Does too much MEKP cause brittle blanks?

[healeydays]

Folks,

I have been working with both Alumilite and Silmar 41 with great results, but do have a question around the PR blanks. Does too much MEKP cause the blanks to become brittle? I know I probably have been a bit heavy handed at times...

Mike B

 

[ed4copies]

Yes

 

[Ed McDonnell]

My view of the world:

Too much heat during curing is a problem. More MEKP = more heat all other things being equal. But all other things are seldom equal.

Your shop temp, resin temp, the mass of your cast, the shape of your cast , the properties of anything you added to the resin, the insulating properties of your mold and probably other things I'm can't think of right now will all determine how hot a particular cast will get given any quantity of MEKP.

There are already enough variables in play. Amount of MEKP is something you can control. Or at least you should be able to. What is causing your periodic "heavy handedness"?

Ed

 

[healeydays]

I'm probably heavy handed when doing different type pours, what I am using for colorant, and on what I am making and amount of resin I'm working with at the moment. Some of my castings take more of less resin and I'm still working on my formulas at times.

 

[Joe S.]

Yes

What Ed said.

 

[healeydays]

I'm doing around 6cc for a 16oz pour and I use liquid lacquer that has Ethyl Acetate Butyl Acetate in it for colorization. I wonder if that is also an issue. I'm gonna try a batch dropping it to 4-4.5cc.

 

[Ed McDonnell]

I'm doing around 6cc for a 16oz pour and I use liquid lacquer that has Ethyl Acetate Butyl Acetate in it for colorization. I wonder if that is also an issue. I'm gonna try a batch dropping it to 4-4.5cc.

Ballpark (and it's a big ballpark), there are 20 drops in a cc. USComposites recommends 10 drops per oz in the instructions they provide with Silmar 41. That would be 160 drops or 8 CC (ml) in 16 oz, if the recommended ratio were linear with volume. But it's not.

The recommended amount for a pint of resin is 1/8 oz MEKP. Thats about 74 drops (3.7cc) or 4.62 drops per oz.

Your 6 CC for 16 oz = 7.5 drops per oz.

So, which is the right amount?

Depends on what you are casting. 10 drops would be right for a 1 oz cube. 74 drops (3.7ml) would be about right for a 16 oz cube.

Pouring 16 oz of catalyzed resin into shapes other than a single cube should require a little more catalyst than the single cube. Going from 6cc to 4cc sounds like a reasonable change to make.

I can't comment on the lacquer other than to say that I've had wildly variable results with different additives I've tried in Silmar 41. I don't know of anything other than trial and error to figure it out.

Ed

 

[healeydays]

The interesting thing is these pours I have been doing is that they are into blanks with lots of approximately 320 1/8" cavities in a 5"x1" block, so that's why I was a bit higher in my mekp. I will try a couple different pours over the holiday and see what results I get.

 

[its_virgil]

Why are you using liquid lacquer as a colorant? There are colorants and dyes, (liquid, paste, and powder) sold by resin suppliers that work well with poly resin. Also, many IAP members use mica powder with excellent success. I use 3 drops of MEKP per ounce but only clear cast with single tube in casting molds.
Do a good tun daily!
Don

I'm doing around 6cc for a 16oz pour and I use liquid lacquer that has Ethyl Acetate Butyl Acetate in it for colorization. I wonder if that is also an issue. I'm gonna try a batch dropping it to 4-4.5cc.

 

[healeydays]

Why are you using liquid lacquer as a colorant? There are colorants and dyes, (liquid, paste, and powder) sold by resin suppliers that work well with poly resin. Also, many IAP members use mica powder with excellent success. I use 3 drops of MEKP per ounce but only clear cast with single tube in casting molds.
Do a good tun daily!
Don

I'm doing around 6cc for a 16oz pour and I use liquid lacquer that has Ethyl Acetate Butyl Acetate in it for colorization. I wonder if that is also an issue. I'm gonna try a batch dropping it to 4-4.5cc.

I use both those too. I can get some very unique colors from basically lacquer nail polish that just would be near impossible to get any other way.