Poly over acrylic paint????

[CPDDET]

Does one need to put a poly finish over acrylic paint? I recall reading somewhere (not on this site) that acrylic paint needs this for long term protection.

 

Dave

[Keith Black]

Dave

 I apply poly over acrylic paint without issue. It doesn't seem to matter how dry an acrylic painted surface is, if it hasn't been sealed you'll get some paint removal with a wet Q-tip. Painting is too tedious a job not to lock it in once done.

 Keith

 

One note.

 Above I said I applied poly over acrylic paint without issue. That's not exactly correct. When poly is applied over white acrylic, it yellows. I've only ever tried Minwax polyurethane so I have no knowledge about other poly manufactures. Minwax says their product dries crystal clear, it doesn't dry crystal clear. Obviously this isn't a problem with black or a yellow acrylic but I can't help but believe that the same doesn't hold true for all lighter shades of acrylic paint. 

Edited November 24, 2019 by Keith Black

[wefalck]

I would always be very hesitant to mix two paint systems. You may be lucky, but it can also spell desaster, depending on what the products actually are made of.

 

Why would you want to put varnish over a painted surface. I would carefully reflect on the reason. Perhaps, acrylic paint isn't the right paint for the job, if you think you need to further protect it. Perhaps you should use a different paint system - there are also many different acrylics-based paint systems.

 

Depending on the type of model, I personally also like the different sheens of different paints for different parts. A real ship would not be all over glossy or matt or satin.

[JohnLea]

18 minutes ago, wefalck said:

I would always be very hesitant to mix two paint systems.

Not a paint system (at least I don't think so.) but a friend who was a brilliant figure painter painted a 12" Catwoman.  He was in the habit of putting on coats of Future floor wax as the final finish if a high shine was wanted.  It didn't work.  Her uniform developed a crackle finish rather than the shiny patent leather look. He thought it had something to do with the dryness of the underpaint but he was never sure.  I avoided anything more adventurous than oils over acrylics since then.

[jwvolz]

9 minutes ago, JohnLea said:

Not a paint system (at least I don't think so.) but a friend who was a brilliant figure painter painted a 12" Catwoman.  He was in the habit of putting on coats of Future floor wax as the final finish if a high shine was wanted.  It didn't work.  Her uniform developed a crackle finish rather than the shiny patent leather look. He thought it had something to do with the dryness of the underpaint but he was never sure.  I avoided anything more adventurous than oils over acrylics since then.

The paint underneath was definitely not dry.

 

When I used to build plastic aircraft models I (and many others) swore by Future as a gloss coat over flat acrylics to provide a proper surface for decals. I always waited a week before applying it and never had a problem, and I only used acrylic paints (Tamiya, Polly Scale, Vallejo etc...). For final flat coat I typically used Polly Scale flat, but if you wait long enough and apply light mist coats with an airbrush you can even apply lacquer based Testor's Dullcote over acrylics. 

[CPDDET]

Per Minwax the only product they recommend over acrylic paint is their Water Based Helmsman® Spar Urethane.

[wefalck]

Future and similar 'self-shining' floor products are essentially dispersions of acrylic resins. So they are safe to use on acrylic paints.

 

The curing of acrylic paints is a mixed process of forming cross-links of the dispersed acrylic resins and dewatering. The dewatering is a relatively slow process based on diffusion. This is why acrylic paints dry up rather fast, but stay somewhat soft for a considerable amount of time.

 

When you apply a relatively thick layer of varnish (e.g. 'Future') over a relatively thick layer of acrylic paint, the latter will be prevented from diffusing out the water. In other words, the varnish might cure faster than the paint, resulting in shrivelling and cracking of the paint underneath. The same can happen, when you apply layers of oil-paint too early onto acrylic paint.

 

Spray-painting of several thin layers of acrylics with some time between coats, give the paint enough time to cure thoroughly.

[CPDDET]

I think I will use this product to seal the paint on my model.

 

Crystal Clear Krylon Acrylic Coating Spray Finish.

[wefalck]

I am still wondering what, objectively speaking, the purpose of the sealing is ? Unless it is an operational model, there is not really a need to toughen the surface.

[CPDDET]

My situation is placement of the finished model. I have limited space so the model may very well be placed in a spot that received some amount of sunlight.

 

The sealant will provide UV protection and help reduce fading. Aesthetically it will give more "pop" to the colors.

Edited November 27, 2019 by CPDDET
change

[Maury S]

If the model has value to you, spend the money on "museum glass" for the case.  Not cheap, but a significant amount of UV protection.

Maury