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Paint over varnish or oil etc


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I am a TERRIBLE painter  - its just a fact. So most of my models I finish in varnish or oil with maybe a few fittings etc in paint and I generally prefer that as a finish.

 

But the Pegasus I am on now has all that nice decoration which I didnt bother with in my Fly builds - so I thought it was time to try it.

 

My default approach is to first plank whole hull without piercing gunports etc so that  can be sanded nicely and I

frequently put on a light varnish coat at this point to help see all is smooth.

 

Then i do a much more robust varnish but protect with sticky tape, or something similar, areas where channels etc may be glued.

 

So, if I do that on the present hull - what do I need to do (if anything) so I can paint on top of the varnish to give a satisfactory adhesion.

 

Or is this just a no go ?

Does waxing or oiling instead of varnish make a difference to the answer

 

I painted some test pieces and actually the paint seemed to go on well - but my brain is telling me that this isnt a sensible thing to do.

 

 Advice from expert painters please !!

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Hi  Spy,

 

I don't consider myself to be an expert painter, they seem to be thin on the ground given the response to your post ;)

 

 but......

 

I don't think painting over varnish is going to create a problem provided the varnish is given a light sanding beforehand, it is then effectively acting as a sanding sealer.

 

I would be less happy about painting over a waxed or oiled surface which may give adhesion  problems unless it is thoroughly cleaned down.

 

B.E.

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I agree with BE, the only thing needed is a light sanding to give the varnish a 'tooth' that the paint will stick to. It also smooths out all the rough fibres in the surface. I use fine wire wool myself but you can use whatever works for you.

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Yes thanks for that chaps.  As I say i tried several test pieces rubbed down with  a very fine glass paper and they seem fine - it was just that nagging doubt.

 

Incidentally though i do use wire wool in general because I find it best but it does have a problem sometimes if any trace of iron is left and you can get teeny rust stains after a while.  It always wise to do a  really good surface cleaning after finishing with wire wool

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I don’t use any paint on the hulls, preferring stain to highlight the wood.  See rattlesnake by mog in the build log.  Of course whatever finish you use depends on the end result your looking for.    I use both sanding seal and thinned lacquer rubbed down with very fine steel wool, a tack cloth will get out most of the fibres left behind. As others have said you can paint over both as  long as you fine sand or rub to a smooth finish, on things I do paint I don’t think I would use oil or wax as a base as the paint might not jell well with the small bits of oil that never dry totally, wax sometimes makes the paint look grainy

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I agree with BE, the only thing needed is a light sanding to give the varnish a 'tooth' that the paint will stick to. It also smooths out all the rough fibres in the surface. I use fine wire wool myself but you can use whatever works for you.

 

If you have a compressor for a spray gun, you can give the surface a blast of air which usually cleans all the wire wool dust off. 

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An old painters' rule is: fat over lean, meaning you can use oil-paints over say guache or acrylics (nowadays), but not the other way around. So acrylics would not stick on waxed or oiled surfaces. However, you can use acrylics on many varnishes, particularly, when they have been sanded down, as noted before.

 

wefalck

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Primer over varnish ? What for ? If the primer contains a solvent for the varnish, you might be in trouble. No, in general rubbing down the varnish with fine wet-and-dry paper or fine steel is sufficient to provide a key for the following paint.

 

wefalck

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There are many different types of varnish around these days. Essentially, they are paints without pigments and can have various agents added that e.g. make them more elastic in order to improve their wear-resistance. I believe many furniture varnishes now are polyurethane-based.

 

Shellac (http://en.wikipedia.org/wiki/Shellac) is an excretion from a particular species of lice that is dissolved in alcohol. If no additional things, such as waxes are dissolved in the shellac-solution, there should be no problem with the adhesion of paints that use water as solvent, e.g. artists/modellers acrylics or latex dispersions. There should also be no problem for oil-based or similar paints as you follow the 'fat (=oily) over lean' principle. Sanding the varnished areas, of course, smoothes the surface and provides a better key for the paint. I do not foresee any problems in applying acrylics on shellac-based varnish with an airbrush.

 

BTW, I would not use shellac varnish on working models, as this varnish is not water resistant !

 

wefalck

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That article refers to painting a wooden floor.  I doubt your model is going to get the use and abuse a wood floor gets, and adding primer only makes the overall covering thicker and will obscure fine details.

 

wefalck is right, you don't need primer if you just rub the gloss off the shellac with steel wool or wet-and-dry paper before you paint it.

 

Dan.

Edited by overdale
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Ahoy wefalck and Dan :D

 

Thank you so much for the responses. It takes so much work to get to this phase.

 

I will be sure to post the final results in my log for others.

Edited by JPett
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donfarr, I don't think your question(s) fit here. This is a rather different problem. Why don't you start a new thread on how to surface-finish solid wood, if this is what you where after - due to the absence of any full-stops and commas it is very difficult to read.

 

wefalck

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Wow what a lot of info.

 

Last call for input.!!

 

I am just about to put on my varnish coat - Ronseal polyurethane satin (or matt maybe) clear Varnish.

Rubbed down for a key in the areas concerned and will be using the "Admiralty " water based  paints from Jotika.

 

Unless someone advises differently !!

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Caldercraft used to do an enamel paint in their Admiralty range, which I preferred, but they stopped doing it. Still like their Red and Yellow ochres though.

 

One strange thing about their black paints is the dull black has quite a sheen, the Matt (metal) black much less so.

 

 Their Flat Matt Varnish produces just that, ideal for decks, but I've never really taken to these milky water based varnishes, hard to see how they are going on.

 

B.E.

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Yes  B.E.  these these milky varnishes really not my thing - there always seems to be just a trace of that  milky look even when they are fully dry.  I use the Ronseal thinned a bit wiith white spirit.

 

The Jotika/Caldercraft site still shows the Enamels as available

Edited by SpyGlass
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You raised my hopes there for a minute Spy, but sadly not to be.

 

Note on their website re Enamels.

 

Discontinued please note that, due to the overwhelming popularity of the waterbased paints, we have now discontinued the enamels. We still have a limited number of enamel paints in stock which we are keeping for customers already using enamels and finding they need a small amount more to finish their project. Please contact us for enamel paint availability.

 

Trouble is even the enamel paints these days are often quite awful, I even find some of the Humbrol  very plasticky, not like the good old stuff.

 

B.E.

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