Hydrocal - What did I do wrong

[ARTHILL]

After 40 years of plaster of paris I tried light Hydrocal. I tried to cast some tunnel liners. They took hours to harden and then cracked. I tried some rock, same results. I tried a little old plaster of paris and got great castings. What did I do wrong? Same with the plaster cloth. It sees that Pof P and screen gave better and faster hardshell. I must be dense. What did I do wrong?

[Pennsy58]

If it took hours to set, I would suspect that either the hydrocal was very old or the amount of water was way to high. The cracking of the casts also smells of to much water. Hydrocal sets up in about 10 minutes for me.

[dragenrider]

I have to agree with Pennsy58. It sounds like too much water. I tried fixing my Hydrocal recipe like Plaster of Paris and ended up with too much water, too. Go easy on the H20. Mix in a little at a time until you get the consistency of syrup. Then you should be good to go. It'll dry fast, so fix small amounts as you need them.

Good luck!

[howmus]

I agree with the others, it sounds like too much water is the likely culprit. Also, make sure you use clean equipment and.... don't pour leftover plaster down the drain (unless you like paying the plumber). Be accurate in measuring both the plaster and the water and it should work out well. Hydrocal sets very quickly so be prepared and have the mold ready before you mix (Make sure the mold is clean and wet before pouring). Hope you have better luck next time.

[selector]

Just free thinking, but could you have placed the molds against other moisture-absorbing plaster when they were not yet set up? Or used not-yet-set PoP or Hydrocal to cement them in place next to dry plaster? If so, it just might be that the drier stuff sucked moisture out of the mix before it had a chance to dry, or caused stress fractures during the drying. Again, this is purely speculation, because I think the others might have the more likely cause.

These materials are strongly hydroscopic, so if you make the mistake of trying to cement cured moldings against other cured moldings, the drier stuff wicks moisture needed for setting up away from the other parts and the cementing plaster....if that is what you use.

[Anonymous]

I just finished the rock castings on my layout using Hydrocal. I mix the hydocal for casting to the consistency of pancake batter, easy to pour but won't run out of the edges of the molds when I pour it. Two very important point already made.
1, wet the mold. I soak mine in a bucket of water until I'm ready to use it on the layout. The wet in the mold helps the hydrocal flow into all the nooks and cranies in the mold.
2. Make sure you spray the hardshell plaster with water (I keep a spray bottle for just that purpose. A slightly damp surface will keep the already dried hydocal from leaching all the moisture out of the fresh casting and will thus let the new casting bond with the older hardshell scenery.

[dharmon]

Shake the hydrocal up in the box before you use it. Then as Glen mentions a panacake batter consistancy. Also tap the molds after pouring it in to make sure all the air bubbles surface.

Dan

[Anonymous]

Sounds like too much water to me too.

I generaly use two parts hydrocal to one part water. I put water into a specially designed mixing container (aka old Cool Whip bowl) and sift in the H-cal. Let it sit for about a minute and then mix it up.

Good luck!

-slim

[MisterBeasley]

Thank you, Slim! At last, a quantitative analysis of the appropriate mixture. Pancake batter? Syrup? My mold's instructions said, "fresh cream." What is this, a model railroad or a waffle house?

Mmmm, buttermilk pancakes. Vermont Grade B syrup. (Here is a secret. Vermonters sell the Grade A syrup to the New Yorkers, and keep the Grade B for themselves. Guess which one is better.)

[Budliner]

for some strange reson I just got very hungry

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B-

[howmus]

QUOTE: Originally posted by MisterBeasley
Mmmm, buttermilk pancakes. Vermont Grade B syrup. (Here is a secret. Vermonters sell the Grade A syrup to the New Yorkers, and keep the Grade B for themselves. Guess which one is better.)

That's because most Vermont Maple Syrup comes from New York...... [}:)] [:D]

[loathar]

MMMMMM.......Pancakes.....
loathar

[Anonymous]

Well I know what I'm having for breakfast!

[chateauricher]

Maple syrup from Vermont ??? New York ??? [:O] [V]

For the real stuff, come to Canada. [swg]

[Anonymous]

mmmmmm sedimentary rocks with maple syrup!!!!!!! Nothing like a little limestone in your diet.....

[Anonymous]

oh yeah by the way....i vote for too much water or stale hydrocal...it has to be fresh and dry....before you add water of course!

[wp8thsub]

QUOTE: Originally posted by ARTHILL

After 40 years of plaster of paris I tried light Hydrocal. I tried to cast some tunnel liners. They took hours to harden and then cracked. I tried some rock, same results. I tried a little old plaster of paris and got great castings. What did I do wrong

Maybe nothing. Are you using Woodland Scenics "Lightweight Hydrocal?" It's a very weak setting variation of normal Hydrocal that I don't like to mess with because of problems like you're describing. I've always achieved good results using various types of casting plaster or regular Hydrocal, and have literally used over 1,000 pounds of these products over the years. The results I got from Lightweight Hydrocal were awful; the castings were soft and took forever to cure. I know the issue wasn't too much water. Another member of our local round-robin group reported similar results from the lightweight stuff, also despite repeated success with other types of plaster. Hydrocal is only a brand name, and for most scenery use is no better than any other gypsum plaster. Chuck the lightweight version and go back to plaster of Paris.