Hydrocal. Primer or not?

Model Railroader General Discussion (Model Railroader)
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People ask this all the time so I thought I’d post my basic thoughts on the subject.

I always recommend at least “sort of” sealing plaster castings to remove some of the porosity. Perhaps “priming” would be even a better word than sealing. I use flat white spray paint. A couple of light coats. That way when you apply either your paint or stain it will flow on more naturally and evenly than if you applied it to raw plaster. It allows you to get a smoother looking, more even tone to the base coat. You also have a little bit of time to “work” the color. You have less of a chance of the color coming out too intense or dark as well. Finally, when your painting/staining is all done, you can ever so lightly “buff” the surfaces with very fine steel wool or polishing sandpaper to make all of the details and highlights “pop out”. It’s sort of like dry brushing but instead of adding paint you’re taking just a tiniest bit of paint off the tops of the high points. It really “makes” the model IMO. Understand that I’m not saying to seal the plaster so that is like plastic or resin, but rather, just enough so that each and every brush stroke does not get soaked in instantly.

Not sealing the castings, IMO, increases the risk of the following happening: A blotchy looking, uneven finish that looks “brushy”. It also increases the chance that you’ll end up with “solid looking” dead toned walls, rather than richly toned parts that look like they have natural age, patina and years on them. You don’t have any time to “work” the color you’re adding, as each and every brush stroke is soaked in instantly. True, you can “build up” colors, one thin wash at a time, but you can do that ever better when the castings are sealed because you can control it so much better. Also, unsealed you have to wait long periods waiting for the castings to completely dry so you can

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Generally I agree, but it really depends on the casting. For a rock tunnel portal, for example, or even an older concrete one, priming for the sake of anything but sealing is probably a waste of time and materials. Yes, if you desire a uniform look, such as on the side of a building freshly painted, or for some other application of that nature where you want as little variation as possible and as little texture as possible, priming makes abundant sense. I have never primed my rock tunnel portals, though, plaster of hydrocal, and I have been pleased with the look.

It seems to be that a good reason to prime hydrocal, specifically, is that it doesn’t take water-based paints very well anyway. Priming could help in that respect.

Crandell

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Sometimes I prime plaster kit parts, sometimes not. I usually spray paint brick or concrete instead of staining it, but will typically just apply coloring for simulated stone or wood without priming. The methods I use employ dry-brushing full strength paint as opposed to staining however.

Here’s a plaster kit from Cigar Box Models painted using dry brushing and washes.

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