Acoustic Guitar Construction

Dave, thank you for the advice

So I decided to sand the back down to start over. 120,220,400,600 grits. I applied three coats of TO and the spots have appeared once more. After the first two coats, they were not visible, but they reared their ugly head after the third. I'm not quite sure what to do about it. A coworker of mine who makes furniture suggested Minwax pre stain wood conditioner. Any opinions on that?

My process of applying the oil has been this: Using a french polish pad made of old tshirt, put a little TO onto the pad, much like you'd do with a cotton ball, then swirl the oil over the surface. Then wipe off using a paper towel with a credit card in the fold of the towel for stability. I didn't sand at all this time. I waited an hour between coats.

This is a total guess since I have never used that chemical -- but those flaws appear to be a sort of blush which happens when the previous coats are not completely dry -- the solvent evaporation has no place to go, so the gases seep in between the layers. At any rate there seems to be some sort of contamination -- maybe "stearate" sand paper residue?

I would suggest some experimentation -- maybe seal with a wash coat of shellac or lacquer?

So I did go to the Birchwood Tru Oil site their video says to wait over night between coats, Might want to contact their tech support. But I have seen DB work and it looks great using his application system. Its a mystery?

More from Birchwood -- interesting comment relative to Rosewood


FAQ

Q: How can I increase the shelf life of Tru-Oil? A: To increase the shelf life of Tru-Oil poke, a small hole in the foil instead of pulling it all the way off and store the bottle upside down after opening.

Q: Can Tru-Oil be thinned out? A: Tru-Oil can be thinned out using mineral spirits. Please note: Adding mineral spirits will increase drying time.

Q: Will Tru-Oil change the color of the wood? A: No, Tru-Oil will not change the color, however it does have a golden hue amber tint that will enhance the wood.

Q: Are Tru-Oil and lacquer compatible? A: No.

Q: Will Tru-Oil work on laminate? A: Yes.

Q: Before using Tru-Oil should I use a water-based stain or an oil-based stain? A: We recommend using a water-based stain. If using an oil-based stain, allow extra dry time.

Q: How do I apply Tru-Oil? A: Apply Tru-Oil using your finger or a lint free cloth.

Q: How long until Tru-Oil is dry to the touch? A: Tru-Oil will be dry to the touch in approximately 2-4 hours, depending on climate. We recommending allowing 12 + hours between coats of Tru-Oil.

Q: How long is recommended between coats of Tru-Oil? A: We recommending allowing 12 + hours between coats.

Q: What temperature works best for applying Tru-Oil? A: Room temperature is ideal for applying Tru-Oil. It will dry faster in low humidity as well.

Q: Can I add linseed to increase dry time? A: Not recommended.

Q: Will Tru-Oil penetrate oily wood? A: Tru-Oil has a difficult time penetrating and drying on oily woods (i.e. ebony rosewood and cocobolo). If using an oily wood, you can try using mineral spirits to thin out the Tru-Oil or seal the wood prior to the Tru-Oil application.

Q: How long do I need to wait until rubbing Tru-Oil out with abrasive agent? A: If using Stock Sheen and Conditioner, wait a minimum of 7 days. If using Rotten stone, wait one month after Tru-Oil application.

Have a question about this product? Contact Birchwood Casey Customer Service: Toll-Free: 800-Shoot-N-C (746-6862) Or by email: customerservice@birchwoodcasey.com

I think Ken is right about the TO not being completely dry? I will put up to 4 coats a day with my method, but only if the humidity is under 50% and the temperature above 65* or so. If you are already doing those things, maybe you do need to wait overnight for a thorough dry.
I've contacted Birchwood-Casey a number of times and they are very helpful - I sent them some pix of my work that I finished with TO and they are happy about that - so maybe send them a pic like the one you posted above, and just ask them what they think. And let us know. :-)

In any case, you are going to end up with a nice finish.

Thanks Ken, Thanks Dave, you've been very helpful!

Ken, I never thought of the sandpaper, however when taking a look at the fine print on the paper I bought (3M Pro grade advanced sandpaper), it says it 'has an anti-load coating for long life'. If this is a waxy coating, perhaps this is the cause. Also, I absolutely was not following BC's recommendation for 12+ hours between coats. I just now applied one coat, and it looks good - no spots, very thin. I will wait 24 hours before applying the next coat. I've been in air conditioned temps between 68-75, however my humidity is higher than 50% for sure. It's been quite humid here in the Chicago 'burbs lately. So for now, I will be doing one coat a day. If it seems to be working, I'll stick with it! Thanks again!

In the meantime, I've made the 'C' inlay from a white MOP blank, set it, and am finishing the neck. I cut the letter using the dremel and a tiny downcut bit. And set it with CA glue and rosewood sanding dust. It was a little scary putting so much CA all over the thing, but it sanded down nicely. It's my first effort at cutting pearl and inlaying - I'm happy with it but I know I can improve vastly.

You are too hard on yourself - I would have given you an A- at the very least!! :-)