2-part epoxy over nitro?

[eb0248]

Hi, new here, thanks. Hope this is in the right place. I've used 2-part epoxy over acrylic and poly, bought color that I wasn't aware was nitro until it arrived. Can I use 2-part epoxy clear over it if I let the nitro sit for a LONG time? 

[Bizman62]

Hi and welcome!

To answer your question I don't know for sure but for what I've heard and read nitro keeps shrinking forever. And I really mean forever, like decades. Just look at the crackled vintage guitars! Also, unlike 2-part stuff, the drying of nitro is based on evaporating the solvents. So you'd have to wait at least until there's no smell - I just read about a guitar that had the smell after a year! Obviously, if the underlaying nitro keeps gassing it will try to push the epoxy layer off.

Doesn't the above sound like "no"? As said, I don't know for sure but knowing that certain coats don't work together (like oil based wall paint over latex) I'd be very cautious with nitro. A nitro clearcoat would be the safest bet and give a similar lustre and if stored properly it would also last.

[eb0248]

Thanks, kinda knew answer, was hoping someone would call me out for the novice I am and say it was fine. Nitro clear it is, then.

[Bizman62]

7 hours ago, eb0248 said:

was hoping someone would call me out for the novice I am and say it was fine

As I'm no expert either I was hoping the same but since none of the more savvy active ones has chimed in and corrected my answer I guess the advice of using nitro on nitro has silently been accepted.

[henrim]

Not that I have ever tried, but it makes sense not to spray poly(anything) over nitro. Nitro will probably keep living under the clear on top of it and cause problems. The other way around it probably works just fine. But all in all, I have experienced so many unpleasant surprises when coating over with paint that has different base that I rather just use one product on one project. There are still great many possibilities to screw up even with that approach.

[Professor Woozle]

Apologies for taking the thread off at a bit of a tangent, but has anyone ever tried accelerating the curing of nitrocellulose using a vaccuum? I've been wondering for a while what effect that would have on the speed of solvent evaporation, and whether it would cause the nitro to shrink too quickly and check? Could be a way of artificially ageing  a guitar if it did do that!

[Bizman62]

That might work to some extent, shrinking and checking are the results I'm tempted to suppose as well. Interesting...

There's a technical issue, though: If you just lay a freshly lacquered guitar into a vacuum bag the nitro will most likely stick to the plastic. A basket of sorts would solve that problem but the guitar will still lay on a couple of slats. A vacuum chamber where the guitar could hang freely would be the optimal solution.

Thinking further about a vacuum chamber or cabinet... The size doesn't have to be huge so one could easily build one into the workshop - something like 1200H x 500W x 300D in millimetres would suffice with the door being in front on the largest panel. 12 mm thick coated plywood should be sturdy enough to prevent collapsing and the automatic electric pump of a vacuum bag system should be plenty strong. If you already have the vacuum bag building such a cabinet wouldn't cost too much.