Newbie Casting/Stabilization Questions - a bit long

[TXPhi67]

Hello all,

To begin with, let me say that I have read every casting tutorial that I could find on this site as well as two others that I check out from time to time. Also, I did my homework in terms of multiple searches and reading pretty much every post I could find that had anything remotely to do with casting, stabilization, PR, Aluminite, Pressure Pots, Vacuums, etc.

Also, please excuse the length - but I've been researching this for some time.

The first thing that I figured out from all of this is that there is a HUGE amount of info available and there are some incredibly talented and generous folks who have donated significant time in making information available. And for that - I want to say thank you!

The second thing I figured out is even with all of that info readily available, I still have some questions.

So, any assistance or advice would be greatly appreciated with the questions below:

PR vs Aluminite: Aside from odor and what seems to be compatibility in terms of casting with wood, are there any significant advantages of Aluminite over PR (or PR over Aluminite)? Where I want to get to is the ability to do both all resin castings as well as Worthless Wood style casting. If one resin is overall better than the other - that is nice to know. As well as knowing that each as advantages over the other in specific uses.

Mixing:
Is there any value in utilizing weights versus volume measurements when mixing PR? This question really is specific to the affect of temperature on the density of the resin. If the working temps don't have an appreciable affect on the density (and thus the rations of resin to catalyst), that is good info as well.

There are several different suggestions floating around re: mixing vessels. To begin with, how hard is it to clean partially cured PR out of glass vessels? One thought I'm kicking around is using glass beakers (with w/ volume measurements on side) for mixing and then cleaning and reusing. So, are there solvents that make it easy to clean whatever is left in the vessel after mechanical cleaning (pouring, scrapping, etc) so that there is no residue for the next time?

If the above is not feasible, what plastics do not react well to PR and/or Aluminite? In several tutorials, there were mention that certain cups (mentioned by either brand name or the store it was bought from) tend to break down if PR is left in the for "any time". That tends to make me nervous as "any time" is a little non-specific and the idea of the cup melting in my hand with warm curing PR going all over my hand is just not a "good thing" to me. So, if there are certain types of cups that I should avoid - that would be really good to know.

Storage Considerations:
What storage considerations should I be looking at for PR, MEKP, & DPM? Granted, I do not intend to purchase massive quantities of any of these chemicals and the goal will be to use them up fairly quickly. However, any environmental (temperature for example) considerations would be a good thing to know up front. If this info is listed on the containers, then no big deal - I'll read them when I get it. However, any cautions would be greatly appreciated.

Bubble Removal:
There seems to be a little variance re: the "best" method of removing (or at least limiting their occurrence) in casting. However, there doesn't seem to be any conversations regarding that for Aluminite.
Can Aluminite be cast with out pressure? If not, is that why there is little or not bubble conversations since the pressure would remove the bubbles?
Can anyone explain to me why pressure is used for Worthless Wood style casting and vacuum is used for stabilizing? To me, the two seem to be very similar in that both include forcing resins (of one type or another) into the wood pores.
Can anyone explain how Ultrasound eliminates bubbles? I get the "physics" of pressure and vacuum. But, what I read on how to use ultrasound simply confused me in terms of how it eliminates bubbles as it seemed the tutorial had the PR ultrasound treated then added the catalyst and then poured. So, the mechanics of mixing the catalyst (great place to introduce bubbles) came after the ultrasound and hence my confusion.

"Tempering": In one of the tutorials, it talks about "tempering" the PR blanks by doing a second curing in a kiln. Is a kiln and high tempatures (475 degrees for one hour and then let to cool down in the kiln) critical? Or could this be accomplished with out a kiln (toaster oven for example) at a lower temp? Follow up is that if the answer is yes - how is the time component adjusted? Longer, not adjusted, etc.

There isn't much that I could find re: the "best" mixture to use for stabilization. I understand that the professional have very proprietary mixtures. However, my interest is purely hobbyist. So, any suggestions would be welcome. Especially, suggestions on what to stay away from. :redface:

Thanks in advance for any help or suggestions!

 

[JoeHodge1978]

I cant wait to see some of these answers too.You have about the same questions as I.

 

[ed4copies]

I believe you are attempting to make a scientific study in a group of "hands-on" users.

You neglect ambient temp, humidity, manufacturer of material, etc.

If someone COULD answer all your questions, it would make a great book and save thousands of dollars of wasted resin. I don't think anyone here CAN. But, good luck.

 

[TXPhi67]

Hmm - that may explain the amount of views being just a little out of whack from the number of responses.

In this case - do any of my questions have a reasonable impact on the quality of the products? Or am I chasing inconsequential details?

Thanks,

 

[PaulDoug]

Darn, as a person wanting to get into some casting, I think all your questions are great. The only one I can think of an answer for is the ultrasound getting rid of bubbles. Seems to me the vibration would move the bubbles to the top of the fluid and from there they are released or scooped away. Not sure about this but this is what I surmise. I've also read of pouring the fluid through a strainer (screen door screen or maybe a paint strainer) will help eliminate some bubbles.

Great questions. I hope this thread gets more attention.

Oh, I think your PR has a pretty long shelf life. At least that have been my experience with epoxies in boat building.

 

[NewLondon88]

Keep in mind that I don't cast that much, so what I'm saying is
just from my own limited understanding, not that of an expert.

PR vs Aluminite: Aside from odor and what seems to be compatibility in terms of casting with wood, are there any significant advantages of Aluminite over PR (or PR over Aluminite)?

The consensus seems to be that the Alumilite will work better with
woods. PR may not grip well enough.

Mixing:
Is there any value in utilizing weights versus volume measurements when mixing PR?

The advantage to weight vs volume is that the amount of catalyst
used is very small and would be difficult to measure by volume. The
amount of catalyst used is still more art than science.. but the latitude
is pretty wide, so the results aren't critical. I believe that the mixing
instructions (use x number of drops for x thickness of pour) refer to
pouring in a cool, thin walled mold. Many are using warmed silicone
molds, so the amount of heat loss is much less .. therefore the amount
of catalyst needed is less. The catalyst mostly affects the speed of
curing. PR can cure without catalyst, it just takes much longer. (months)
I don't believe that the amount of catalyst affects resin density.

There are several different suggestions floating around re: mixing vessels. To begin with, how hard is it to clean partially cured PR out of glass vessels?

I don't know about partially cured PR and glass. Cured Alumilite will
break down in acetone, but PR will not. (at least not what most of us
use) Liquid styrene will thin PR before it is cured. Seems like
an expensive way to clean out a glass container, though.

Storage Considerations:
What storage considerations should I be looking at for PR, MEKP, & DPM?

Plan on using everything within 6 months if stored at room temp.
Catalysts can become less effective, PR can harden on it's own.

Can Aluminite be cast with out pressure? If not, is that why there is little or not bubble conversations since the pressure would remove the bubbles?
Can anyone explain to me why pressure is used for Worthless Wood style casting and vacuum is used for stabilizing? To me, the two seem to be very similar in that both include forcing resins (of one type or another) into the wood pores.

Vacuum will not force resin into the pores. Vacuum causes the air bubbles
to expand and float out of the voids. These spaces will be filled with resin
once the vacuum is released. Many people will do a series of vacuum and
release before the resin is 'set'. This gives you the best chance of filling
the voids. When you release the vacuum and return to ambient pressure,
something has to fill the space formerly occupied by air. If the wood is
above the liquid, it will simply fill with air again. If it is below the liquid
level, it will fill with resin.

Any resin can be cast without pressure or vacuum, but we need to
take extra precautions to eliminate known problems. This is why people
are using vibration and heat. Some will use the Ultrasonic, some will
warm resin in a pan of hot water, some will vibrate molds on their scroll
saw table.. whatever helps you eliminate the bubbles.

I have heard/seen the explanation that pressure causes the bubbles to
be 'squished' so small that they can't be seen. I'm still not convinced
that this is true. Perhaps I just need to watch it happen with my own
eyes, or perhaps it is just an easier way for people to remember to use
pressure or to think about the process.
But pressure will keep new bubbles from forming in the resin, similar to
the way pressure keeps air in suspension in a bottle of seltzer.

Can anyone explain how Ultrasound eliminates bubbles? I get the "physics" of pressure and vacuum. But, what I read on how to use ultrasound simply confused me in terms of how it eliminates bubbles as it seemed the tutorial had the PR ultrasound treated then added the catalyst and then poured. So, the mechanics of mixing the catalyst (great place to introduce bubbles) came after the ultrasound and hence my confusion.

The ultrasound uses two things that help.. vibration and heat. The
vibration helps move the air bubbles to the top. The heat thins the resin
and the lower viscosity means the bubbles can move more freely to
the top. You're right that mixing introduces bubbles, but there is no way
to avoid that. and the bubbles introduced by mixing are fairly large, so
with vibration and heat they are much easier to clear.

"Tempering": In one of the tutorials, it talks about "tempering" the PR blanks by doing a second curing in a kiln. Is a kiln and high tempatures (475 degrees for one hour and then let to cool down in the kiln) critical? Or could this be accomplished with out a kiln (toaster oven for example) at a lower temp? Follow up is that if the answer is yes - how is the time component adjusted? Longer, not adjusted, etc.

I admit that I have never seen 475 degrees in a tutorial, so I can't
answer to that. I believe that the 'kilns' referred to are using light
bulbs as a heat source. It is a 'kiln' in that it is a closed container meant
to hold in heat. 125 degrees F would be a better working temp IMHO, and
this can be accomplished with a toaster oven (provided it has a setting
marked 'Warm' and in that temp range)
I believe that 475 degrees is far above the deformation temp of the resins
we are using. I also believe it is above the working range of any of the
mold materials we're using, but I could be wrong about that.

The 'post cure' you may see referred to often is simply putting the blanks
in the toaster oven so that the top surface doesn't stay tacky. These
are laminating resins, meant to layer.. the tacky surface is deliberate so
that another layer can bond to it more effectively. We don't need or
want that, so we give it a little heat to fully cure the top of the casting.

ok, that's all I got..

 

[Pioneerpens]

Very informative! Thanks

 

[PaulDoug]

Thanks Charlie. Great info. Thanks for taking the time to respond.

 

[Glass Scratcher]

Keep in mind that I don't cast that much, so what I'm saying is just from my own limited understanding, not that of an expert.

The consensus seems to be that the Alumilite will work better with
woods. PR may not grip well enough.

Alumilite is Alumilite. But PR is Silmar, AOC, ETI, Reichhold, Cooks... There is no consensus because no-one across the country is using the same PR. They have significant differences. Some are countertop resins such as swing resins. Some are casting/laminating resins. Some are an inbetween. All can be used for imbedments. The problem comes from the resin being ultimately harder than the wood and not cutting and sanding evenly with the wood. For the casting itself the various PRs have different viscosities. Cooks is in the 4000cps range if memory serves. Reichhold Polylite are 1200-2000cps, Silmar 41 is in the 400cps range. So how well they will wet and saturate the wood or imbedment is a consideration.

The advantage to weight vs volume is that the amount of catalyst
used is very small and would be difficult to measure by volume. The
amount of catalyst used is still more art than science.. but the latitude
is pretty wide, so the results aren't critical. I believe that the mixing
instructions (use x number of drops for x thickness of pour) refer to
pouring in a cool, thin walled mold. Many are using warmed silicone
molds, so the amount of heat loss is much less .. therefore the amount
of catalyst needed is less. The catalyst mostly affects the speed of
curing. PR can cure without catalyst, it just takes much longer. (months)
I don't believe that the amount of catalyst affects resin density.

Every bottle of MEKp I have ever seen, for every PR I have ever used has printed plainly on the label use at 1%, you then can then change the ratio upto +/- .5% based on ambient temperature. In some cases because of specific conditions, additions and fill, the catalyst ratio may very well be as much art as science, but if you are mixing a single volume of resin that is 8oz the Metric equivalent is approximatly 240mL (1 metric ounce is 30mL, anyone should be able to do the math) 1% of 240mL is 2.4mL and easily measured and dispenced with a hyperdermic syringe. If your fill(additions and pigments) ratios are within the limits of the resin then your time to soft gel and hard gel are pretty spot on across the board. There are always exceptions depending on the composition of your organic and inorganic dyes and pigments. That is why you need to keep a log book of all your casting.

You should heat your molds regardless of what they are made of. Silicone is an insulator, and transmits heat much more slowly than molds made of PP or HDPE. Consequently Silicone molds can, if they are unheated and you are casting in an environment below the recommended casting temp (72F for PRs), absorb some of the heat out of the catalytic reaction and cause an temperature induced or thermal inhibition. In some cases this inhibiton may be long enough for your powder additions to de-suspend or settle out, if you are casting multiple colors then one color with heavier pigments may settle through.

PRs that are pre-promoted can harden without the use of catalyst over time typically 6 months, sometimes longer depending on the environment and temperature the resin is stored in. However the resulting block of resin will not have the same properties as catalysed, fully crosslinked, cured resin.

I don't know about partially cured PR and glass. Cured Alumilite will
break down in acetone, but PR will not. (at least not what most of us
use) Liquid styrene will thin PR before it is cured. Seems like
an expensive way to clean out a glass container, though.

Silmar 41 and Reichhold Polylight PRs will desolve in acetone, and will get gummy with DNA. Finish gelcoats are not as susceptable to chemical reaction.

Plan on using everything within 6 months if stored at room temp.
Catalysts can become less effective, PR can harden on it's own.

Vacuum will not force resin into the pores. Vacuum causes the air bubbles
to expand and float out of the voids. These spaces will be filled with resin
once the vacuum is released. Many people will do a series of vacuum and
release before the resin is 'set'. This gives you the best chance of filling
the voids. When you release the vacuum and return to ambient pressure,
something has to fill the space formerly occupied by air. If the wood is
above the liquid, it will simply fill with air again. If it is below the liquid
level, it will fill with resin.

Vacuum can be used with PR to impregnate many materials, however the amount of wicking depends on the viscosity of the PR used. The thinner- the more wicking. Casting/Laminating resins have been used in vacuum bagging/impregnating/laminating for years to make model boat/car/plane hulls and on surfboards, and various fenders and body panels for custom cars and motorcycles. The difference is that the final surface will be sanded and painted but you can vacuum impregnate many materials in for blank casting as long as after vacuuming one allows the bubbles to rise out then follow with pressure casting.

Any resin can be cast without pressure or vacuum, but we need to
take extra precautions to eliminate known problems. This is why people
are using vibration and heat. Some will use the Ultrasonic, some will
warm resin in a pan of hot water, some will vibrate molds on their scroll
saw table.. whatever helps you eliminate the bubbles.

I have heard/seen the explanation that pressure causes the bubbles to
be 'squished' so small that they can't be seen. I'm still not convinced
that this is true. Perhaps I just need to watch it happen with my own
eyes, or perhaps it is just an easier way for people to remember to use
pressure or to think about the process.
But pressure will keep new bubbles from forming in the resin, similar to
the way pressure keeps air in suspension in a bottle of seltzer.

Some PRs (Silmar 41) are thin enough that most bubbles will rise out without aid, however if you wait to pour till just before the resin goes into soft gel, then you can trap air bubbles and you need pressure to collapse the void in the resin. Thicker resins really need to be pressure cast, but you can decide for yourself if you want to go to the expense to insure success. Urethane resins (Alumilite) express CO2 during curing. Some remain thin right up to seconds before suddenly blooming(gelling) and the bubbles formed have time to rise out, some do not, and need to be put under pressure.

Alumilite has a nice page on pressure casting urethane resin
http://www.alumilite.com/HowTos/PressureCastingClear.cfm

ultrasound uses two things that help.. vibration and heat. The
vibration helps move the air bubbles to the top. The heat thins the resin
and the lower viscosity means the bubbles can move more freely to
the top. You're right that mixing introduces bubbles, but there is no way
to avoid that. and the bubbles introduced by mixing are fairly large, so
with vibration and heat they are much easier to clear.

I admit that I have never seen 475 degrees in a tutorial, so I can't
answer to that. I believe that the 'kilns' referred to are using light
bulbs as a heat source. It is a 'kiln' in that it is a closed container meant
to hold in heat. 125 degrees F would be a better working temp IMHO, and
this can be accomplished with a toaster oven (provided it has a setting
marked 'Warm' and in that temp range)
I believe that 475 degrees is far above the deformation temp of the resins
we are using. I also believe it is above the working range of any of the
mold materials we're using, but I could be wrong about that.

The 'post cure' you may see referred to often is simply putting the blanks
in the toaster oven so that the top surface doesn't stay tacky. These
are laminating resins, meant to layer.. the tacky surface is deliberate so
that another layer can bond to it more effectively. We don't need or
want that, so we give it a little heat to fully cure the top of the casting.

ok, that's all I got..

If you heat your resin to 475F you will have a fire. To postcure your PR, set your dedicated toaster oven at 130F and leave it there, you can preheat your molds at that temperature as well. Postcuring PR does more than cure the Air-Inhibited (tacky) surface. It gives the casting enough heat and molecular energy for the resin to fully cross-link and reach its full physical charateristics.

Urethanes you can post-cure at a higher temp. But check with the manufacturer of the particular urethane to know what that is.

Never work with liquid resins in the presence of an open flame. Always use some sort of fume control or fume extraction system. Just because you can't smell it, doesn't mean it can't hurt you, your family, or your pets.

 

[Ankrom Exotics]

I have heard/seen the explanation that pressure causes the bubbles to
be 'squished' so small that they can't be seen. I'm still not convinced
that this is true. Perhaps I just need to watch it happen with my own
eyes, or perhaps it is just an easier way for people to remember to use
pressure or to think about the process.
But pressure will keep new bubbles from forming in the resin, similar to
the way pressure keeps air in suspension in a bottle of seltzer.
QUOTE]

It is definitely true. An example of this process that most people are familiar with is SCUBA divers having to go through decompression to keep the oxygen in their blood from expanding too quickly and killing them.

 

[DurocShark]

I've found that post curing at 125 - 150-ish does more than just remove the tackiness on the surface. It makes the resin less likely to dent or deform under pressure (such as the pressure the foot of a clip places on the barrel).

Never go over 175*!!

I've cured uncatalyzed resin at 150 for 2 hours. Works great as long as it's a solid color. If you mix swirls and such, you will see smearing as one color is heavier than the other. Catalyst cures it faster so the colors have less time to move. It can be a pretty cool effect though...

Whatever the actual resin is that Artstuf sells, that's what I've been using for a while. Seems less brittle than the Castin' Craft stuff at Michaels.

I've never had the opportunity to use pressure or vacuum. So my casting stuff other than just resin is pretty limited. I've been successful with coffee beans and peas and whatnot, because they can be mixed with the uncatalyzed resin pretty thoroughly.

I use vibration of various types to work the bubbles out after mixing color, then again after mixing catalyst. I used to use a ultrasonic cleaner till mine broke. Since then I've been using my scroll saw table as mentioned above. This is critically important if I mix stuff like beans in the resin.

My recommendation is to take the ideas you've read here and elsewhere, buy some stuff, and start casting. See what it's like and what works for you.

 

[PaulDoug]

I've found that post curing at 125 - 150-ish does more than just remove the tackiness on the surface. It makes the resin less likely to dent or deform under pressure (such as the pressure the foot of a clip places on the barrel).

Never go over 175*!!

I've cured uncatalyzed resin at 150 for 2 hours. Works great as long as it's a solid color. If you mix swirls and such, you will see smearing as one color is heavier than the other. Catalyst cures it faster so the colors have less time to move. It can be a pretty cool effect though...

Whatever the actual resin is that Artstuf sells, that's what I've been using for a while. Seems less brittle than the Castin' Craft stuff at Michaels.

I've never had the opportunity to use pressure or vacuum. So my casting stuff other than just resin is pretty limited. I've been successful with coffee beans and peas and whatnot, because they can be mixed with the uncatalyzed resin pretty thoroughly.

I use vibration of various types to work the bubbles out after mixing color, then again after mixing catalyst. I used to use a ultrasonic cleaner till mine broke. Since then I've been using my scroll saw table as mentioned above. This is critically important if I mix stuff like beans in the resin.

My recommendation is to take the ideas you've read here and elsewhere, buy some stuff, and start casting. See what it's like and what works for you.

Just wondering, if you vibrate swirl colors, the vibrating ruin the swirls? Does the question make sense?

 

[DurocShark]

Just wondering, if you vibrate swirl colors, the vibrating ruin the swirls? Does the question make sense?

Yes it does, and yes it does.

You have to vibrate them separately before swirling them together.

 

[TXPhi67]

All,

Thank you very much for all of the advice and answers. This is exactly what I was hoping to get from everyone.

Another reason this group is one I'm proud to associate with!

Again - thanks!

 

[PenMan1]

Darn, as a person wanting to get into some casting, I think all your questions are great. The only one I can think of an answer for is the ultrasound getting rid of bubbles. Seems to me the vibration would move the bubbles to the top of the fluid and from there they are released or scooped away. Not sure about this but this is what I surmise. I've also read of pouring the fluid through a strainer (screen door screen or maybe a paint strainer) will help eliminate some bubbles.

I actually use ultrasound as well as plastic window screen to do pr casting and it works well. The ultrasound actually heats and vibrates the solution forcing air bubbles to the top. If you pour the resin through the screen slowly enough, you can actually see bubbles getting caught in the screen grid and "popping" the bubbles.

I think I picked up the ultra sound tip from ITS_VIRGIL and a denture maker friend actually showed me screen trick.

The only other tip that goes against everything that I have read is to stir the resin/MEKP SLOWLY and NOT aggressively. The therory here is the fewer bubbles in, the few bubbles out.