Polytek mold rubber failure

[LostNYC]

Last edited by LostNYC : Today at 06:57 PM.

[GaryR52]

Not good. One question, though; is this mold rubber you had to mix from two or more components? I'm thinking maybe you didn't get the mix quite right. If not, well...never mind.

I've heard Polytek's supposed to be a good product. Now I'm not so sure.

Gary

[GaryR52]

Hmmm...well, I've never used the stuff, myself, so I'm just guessing. what is the working time, usually? Could it be that the various batches added together at different times would affect the overall cure time? This is something I've been wondering about.

Gary

[GaryR52]

Ah, I see. Just like plaster, then.

Gary

[GaryR52]

Yep, sounds like a waste of time and money, to me. Best to go ahead and use something else, just start all over again. By the time you've heard from Polytek, it could be October, for all you know. Bummer. I hope it works out for you.

Gary

[GaryR52]

Yep, I agree. That would be the smart thing to do, on their part, instead of letting their egos get in the way and assuming the customer, an experienced user of their products, must have screwed up somehow. Apparently, they never heard the old saying, "the customer is always right." ;)

Gary

[GaryR52]

My own experience with businesses (of any type) is that sometimes it depends on who in the company you are dealing with. Some clerks or other employees tend to take customer complaints personally, even if they are not the owner of the business. I've often had this happen and, when I asked for their supervisor, I got an immediate replacement. Sometimes not, also. It depends on who the people are and their attitude. I'm not saying this is necessarily the case with Polytek, but it could be.

Gary

[Mordachai]

My own experience with businesses (of any type) is that sometimes it depends on who in the company you are dealing with. Some clerks or other employees tend to take customer complaints personally, even if they are not the owner of the business. I've often had this happen and, when I asked for their supervisor, I got an immediate replacement. Sometimes not, also. It depends on who the people are and their attitude. I'm not saying this is necessarily the case with Polytek, but it could be.

Gary
yeah, I feel the same way about that. ( OT- that's why the big Corp. Airlines are all going bust and the employee owned lines are doing good)

Well, LostNYC, This disheartens me on so many levels. I'm so sorry this has happened to you. I know what is involved in making large molds, and to have to scrap one is even worse. I've had mold rubbers that didn't even cure as good as that and ended up destroying the model cause they just stayed sticky liquid rubber

Let me say right off, I have NO affiliation with polytek, REPEAT - NO CONNECTION.

As far as you're being a volume user of thier product, I really doubt it. I'm not downtalking you in anyway at all. Please understand that.reason I say that is that I worked for an Archetectual Detail Company that produced detail and pavers in cast concrete. We used 2 55 gallon drums of a 74 series(74-30) and 4 55 gallon drums of thier 75(75-40 75-60) series rubbers a week. Yes , everyweek! They really make loads of stone, and need many many molds to cycle them to produce them fast enough.
There was a tech guy from polytek who was only mildly helpful, if that, and said that we are not 'volume users'!!!!! ( so then what Is ???) We did have problems with fast curing, and problems because of , and they actually sent another guy down ( appantly 100 + degrees, 80-100% humidity, and an outdoor shop are not condusive to a good cure!( LOL had so much to learn then- still do!)

More recently I worked for a SS and Bronze Sculptor as his main moldmaker for lost-wax cast bronze. We used maybe 2 5 gallon drum kits every month, and there was a tech guy who was so very helpful. Really, even for the smallest question, he'd make sure I understood.

I will Get the guys name and PM it to you if you'd like. I really think they will make it right, unfortunatly you might have to deal with a jerk on the way.


As far as your bad cure(or no cure) problem.
So many Questions........
Just to pique my curiosity..:and maybe help solve the problem....
Are you making the mold in a controlled environment? A/c to keep the temp. and humidity the same? Was the product you used old? Did you mix some new and some old material?? even if it's the exact same type of rubber, mixing an old component with a new one can spell disaster. If it was old, do you use the gas purge to force O2 out of the container? Did it sit direct sun(UV)? Did it Sit where it got really hot? ( this could have happened on the truck on the way to you btw)Did it get water in/on the mix? The other thing is did you mix the indivdual parts? before mixing the two parts together?
I have found that by not mixing them at first will cause big problems later (and phew boy, it is hard as hell to shake a 5 gallon of rubber without a paintmixer!) ( at the Cast Concrete place, we had long mixers attached to a high speed motor to do the mixing for us.) I guess there are different fillers and compounds that will seperate and settle in the components, making mixing before your mix a must. If you do not mix it first, your first mixes out of the bottle will not have enough of the seperated parts, and the last mixes will have too much!

Also, it seems you are mixing the 2 parts by volume instead of weight, as you said you fill 2 buckets to the same level, and then mix them together. All the polytek products are designed to be mixed 1:1 by weight, not volume.
Although most of the time the weight ratio will be close or the same as the
Volume ratio.
But if the two parts are of a different density, 2 equal volumes will have different weights, thereby, throwing the mix off. I belive that a 2-5% variance is all you need to mess up a mix! ( like honey and vinegar, the same weight will be different volume and vice-versa. )
Additionally, Not all the polytek products will use that 1:1 ratio. Just because the 74-30 was 1:1 does not mean the 74-40 will be a 1:1 (I think it's 2:1 a:b) . I belive some of thier polys are even 1:4 or 1:10. I know some of thier silicones are 1:10 and some of thier rubbers are weird ratios(100:20)and others........

There are so many things to think of, and so many to go wrong, it's alot of experimenting.

The other thing I wonder is are you Positivly sure that you used the same components together? The helpful guy from polytek told me that the partA of one series rubber( IE 74-30) cannot be interchanged with the partA of (say IE: 74-55) and the same goes for the partB. They cannot be interchanged. I accidentally used a B and A from different hardnesses and it turned into a sticky goo that ended up in the most labor intensive, messy clean up I've done on a mold!

Other times, I'm sure that polytek messes up. Maybe they mis-labeled the parts from different series rubbers. And there is always the chance of a bad batch( a bad batch of dupont's benolate killed about 90% of the Tropical, foliage, and orchid nurseries in the early 90's). It's hard to say, But I hope that something positive happens for you. I know how frustrating it is when things like that go wrong. :(

I really hope that polytek makes it right for you. I understand it will still be time and labor lost( that alone could be terrible if this was a deadlined project), but hopefully you will get more material to finish the mold.

Kind of off topic, but not really.
I have tried both smooth-on and Synair products. I personally found polytek stuff much easier to use. But that's just me. Everyone will find differnt products easier to mix and easier to apply for them. My experience with smooth-on is that of wacky ratios, and the two parts are like mixing peanut butter and alcohol together- no easy task! that on top of quick working times( quick cause it takes so darn long to get a good mix) made me unsatisfied with thier products.
Synair stuff might be the way for you to go, as thier stuff is designed to be mixed by volume , not weight, thereby not requiring a decent accurate scale. Thier products(that I tried) seemed to have the thick and thin parts that needed to be mixed, but not as bad as the smooth-on.
It is definitly worth a trial of a few of thier rubbers to see if the prices and product are right for you.
Dow corning,and silicones-inc are just two more companies that make mold rubber..

I hope you don't take this as dogging on you. I simply want to try to help out!

I think that about gets the junk outta the brain. I hope this is helpful in someway or another to you.


|M|

[bluedogshuz]

Randall,
Are you saying Polytek made good on a bad batch? I'm confused. I am going to start casting and I thoght Polytec was what most reccommended?

[bluedogshuz]

Excellent!

[Blake]

Randall
I am glad that this has worked out for you and I am pleased that the company stood behind their product, it gives me faith. I lost a mould last year as the rubber just fell apart after about 5 years of sitting in a fibreglass mother mould, I have a resine of the original sculpture but I will have to make another mould if I ever sell a copy.
In any case keep us informed with your progress on this piece. I am interested to see the work once cast.
Blake

[Blake]

Randall
This is a fantastic project and one that only you would take on. The size of this piece alone is quite daunting but it will be very beautiful. People often ask me what I will do with a piece once I have finished it and I reply that it doesn't really matter, I will worry about that when the time comes, is this what you are doing with this piece or is there a spot for it?
Personally I love the geometry and symmetry of the ancient buildings and designs and the Corinthian capital is an example of their finest work. I didn't realize that it was made of many pieces I thought that it was carved from one piece. In any case good luck and keep this thread going as I think that there are quite a number of us interested.
Blake

[Blake]

Randall
I am glad that you are having so much fun with this capital. Actually the greek and roman capitals that I have seen are carved out of one piece of stone as they were load bearing, and like yours very large. It is also good to know where it will go I am sure it will make a fantastic table.
We both are fans of Key stones and have made a series of four of them some time ago.
The picture is good but you don't get a sense of the size perhaps you could put down a dollar bill next to it so that we get a feeling for the immensity of your project.
I can hardly wait to see it the right way around.
P.S. I like your new picture

Blake