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Hello all, I've been having an issue with finishing my latest guitar (#2). I'm hoping to get some reassurance that the problem is what I think it is (other than I stink at finishing).

The guitar is a mahogany dread with adi spruce top. I stained the mahogany a little darker and used system 3 epoxy pore fill over that again as on my first build last year (and had a much better experience this time with that part). I ended up doing 3 coats. I used em6000 on my first and for this one I decided to try the new Polywhey finish.

I applied 5 coats the first day, 2 hours apart with a light spray of DA between each coat. The next day, I level sanded with P600 (wet with mineral spirits) and sprayed 5 more coats. I then let it cure for 2 weeks. I level sanded (wet again) with P800 and began to buff out the finish with Menzerna 2l pre-polish paste. That when I noticed 2 spots on the back that wouldn't shine up. I found one more on the top and 2 more on the sides. I assumed they were sand through and tried to repair them by brushing on a couple more coats over the spots. I let it cure for a week this time and then level sanded again but each one of the spots reappeared.

Round 2, I bit the bullet and decided to spray 5 more top coats after I scuff sanded with 400 I think. Let cure for 2 weeks and level sanded yesterday. The largest spot on the back reappeared. and I have a small spot on the side. The good news is the other spots didn't come back so I'm thinking it was indeed just sand through however, before I sprayed more coats and wait 2 more weeks I want to make sure there isn't anything I'm missing. This time, I'm probably going to spray more than 5 to be safe and since it's just the back and sides. Here is a picture of the spot I'm talking about. You have to look from a certain angle to see it.



I know that was a lot of babbling just to ask if that looks like sand though haha.

Any input would be appreciated!

Jeff

That looks like blushing to me but you'd think if would be less localized. I'd let it sit for a month or more (set it up and play it though) to see if it clears up....

Can't really see if that's sand through from the picture.

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Was it very humid when you sprayed? If so there's a good chance it's blushing like Rod indicated.

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It was actually around 30% when i sprayed. I only know that because the same week (after I sprayed) I decided to get my shop humidity under control. I'm going to spend some time in the shop this afternoon so I'll post anything else I might find.

I also edited the first post so you could click on the picture to enlarge it.

Thanks guys.

Jeff

Well it's probably not blush then, unless it's amine blush from the epoxy, in which case it's likely to get worse, or a sand through like you think.

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Jim Watts
http://jameswattsguitars.com

Looking at the bigger picture on my PC instead of my iPhone, it does look more like sand through to me. I don't know what amine blush is as I've not used epoxy to pore fill.....might want to do a search on it.

Mind you, does it fully go away when you spray new coats on it? What's it look like before you sanded/buffed out, after waiting the 2 weeks (second time...)?

If it wasn't there than you probably have sand through....

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Jeff,

I think I would only wipe with a damp cloth between coats and only use the mineral spirits on final leveling. I would be concerned that you might get some contamination with the mineral spirits between coats.

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Steve Smith
"Music is what feelings sound like"

Totally looks like sand through to me, especially with the lighter spot in the middle of the dull circle.

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Thanks for the help guys. I wanted to be reasonably confident that I am fixing the right problem before I shot more top coats. As frustrating as this is, at least I know where to go with it.

Thanks again.

Still fighting it, eh, Jeff?! Bummer! Could you see the spot before you level sanded prior to buffing? If not, I'd certainly attribute it to sand through.

BTW, denatured alcohol is not the same as mineral spirits. You should be okay using DA, but I don't know for certain with respect to your poly whey stuff. I swab my EM6000 between coats using a cloth moistened with a 50/50 mix of DA and water. Never, ever had an issue.

Ken

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Yep! Can't quite close the book on this one! I didn't buff it out this time, but yes I noticed the spot after level sanding and not before. After thinking about it since this weekend, it's not all that surprising that I sanded through there again because there were only 5 coats over that spot and no one would expect to just put 5 coats of waterborne finish on a guitar and not sand through. Live and learn...live and learn.

As far as the DA, what I've been doing is wiping down with that 50/50 mix (DA and water) like you said after I do any level or scuff sanding and then I spray the the DA left in the spray gun on the guitar before spraying the next coat of finish. As far as I can tell, that's been working out great.

Were you using an ROS or hand sanding?

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Hi Colin, I was handing sanding. I have a ROS but haven't used it for sanding finish yet.