Casting Pourous Materials

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jttheclockman

jttheclockman

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For those that casted pourous materials such as pine cones or banksia nuts, what resins is best??? Has anyone tried with both alumilite and poly resins??? Which is better suited to get in all the nooks and crannies??? I assume a pressure pot is needed. At what pressure would be good to drive the resin in the nooks and crannies??? Thanks for the replys.
 
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John, I have used both and I prefer Alumilite. Not just for the normal reasons, but I found that the PR has too much shrinkage and it has pulled away from some of the WW casts I had done in the past. You are aware that this is going to start the whole PR vs. Alumilite argument again?:biggrin:
I cast at a very high pressure, but have seen good result with as low as 35#. And a pressure pot is needed to do them. If you want to just try this out before you make the investment, please feel free to come by and give it a shot, I'm not that far away.
 
hi John,
I have cast Pine cones with both...I prefer PR because it has a longer working time... I pull 20 inches of vacuum for 5 minutes and then pressurize to 50 PSI for 24 hours. I still have to keep my CA handy. I'm sure Curtis and others will give you a different opinion. But that's my 2 cents.
 
1TJTurner said:
hi John,
I have cast Pine cones with both...I prefer PR because it has a longer working time... I pull 20 inches of vacuum for 5 minutes and then pressurize to 50 PSI for 24 hours. I still have to keep my CA handy. I'm sure Curtis and others will give you a different opinion. But that's my 2 cents.
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That is another question I should have asked. Is it a good idea to use vaccuum and pressure and is there a difference if you don't??? I am liking the people who have used both are giving their opinions. I know I can try both myself but thought I would get some opinions to get me pointed in the right direction first. Thanks and keep them coming.
 
Here's the way to think of pressure vs vacuum. Pressure compresses any bubbles to a smaller size. A small bubble becomes nearly invisible, a large bubble becomes a small bubble.

Vacuum causes bubbles to expand, most often until bursting but not always. Big bubbles go away, small bubbles get big. (Hint, don't let your resin harden under vacuum unless you like the bubbled look).

If you are casting porous materials vacuum will pull most of the bubbles out of the nooks and crannies of the material. Pressure will then compress whatever is left to invisibility.

Alumilite is thinner so will wick its way into the nooks and crannies better than PR but you don't have time to do vacuum then pressure. But using pressure alone works better than using PR does with pressure alone because of the thinner consistency. Where is the break even point? *shrug*

When doing something like a punky wood I would use either PR or a thinner, slow setting stabilizing solution, pull a vacuum, apply pressure, pull a vacuum again, apply pressure again. If you have a clear lid (gotta be really thick and strong) then repeat until you see no more bubbles under vacuum. If no clear lid, do it "several" times. Finally set it under pressure until hard.

GK
 
What is the maximum working time for the PR, in other words, how long do you vacuum & pressure each time?
 
With PR the working time is adjustable based on how much accelerator you put in. With Alumilite it is a 1:1 mix ratio and you have no flexibility; you have 3-4 minutes.

With PR it is X drops of accelerator per ounce of PR. At 10 drops of accelerator you have a few minutes of working time. At 3 drops of PR you have hours and hours. I think most people use 5-7 drops for pen blanks.

GK
 
You meant "working time" not "pot life" right Tom?

GK - 10 drops of MEKp per ounce and your blank is going to be so brittle that IF you get it turned and made into a pen it will shatter the first time it's dropped on a pillow.

I am a PR enthusiast - that being said Alumilite works better for "worthless wood because it doesn't have anywhere close to the "shrink" value PR does. That didn't keep me from casting some pretty neat pine cones though. (There's a reason for the shrink value but people tend to quit reading when you get technical)
 
td said:
GK - 10 drops of MEKp per ounce and your blank is going to be so brittle that IF you get it turned and made into a pen it will shatter the first time it's dropped on a pillow.

I am a PR enthusiast
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That is not entirely true.

I've used as much as 20 drops without any brittle issues during or after turning. There are so many variables with casting, one being the total amount of the pour. That alone will affect how much catalyst to use. Now if that is taken into consideration along with everything else that affects PR, only experimentation will determine how much of anything can be added in a particular situation in a particular location.
 
Of course 10 drops per quart/gallon/tankertruck will not have the same effect as 10 drops per 3/4"x3/4"x5 1/2" pen blank.

I do believe that TD in his above post was referrencing the use of 10 drops per pen blank. And that indeed can AND WILL make a difference. :eek:

Then again, so does the temperature of the pour, the amound of pigments added, the position in the nightly sky of the moon, etc ... just kidding about the moon!

But sometimes ya just have to wonder what was not quite right at the time. Maybe adjusting the position of one's mouth will help!
 
That is my point, I have used 20 drops for one blank with no adverse affects. The more resin...the less catalyst. With more resin, there will be more heat generated.
 
wolftat said:
John, I have used both and I prefer Alumilite. Not just for the normal reasons, but I found that the PR has too much shrinkage and it has pulled away from some of the WW casts I had done in the past. You are aware that this is going to start the whole PR vs. Alumilite argument again?:biggrin:
I cast at a very high pressure, but have seen good result with as low as 35#. And a pressure pot is needed to do them. If you want to just try this out before you make the investment, please feel free to come by and give it a shot, I'm not that far away.
Click to expand...

Thanks! You just answered a question I have had for a long time! Alice
 
Fred said:
Of course 10 drops per quart/gallon/tankertruck will not have the same effect as 10 drops per 3/4"x3/4"x5 1/2" pen blank.

I do believe that TD in his above post was referrencing the use of 10 drops per pen blank. And that indeed can AND WILL make a difference. :eek:

Then again, so does the temperature of the pour, the amound of pigments added, the position in the nightly sky of the moon, etc ... just kidding about the moon!

But sometimes ya just have to wonder what was not quite right at the time. Maybe adjusting the position of one's mouth will help!
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USUALLY!! The standard terminology is per ounce, regarding PR. Now, an ounce WILL make a pen blank, if you make very small pens.

Just a FWIW.
 
Ed nailed it.

As I posted and as people talk about casting PR it is drops per ounce. Yet, as Dozer says, the equation isn't just PR X accelerator, it is PR X accelerator + temperature + thickness of cast (the thinner the cast the more accelerator you need to get it to set) + additives + humidity + + +

And if you talk to the resin manufacturers additional accelerator will NOT make the resin more brittle. But experience seems to tell many of us otherwise.

GK
 
MesquiteMan said:
And if you use Alumilite, you do not have to worry about drops per ounce!
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But you do have to worry about getting the weight exactly equal. If you can't control the drops that come out of those little bottles of MEKP, you won't be able to control the amount of resin coming out of the alumilite bottles or, God forbid, one of the gallon jugs, lol.

With regard to the topic of the thread, John, as has already been said, PR will shrink, Alumilite will not shrink noticeably, so when you're casting with something in the resin, Alumilite works much better, IMO. If you're using pressure, the consistency of the resin isn't going to be an issue because you can just set your pressure wherever you think you need it. You do have a much shorter working time with Alumilite, but 7 minutes should be enough time to mix your colors and pour the resin.

I guess I don't see what the big deal is working with PR. Why do we need it to cure in exactly the same amount of time under every possible set of conditions? Accept that it will behave differently in different situations and WAIT for it to cure. If tackiness is the issue, you can mix surface wax with the resin. PR isn't designed to be used the way we use it, although we can make it work. Most applications for PR involve layers, ie boats, surf boards, art etc. The surface is intended to stay tacky so that subsequent layers can be applied and adhere to the previous layer. Surface wax is added to the final layer to make sanding and finishing easier. We don't have to know all of the variables to work with it. If it's not cured in a few hours...just wait...it will cure. Patience is a virtue.
 
Depends on what you call "exactly equal" on the weight. It is important that the ratios be the same but EXACT is not a requirement. I use a dial postal scale that has 1/2 ounce graduations. If I am casting 6 ounces of resin, I pour part A until it reaches the 3 ounce mark. If it is a little off, no big deal. I then pour in part B until the dial reaches the 6 ounce mark. A dial scale is not precise like a digital scale is. I may actually be using 2.8798 ounces of A and 3.1298 ounces of B but I still never have a problem.
 
MesquiteMan said:
Depends on what you call "exactly equal" on the weight. It is important that the ratios be the same but EXACT is not a requirement. I use a dial postal scale that has 1/2 ounce graduations. If I am casting 6 ounces of resin, I pour part A until it reaches the 3 ounce mark. If it is a little off, no big deal. I then pour in part B until the dial reaches the 6 ounce mark. A dial scale is not precise like a digital scale is. I may actually be using 2.8798 ounces of A and 3.1298 ounces of B but I still never have a problem.
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Agreed.

I really believe that the need for measuring alumilite exactly is overblown. Back when I was casting and selling lots of stuff out of alumilite, I never weighed the goo. I used two identical graduated beakers. I dumped 'A' into one of them and 'B' into the other, eyeballing to match the amounts. I never had a failure related to my method. (I had a rather glorious failure due to moisture and another due to a mixing problem, but never one due to faulty measurement.)
 
Wow, surface wax. That's a whole other bowl of beans.
With surface wax, the amount of catalyst doubles just for starters.

The resin we use is intended for thick casts and is suitable for machining. Although probably not for what we do with it. But hey, it works great.
 
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