Silmar 41 First casts

Signed-In Members Don't See This Ad
C

cpmech425

Member
Joined
Dec 20, 2014
Messages
105
Location
Bellevue. Ohio
Saturday afternoon I cast 11 tube in blanks. I mixed 11 ounces of SILMAR 41 with 22 drops of MEKP. Put in pot for 20 hours.
The blanks are still quite soft. Will they set up over time? Should I warm them up? Should I start over? Thanks!
 
Signed-In Members Don't See This Ad
I don't use Silmar 41, but from what I've read, Silmar 41 gets mixed with a minimum of 3 or 4 drops of hardener per ounce of resin and I recall several of the experts here on IAP indicating even more than that depending on the volume that is being mixed. It looks like you might have gone a little light on the hardener. I think John, JT, (jttheclockman) uses Silmar 41 for casting, so perhaps you can check with him.

I'm no expert on Silmar 41, but the polyester resins we used to use at work would either take a very long time, like 24 hours to cure or would not cure at all if we didn't get enough catalyst mixed in.

Dave
 
Dave said it well. When you start getting into batches over 5 or 6 ounces you need to increase the hardener. But even before that I use 4 to 5 drops even with small batches below 5 or 6 ounces. I get over that I use about 7 drops per. ounce. Some will say because of the more resin means more heat. To a point that is true but you need more drops to harden that much resin. Everyone is different because the temp they are working it may vary. The warmer the temp the faster it will kick. I found these numbers work well for me the blanks are solid and turn well. 2 drops is a little light. next time try 4 drops. Will it harden, it should but now will take a little longer. You could set it by a warm heat source but something gentle because if you direct heat to one side of the blank you could possible cause broken glass look. Many times I set on top of the baseboard radiator so heat surrounds the entire blank as it rises. John U is probably the expert with this resin for he uses alot more than I. I should mention too I use a pressure pot and always leave my castings in over night so close to 24 hours because I am never in a hurry.
 
It's been a while, but I used to work extensively with Silmar resin. My go-to ratio was 3 drops of catalyst per ounce of resin. In my experience, using more than that often made the resin prone to becoming brittle or "chippy." That said, factors like weather, temperature, and even the age of the resin and MEKP can all impact the curing process.

If your resin and workspace are cold, the exothermic reaction may slow down, preventing the resin from curing properly. I agree with JT—your first step should be to apply some heat and see if that helps your blanks fully cure.
 
It's been my go to resin for certain projects since 2008. Anyone who uses Silmar PR has been where you are. When you say soft… do you mean you can squeeze the sides of your molds and the resin squishes in or do you mean the top is slimy? It will harden. The above advice is good - give it a little heat and time. This time of year can add to longer curing times. Also, compressed air in a metal tank … it's also cold.

I typically use 3-4 drops per ounce. I don't precisely measure the amount of resin- it's just a guess by how deep the 19oz cup is. I feel 3-4 drops allows me to be off a little so if I add a couple extra or leave out a couple drops I'm still ok. The higher numbers suggested on the label are for thin pours like in fiberglass applications. With pen blanks the resin is a larger volume so heat will generate a little more to help cure them. Something I do to help this time of year is warm the resin to around 90° +/-
Mostly for easier mixing but it helps the curing process also.

The top of your pours will usually be sticky when you first check them. This is a quality of the resin that allows you to pour more layers with good adhesion between them. I usually let my blanks core for 18-24 hours depending on the time of year. Colder seasons I let sit longer. Then I open the tank and let the blanks sit another day to cure the stickiness.

Don't get discouraged. This is all part of learning the resin. The more you understand it the better caster you will be in trying new ideas and pours.
 
You must log in or register to reply here.
Back
Top Bottom