Colder temps = slower gels

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Russianwolf

Russianwolf

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Joined
Jul 13, 2007
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Martinsburg, WV, USA.
I do my casting out on my deck, and this weekend the temps were in the mid-high 60's. I put 40 drops of catalyst in each cup (about 8 ounces) of PR to begin with. And 2 cups go into each pour (so 80 drops total). After checking back several times, I added another 80 drops and still took a while.

On the second cast, I started with 50 drops per cup. Checking back in several times, nothing. Added another 50 drops and it slowly gelled.

Heads up to anyone doing cold weather pours, you will likey need to up the catalyst to about double what's normal.

I'll be doing more pours this week, and will let you know how they go. Next batch will be at 70 drops per cup. Let's see if I can get the gel time under a half hour.
 
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Most definatly. I've found that anything below mid 70s is a horror show. I think mid 80s are great. What I'm going to do this fall and winter is beyond me. Maybe I'll make a small wooden booth with a heating pad or low wat bulb in it, a sort of curing oven. Maybe I'll find a dead freezer somewhere....
 
I've got the opposite problem. I finally got back out to do some casting just now
with Pearl-Ex and the Coastal Scents Mica. The red gelled in 15minutes- about
5 minutes ahead of what I was expecting and still in the cup. The blue was about 2
minutes later, but at least I got it out of the cup. (Not that it really matters, as the result
will be too thin to do anything with).

Before dividing into halves for different colors it was ~5oz of resin w 20 drops MEKP.

Weather now says about 88, garage was probably still in the low 90s.

Maybe next time I won't try to keep the colors as distinct.
 
Jason,
It may have been the temperature but it may have been that red & yellow liquid/paste pigments tend to accelerate a resins cure.

I tend to use less MEKp in red and yellow (and colors with red or yellow as components(green, orange...)) to compensate.
 
No argument there on the red making it faster. I really started with 1 cup of ~5oz
of resin I catalyzed/mixed, then split into halves and added pigments.

The red gelled about 2 minutes ahead of the blue. (or about 12% faster).

But even so, they were both about 5 minutes ahead of what I expected.
 
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I use an old refrigerator as a hot box. A 100W bulb generates heat up to about 120 degrees. No problem curing resins! Now before the safety police goes nuts, yes, the fridge is vented! I also use a dimmer switch to control the bulb thus the temp, and a timer to shut the bulb off.

Getting ready to set the freezer up with a warming system to keep the resin comfy while not in use.

I also use the hot box to cure stabilized items and other things needing to be dried or cured.
 
Jason, I add my pigments to get the colors correct first, then catalyze.

Greg, you have my perfect world....... one of these days....
 
A caution about over catalyzing; more catalyst will advance the gel time and also the final curing time, but it will also make the finished casting more brittle. You may find that the over catalyzed castings have a greater tendency to chip out during turning. To make a softer final casting that will come off your skew like a ribbon instead of micro shrapnel, keep the catalyst ratio as recommended for the resin, or less. Applying heat to accelerate the cure is usually a better option.
 
td said:
Jason, I add my pigments to get the colors correct first, then catalyze.
Click to expand...

Normally, I'd do it that way. But these were small pours and I was mostly
playing with the coastal scents / Pearl Ex colors instead of going for specific
colors.

So I catalized then pigmented to make sure I had the right total amount of resin
for my mold and so as to minimize the effects of any "oops"es.

It's made for some interesting swirls. Barely got the blue-green one
into the mold last night- swirling in the green with a toothpick it tried
to come back out.
 
Almost forgot to add something concerning pigment colors and cure times. If a pigment has any copper in it (some reds may well have) this can speed up the gel and cure times. DO NOT use copper tubing as a mold for PR. DAMHIKT!!!!
 
That's interresting Greg. I may have to grab some copper and cut it up to use a stir paddles for when I mix black- as black paste/pigments usually inhibit and delay curing, even if the resin has been pre-catalysed.
 
Cozee,
You mentioned that you use an old refrigerator as a hot box for your resins and use the hot box to cure stabilized items. If you do not mind, could you expand on your stabilizing process, what material do you use? I have a pressure/vacuum pot and a lot of Maple burl that needs the process.
Thank you for the info
 
Chasper said:
A caution about over catalyzing; more catalyst will advance the gel time and also the final curing time, but it will also make the finished casting more brittle. You may find that the over catalyzed castings have a greater tendency to chip out during turning. To make a softer final casting that will come off your skew like a ribbon instead of micro shrapnel, keep the catalyst ratio as recommended for the resin, or less. Applying heat to accelerate the cure is usually a better option.
Click to expand...

Can someone explain what's going on during the cure better? I was under the impression that the catalyst was basically just adding heat (albeit through a chemical reaction) to the PR which causes it to cure. Is there more going on?
 
Nick said:
Cozee,
You mentioned that you use an old refrigerator as a hot box for your resins and use the hot box to cure stabilized items. If you do not mind, could you expand on your stabilizing process, what material do you use? I have a pressure/vacuum pot and a lot of Maple burl that needs the process.
Thank you for the info
Click to expand...

I use what I have on hand and what look I am going for. I use Min Wax Clear Poly (darkens wood a bit) and either Min Wax wood hardener or my own acetone-plexi mix. Of course I stabilized under a vacuum.
 
Mike, If no one else answers this query you might PM Glass Scratcher. There are questions that i have asked a dozen people that no one seemed to be able to answer and one Personal Message from him connected so many dots for me that it was amazing. He's clear, concise and technical.

One of my questions to him was not understanding why my casts in silicone remain tacky when the same PR cast in plastic trays cures hard and smooth. He not only addressed this issue but also got into the cross-linking that occurs during the cure.

Castin' Craft explains that for a "soft cure" wait a few hours.... for a "hard cure" wait 24 hours. What that breaks down to is it can take up to 24 hours (sometimes longer w/ temp....humidity....etc.) for the entire chemical reaction to finish.
Some people using this product don't wait for the conclusion..... they let it get "mostly hard" and then spin it.

Other products like alumilite are a completely different chemical makeup and none of the above apply to it.

Probably better if you talk with someone with more chemical experience than reading me ramble.
 
I did a first pour with some micheals resin last night. 66 in the shop. I poured clear, 8 ounces with 16 drops, just followed the instructions. It is 12 hrs later now and the pour is solid, but sticky. I'm just going to let it sit a few days and see what happens I guess. The pour does look pretty good far as I can see, although there's a couple micro bubbles stuck on the object I poured over, which kinda sucks as I didn't want any bubbles at all.
 
You can try vibration for a few minutes - that will help somewhat but for the most part embedded tubes really need pressure.
 
Jeff,
I use a hobby brush and coat whatever I am casting with a good coat of PR before I place it in the mold. I have found this helps reduce the air bubbles in the finished product. In fact, I haven't had any air bubbles since trying this method. Hope this helps.
 
I'm in the watch how much MEK you put in group, I use either 3/4 PVC pipe or one of Gadgets 3/4 silicon molds, even with a black dye I only use 5 drops per OZ, with reds 3-4 depending on the amount of dye, with Pearl-Ex and no dye I use 4 drops per OZ since I only cast 4or 6 blanks at a time, I will help the cure by putting the molds/pipes in my toaster oven that get's used for powder coating, I can force a full cure in about 3 hrs from start mixing to start turning, during the summer, I have to watch it due to natural heat, but an hour or so in a 120 to 150 degree oven or heat box will get you a fully cured easy to turn not too brittle blank, and they aren't sticky on the sides coming out of a silicon mold. Some folks are using a Gel promoter but I understand that the gel time is so short that you don't have tim to manipulate the colors much.
 
DUH yup funny how one little letter can mean so much, I wish I could blame it on my missing finger but wrong side of the keyboard. Yes MEKp the catalyst not MEK the solvent,
 

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Polyester Resin is a liquid which when the catalyst is added, will cure to a solid. It has been specially formulated to cure at room temperature. The hardener, usually MEKP (Methyl Ethyl Ketone Peroxide) is added to begin the curing process. When polyester resin "cures", it goes through a polymerization process. This process brings it from a liquid state to a solid state. The "polymerization" involved is the connecting of molecules in a grid pattern, which is permanent and results in the resin going from liquid to solid (hard). The MEKP hardener begins this process. Always consult the manufacturer's instructions for mixing the correct proportions of resin to hardener. Factors that will affect the hardening time and working time are temperature, thickness of the application, quantities of resin mixed per batch and humidity.

There are two general types of polyester resin used for repair. Laminating or Bonding resin which cure to a tacky surface and Fiberglass or Marine Finish resin which cures to a non-tacky surface.
[FONT=Arial,Arial]Laminating resin [/FONT]is used for initial coats on wood or for multiple applications with fiberglass cloth or mat. This resin is air-inhibited which means it will cure to a tacky finish and does not require sanding between coats. This is desirable in laminating because the layers adhere to each other better. This product should not be used as a final coat unless measures are taken to seal out the air during the curing process.
[FONT=Arial,Arial]Marine and Fiberglass resin [/FONT]is non air-inhibited or [FONT=Arial,Arial]waxed resin[/FONT]. It is for the final coat. This resin cures with a hard non-tacky surface. When the catalyzed resin is applied as a final coat to the laminate coats of resin, the wax rises to the top, sealing off the air and allows the resin to cure to a hard finish, which can then be sanded, painted or gel coated.

Source: http://www.americanmarinesupply.com/pdf/PolyResin.pdf
 
Here is a trick that helps accelereate gel times in open backed molds. Cut a piece of clear acetate a little larger than the back of the mold. Fill the mold to slightly overflowing, just surface tension lift above full is adequate. Start from one side and put the acetate on the edge of the mold, bend up the other side of the acetate and carefully roll it down and across. If you just drop the acetate flat over the back of the mold it will get the job done, but you will have air cavities under the acetate.

The acetate closes the mold and keeps most of the heat in, speeding up the gel time. It also leaves a nice slick, clear, non sticky surface on the back side of the mold. It works great for putting bugs and other little critters inside of paperweights when you want to be able to see them from all sides.
 
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