Naphtha

[dmlinger]

Trying I've finished several guitars and ran into an issue with a new one I'm working on. Note the only difference is in the past I've used Behlen/Mohawk Classical Instrument Lacquer and this time I used Mohawks "Finisher's Choice Clear Lacquer"

Here are the steps I always use:

Grain fill with Aqua Coat
Let dry 24 hours, sand, repeat as necessary
2 coats Mohawk Vinyl Sealer
24 hour dry, sand
Color coat - used StewMac's black in aerosol because I don't like pigmenting black myself
Waited a few hours and laid down a few coats of the "Finishers Choice Gloss Lacquer"

Here is where it goes bad. Went out of town for a week for work. Came back and was going to do some more top coats. The finish was hard after a week, so I wiped it down with Naphtha to get the dust off and any oils from handling. Have done this dozens of time on previous builds. A few moments after the naphtha hit it, the finish got instantly gummy/sticky.

I've waited several days and went to sand it all off to start fresh, and it's still gummy. Won't hardly even sand it's so bad.

What happened? The naphtha I use is Klean Strip brand VM&P Naphtha.

 

[Spud]

I wonder if the Stew Mac aerosol black lacquer wasn't fully dry? Is Mohawk a nitro base or an acrylic base lacquer?

Someone else who has used these specific brands will chime in as I have not. I have personally run into problems MIXING DIFFERENT BRANDS of rattle cans when refinishing antique floor vent covers and had to strip them down and start over.
Naptha itself shouldn't have done that to the finish.

 

[Rick]

Sounds like it wasn’t fully cured.  Why … I dunno.

 

[BroccoliRob]

in the 90s i told my gf (short for girl friend, but when she's more than a friend-friend, it usually has to be romance) that i wanted to go to nappa valley and try the wine, but i was a little, how you say..., "hyper-stimulated," and accidentally said "Naptha valley" and she laughed so hard that she dropped the bag of heirloom tomatoes we had just harvested from our garden (well... a garden). because of that we couldnt make our own ketchup until we made it to the next town and found more gardens and by that time we had already gotten dozens of packets from fast food places. it set my Hard Condiments project back years. tbh i'm still working out the various ratio. why must i suffer in this #meatprison??

 

[DuckBaloo]

Doesn't the Finishers Choice have a drying retarder and an increased drying time? I know the Stew Mac does.

 

[raystankewitz]

VM&P Naptha shouldn't have affected cured lacquer to any great extent, short of giving it a slight hazy appearance that goes away when you buff the finish. The fact that it went gummy and stayed that way means something was not cured or not compatible. My guess is a lack of drying time between the black and the clear, being they were not from the same source and some incompatibility may exist. Or, the black may not have been fully cured. Before I clearcoat things, I let the substrate finishes cure for at least a week or more, just to be sure the finish has had ample time to outgas.

 

[NedRyerson]

Note the only difference is in the past I've used Behlen/Mohawk Classical Instrument Lacquer and this time I used Mohawks "Finisher's Choice Clear Lacquer"

Color coat - used StewMac's black in aerosol because I don't like pigmenting black myself
Waited a few hours and laid down a few coats of the "Finishers Choice Gloss Lacquer"

This right here tells me "chemical incompatibility."  The naphtha wasn't the cause, but the catalyst and symptom.