Exhaust stain issue

If your useing pastels, they need to be applied on top of any clear coats.

FWIW, this is why I stopped using pastels for weathering.

Some folks are ok with not being able to handle finished models, I'm just not wired that way.

I think pastels look great, so if you are ok with them not being sealed, you should be golden with Bish's advice.

I'll never forget that first time all those decades ago, spent forever getting a boxcar all pasteled up perfectly, hit it with some Dullcoat. Gone. I know just how you feel!

Greg

I'll never forget that first time all those decades ago, spent forever getting a boxcar all pasteled up perfectly, hit it with some Dullcoat. Gone. I know just how you feel!

My experience almost exactly!

That's when I started becoming a dry-brushing fanatic. It's pretty easy to replicate many pastel effects with a stiff-ish brush and a few complimentary tones of your base color.

Do you really need to seal pastels or other weathering powders?  If they are finely ground enough they should stick like gangbusters.  I also do translucent exhaust stains and such by drybrushing paint and find few compatibility problems between finish types.  BTW, watercolors are great for drybrushing.  Add a tiny drop of soap or vinegar to the water.