Plaster rocks.

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b9y
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Plaster rocks.

Postby b9y » Mon Feb 12, 2018 5:21 am

Hi guys,

Has anyone here used plaster of paris to make rock formations? I've seen people online use a plaster-based product such as carving plaster from Woodland Scenics, but not sure if PoP would be similar? Not looking to cast, just to slap it on, wait for it to dry then carve / brush / paint.

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TimberSurf
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Re: Plaster rocks.

Postby TimberSurf » Mon Feb 12, 2018 8:12 am

PoP is NOT advisable. Goes off very quickly, so no time to "work" it, very brittle (weak if thin), etc, etc.
For casting use proprietary brands like herculite, for terrain, use Mod-Roc or equivalent.
But before you decide, read this Guide
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b308
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Re: Plaster rocks.

Postby b308 » Mon Feb 12, 2018 8:30 am

I'd add that it's light to the advantages of chicken wire/modroc, L. Also I glue my expanded polystyrene (the white ball stuff!) to the baseboards and each other using PVA glue, I don't use any special stuff!

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carnehan
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Re: Plaster rocks.

Postby carnehan » Mon Feb 12, 2018 9:32 am

As an alternative to using plaster based materials I have seen cereal packet card made in to very effective rock faces. Simply scrunch it up and unfold again and place in the required area. Little tabs made top and bottom help to bond it to the surface. Check out Tony North Easterns channel on YouTube for a tutorial.

As with much in the modelling world it is the final painting of the thing that really brings a feature to life and not the material used to produce it.

Paul

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Mountain
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Re: Plaster rocks.

Postby Mountain » Mon Feb 12, 2018 10:29 am

I have used plaster of Paris for making level crossings and it worked well. I did use a coarse scale wagon I didnt mind getting messed up to cut some wheel flanges as the plaster was drying. I did rescue the wagon afterwards. With roadways, it does not matter so much if it cracks. Mine didnt crack at all, but if it did it would still look the part. One may have to paint down the crack so the whiteness of the material does not show up.
In the past I have used more traditional paper maché for hills. On my last layout this was half formed over expanding polystyrene as my dad often came home from work having some left in a tube in his work, and the rest of the contents were not really sufficient to complete a second job etc. I did have to wait a while before I had enough to form the hills! I found that it did work, but over time my paper maché broke lose from the expanding polystyrene. Part of the hills had a card frame to lean on the polystyrene base, as when one applies the expanding foam stuff, it is not easy to judge as it expands to a few times its size. Some older tubes of the stuff didnt expand so large and were more compact. At least the hills ended up random which looks real. The only concern I had was I had an upper level to the layout, and I didnt want the expanding polystyrene to push up the upper level boards, and it was a close thing as it almost did.
Enjoying 7mm narrow gauge.

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flying scotsman123
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Re: Plaster rocks.

Postby flying scotsman123 » Mon Feb 12, 2018 11:42 am

Plaster of paris is ok if you're casting rocks as long as they're fairly bulky and you don't plan on doing much work on them afterwards other than painting. Woodland scenics sell moulds, alternatively scrunched up tin foil works. As Timbersurf says, I wouldn't want to carve it, I'd be afraid it would just chip and fracture.
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Pete
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Re: Plaster rocks.

Postby Pete » Mon Feb 12, 2018 2:19 pm

I've always used Polyfiller or Tetrion onto a polystyrene base for rock faces, mix some colour into it so that the white doesn't show if you chip it.

Plaster of Paris is a black art, it's great if you know how to handle it, but utterly frustrating if it sets on you :)
Once you mix it, let it stand for five minutes, you'll feel the temperature rise as it begins to set, that's the moment to slap it on! Once hard you can build it up with a fresh mix as required, it sticks to itself with no problems.
Another trick to get very hard and strong PoP is to sand some set plaster into your fresh mix, it acts as a seed to the process. Also you need to use it when fresh, old PoP that's been kept in a bag can be very variable.

If you're interested by far the best supplier:

https://tiranti.co.uk/product-category/casting/plaster/


Pete
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The dinosaurs went to Hell

b9y
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Re: Plaster rocks.

Postby b9y » Mon Feb 12, 2018 7:18 pm

The only reason I'd want to use PoP is for the price, I have heard you can mix things with it for strength but I think I may just experiment. I'm trying to avoid the main names because I need to keep the costs down as much as possible. I want to try and figure out what Woodland Scenics Carving Plaster is, but info on it's makeup is scarce.

b9y
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Re: Plaster rocks.

Postby b9y » Mon Feb 12, 2018 7:19 pm

Pete wrote:I've always used Polyfiller or Tetrion onto a polystyrene base for rock faces, mix some colour into it so that the white doesn't show if you chip it.

Plaster of Paris is a black art, it's great if you know how to handle it, but utterly frustrating if it sets on you :)
Once you mix it, let it stand for five minutes, you'll feel the temperature rise as it begins to set, that's the moment to slap it on! Once hard you can build it up with a fresh mix as required, it sticks to itself with no problems.
Another trick to get very hard and strong PoP is to sand some set plaster into your fresh mix, it acts as a seed to the process. Also you need to use it when fresh, old PoP that's been kept in a bag can be very variable.

If you're interested by far the best supplier:

https://tiranti.co.uk/product-category/casting/plaster/


Pete


This sounds good! May give it a shot.

Thanks for the advice guys :)

b9y
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Re: Plaster rocks.

Postby b9y » Mon Mar 12, 2018 4:34 pm

Update. Used PoP from Hobbycraft, it's great. Put a couple of layers on, cracks easily but because of the layers I have it works amazingly well! I'm able to create undercuts down to the previous later and it looks pretty realistic. Ultimately I need another layer but I cannot be bothered truth be told, just wanna get on with it, but so far so good!

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luckymucklebackit
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Re: Plaster rocks.

Postby luckymucklebackit » Tue Mar 13, 2018 1:02 pm

I have used B&Qs own brand Diall Filler, cheap and easy to use, the trick is getting the mixture just right, not too runny not too dry. I used it extensively to build up the terrain to the east end of Northbridge

Before

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After - the rocky surface texture is created by crunching up cooking foil then flattening it out and pressing it into the soft plaster, this is then removed once the plaster is set, the whole surface gets a spray of matt grey car primer before applying detail in browns, blacks and liberal amounts of flock. Tip: when applying the flock tray use the cheap spray glue from the pond shop and spray down from above, that ensures that the vertical surfaces don't have flock and look like bare rock.

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Jim
This Signature Left Intentionally Blank, but since I have written this and I intended to do it, this Signature is intentionally not blank. Paradox or What?
My layout - Gateside and Northbridge
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b9y
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Re: Plaster rocks.

Postby b9y » Wed Mar 14, 2018 12:46 am

That looks awesome Jim!

I'll stick some pictures up at some point. Really need to make a blog to be honest.


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