Light Hydro and Rock Molds Problem

I just looked at the Woodland scenics lightweight hydrocal box and it does say 40 minutes. From my experience this is much too soon. I would leave for 8-10 hours. After I took it out of the rubber mold it would let it sit on a block of wood to dry afterwards. You will get a sense when it becomes very white and not the "grey" white when it is wet. I have made a lot of rocks from this combo, but 40 minutes is much to soon. Have fun with this.

We did these with casting plaster and pulled them out of the molds in under an hour.

These were done with hydrocal and light weight hydrocal, also pulled out in about an hour or so. We live in CA though, where it's much warmer and drier, not that that had anything to do with the results.

Try giving the mold cavities a wash with some detergent water before pouring the Hydrocal.  Pour in the water (couple drops of detergent) and pour out the excess with a quick shake.  Then pour in the Hydrocal.

I've found this helps me.  Humidity and temperature might be factors, though.  And the age of the Hydrocal, too, although you stated that you had just bought this.

OTOH, several articles, scenery help books, DVD diy's, etc., suggest that in some cases you may not want the casting to have fully set.  If you are going to place the casting onto an irregular surface...say a slightly rounded knoll...some of the 'pros' advocate putting a coat of Hydrocal onto the layout surface, and while the poured casting is yet a tad green (not runny, though!), place the mold and casting onto the layout surface, adjust it to the contour, and hold it in place for the 40 minutes or so.  Then carefully peel away the mold, leaving the casting in place.  Yeah, it might have a crack or two in it.  But, hey, so might the real rocks!!!  Besides you can touch up any bothersome cracks with a soupy hydrocal and paint brush.

I've de-molded countless Hydrocal rocks from different molds, not just WS.  30-40 minutes, depending on the thickness of the casting, is about right....no breakage.

But, aside from the breakage issue, one thing I have learned is to NOT rub the outer surface of the rock castings with your fingers or allow the castings to rub against each other in storage.  The beauty of tinting the rocks with subsequent washes of color and getting an even appearance depends on keeping the surface freshly porous...not smooshed over, damaged.  Hydrocal cast surfaces that have been banged or roughly handled will have white spots...poor absorption...after being color washed. 

But an even more important suggestion for WS problems is to call them.  Ask to speak with a technical help person regarding the particular product you're having trouble with.  I've done this several times and found them to always be helpful, conversational, and pleasant.  Problems solved.

FWIW, always...

KD

Did you pre wet the mold with a soap solution?  Save yourself some money and go to one of the big box stores and buy a bag of plaster.  50 lbs bag cost as much as the WS milk carton.

The hydrocal mix cannot be too watery or else it will crack easily. It needs to be more like a thick applesauce consistancy. Also don't forget to pre wet the mold with a soap solution as stated above. I usually remove my cast from the mold after about 90 mins and never have a problem.

Rich

When you get tired of spending too much for the milk carton sizes of hydrocal, use this site:

http://www.sheffield-pottery.c....x=10&Search.y=3

The shipping is as much as the product but 50lbs for $50 can't be beat if you need large quantities. I almost went thru 2 bags. Made all my landscaping with plaster cloth rolls covered with hydrocal for strength and Home Depot $9 structolite for realistic texture. When used correctly, extremely strong.

Rich

I buy my Hydrocal at a ceramics supply store for $42 a hundred pounds. Used to get it at a lumber yard. Use Palmolive dish washing soap. Most others foam and cause bubbles. You don't need a lot of soap in the water - just a few drops. I put mine in a spray bottle. Lightly blow out mold to remove any bubbles. Hydrocal should be mixed well to a consistency of heavy cream. Pour slowly into mold from one corner and let set. I demoed my casts in about a half hour unless really delicately detailed and then about an hour. I find white Hydrocal best for my use.

I also bought the hydrocal in bulk bags. I also added some tint to the plaster to kill the bright white a bit. You still need to paint it, but it makes it a little less noticeable if chipped. I went on line to US Gypsum and followed their mixing chart using a digital scale to measure the water/plaster ratio. It made for very repeatable batches. It sets in an hour and can be de-molded. Structolite, on the other hand, takes 24 hours to cure.

Lance, your not illiterate, I've been modeling for well over forty years and can't get light hydrocal to work worth a darn. When we lived on the mainland I would buy 80 lbs of regular hydrocal for about $30 and it worked fast and good. On the island there is none to be had so I switched to plaster of Paris. About $20 for a twenty five lbs bag. It works great in molds and is almost as strong. When it dries it's very light. I'm on my 8th bag because I'm making lots of very large molds and need more. Don't mess with the light stuff. These stacks of molded "rock" are only a few I have made and not put in place yet. Some are over three ft. long.Don