Let him cast the first stones

[inobu]

Casting stones with Hydrocal can be tricky. It is pretty much a juggling act. You need to keep the casting sturdy, thin and bubble free. Trying to keep

these three factors in check is a challenge but here is how you can do it. 

 

Before we start I should add this.

 

Using Woodland Scenic Lightweight Hydrocal 1/2 gallon may not be a good starting point. In hind sight I think a bulk container is better in the long run. You can get hydrocal non WS cheaper in larger quantities but the question is how much you are going to actually use. There are a lot of alternatives but I had the WS stuff already and it is the most convenient so I used it. I also found that there was a substantial weigh difference in the mix. I had some joint compound and it weight a lot more compared to the WS stuff.

 

Depending on your needs the 5 gallon may be your best choice. I opted for the 1/2 gallon but went through that rather quickly as I used much of it learning how to get the mixture right. Getting the second 1/2 gallon got me to $24 add another $6 and you are at $30. That is a 5 Gallon bulk container is $30. So keep that in mind. 

 

Now lets get into it.

 

We need the casting to be Sturdy, Thin and Bubble Free

 

STURDY

 

The last thing you need is a casting that crumbles or cracks during the demolding step. This is dependent on how well the mixing process is conducted. The mixing process is tricky in that there are two phases.

 

1. Water absorption
2. Catalyst activation 

If you create an out of sequence mixture your casting will have weak spots. These weak spots will be the breaking points of your casting. To avoid this issue you need to have a good mixing process to enable a solid cure. 

 

Water Absorption

 

You want to let the hydrocal molecules to draw in all the water. There is a formula that allocates just the right amount of water. 10oz Hydrocal to 4oz water. DO NOT MIX. Let the hydrocal attach itself to the water without activating the bonding agent. There is a bonding agent in the mix. This is why the directions instructs you to shake the box before using. One of the agents is heavier than the other hense it separates.  

 

IF you can't resist mixing it just leave for a few minutes. When you return the Hydrocal will have done it thing and be ready to mix.

 

 

Catalyst activation

 

When you start mixing you are now executing the second phase of the mixing. This is activating the bonding agent. As you mix the bonding agent is attaching itself starting a chemical reaction. This reaction is the "kick" that people refer to. This kicking process is from the mixing motion. The direction does not stress the importance of this step but it is critical to the complete casting process.

 

For the moment we are going to leave this step and look ahead to what we need to focus on in order to keep the juggling act going.

 

Thin

 

We do not want the casting too thick. Thick casting prevents us from attaching or breaking portions apart. A thick casting broken in the middle will not butt up against another piece. This causes odd and ends to stick out. Also controlling how thick or hollowing out the casting can aid in the placement of the rock.

 

This casting is like a bowl verses a solid casting. In order to achieve this the hydrocal need to be at the correct consistency or curing time.

 

 

 

  This curing time needs to be monitored. With this in mind we need to jump ahead again.

 

Bubbles

 

Bubbles are created by either air trapped in the mold or the chemical reaction of the bonding agent. Trying to eliminate two forms of bubbles creates yet another obstacle. The remedy is to tap, brush or shake the bubbles free but in order to achieve this one must have the hydrocal in a liquid state. The creates another problem that references the sturdy requirement. The hydrocal need to be mixrd thoroughly in order to achieve a good bonding process.

 

Solution

   

The key is timing.

 

You must time the pouring of the hydrocal where it is still in a liquid state but moments away from hardening. The best example is Wendy's Frosty. There is a point where a Frosty melts just enough to drink through a straw but still maintains it firmness. There is a convergence of the two where the frosty melts and the Hydrocal hardens. When the Hydrocal is poured at this point the center area can be spread back to the walls creating the thin casting. The liquid state avoids the bubbles but well ahead in its curing process where chemical bubbles are not created. 

 

This seem to be the best method for me so far in casting rocks.

 

Here is another example:

 

This rock would have broken in two as the center is extremely thin. In this case I pulled the hydrocal up and made it thicker in that area. Notice how it dries looking like ice cream or like a Frosty.

When it is at that consistency you can manipulate it for a short while. 

 

 

Hope this helps

 

Inobu

 

I forgot one more tip.

 

Cast the rocks one at a time. Removing the rocks can be problematic so select the rock you want and cast it. I started casting them one at a time and

had an easier time getting them out with no major problems.

 

For example  C1247 is long so dealing with only one stone allows you to grab the mold in a manner that the rocks will drop out. 

 

 

 

 

Edited July 11, 2016 by inobu

[inobu]

I though I would come back and show the benefits of controlling the minute consistency of the Light Hydrocal.

 

In the previous post I was able to time the application of the hydrocal to create a bowl like casting. Meaning to create a bowl effect where as the casting was not a solid piece. This helped to better control the placement of the rock casting on the layout. 

 

After learning how to mix smaller batches of hydrocal the thin wall process can be further expounded upon. The wall of the casting can be as thin as 1/8" of an inch. With casting like this you can place the rock mold on a mound or corner covering making placement a lot easier and controllable. Although the rocks are fragile you can pack in recessed area with compound to reinforce the rock during the mounting process. 

 

 

 

 

although the demolding process is harder the yield out weights the labor.

 

Inobu