Simlar 41

[Janster]

...while I am having great results w/Simlar I do have a question. When I do a casting I leave it sit the rest of the day and overnight too. Every time I have done this they come out of the mold a bit "sticky to the touch". I place them in direct sunlight and they finish up solid and non-sticky. Has anyone removed the casts from the pressure pot after maybe 6 hours and then to sunlight with good results? TIA.....Jan


..until then, I'll continue on as posted.

 

[JohnU]

Here in IL I leave my clear casts in the tank for 18 -20 hours. In the summer I've left open molds of color poured blanks outside in the sun light and had them cure in a less than 8 hours. My only issue is they get brittle when heated and cured to quickly. They always come out tacky, which I believe is a quality of PR.

 

[Janster]

....thanks for your input. I just called US Composites and the Tech told me I could remove the molds after 6 hrs. At that point use a heat lamp or sunlight to post cure. He asked what type of mold I was using ,I use Silicone molds from Fred. He advised me to use a PLATSIL Molds (sp) as Silicone is causing the tackiness. I think 75% of the casters here in IAP use Fred's molds? Could be more or less? So, I may try removing the mold after the 6 hours and place it in direct sunlight. I told him I had used Simlar41 in a toaster oven @ 120º for 25 minutes to cure it and never had a problem. He told me I was lucky as that stuff is extremely flammable, and it is! My Toaster bit the dust so I now use a Pressure Pot. Hope all this makes sense. In reality I'll probably go about it as I am now doing. I was just wanting to speed up the process w/o purchasing more molds..... Jan

 

[PSNCO]

Googling Platsil, it looks like it's just another brand of a silicone used for mold making.

I haven't done any casting in the molds I got from Fred, yet. I've used PVC pipe and plastic trays. I get some tackiness when I tap them out of the PVC after about 4-6 hours on warm days, but it's fine after about 6-12 hours later. I wonder if it has to do with the age of the Silmar. I used the Silmar from US composites initially, but then switched to buying it from a local company here in the Twin Cities. Silmar 41 is made in St Paul and the oldest I get is 10 days old here locally. I think I got some tackiness with the Silmar 41 from U.S. Composites but that was a year ago and only 2 gallons that I bought from them. It could of been inexperience in my casting or it could have been the age of the Silmar.

I don't think in a mostly cured state that Silmar is going to combust at 120 degrees.

 

[Janster]

...US Composites stated to me that the Tackiness was normal. The PR I have in about 10 months old?.... Jan

 

[sbell111]

As I understand it, the initial tackiness is a feature, not a problem. This tackiness allows you to build layers of PR and be certain that they come out in one perfect piece, rather than splitting at the joint.

The tackiness goes away with time or heat. I prefer time. Of course, you need not do anything about this tackiness, since you are going to turn away this outer bit anyway.

 

[Janster]

As I understand it, the initial tackiness is a feature, not a problem. This tackiness allows you to build layers of PR and be certain that they come out in one perfect piece, rather than splitting at the joint.

The tackiness goes away with time or heat. I prefer time. Of course, you need not do anything about this tackiness, since you are going to turn away this outer bit anyway.

....thanks.........Jan

 

[BSea]

....thanks for your input. I just called US Composites and the Tech told me I could remove the molds after 6 hrs. At that point use a heat lamp or sunlight to post cure. He asked what type of mold I was using ,I use Silicone molds from Fred. He advised me to use a PLATSIL Molds (sp) as Silicone is causing the tackiness. I think 75% of the casters here in IAP use Fred's molds? Could be more or less? So, I may try removing the mold after the 6 hours and place it in direct sunlight. I told him I had used Simlar41 in a toaster oven @ 120º for 25 minutes to cure it and never had a problem. He told me I was lucky as that stuff is extremely flammable, and it is! My Toaster bit the dust so I now use a Pressure Pot. Hope all this makes sense. In reality I'll probably go about it as I am now doing. I was just wanting to speed up the process w/o purchasing more molds..... Jan

I've used Fred's molds, and PVC pipe. Frankly, I don't think there is a difference in how tacky the blanks feel. I have also taken blanks out of the molds at 6 hours (maybe a bit less when I was in a hurry), and they might be a bit more tacky. The only issue you might have is that the blanks may not be fully set, and they can bend. Just lay them flat, and you'll be fine.

Another thing you can do is place the mold with the blanks out in the sun. I've done that a few times with PVC when the blanks were a bit stubborn. I don't know if it would really speed up the process much since the PR generates a lot of heat by themselves.

 

[Janster]

..thanks Bob. I sent you a couple of PM to no avail. Please contact me via PM......Jan

 

[its_virgil]

As noted previously, polyester resin is formulated for the surface exposed to air to remain tacky for subsequent layers to bond. For those casting in tubes check the ends. One or both will be tacky if left exposed to air during casting. And, as noted, it will dry up with time. I cast in the evenings and place the molds outside in the sun in the morning. By afternoon no tackiness.

Polyester resin has a flash point in the mid 90 degrees...96 if I recall correctly. There have been reports of the fumes igniting in a toaster oven. I would not leave blanks curing or post-curing unattended in a toaster oven
Do a good turn daily!
Don

.

I don't think in a mostly cured state that Silmar is going to combust at 120 degrees.

 

[Jim Burr]

Tacky has been normal for me and I don't put PR or S41 in a pot unless it's a WW casting...just vibrate the crap out of it for foil and stuff has been fine...JMHO

 

[Janster]

..thanks Don. I was hoping to speed up my output w/o purchasing more molds. I can do 4 blanks at a time or purchase 2 more mold to double that! As stated above I was hoping also to be able to remove the molds from pressure after 6 hours and then sun dry, pour the new blanks in the evening, demold in the AM and by 4PM, repeat the process. Be well......Jan

 

[Cmiles1985]

Good info on the Silmar! My first gallon should be here tomorrow, and my wife and I both look forward to trying it out. That mid-90 degree flashpoint could be a bit worrisome, as that is the typical ambient air temperature right now!

 

[sbell111]

Good info on the Silmar! My first gallon should be here tomorrow, and my wife and I both look forward to trying it out. That mid-90 degree flashpoint could be a bit worrisome, as that is the typical ambient air temperature right now!

I read that the flashpoint is 88 degrees. That being said, I think that many of us pour at higher temperatures and, as far as I know, none of us have burst into flames.