MIMF

Dear friends
What do you use as time after applying last coat of NC before polishing?
I finished one guitar now that just does not seem to harden out like normal. I used plenty of time in between layers. Maybe the lacquer or thinner has a deficiency?? It has not been too warm yet here so that has not helped either but still this one looks like the layers have not hardened in between though timewise it has to. Any suggestions?

For me, I usually wait 2 weeks after the last coat of nitro cell before polishing.
Also, I don't spray lacquer until it's above 60 degrees F. Maybe, eventually your finish will harden. It may just take a little longer.

It helps to keep the guitar at a high temp after final coat. I usually have it at 80 degrees for a few days.

I've always heard that cutting through the sprayed surface early on helps the lacquer gas off more quickly. I really don't know if this is true but it makes some sense to me. Heat and airflow do help but only in moderation and be very aware of the RH if you are doing this in an enclosed space. You can level and polish as soon as you want but if you want that buffed surface to stay flat later you've got to wait a month minimum unless you are using a high-solids lacquer that's in the 50+% solids, trad lacquer is only 15%.

I wait one month.

Lacquer not hardening could be old material. Most manufacturers place a use-by date or instructions to use it before one year. I have had issues from using nitro lacquer that was too old, and it doesn't get hard. If your finish is very thick it will be soft for a long time even if the lacquer is fairly new.

I usually do a high gloss nitro finish with 7 or 8 coats total, and sanded between coats so most of it has been sanded off. 8 weeks before final sanding with 1000 or 1200 and buffing out. This gives a very nice finish that doesn't sink or shrink noticeably.

Three weeks without a drying box; 10 days with one. Old nitro should cure as well as new nitro - nothing in the formulation that degrades over time that I've seen. Shelf life is more an issue of corrosion of cans, versus anything else, according to the product guys at McFaddens. Cardinal may be different, but Behlens/Mohawk and Seagraves not so much.

Both Seagraves and McFadden have done the never- get- totally-hard thing on some of my guitars. If your lacquer is a couple years old it is very likely to happen to you too. The older lacquers I used 20 or more years ago would work well as long as you could thin them enough to spray them, and they got hard when dry. I first had this issue with a Simpson product, then McFadden, and finally Seagraves as it was the replacement for McFadden. I don't know the chemistry of these proprietary products, but lacquer formulations have changed over the years, especially here in California. Either the new Cardinal lacquer will work better of i will move to other finishes and just not use lacquer.

Quite a bit of time has passed and it is still worthless. Not nearly hard enough to do a normal polishing. I consider this one as failed.

i have taken the whole lacquer off. What an incredible waste of time The customer wants nitro. Nothing else will do. My preference would be to use a 2k lacquer with some added product to give it the properties nitro has for elasticity for instance. Now I can order some other nc if I can find it here, and just start trying again.
Unfortunately the brands mentioned are not available here, if you can get nitro it comes via the webshops from an unknown supplier...