varnishing

Steve

You have used two different material names. Varnish and Lacquer are two different materials. These used to be solvent based but in todays world they may be water based even if they are in spray cans. I also am assuming you are talking about some sort of plastic kit not the real thing.

In any event I would find a piece of scrap material that you used to build your boat, paint it with your water based paint and then trial spray it with what you plan to use as a finish.

Amphib

Are you  talking about a clear coat, or do you want to apply more colored paint?

a clear coat, as some of the top coats were a bit dull in finish

Clear acrylic lacquer can be applied over acrylics okay, but a real old fashioned lacquer may give problems.  I know several friends who use Testors Glosscoat lacquer over acrylics without problems but I personally try to avoid it.

If you mean trying to get a glossy varnished look, try Future floor polish. It can be airbrushed, cleans up with Windex. It can also be brushed on with a soft clean and wide brush. Just go slowly to avoid bubbles and apply sparingly in several coats as it tends to run pretty easily.

Take a look at the hull of my Felixstowe in the FSM WW1 GB. It came out looking pretty much like varnished mahogany.

In my experience, you can varnish over acrylic paint but the varnish will not really adhear to the paint. Rather, it will lay over the acrylic paint and thus it will be very fragil.

Polyurethane varnish adheres to most paints reasonably well. I have used it as a clearcoat several times. It must be thinned way down, but can be airbrushed okay. It is nice because it comes in three surface finishes- gloss, semi-matt and matt.

thanks to everyone who answered my post, I'll have a go and see what happens.