Problem with Silmar

[Rangertrek]

I tried a cast today using Silmar. The block of resing is like jello after 6 hours. I used 4 drops of mekp per ounce or resin. Poured outside, temp in the 60s, fairly high humidity. Pressure pot for 4 hours, craft oven for over an hour.
Any ideas on what went wrong?

Do you think this block will eventually get hard.

 

[ldb2000]

there are several reasons for PR to cure slowly , Bad MEKP , not enough MEKP to start the reaction in cold weather and certain pigments slow down the cure reaction . If left long enough PR will cure without any help .
Heat is needed to cure PR , that's why many of us use some type of oven or kiln to post cure our PR . Just remember the vapors from PR are flammable , so no open flames or sparks .

 

[jttheclockman]

You do not say how much resin you are using. The more resin the longer the cure time. I use nothing less than 5 drops per ounce and if going over 2 ounces I add an extr drop for every ounce over 2 ounces. Has worked real well for me. But another key is to mix thouroughly. I also heat my resin before adding the catalyst. Less bubbles. Don't need much. Maybe 5 minutes is all that is needed.

 

[Rangertrek]

I was making a mix of three colors, each using 4 oz of resin. I appears I did not have enough mekp for the volume of the resin. Will try at least 5 drops on the next attempt. Thanks for the info.

 

[its_virgil]

I clear cast only and use 3 drops per ounce and have no problems with non curing. The pressure pot has nothing to do with curing time nor does the pressure used. When I did use the pressure pot I cast at 20-25 psi but I no longer use it. I never post cure clear castings. I suppose your problems stem from the pigments used. When I was casting colors I remember all colors did not behave equally nor did different types of pigments.
Do a good turn daily!
Don

 

[ldb2000]

If I preheat my PR and mold I use 3 drops per ounce . Without preheating I use up to 10 drops per ounce depending on the temperature in my shop .
Preheated the resin gels in about 10 minutes and without preheating it can take an hour or more to kickoff sometimes .
Oh , and like Don I don't use pressure for casting PR anymore . Preheating thins the PR enough that any bubbles just rise to the top right away .

 

[JohnU]

I use 3 drops per ounce but most of my casts are clear. In cold weather I put the mold in my tank and set it in front of the heat vent in the back room. I let my molds set over night (no less than 8 hours) and I pour 10 oz at a time. It comes out sticky but I put in in the sun light during the summer and by the heat vent in the winter. You can also turn the oven on warm and let it sit for 10 mins before turning it off to cool. My opinion and experience has lead me to believe if theres too much heat or for too long it will make the blanks brittle. It also might make a difference what your coloring your pr with. If its oil based paints you might need more MEKP per ounce. I felt it made a softer blank, less brittle and took a little longer to set up. I now use tints from US Composits and PearlX with no problems. Im no expert but this works for me.

 

[jason_r]

New resin cures slower than old.

Larger blocks of resin cure faster- they feed themselves more.
(this is why you don't cast with a layup resin-it'd get too hot and crack)

Jello after 24hrs and a post-cure seems slow, but like ldb2000 said it'll get there eventually. There is some data on amounts of MEKP+temp vs gel time in the Resin Color Library

One other variable- what pigment(s) did you use? Some pigments do affect cure time.

 

[jttheclockman]

Not sure everyone is talking about the same product here. Silmar does not get hot like a Cast-N-Craft resin. It does not kick off like that either. It is a slow process to cure and that is what I love about it. I do warm mine before casting and use 5 drops and if adding color I will add a drop or 2 extra because yes colorant will change the cure rate and if it is liquid even more so. I let sit for 24 hours then I do heat in an oven to get rid of the sticky feel.

 

[Brooks803]

I'm also casting with Silmar 41 and I have had both experiences with not curing for a long while and curing very quickly. I don't heat my resin beforehand bc I like to have plenty of play time with coloring the resin. I have found different colors (when it comes to mica powders) do set up at different intervals. I'm using between 4-5 drops catalyst per 1oz of resin. It usually takes each color (I do either 2 or 3 usually) 35-50mins to gel. I usually won't leave the table when I'm casting and I do a slow stir to check the viscosity every 5-10mins. I have tried testers enamel and acrylic paints before too and they took forever to setup and overnight and sometimes longer to cure properly. Also, the set time in the molds can depend on the molds themselves. I have 3 different molds right now, 1 plastic from kitkraft.com, 1 home made from a block of nylon, and 1 from teflon and each has a very different cure time. Once they are cured but maybe still tacky on the surface I'll put them in my toaster oven at 150 for 15min intervals. I do agree that too much heat can make them brittle, as well as more MKEP. Hope some of this has been helpful and best of luck with future castings!

 

[Silly Rabbit]

That is odd, I have never had any heat from the Cast-n-Craft stuff that I have used and I have done well over 100 casts with it. The Silmar on the other hand that I recently started using gets really hot. I just did some blanks over the weekend in a pvc pipe and I could barely touch the pipe. I had some extra resin that was in a clear plastic cup with 2 outer cups in case it leaked through. It melted the 2 outer cups that were around it.

 

[ldb2000]

I had some extra resin that was in a clear plastic cup with 2 outer cups in case it leaked through. It melted the 2 outer cups that were around it.

It most likely wasn't the heat that melted the cups , it was the chemicals in the resin reacting with the styrene in the cups .
Heat is REQUIRED to cure the resin , no matter which brand you use . The MEKP starts a reaction to create the heat which then causes the resin to cure . You can cure most PR just by heating it long enough . All of the resins we use including PR and Alumilite are thermoset types of resin .
There have been several threads about this . Do a search for more info .

 

[PenMan1]

Butch or Don likely hit on the problem. it could be old or bad MEKP or something in the pigments used. Make a small pour with NO pigments using the same ratio of catalyst to S41. If the same thing happens it old MEKP, If it hardens right up it is a chemical reaction between the pigments and the resin.

 

[jttheclockman]

That is odd, I have never had any heat from the Cast-n-Craft stuff that I have used and I have done well over 100 casts with it. The Silmar on the other hand that I recently started using gets really hot. I just did some blanks over the weekend in a pvc pipe and I could barely touch the pipe. I had some extra resin that was in a clear plastic cup with 2 outer cups in case it leaked through. It melted the 2 outer cups that were around it.

Wow that is odd because I see it just the opposite way. How much catalyst did you use per ounce???? I am very curious. Unless they changed the formula from the time I bought mine, I have now done quite afew pours and not once has the resin got hot. Now when using the cast-n-craft stuff when it kicks off it will get real hot for a short period of time and this will melt plastic cups. I use pill bottles with that stuff to make bottlestoppers.

 

[jocat54]

Wow that is odd because I see it just the opposite way. How much catalyst did you use per ounce???? I am very curious. Unless they changed the formula from the time I bought mine, I have now done quite afew pours and not once has the resin got hot. Now when using the cast-n-craft stuff when it kicks off it will get real hot for a short period of time and this will melt plastic cups. I use pill bottles with that stuff to make bottlestoppers.

That's the same experinence I have had--PR no heat-casting craft gets pretty warm.

 

[Glass Scratcher]

Under-catalysing S41 will cause it to not generate the same amount of heat as catalysing at the recommended 1%. You are curing it cold, this may not cause problems if you are in the recommended working temp range and you stay below the 5%-7% pigment/load range.

 

[its_virgil]

Charles,
Isn't a swing resin better for using pigments and dyes that S41? From what I think I understand swing resin can take the pigment or dye loads better than S41. Anything to this?
Do a good turn daily!
Don

Under-catalysing S41 will cause it to not generate the same amount of heat as catalysing at the recommended 1%. You are curing it cold, this may not cause problems if you are in the recommended working temp range and you stay below the 5%-7% pigment/load range.

 

[Glass Scratcher]

Charles,
Isn't a swing resin better for using pigments and dyes that S41? From what I think I understand swing resin can take the pigment or dye loads better than S41. Anything to this?
Do a good turn daily!
Don

Don,

Swing resins (Onyx and Marble resins) can take more filler, whether that is dyes or powder pigments. Swing resins are superior at handling pure metals, and natural stone pigments, due to the viscosity for physically suspending the load, and the fact that they use different reactants that provide enough continued heat during the catalytic reaction that can power through any heat absorbing load, which would effectively kill the reaction in standard cobalted casting/laminating resins. The downside is that the more pigments and powders you add the more solid the cast, the less liquid and swirly it will appear.

S41 and most other casting resins should be catalyzed prior to adding pigments and powders. If they are catalyzed prior to mixing in additives, the reaction will start to kick, and the resin is less susceptible to inhibitions. Catalyzing first then waiting 3 or 4 minutes to add your pigments and powders, the pigments and powders will -usually- not have time to fall out of suspension. Even if you break it out and only mix in Pearl-Ex, then catalyze the resin, wait 2 or 3 minutes before adding your liquid/paste pigments, one should have greater success at those color liquid/paste pigments that are heavy(white paste pigments), problematic and prone to cure inhibitions(reds, blacks and whites). S41 that is unpigmented and catalyzed at 1% MEKp at 70F will accelerate to soft gel in 8-10 minutes and reach hard gel in 20 minutes. This is my experience as well as what Silmar states in their literature. I prefer to use .75% MEKp measured and dispensed with a syringe.

It is really a case of, for some materials and types of casting S41 is fine, and for others it isn't. I hate to say it all depends- but that is the truth of the matter. If you are trying to make your own Tru-stone, or a variation of 3M blanks with funerary metal pigments, then you need to be using a Swing resin. But if you are just doing embedments or swirled colors, then you could use either. However, if you are doing clear embedments, S41 is significantly thinner than Swing resins, and bubbles will rise out more easily. Some (not all) Swing resins of the Onyx or Marble variety have a slight pink tone.

As with everything it may also come down to, you just may like Swing resins for the versatility of what can be done with them, you can use a light pigment load with them or a very heavy load.