I recently bought a 100lb bag of hydrocal for about $35. On the back of the bag it states:

"Contents-Plaster of Paris"

My question is.....

Are they one and the same??


Reply to
Dirty Angel
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Hydrocal is a trademark of the US Gypsum Company for calcined gypsum (aka plaster of paris). It has been in use since 1930.

PLASTER OF PARIS, a variety of calcined gypsum (calcium sulphate) which forms a hard cement when treated with water (see CEMENT). The substance obtained its name in consequence of being largely manufactured in the neighbourhood of Paris.

Reply to
Ken Rice

Hdrocal is much harder. Mix some up with water and let it harden. Now try to carve it with a knife. Plaster of Paris is very soft and can be carved quite easy. Pick up a box of Hydrcal from Woodland Scenics - it is pricy, but is very hard when dry.

Jim Bernier

Dirty Angel wrote:

Reply to
Jim Bernier

Thanks to Ken and everyone for feedback on this thread.

I too have been around for awhile(1/2 century) and I've heard of Hydrocal and hard shell scenery.

I've tried the other products like Plaster of Paris(It does break off with little effort), Joint compound, which is not too bad if you have nothing else hanging around and I've tried the Woodland Scenics hydrocal dipped in cloth product.

After building with the WS product, I wanted the hydrocal. It does what has been said over the decades. It's tuff, My son's (10 yrs old)Hots wheels cars running over the paper thin mountain haven't destroyed it. I'm sold on it.

One comment that Ken mentioned that I'm not experiencing is the coloring of the hydrocal of the Woodlands product. My latex earth paints seem to hold fine. Just a footnote.

Anyone else have other tips and experiences, let's hear them!!!

Reply to
Dirty Angel

I'm not too sure why he should buy WS repackaged stuff when he has the real thing?

"Plaster of Paris" is a generic term for white plasters made by a specific process. There are also brown and green plasters. (They actually look pale gray.) "Hydrocal" has specific characteristics of hardness, density, expansion/shrinkage, setting time and so forth.

So, Hydrocal is a Plaster of Paris, but Plaster of Paris is not commonly Hydrocal!

CTucker NY

Reply to

=>I recently bought a 100lb bag of hydrocal for about $35. On the back of the =>bag it states: =>

=>"Contents-Plaster of Paris" =>

=>My question is..... =>

=>Are they one and the same??

Hydrocal is plaster of paris with additives, and I believe ground finer, too. It's harder and stronger than plain PoP, and takes much finer detail when used as a casting material.

Unless you want to walk or sleep on your layout, it's not worth the extra money. I've found that paper towels soaked in creamy PoP and applied two or three layers thick over a web made of woven box-board strips is plenty strong enough.

OTOH, if you want to make your own plaster castings, Hydrocal (or equivalent brand) is best.


Reply to
Wolf Kirchmeir

Sorry...I wasn't trying to insult your knowledge of the hobby. I thought maybe you were new at this and I would mention it.. Just trying to be of help.

I certainly think the Hydrocal is worth the extra money. Considering it takes more layers to make a terrrain that is strong enough I'm not sure that it's really more expensive , especially if you consider the extra time involved in doing the extra layers. Also , I feel much better knowing that I have a terrain that will stand up to some hard knocks. I build modules and dioramas that I take to various shows and they have received some pretty good hits and survived.

Maybe I shoud have explained a little better what I meant by taking paints and stains. Most all of the painting I do on the plaster is rock castings and carvings. Due to the more porous nature of moulding plaster you can spray a little water on and then come right behind with latex or acrylic paints and it gives it more of wash/stain effect and highlights the details. It also gives a more varigated ?? appearance since it takes on more different shades by soaking in at different rates. I guess I should say , "works for me" and maybe not for everyone.

I do like the name ...the U&I RR.

Ken Day

Reply to
Ken Day


The poster was not sure he had the 'real th>

Reply to
Jim Bernier

Actually , someone mentioned this earlier. All the plasters we are talking about here are a product of Plaster Paris. Hydrocal, Moulding Plaster ,other plasters , of which there are a number of varieties are made from Plaster of Paris.

Of all the USG products , of which there are about 200 , most start as Plaster of Paris. They have different additives , cook rates etc. As far as I know all of the products are made by ADDING other things to Plaster of Paris and cooking differently. Being associated with the Architectural , Construction industry I have seen many different products for almost endless applications.

Normally though , when you pick up Hydrocal at a lumber yard ,or at least in my area you usually get Hydrocal white gypsum cement. Hydrocal is really a brand name , not a product name so there are many different variations.

Go here and you can see all the different products and if you are associated with a construction or architectural outfit there is a number you can call and they will send you all the technical data if you would like.

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I like to use Plaster of Paris to make a blank wall to carve a master wall from , such as a stone or brick wall. Then I use RTV to make a mold and then cast all I need with Hydrocal. It's very easy to carve during the first few hours.

There is a base product , Plaster of Paris but I don't know if an individual can do all the additives himself. I'm almost positive you can't do the cooking required. Again , Try the USG site.

Reply to
Ken Day

Hey Ken,

No insult taken on the age thing. I was just commenting on the relationship of hydrocal to Plaster of Paris. I don't think a thread was run on this subject before on this newsgroup, at least in the last couple of years.

and thanks on the RR name compliment.

Reply to
Mr Leftie

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