Did I mix the hydrocoal wrong?

[Anonymous]

Greetings,

I recently started making some rock molds out of Hydrocoal for my layout. When you mix it like they want you to on the back of the box, it is way too liquid so I added some more Hydrocoal till it was closer to a paste and put it into the molds.

I had a bit left over so I smoothed out some bumps on my road with it. It dried all night long and still feels wet to the touch this morning. Also the areas that are dry I can practically sand with my finger. Did I mix the stuff wrong or is it just taking longer to dry and I'm being impatient? [}:)]

Thanks!
-Dale

[eastcoast]

(scratching my head)
I have tried premixed most of my time. But this is slightly more costly than dry bags. Actually I think I am using plaster for mountains. Either way, try to go by the instuctions and just add a 1/8 cup of mix to your bowl. What is the room like? Is it damp or dry? That makes a difference as well. It's like a scientist, try until you get it right for your purpose.
ken_ecr

[n2mopac]

I have used Hydrocal for rock molds dozens of times. It always seems soupy when first mixed but usually sets up too thick to use within 5 minutes. The softness the next day is uncertain. It always feels cold the next day as it is not fully cured, but it should not be wet. I can easily scratch it the next day, but not rub it off with my finger tips.

Your mixture should be approximately 3 parts hydorcal to 5 parts water or 60%-40%. Always measure out your dry goods first and SLOWLY add the water to it while mixing constantly, then when fully mixed use it as quickly as possible. Adding too much water will weaken the final product.

I always try to remove my castings from the molds after 24 hours, but be careful because they are not fully cured and will break easily. Hydrocal takes about 3 days to fully cure.

Hope that helps,
Ron

[Anonymous]

The ratio I use is one part water to 3 parts powder, easier to remember and works. As others have said, it should be the consistency of a bit thicker soup. Also I usually squi***he stuff through my fingers to make sure there are no lumps in it. Sounds like you put too much powder in to me.

Also water always goes in first and add powder in bits to stop lumping.

[Anonymous]

Well, if it takes 3 days to fully cure maybe I'm just jumpin the gun a bit I'll wait 2 more days and get back if I still have probs. Thanks!

-Dale

[wp8thsub]

You may have old plaster. If it sits around too long (or started to get wet in transit) the ambient humidity can affect the ability of the plaster to properly set.

Hydrocal's tendency to set up too powdery if the mixture is at all off is a major reason I use US Gypsum's casting plaster instead. I've never had the problem you describe with casting plaster but ran into it often with Hydrocal. Also, when Hydrocal sets up funny it can take stain far too easily and go too dark.

[Anonymous]

Well here's the issue. Stuff dried ok but feels so light that I'm afraid to touch it. I think I agree with the too much powder since the stuff was thicker than thick soup but thinner than spackling. But I'm making tunnel forms (natural scenics) to make some tunnel walls. How can I get the soupy stuff to stay in the form? That was why I was making the hydrocoal thicker in the first place. Could I let the soupy stuff start to set (just a bit) and then pour it???

Thanks!
-Dale

[Anonymous]

I had all these frustrations with hydrocal way back when, and it is why I do not use a hard plaster at all anymore. I remain befuddled as to why the stuff remains such a staple.

I use a home-brew papier-mache based on Cell-u-Clay, which is essentially the same thing as newsprint shredded into fine particles. You can even make your own if you don't mind shredding old papers and ruining a blender. To this, I add a variety of color and texture ingredients, in addition to joint compound; varying the composition can produce vastly different finished textures. In the end, what I have is a much lighter-weight coating, with integral color and texture, which I can mix up in small dixie cups and work at my leisure. When it dries, it maintains some flexibility so you don't get chipping, and it is far easier to plant trees into (just poke a hole with an awl). The only drawback is that it needs support (it isn't "hardshell"), but for this I use expanding foam insulation which I can carve readily; other types of foam construction would work fine, also.

For casting rocks, I don't: the papier-mache mix can be mixed to any consistency, and for cliff faces I just make it solid enough that I can carve it as it is placed. Certainly, it can also be carved once it is dry. By working with small batches and laying them up in horizontal layers, I get a natural-looking stratification, due to inherent differences in color and texture of different batches. And with an admixture of scoopable kitty litter (or any other granular material), I can easily create convincing rough stone surfaces, using just a plastic spoon to apply it.

There may still be a place for old-fashioned castings, though. At the train show last week I saw some ready-made ones for sale, and WOW did they look good. One could easily incorporate such a casting (I am going to try to include real stones harvested from the Appalachians) into a spoon-troweled papier-mache scenic contour.

[Anonymous]

I just starterd using hyrocal to cast holiday figures, I am mixing half hydocal and half water. It is setting realy quick...........Does anyone have any suggestions

[Anonymous]

Dale,

I have carved hydocal for years. Sounds to me like you overmixed it. If you keep adding to it after it is setting (changing the mix). I have found that it wont cure right. It should be ROCK hard in 20 or 30 minutes from mixing. It will also heat up as it sets, no heat , no set. You could have a bad bag as well...

I know there are lots of alternatives to plaster out there. I like plaster, particularly Hydrocal, because of its strength. Plaster is not for everyone, but I enjoy working with it.

For carving and hardshell, my method is to cut the tops off of a few one gallon milk jugs to use as mixing bowls. You will have to experiment with the mix of water to plaster to get it right. It is not too sensitive here. After you have ratio down use the same amounts in every batch.

I mix up a jug and then wait about 10 minutes and mix another, as the first is thickening I apply it and carve, as it gets too hard to carve the next batch is ready to go. You can get caught with too much plaster hardening at once, but usually it works out well. You have about 10 minutes to carve before it turns to stone. I use a chisel to break the plaster into jagged edges and a utility knife to make the crosscuts and fine lines. You have to work fast and decisively. If something doesn't work, I put more plaster over the top or break it out with a hammer.

The jug bottoms can be cleaned by cracking out the plaster by flexing them. Here is an example of the rocks I carved:




My 2 cents,

Guy

[twhite]

I've used Hydrocal for rock molds and a sealing plaster for some time. Believe it or not, I've found that the setting time doesn't pertain to the mixture--if you follow the directions--but to the humidity. I live in a dry climate, for the most part, my Hydrocal castings are ready for installation in about 20 minutes, and set up within 2 hours. However, I've found that on humid days, the installation and setting time can be almost twice the normal time. Frankly, I watch the weather and the humidity as to whether or not I'm going to cast that day. I don't know if anyone else has this problem, but we in California, with our garage 'basements' have to deal with some very tricky situations.

[rexhea]

I have experienced the same problems above at one time or another, but if I stick to the box instructions it works out everytime. I add the Hydrocal to the water slowly and continuously stir the mix even after the plaster has been added. This keeps it from gunking up on you and creating air pockets. As it begins to thicken toward pancake batter, I then pour it quickly into the molds. Be ready to use your fingers because it will not take a minute for it to get real thick. Wet your fingers to smooth it. Hint: you can use sand or paper wads around the mold to hold it's shape.

One thing to give a little more time is to use distilled water for your mix. There is something about the chemicals in tap water that speeds the process. I have also had someone on this forum to suggest a couple of dashes of vinegar.

The first thing you will notice is heat generated by the chemical reaction going on during the set time. This doesn't last more than about 15 minutes. When you feel it and its cool, then you can carefully take it out of the molds and let it finish drying ( about 24 hours).

I have used plaster of paris in some of my rock molds and have had very good luck. The disadvantage is that it is much heavier than Hydrocal and it will take a couple of days to dry.

Good Luck , REX

[Anonymous]

DT, I had a similar experience. I brought in my dehumdifier and that dried it out in about 6 hours, worked good for me. I placed the dehumdifier under my layout where I need the drying.