Hairspray as a finish coat??

It's work, but I don't recommend it. Not only have model railroaders used hairspray as a fixative, but artists have done so as well. Art supply and craft stores sell workable and non-workable fixatives in rattle cans, but they can be pricey. Hairspray is a cheaper alternative used by many art students or artists short on cash. They apply it over their charcoal drawings or pastel paintings. I've used it to get pastels to adhere to brass--it worked, it dried rock hard.

In a way, hairspray has similarities to paint. Hairspray has a film-former (binder) and solvents. It usually has fragrances as well, which I can't stand personally. But hairspray formulas vary so much that experimentation is an absolute must.

So yeah, it will work, but I wouldn't recommend it for an entire model. Hairspray is made to last a day at most, and is designed to be easily washed away. These aren't qualities I'd want for a finish. Better to stick with something meant to last. The artist grade fixatives would be a better choice, but their ingredient list resembles a spray lacquer, which leads us back to dullcote.

Personally, I haven't had good luck using thinner as a fixer. It is better than nothing, but it doesn't leave a protective film when it evaporates. I have used AK Interactive pigment fixer and Humbrol matte cote with greater success, but those products can also alter the appearance of the powders. I've given up on using weathering powder/pastels for things like dusting and staining, preferring to dry brush with oil paints instead. The oil paint has it's own fixer built right in!

I fix my pigments with thinner,and they hold up to light handling.really no need to seal pigments,once your build is done,how much and how roughly  will you really  handle it anyway ?

Also I wouldn't seal with hairspray,I would think the heat from your hands could cause problems with the finish.

Well, that's certainly contrary to my experience. Model railroaders have been using hair spray as a fixative for years. Perhaps certain brands dry glossy, but I haven't seen that. And, unless you're modeling a working ship or storing your models outdoors, how much water do you expect to get on your models?

Good god, no. Don't use hair spray. It comes out glossy, and can get sticky. And if water hits it, it'll be a mess. Seriously, just use acrylic Model Master if you feel the need to seal your models. I don't seal 9% of my models, by the way.

I've used hairspray on a number of models, but the results have been very mixed, although I've found no more so than Dullcote. Some pigments seem to melt away and some withstand it well and it's generally just trial and error. The best results I've had involved spraying the hair spray first, allowing it to semi-dry, and then applying the pigment. The hair spray acted both as a fixative and seemed to give the surface more "tooth" for the pigment to grip onto. It dries matte.