Combining enamel and polyurethane finishes

[Richard Braithwaite]

The upper image in the picture below shows some wood (Ash) that I painted 40 years ago. All the planking was coated with  about 5 coats of polyurethane varnish and a couple of coats of black/white Humbrol Enamel was applied directly on top with a further coat of polyurethane varnish on top to proect it.

 

As you can see the white paint has discoloured slightly , Im not sure whether this is due to the yellowing of the polyurethane on top or pigments comening through from underneath...

 

The lower image shows part of the full size Trireme reconstruction "Olympias". I am building a model of this vessel (Trireme Olympias by Richard Braithwaite - - Subjects built Up to and including 1500 AD - Model Ship World™) . The model is finished with polyurethane varnish and I need to decide how to finish the oars (varnished shaft, white painted blades)

So far Im thinking of two alternatives:

 

1. Coat the entire oar (blade and shaft) with polyurethane and then coat the bade with primer and overcoat with white enamel.

2. coat the shaft with polyurethane up to the boundary with the blade. Apply primer to the bare wood of the blade and overcoat with enamel.

 

The second option would make most sense in terms of keeping the different paint systems separate, but I suspect i could do a neater job with the boundary with the first option.

 

What experience do you have with this sort of paint scheme?

[Capt. Kelso]

From my experience anything I have painted with enamel or lacquer white paint has "discolored" or faded over time. I was looking at one of my builds completed in 1992, kept in a glass case and noticed how the white paint has faded. I typically apply (airbrush) a coat of flat Dullcote finish to my entire build, hard to tell if that is the cause. 

[paul ron]

i use to oil paint and learned white comes in many different formulas. eg; zink white eventually takes on a bone color as it oxidizes. where titanium white will not change color over time.  

 

another factor is what you are painting over. if your primer changes tint over time, the color coat will change as the base color bleeds through. 

 

so paint selection for each coat is very important. also note the varnish over coat may be changing to a darker color as it ages, not the white changing at all.

 

my suspicion says its your varnish overcoat. why do you need to varnish over the enamel? its not a weathering situation or protective coating... the enamel should be sufficient.

 

as for primers... the reason for a primer on wood is to seal it from absorbing the paint so you can get an even color coat and help from raising the grain. just use thinned paint we call a **** coat. that hardens in the surface wood and allows you to sand off the fuzz. now the finish color coat will go on evenly. sometimes you may need extra prime coat and or color coats depending how porous the wood is.

 

 

 

 

 

[Richard Braithwaite]

I wont be overcoating the white enamel paint with varnish this time. Just trying to decide what to do underneath it. Have heard that a shellac primer might help prevent pigments coming through.