious.

Was the wood really properly dry? Temperature OK, how about humidity? You live in Florida or California?

Soft-ish wood (or a wood that moves a bunch - what is it?), dry climate and you play like Ben Harper (you smack that puppy with the heel of your palm)? Parked the guitar next to an air conditioner?

What brand of nitro (curious cause I'm seeing something fishy with what I used recently)?

Here's Franks very swanky article on fixing nitro cracks:
http://www.frets.com/FRETSPages/Luthier/Technique/Finish/Lacquer/Ch...

[Ron Frazier]

What did you use to wet sand the finish for lube on the sandpaper?
I used one time only water and it got into all the screw holes and swelled the wood so it cracked! That meant another finish job with all the red black yellow sunbursts. I now only use paint thinner to sand!

Ron

[Frank Ford]

NItrocellulose lacquer varies in formulation, so if you get lacquer that is either not made for our purposes (McFadden, for example, is a good one) or a "bad batch," all manner of problems may arise.

That said, nitrocellulose lacquer will check spontaneously if it is applied too thickly. A good example here is Gibson - famous for old cracked lacquer finishes. The finish on those instruments is often twice as thick as Martin's or even significantly more that that. The generally accepted "target" is .006" film thickness. In order to avoid checking, Collings aims for half that, with a solid UV cured undercoat.

And, the thicker the finish, the more likely it will respond to humidity, temperature, and other influences by cracking.

Really thin nitrocellulose lacquer doesn't check at all, but it's so thin it can't be leveled and polished with abrasives.

[Ed Perkins]

Ron and Pengl thank you for your replies, I am in Sacramento, ca area I am sure this is not due to moisture in the wood - the guitar top was made from a spruce 1947 piano sound board ( the guitar does sound great in spite of the cracking). There were no screw holes in line with the cracks wet sanding was done with the water sprayed on the sand paper not the guitar. The Nitro finish material was McFadden brand (purchased from lmii). I followed instructions from lmii info pages on finishing.

However it may be that Frank hit it on the head. Being this was my first instrument I sanded lightly in between coats and may have applied too much lacquer. I just started to suspect that the thickness of the lacquer may be the culprit but I was not certain.

Again thank you all for your input I needed some opions as I am working on my second guitar and don't want to have this problem again.

[Russell Vance]

I'm with Frank on this one - my initial attempts at nitro spraying many years ago resulted in longitudinal cracks throughout the lacquer (on swamp ash mainly) and this was definitely a result of too much lacquer, too soon with too little thinner. I was also using a commercial brand of Nitro which was definitely a problem when used on wood. I have, over the years, evolved to spray 50% thinned light coats of a lacquer formulated for guitar work with little sanding between coats over skinny sanding sealer coats (not too many coats). My experience is that thick applications are prone to checking. Rusty.

[William F.Eden]

Ed it is not that hard to fix the cracks in the finish any ways. But if you think your getting to much finsh on just sand it a little more be- for you buff it up . I use kerosene for my lubricant when sanding. Most always it will crack from the edge in word so you don't want to put your finish on to heavy in those area's Bill.:::::::::;