Ratio of catalyst to resin

[bgibb42]

Just as a general rule of thumb: is there a good ratio to follow for (X) drops of catalyst to harden (X) amount of PR?

I'll be using Castin' Craft resin, because that's what I have. On their can though, it calls for a certain amount of drops to be added to the resin depending on the thickness of the cast. From reading a bit around here, I notice that a lot of folks measure out their resin in ounces and then add catalyst based on that number (I think). From my own experience, I've found that less catalyst tends to equal less brittle blanks, to a point.

I'm looking for a good starting point, so I don't have to spend a lot on expensive resin experimenting.

Any suggestions?

 

[OKLAHOMAN]

3 drops per oz.

 

[Craftdiggity]

I use Simlar41 and the directions say 10 drops per ounce. I cast outside and if it is hot out, I usually cut that to 7 drops to give me a little more time to work with it.

 

[bitshird]

The ratio of Catalyst to resin depends on the thickness of the casting, some times casting with things like rice and coffee beans much of the volume of the mold is taken up by the material so you will have to add more MEKP for a 3/4 inch thick casting normal temperatures above 70 degrees 3 to 4 drops per ounce, for castings with crushed pepper, rice, grass clippings you may need to at least double the amount of MEKP with Silmar 41, Alumilite doesn't work the same way it's equal parts period, casting ribbons on a piece of wax paper or on a sheet of glass at least 20 to 30 drops per ounce since you casting is going to be paper thin. It can also fluctuate a slight bit based on what colorant and or dyes you use but for normal 3/4 and 1 inch castings 3 drops will usually give you an excellent piece. Heat created by the MEKP and the resin are wht cures the PR the thicker the casting the hotter it will become on curing. also the gel time usually decreases with thicker castings,. Ambient temperature also helps it cure faster. And you are correct adding too much catalyst will make the blank more brittle, Blessed be the toaster oven for cold weather casting of castings that didn't quite get enough catalyst, 150 degrees for 45 min to an hour, let sit over night and bada bing!! good blanks.

 

[bruce119]

As said temp will effect it tremendously. I heat the resin put my mixing cup in a container of hot water. To about 90-100 I use 3 drops that gives you about 20 min. working time. I let cure for 12 hrs. Air temp is about 78.

Now keep in mind depending what mold you use the smaller the worse like the resin saver. With less MEK 3 drops you will have a sticky gluey surface you mite be able to put a stick into it a 32" or so. That is normal I just leave it in the mold and put it outside in the sun fort a few hours and it sets up. More drops will fix also but then you cured resin will create more heat and I think that makes it more brittle like hard glass when turning.

good luck you will get lots of different answers

 

[witz1976]

I am using Castin' Craft too, first batch did what the can recommended. It was 80 deg. out with very high humidity, and it was done in about 2.5 hours. Next day I cast with 5 drops and it was around 70 with low humidity and it actually sat overnight and was still soft until the sun was beating on it... just make sure you write everything down so you can use refer to what worked and what didn't.

 

[Craftdiggity]

As I said I use Simlar41 and 7 drops/oz and I have to pour it pretty fast if it is hot outside. I like the way it turns out though. I have had very few pinholes and air bubbles. They have turned very nicely for me and I'm hoping to hear the same from those who have gotten blanks from me. It usually takes a couple of hours for mine to set up in the mold, but sometimes they are a little sticky. I let them sit for 3-4 hours and I'm usually good to go.

 

[bruce119]

As I said I use Simlar41 and 7 drops/oz and I have to pour it pretty fast if it is hot outside. I like the way it turns out though. I have had very few pinholes and air bubbles. They have turned very nicely for me and I'm hoping to hear the same from those who have gotten blanks from me. It usually takes a couple of hours for mine to set up in the mold, but sometimes they are a little sticky. I let them sit for 3-4 hours and I'm usually good to go.

Try cutting back to 3-4 drops it will take a little longer but your customers will be much happier. The more MEK you put in the more brittle it is. If you where to put in what the manufacture suggest I think it works out to be about 21 drops it would be like glass and very difficult to turn. Remember these resins were not made for turning none of them we are doing stuff they aren't intended for.

Any way give a try you mite like it.

 

[PenMan1]

Brian:
We are pretty close, geographically. When making blanks in a 3/4 inch mold, this time of year, 6 to 7 drops per ounce in S41 works nicely for me. It begins to set up in about 20 to 30 minutes, just a little "tacky" in 24 hours.

It changes a little bit once some of the 100+ days (and super humidity) quit coming so regularly.

 

[JohnU]

I use 3 drops in all of my blanks. I use a pressure tank and let them cure for 12 hours before I open it. Like Bruce said, they will come out tacky. I set mine in the sun for about an hour and it takes care of that problem.

 

[Brooks803]

Just as a general rule of thumb: is there a good ratio to follow for (X) drops of catalyst to harden (X) amount of PR?

I'll be using Castin' Craft resin, because that's what I have. On their can though, it calls for a certain amount of drops to be added to the resin depending on the thickness of the cast. From reading a bit around here, I notice that a lot of folks measure out their resin in ounces and then add catalyst based on that number (I think). From my own experience, I've found that less catalyst tends to equal less brittle blanks, to a point.

I'm looking for a good starting point, so I don't have to spend a lot on expensive resin experimenting.

Any suggestions?

I started with castin craft and have switched to silmar 41. With silmar I use 3-4 drops per oz in a 6x3x1 mold. When I used castin craft I would use 2-3 drops per oz in the same mold and they weren't as brittle. They may take more time to set up, but hopefully less likely to explode just by looking at it sideways.