"Should resin repel water based paint?" Topic

This is an issue I've not encountered before so I'm wondering if the problem lies in the type of resin used by the manufacturer?

I have a dozen vehicles to prepare for a forthcoming game. They consist of resin bodies and white metal tracks/guns. Having assembled them I washed them in warm soapy water. Once dry I took some Vallejo Foundation White and thinned it roughly 50:50 with tap water as an undercoat. This paint is very thick straight from the dropper.

As I made my first brush stroke across the resin body of the model I saw that the paint wasn't adhering to the model as expected. Instead it was pooling and leaving bare patches. I continued but it didn't get any better. On horizontal surfaces the paint just retreats into the recesses, and on vertical surfaces it flows down until some detail or other stops it.

Thinking that I hadn't washed the model well enough I took a second one, washed it thoroughly and dried it. Same result.

I've always used tap water for thinning for many years and without problem. But this is the first time I have bought this particular manufacturer's product. So could the type of resin used be the problem and how can I avoid this result on the remaining ten models?

Thanks.

Exactly the same thing happened to me and it doesn't matter how much stuff you pile on it will not cover and pools on the surface. I stuck the resin item in warm soapy water, scrubbed it clean and sprayed it with car primer. The water based paint then went on a treat.

50/50 is a heavy dilution for straight onto resin I reckon. Use a primer, cheap spray stuff from Halfords will do the trick.

Acrylic loses its' molecular bond when it is heavily diluted with plain water(that is why cleaning your brush in water works). Even if you have done so in the past with no problems it will become apparent when used on a less than ideal(i.e. very smooth) surface. You would be better advised to use a dedicated acrylic thinner in these cases.

It may also be the type of resin. Polyester resins take water based coatings well, polyurethane resins don't. I'm not sure about epoxy resin, I don't think I've come across a manufacturer that uses them for casting.

The catchall terms "resin" and "plastic" are very unhelpful when it comes to the appropriate adhesives and paints to use. It would be more useful if manufactures would identify the materials they use for their model, and provide information concerning preparation and priming.

I was told as a general rule with resin, always wash it in warm soapy water to get all the release agents off of it.

I have done this since I was told and have never had a issue since.

Just my .02

I'd try a primer first.

Had that exact issue, found that washing and primer took care of it

Does thinned pva or matt medium adhere to it? That would be an ideal cheap primer. If it doesn't then car primer seems like the way to go. What does the manufacturer recommend?

Always, always, always use primer.

"Tooth" is the professional paint technologiccal term for the roughness of a surface to be painted. The tooth affects how the paint gets pulled off of the brush and how it is distributed onto the surface (coats).

It has nothing to do with adhesion, that a molecular bonding process.

Primer does TWO things:

Adheres to the model (metal/plastic) AND to the paint.
Provides the proper tooth to get a good coat.

A light sanding all over, to roughen up the surface might be a good idea as well, e.g. with a 320 – 400 grit sandpaper.

I wash and use krylon primer. Never a problem.

It could be the barrier/release coating the caster used.

If you use the wrong type for the resin you are casting with it will bond to the casting preventing paint from sticking.

I have had this problem with some resin buildings, but not others. It is not obvious, at least to me, which ones will give me problems, so I just do a small test to see. For buildings to which acrylic paint wouldn't adhere, I just sprayed them with a sealer, as that was what I had to hand. It worked, so I'm guessing that anything oil-based will do the trick.

Mant thanks for your replies. I was using the Foundation White as an undercoat. Is there a difference between using plain old matt white/black as an undercoat and using something specifically called a primer?

Anyway, I found that I had some Vallejo Thinner Medium in my paint stash, and the coverage was much better using that instead of water.

Primers are designed to slightly etch the surface to get a good bond. You might find Gesso useful as a primer if you want to stick with acrylics. Otherwise use an oil-based primer.

Is there a difference between using plain old matt white/black as an undercoat and using something specifically called a primer?

I have used Humbrol matt white enamel as an undercoat/primer for over 30 years and have never had any problems.

Always wash plastic or resin models in warm soapy water before painting.

If soapy water is not removing the mold release try vinegar.

Also, there is a forum up on the reapermini website dealing with primers and resin minis.

Using acrylic directly as a primer has a double problem. Too thin and it doesn't stick (as you found out), straight from the pot can easily obscure detail. I used to use flat white as a primer, until I discovered actual primer, never looked back!
Gesso is also good as it shrinks to the detail, but for ease of use, big can of spray primer, line them up and blast them.
You can also then do a quick black or dark brown wash over the primer which really makes the detail pop and makes it much easier to paint, for me at least.

I've seen Gesso in artist's shops etc., but have never used it. Do you use it straight from the container or dilute it somehow?

I've used it straight out the bottle. When it drys it really falls nice into the details.

8)

Straight out of the tub. Unless you are putting it through an airbrush.

youtu.be/yqja-Z9nfrM

I find it is a lot less susceptible to rubbing off if left to dry for 24 hrs however.

Thanks everyone. Next stop the Gesso Shop.

I have had problems with Gesso rubbing off. It is meant for porous surfaces like canvas. Gesso will cover but it will not bond.

I have used Floquil for many years. The problem with it is that it is so toxic. Lots of ventilation or outdoor use is a must.

I recently tried Vallejo primer. It's water based. Experiments really impressed me so I bought a big bottle. I've brushed it and shot it through my airbrush. I love this stuff and unreservedly recommend it.

If you like Vallejo primer then you should try Scale 75 primer – more tooth, less shine. I use it for everything now.