Another casting question or two

[ofd8001]

I'm a little confused on the amount of catalyst to use. If I read the Silmar 41 instructions right (which may be doubtful), it says to use 10 drops per ounce. Some of the YouTube videos I've watched have folks using 3-4 drops per ounce.

Also, some of the blanks I have cast are still kind of "gooey" even 48 hours later. When I use a dowel rod to push them out of the PVC, I'm seeing resin on the end of the dowel. Would this be an indicator of too much or too little catalyst?

Workshop is heated - 70 degrees plus.

 

[Brooks803]

The amount of catalyst used in what we do is typically 3-5 drops per 1oz of resin. The recommended amount of 10 drops is for the resins intended use of doing large castings. Also, the more catalyst used the harder (more brittle) the blank becomes. So by using less it keeps the resin more user friendly.

One aspect of S41 is that it bonds to itself chemically. That's why the exposed areas remain tacky. Toss them in a toaster oven around 150 for 10-15mins and that should go away.

One thing you didn't mention is what you are using for pigment. Depending on what it is it could be the culprit. Some things, all though compatible, don't cure as quickly. I don't cast in PVC so I don't know if that's a normal thing or not.

 

[ofd8001]

Thanks. The pigments I used were those on the US Composites site, right there with the S41.

Usually I don't get around to turning the blanks for at least a week after they have been cast and demolded. What was throwing me was on the videos, the dowels used by the video maker were clean, but mine were kind of nasty.

 

[Brooks803]

Ahhh...those paste pigments are very concentrated. Most likely you used to much and overloaded the resin which causes it to cure super slow or not at all. I use those pigments also and it just takes time to learn how much it'll take.

The trick I do is to start with a small amount. Mix it well. Clean off the stir stick. Dip it in and if you can see through the resin (translucent) you need to add more. Once you can't see through it you shouldn't see through it once turned and the brass tube will be hidden. Do this enough times and you'll get a feel for how much you'll need.

 

[ofd8001]

Excellent advice as it makes great sense!

Thanks. . .