Nitro finish challenge

[Steve Sawyer]

I have a guitar body that is shaped, routed and ready for the final sanding schedule.

I'll be finishing it with rattle-can (ReRanch) nitro.

I don't have any kind of spraying facilities, and I had hoped to be ready to start spraying this while I could still do it outside, or hung in my garage with the doors open. I'm still finishing up the shop remodeling project, but I could dig this body out of the storage boxes to hurry up and get it ready for finishing. I could also find someone in my local woodworking club who has a spray booth so I could wait until the shop is done to finish it, but given the geography of our membership it might be a 20-mile drive one-way to their shop to do the finishing.

Either way, I don't want to rush this, but I'm trying to figure out how much good weather I need to get the finish on, OR how much driving back-and-forth to the friend's shop is going to be required. Obviously I don't know how many coats of each type (pigmented and clear-coat) will be required, but it would help to have some idea how long (given typical "room" temperatures of 60-80 degrees and moderate humidity of no more than 50% typical for this area in autumn) must I let each coat cure before sanding?

If it turns out that I really must have a good long spell of good weather to get this done, I might just put this part of the project on the back burner until spring (I'll have to hang the body in the garage for a while after spraying to keep the fumes from collecting in the house), and work on the neck or start another guitar (one that I can finish in my own shop! ) in the meantime.

Any other thoughts or suggestions are appreciated.

[Karl Hoyt]

Jeez...... This sounds like an acoustic I was trying to get the finish on. Back in June/July. I'd have a decent day or two... Then the heat/humidity would roll in... Wait a couple weeks until the next decent day... Shoot some more. Etc etc.....very unnerving.

If you have everything all set to go, you can do it in stages. That's the beauty of Nitro... It burns in the last coat as long as you rough up the finish after it's been sitting a while. Let's say you have a weekend coming up that's going to be cool-ish (above 55 degrees). Shoot three to four coats about a half an hour to an hour apart. Come back the next day.... Use some 400 grit to rough up the finish and get any dust particles or whatever off: Then shoot 3-4 coats again. If you have to put the instrument away (hang it, don't leave it laying on anything.). Just rough the finish back up and shoot another 3-4 coats.... Etc etc. I generally do 3 sealer coats and grain filler if necessary....... Sand back..... 3/4 clear coats.....light sanding 3-4 more coats. Let it sit for a week+... Then level sand and evaluate how many more coats you want to do... Then let it sit for at least a couple weeks before wet sanding and buffing.

I would suspect that Detroit is very similar to Taxachusetts in the fall: We have quite a few weeks where the afternoon temperature is in the 55-70 degree range with much lower humidity and it should be fine for shooting outside... Just hang it someplace warm and dry in between coats.

Hope this was helpful.

[Steve Sawyer]

Thanks, Karl. Good to know I don't have to sand between each coat. That should help things along.

How concerned should I be about overnight temp if I hang it in an unheated attached garage? Nothing extreme, but with daytime temps in that range, it could dip down to the upper 30's overnight which should stay mid-40''s in the garage.

[Bob Gramann]

Watch out for checking if the temperature changes, especially if your finish is thick.

[Steve Sawyer]

Watch out for checking if the temperature changes, especially if your finish is thick.

Is the risk of that dependent on the state of the cure? IOW would it be more likely to check if it cools down 12 hours after shooting, than only 4 hours or vise-versa?

[Karl Hoyt]

I shoot my nitro in an unheated shed. Once the final coat of the day is on , I shut the doors and windows to preserve the heat of the day as much as possible. So even if it goes down to freezing at night , the temp in the shed doesn't.

When the temp is REALLY going to drop, I hang mine in the house ..... Downstairs in my shop.... I have to wait until the last possible minute to get as much off gassing as possible done so my wife doesn't kill me if the smell of lacquer pervades the downstairs....... So far/so good. No checking.

For the dead of winter, I need to find someone with a spray booth, like an auto body guy...that will let me shoot and hang a couple instruments.

Take care

Karl

[Bob Gramann]

When I did nitro (spray can) last, I thought I had it perfect. I sprayed in the 50 degree garage and brought it in when it didn't smell too bad. I repeated this process until I had the thickness I needed to patch the instrument I was working on. I blended to the old finish, polished, all was good. A week later, it crazed. Very sad. I feel that the failure was a combination of the thickness required and the frequent temperature changes. I don't have the right equipment for nitro--I need a temperature controlled fume safe spray booth and a safe place for it to cure. I won't be spraying it at my home ever again.

[Barry Daniels]

I once had a finishing disaster spraying nitro when the outside temperature was dipping down to 32 F. Sprayed the last coat after sanding flat. It looked fine but the next morning my super thick finish had crazed.

[Steve Sawyer]

Well, it's starting to look like I may have missed the magic moment for this year on this project. I just wish there was an alternative to lacquer to get the color I want. There are so many options for clear finishes...

[Bob Gramann]

I have used Target's EM6600--black satin topcoated by gloss clear EM6000 to get a black finish. They sell a white tint base https://www.targetcoatings.com/product/ ... l-lacquer/ that you can tint to any color on a paint store color chart with the paint store pigments. It works better with a bigger spray tip than I normally use for the clear (1.3 mm) but I made it work with the 1.3 tip by thinning it. It's water base (you still ought to wear a respirator) and no more toxic than a low emission latex paint so you can keep it indoors. I haven't any trouble spraying outdoors in cool to hot weather and then bringing the workpiece in. In winter, I set up a fan booth to exhaust the overspray outdoors through a filter.

For my black acoustic guitar, I sprayed 8 coats of clear gloss (after pore filling--I used Target's HSF5000 on this one), leveled the finish, sprayed two coats of black, and finished with 6 of clear before leveling and polishing. With the EM6000, I spray 3 to 4 coats a day with half an hour between coats--no need to clean the gun until the session for the day is over.

These products do require a good gun, but the results are well worth it. The EM6000 burns into itself like nitro, can be finally leveled and polished after 7 days, and doesn't smell. It might not be the answer you're looking for, but it is a possible way forward. It can be brushed (think high quality fine-bristled brush and very thin coats) and leveled with sandpaper, but you won't have fun getting it perfect that way.

[Steve Sawyer]

Bob - that's interesting (beautiful guitar, BTW). Unfortunately I don't have any spray equipment. I understand that folks have had some success using Enduro-Var as a wipe-on clearcoat, but getting a good color-match (I'm going for a vintage Fender seafoam green) for the pigmented coats has me flummoxed other than going with the ReRanch product.

I'm tempted to do some testing with milk paint under Enduro-Var - anyone been down that path before? Even if it works I have no idea how to achieve the color I'm shooting for...

[Karl Hoyt]

I like the Target stuff too, Bob. I did a guitar that was going to be a donation with the EM6000. Built up a nice coat and sanded it flat with (I think) 400..... Then a couple more finishing coats. I let it sit for about a month. Dry sanded through 1000 grit and then 'wet' sanded with 2000 grit and mineral spirits ...then machine buffed (being VERY careful to not catch the corners with the buffing wheel.....).

I'll tell you: I had a client over to the shop and put out two guitars: one with nitro lacquer and one with the target, and asked the person to pick out the Nitro finished guitar: He could not tell the difference. AND I didn't worry about my house blowing up while shooting it. I have some of the 9000 I'm going to try on a couple electric basses. Supposedly that stuff is even harder and shinier!

I have some people who insist on nitro for their acoustic guitars and some who could care less as long as the guitar sounds good. For the Nitro crowd, I'll keep a target finished acoustic around and not tell them what it's finished with.....that should help make the transition to H2O based products easier

Kfh