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Paint + Hydrostone = Splotchy?


morganm
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I use hydrostone to cast with for my Hirst Arts molds. Then paint them with a mix of RMS paints and GW paints. As soon as the props I casted are cured, and I have time, I paint the props.

 

They are not primed; I just put paint right on raw hydrostone. Sometimes it goes on smooth and all is well. Most of the time my basecoats turn out splotchy and thus everything on top of it turns out splotchy. Not a big deal with some of the smaller props that mimic wood as it actually tends to add to the texture. However on some pieces it just looks terrible. It seems as though some parts of the piece are more pourus than others.

 

Would priming them help or would that just soak in all splotchy and make my paint job splotchy as well?

 

Is it perhaps how I'm mixing my paints? They tend to be pretty thin. I usually put on a layer or two of a thin basecoat then come back over it all with a wash and finish up any smaller bits with thicker paint.

 

I'll try to post some pics of what I'm talking about soon. No internet at home right now =P

 

Thanks!

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Interesting.

 

Could you go into more detail as to what the "splotchy" looks like?

 

I use hydrocal for my HA stuff, and generally paint right onto it. Model paints like Reaper and GW tend to get sucked up and take more paint for coverage. So I generally stick to cheap acrylics from the craft store for painting directly, and it looks just fine.

 

Hydrocal is really smooth, through. I can tell you that when I used Ultracal, it was very gritty, and even though the bricks looked okay at first glance, some of the grit dried separate from the pieces, and they felt dusty later. (Possibly the dustiness was from using too "wet" a "wet water method" causing separation?) In some cases, the dustiness made it difficult to glue them together, though I never experienced problems painting them.

 

I wonder, through, if this is similar to your problem? If it is, you probably can ease it a bit by using canned air to blow the pieces clean, or a nice medium-stiffness brush to brush them clean with, before painting.

 

Meanwhile, I have spray primered a few HA pieces. I do it on occasion to make sure paint gets into cracks and onto surfaces that the regular paint is having trouble sticking to (like areas where wood glue has been exposed). Besides the obvious problem of the primer eating foam to which the pieces might be based, the other issue is that, like model paint, the primer tends to get sucked into the material. Thus, it takes more paint to get better coverage. Sometimes this can result in an eventual over-spray and obscured details. This problem was the same with PoP, Hydrocal, and Ultracal. Thus, I would hesitate to recommend the practice.

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If you are having problems with coverage, this is exactly what primer is for. I don't know why there would be any hesitation or expectation that the primer dd to the problem.

 

If you are worried about the action or coverage of spray primer, go with a nice brush-on. A couple of fairly thin coats should help the issue.

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If you are having problems with coverage, this is exactly what primer is for. I don't know why there would be any hesitation or expectation that the primer dd to the problem.

 

If you are worried about the action or coverage of spray primer, go with a nice brush-on. A couple of fairly thin coats should help the issue.

 

 

He's talking about painting directly onto pieces cast from a type of gypsum cement. His issue may not be with paints at all, but with the casting material.

 

After I responded yesterday, I thought about part of what was said in the original post, and it occured to me that the problem may be more basic. Getting back to what I said about the wet water method being too wet and causing me some separation when using Ultracal, it occurred to me that the splotchiness here may have something to do with the statement that some parts of your pieces are more porous than others.

 

Maybe you need to stir your Hydrostone before mixing it up. Perhaps some sort of separation is occuring in the bag, and you're not getting a complete chemical reaction.

 

Dr. Bruunwald prescribes the following:

 

Stir up your powder really good in the bag. When you go to mix it for casting, stir it extra good in the cup. Back off a little bit on the wet water ratio. Pound that table for all you're worth.

 

If the splotchiness is due to grit, this might help. If not, then well, what do I know anyway?

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I'm a Hydrostone person and use 99% cheap craft paints on my terrain. I only use the RMS on details like brazier flames and freehand.

 

I have had some colors not cover completely in one coat but a second one will fix that right up.

 

Remember that plaster is porous and will soak up moisture. So if you're thinning your paints you're doing yourself no good. All you're doing is making the surface of the plaster slightly damp and possibly causing uneven coverage.

 

Try picking up one of those cheap acrylic paint strips and see if you have the same problem as with the 'good paint'.

 

Honestly, use the cheap stuff on terrain unless you're working on a very special piece. You want pigment that isn't so finely ground so it will cover better.

Edited by Rastl_Deeperdown
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Here are some photos to show exactly what I'm talking about.

 

In response to some above posts:

 

I wipe off the powdery residue left on the props after casting.

The slury mixtures I make to cast are stirred well however I have no stirred the actual bag of hydrostone powder so that may be something to try.

I don't mind using quality paints on them but glad to know cheaper paints work OK for these. I consider these good practice so I want to get used to working with the paints I use instead of adding yet another variable into the mix.

 

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Priming anything you plan to paint is always a good idea. If you used foam as part of the piece try undercoating with Krylon H2O paint, won't melt the foam, or a brush on as mentioned earlier. Not as good as primer though. Anyway, remember, several light sprays of primer is always the key to not losing detail. And as Rastl said, just use the craft stuff for terrain unless it's a super special piece that has to be just right.

 

Something else I just thought of, are you making sure each coat of paint is completely dry before applying the next? Some of that looks like it may be brushing over areas that aren't completely dry.

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I've also read that you can tint plaster during the mixing stage. Has anyone tried this? I found this tip in Osprey's Terrain manual. Seems like a good way of getting a good even base color, BUT, future paint applications may still yield splotchy results. Just a thought.

 

-AW

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I tint my plaster using earth pigments. It does change the consistency and setting time of the plaster, however. And even with careful mixing the color isn't always consistent or smooth. I do it more to prevent the glaring white plaster from showing through chips.

 

This has been discussed thoroughly on the Hirst forum, most recently here.

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