# Between the Rocks Patch Material



## Lehigh74 (Sep 25, 2015)

I’m building a rock formation using rocks made of hydrocal glued to pink rigid foam. In the past I have used hydrocal or dry wall compound to patch the areas between rocks. With hydrocal, you get a very short working time between when it is stiff enough to work with and when it is too stiff to work with. Dry wall compound is easy to work with, but does not take wash the same way hydrocal does. That can add some interesting variations in color, but in this case, I would like it too look more uniform. So I’m looking for patch materials that will take wash the same as hydrocal, but give me a longer working time. Regular plaster might work, but I have no experience with it. Any suggestions? 

I have used lichen to hide the pink between rocks, but for this formation, I want to minimize the vegetation.


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## wvgca (Jan 21, 2013)

I have never used Hydrocal, on my layout Plaster of Paris was used for the rock molds , with premixed drywall compound from a tub for patching in between, and washes appeared to turn out the same on either one ...
If you are using hydrocal for the rocks, would small pieces of hydrocal chips glued in between work?? that would reduce the amount of other fillers needed to fill the gaps / spaces


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## Laidoffsick (Sep 20, 2015)

We used Sculptamold to fill in gaps. Longer working time, and like with any of them, using ice water will extend that working time even more.


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## CTValleyRR (Jul 26, 2014)

I like Sculptamold too. In fact, I can carve it into realistic looking rock without using castings.

However, because it contains glue and paper, it most definitely does not take washes in the same way as hydrocal. Hydrocal is porous, and absorbs a lot of the paint wash, whereas Sculptamold doesn't. 

If you're handy, with paints, you can overcome this by using thinner washes on the Sculptamold, or drybrushing highlights on both to blend them.

If you feel this is beyond your skill level, best bet is to patch with your casting plaster.


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## CTValleyRR (Jul 26, 2014)

And now rereading your post, if the gaps are so small that you can hide them with vegetation, you would want a darker pallette anyway, to suggest deeper crevasses and fissures.


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## Lehigh74 (Sep 25, 2015)

Thanks guys.

I should have mentioned that I have used Sculptamold before for making outcroppings and also for patching between rocks. It’s nice to work with. For outcroppings, you can use it to shape the terrain and then press the rock into it (no glue needed). For patching, it looks like earth between the rocks.

Dry wall compound doesn’t take the wash as readily as hydrocal. It comes out lighter which can look interesting, but I’m thinking something different this time.

I looked into plasters today. I’m thinking I’ll try patching plaster (ready mix) and Plaster of Paris and see if I like one or both. I used Plaster of Paris years ago and as I recall, it set up very quickly (about as fast as hydrocal). The Plaster of Paris on the True Value site says 20-30 minutes working time (maybe it has a retarder) so that should give me the time I want.

Whatever I go with, I will most likely stick small chunks of hydrocal rock in the wet patch material for the larger gaps. And I’ll try ice water if the Plaster of Paris wants to set up faster than I want it to.


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## Lehigh74 (Sep 25, 2015)

I did a test with Drywall compound, Plaster of Paris and Durabond 90. Made a few test pieces and applied wash to see how they looked

Drywall compound is great to work with and comes out looking closer to the hydrocal rocks than I remember. But it takes too long to set up.

The Durabond 90 plaster gives you about a 90 minute working time. Great to work with, but unfortunately, it takes the wash even less than drywall compound.

I still had some Plaster of Paris sitting around from years ago. That comes out looking real close to the hydrocal. Even though it says 20-30 minute working time, I found the working time to be only a few minutes, even with ice water.

I ended up mixing small batches and using the P of P. I also started carving/shaping the rocks when I glue them in so there is less patch work.

By the way, last week I had Scuptamold confused with Structolite plaster. The Structolite looks a bit like earth when dry. Sculptamold is white, but doesn’t take wash very well. It might look close if I used an 8:1 wash mix on the Sculptamold and 16:1 on the hydrocal rocks, but I didn’t try that.

At this point, getting this project finished is more important than getting it perfect so I’m leaning more toward using lichen to do the patch work.


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## Laidoffsick (Sep 20, 2015)

You can always prime everything with Gesso and then paint with acrylic washes. We used a lot of the Bragdon foam so we had to prime and paint. Not really much different than staining, but you actually have more color control when you paint.


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## CTValleyRR (Jul 26, 2014)

Leigh74, I politely disagree that Sculptamold "doesn't take washes well". Perhaps I'm being overly semantic, but as I said in my earlier post, it doesn't ABSORB washes in the same way as plasters do, which is somewhat different.

Different products require different techniques (you said as much yourself).


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