PR cure time

[ldb2000]

Hi everybody
Just got my silmar41 from mr fiberglass...great people fast shipping...
and cast my first blank...almost...
I used 10 drops per oz as it says in the instructions and after 2 hours I still had blue soup.
I figured out that the problem is its too cold here in my shop...about 65F...I took my magnetic work light (100w bulb) and put it over the mold to heat the blank and it has almost cured ...about 45 min
The question is :
How do you people up north here get your PR to cure in a reasonable time? , Do you add more MEKP and if so how much?? , do you preheat the mold? , Do you have another way to keep the mold and blanks warm till they cure?
I have heard that adding too much MEKP can hurt workabilty so would prefer not to do that so any ideas welcome
And yes I know Alumilite dont have these problems but its more expensive and I dont like the way it finishes , I dont want to have to CA an acrylic blank
Any ideas welcome

 

[karlkuehn]

Hey Butch, I'm here in Lancaster PA, sorta close to you. I keep my shop around 65 degrees too. I do add a bunch of pigments and such to my resin, which will prolong the cure time, but even casting clear I use way more than 10 drops per ounce. I also have the Silmar 41, and it takes a long time to kick off with what they recommend, especially in the cold. I usually measure out a 1/4 oz. per 5 oz. resin, especially if I've got a lot of pearl and pigment in it. Seems to be working okay so far.

You better watch blaspheming Alumilite. Curtis is around here somewhere, and if he overhears you saying that...lookout! hehe[]

 

[ldb2000]

I've got the flame suit on already [8D] , I'm really not knocking alumilite it IS more expensive and it just seems too....errrr I dont know tough to sand out to a high gloss...shines ok just not enough..if that makes sense...without giving it a CA finish , so I want to give the PR a try just need a way to keep it warm and on that note I had an idea .
I'm gonna try and put a heat tape (the type they put on pipes to keep them from freezing) around my HF paint pot and warm the pot up a bit , should keep it warm enough to help the cure time

 

[karlkuehn]

I know what you mean about the alumilite. The ribbon blanks that I did were alumilite ribbons in PR bodies, and when I sanded them, the PR kept disappearing faster. Made for some neat texture on the ribbons, though.

I like the amount of time you have to work with the PR, too. Seems like whenever I cast with alumilite I've got the theme song from Jeopardy running through my head about three times as fast as normal until I get it into the pot.

 

[sbell111]

Be patient and see if it sets up before tomorrow.

 

[Glass Scratcher]

Try heating your mold before casting.

 

[ldb2000]

ok woke up this morn and checked the blank and it was dry and hard as a rock...left the worklight on it all night to help keep it warm....so heat is the answer.
karl-I know what you mean , yes sanding alumilite is strange to say the least...theres something to be said for brittle...sanding is very predictable
sbell111-yes let it sit overnight but I'm not a very patient person
Glass Scratcher-yes gonna try that too but I need to keep it warm so thats what I'm working on now

 

[follow3]

Hey Guys,

I use Silmar also. I tint with powder coat powder and pearl pigment. I only keep my shop about 70 degrees. I use the 3/4 x 3/4 silicone mold from Gadgets.

I only use 4 drops per ounce and no heat. I pour in the evening about 8:00 pm, put it in the pot under about 40 lbs of pressure.
When I get home from work the next afternoon around 4:00 pm, the blanks are dry and hard.

I like taking the extra time and using less heat and mekp because I have found that the more mekp and the faster you cure the resin, the more brittle it gets. If you take it slow, it is much easier to work.
When I added more mekp and cured it fast it got brittle like Acrylester.

Just my 2 cents worth. The time line also works well for me, pour one evening, take them out the next afternoon, pour another batch the same evening. I am not sure if the cure sooner or not, to be honest I have never opened the pot and checked sooner.

Good Luck,
Steve

 

[ldb2000]

Hi Steve
how do you get your pearl to swirl , when I just cast and let it sit it all seems to level out and I dont get a nice swirly mix , or is PR different then alumilite which I had to swirl it just as it gels

 

[bitshird]

Butch, you have to wait untill the PR starts to gel, it gets kind of thicker as jello would, then you can use a small piece of wire and slowly pull the colors around, the gel time will vary but most people find it happens between 15 and 45 min, I think it depends on the amount of catalyst you put in the mix and the ambient temperature, also some of the mica powders are a little bit heavier than others and like to seperate.

 

[ldb2000]

ok so is about the same as alumilite thats how I do it with that but the problem I was having it never gelled till I hit it with the heat

 

[sbell111]

How long is 'never'?

I've had it go an hour or so before I felt that it was gelling, but it has always gotten hard within a day.

Typically, I'll leave it in the mold for 24 hours and then pop it out. Even then, the top is often still quite sticky. I just leave it on the work table until it's all hard, usually for another day.

 

[ldb2000]

never is about 3 hours then I put the light on it , if it hadnt been for that it might still be soup .
Im now putting in 2% mekp and it is fine

 

[sbell111]

I'd rather have it set up really slowly than increase the amount of catalyst. More catalyst (or more heat, I believe) will cause it to set up faster, but the end product will be much more brittle. By going nice and slow, you'll lose fewer blanks later on.

 

[hughbie]

my shop is chilly too. there have been times i've waited a couple of days and it's still sticky. i heat my oven to 170 let it come to temp and then put the blanks in, turn off the heat after about 1/2 hour and let it set all night. the blanks are perfect after that. my wife suggested, turning on a heating pad and set the mold on it....and maybe putting a cardboard box over it...mini oven.....let your mind run wild

 

[follow3]

A good way to provide some gentle heat is to use an under tank type heat mat from a pet store. they come in different sizes and are a flat plastic matt with heat wires imbedded inside. They usually only get to about 100 to 110 degrees F. I have one that is 12" x 12". I sit my silicone mold on top of it and plug it in. I also have a halogen light that I shine on it from above. I have the light hanging from a bracket on the wall above the work bench. To vary the heat, just move the light farther away.

I don't like to use heat, but when I have to, I make sure it is just a "gentle heat" of no more than about 120 degrees F.

The cooler it is during curing, the less brittle the blank will be.

 

[Mather323]

I am very new to this so here is my observation on this subject. After you have your pr in your pressure pot and you are concerned about the temp, why don't you take your pot inside the house until it cures?