So… if it’s something that’s going to set on a shelf or something like a wh figurine, you don’t need to prime with acrylic or enamel.

If it’s something that’s going the handled (like say, a cosplay prop,) your mileage will vary.

I’d recommend printing off small test parts to see how the paint cures and such. I use small shot-glass-size vase mode prints. (Any one the vases will work, but I suggest anything with more complex contours and a few hard edges.)

Then they get double use as a glue pot when I’m doing glueups with barges cement or similar adhesives (and painting too.)

If you find you do need primer… the stuff I’ve found to work best is rustoleum filler-primer. (Yes. The spray can.) you’ll lose surface details, since it’s designed to fill that in, but makes a wonderful foundation.

Also scuff the surface with a coarse sand paper before you do anything else. This will give whatever base layer you’re using a bit more to bite into.

This is less about 3D printing and more about “what material will adhear to the layer before it?” For example, using both water and oil based products is generally not a great idea. If want to use both then a layer of sealer will help.

How you want to apply the paint (eg air brush vs bristle brush) will greatly impact which paints and finishes you can choose. It will also greatly impact your final finish/look.

In most cases no need to “seal” paint. In fact, depending on the type of paint it might be a sealer itself. A sealer can protect the paint below it from say UV light or water. A sealer can help you achieve a higher gloss finish. However, the paint itself might already be durable, UV stable, and have the sheen you want.

The question isn’t which store sells better paint, it’s what kind of paint do you want to use? After that the choice of store is largely a question of who carries that type of paint with an added wrinkle or brand variation. For example, you’re not going to find miniature airbrush paint at a big box store and you’re probably not going to find automotive paint at either.

These are all valid concerns, and I’m happy to throw my 2¢ in, if it helps. I’ve been printing for a while now, (FDM, MSLA) and even went semi-pro for several years (9 printers, 40+ hrs/wk), but still take this with a grain of salt, of course. Every use case is unique, and there are a wide variety of products and methods out there, so don’t be afraid to experiment to find what works best for your project. 🫡

That said, I’ve had better than average success with Rust-Oleum spray varnishes for all but the most demanding/complicated projects. Be patient (don’t rush), keep the coats thin/light, always use PPE & proper ventilation (no joke), and test print whenever you feel the need to try a new tech/process out.

So, first off:

1. What’s the PLA model going to be used for?

2. How durable does the varnish itself need to be for the intended use of said model?

3. Are there moving parts that need to be masked before spraying so the clear coat doesn’t gum up from friction?

4. Indoor or outdoor use? (ie. Avg temps, weather, etc.)

🖖🏽🤓

I’ve used Minwax Polycrylic Protective Finish Spray for Wood, Clear Satin

A few times with good result. Not too glossy.

I usually use it after staining wood pla but have used it over paint as well

I’ve never actually needed primer to paint PLA unless the paint I was using was terrible, and wouldn’t have stuck to the primer very well, either. Tamiya’s acrylics have been entirely issue-free for me, both with a brush, or thinned and airbrushed, and they’re not that expensive, but I’ve also had acceptable results with random fifteen-year-old tubes of really cheap acrylics that were sold more as a children’s toy than a serious paint (although a lot of these tubes had gone bad in that time) and with Humbrol and Revel acrylics and enamels (although their acrylics come in pots that don’t seal very well, so it’s not that uncommon for them to be already cured when you first open them - if you’re buying liquid acrylics for model painting, Tamiya is a better choice).

I’ve not see anything but hand wavy “add a layer of clear coat” for sealing.

Hmm, maybe I’m mistaken but is this not pretty sound advice? Or is the implication that you want this paint job to be matte and coarse (in which case, clear coat to start and perhaps sanding after a few paint coats?)

Otherwise, I wish I could help, I don’t have much experience printing PLA.