Problems with pr cracking when curing ????

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JohnU

JohnU

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Joined
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Ottawa, Illinois
Ive been casting for a while and never had this problem. Now all of a sudden the last four pours have resulted in a crack in the cured resin. I havent changed anything. Im using 2.5 drops of catalyst per ounce of resin and I dont use any other source of heat. I mix, pour and put in the tank using about 30 lbs of pressure. The next day, "Whammo! a big fat crack looking back at me! The catalyst is only one month old but Im going to change that out with the bottle that came last week. Any ideas would be appreciated. Thanks, John
 

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I'm no PR expert...perhaps now the weather is warming up you should back off a bit on the catalyst. heat causes the cracking far as I know. Those are very interesting looking blanks, that's for sure. Looks like you are re-inventing some sort of African bird. Maybe you are combining a Zebra with a Parrot?:biggrin:
 
LOL, those are amherst pheasant red tips over a silver pheasant striped wind feather. They seemed to complement each other until the crack. Im using silmar 41 with drops from their supplied bottle. I was thinking heat was the problem too and cut back from 3 drops to 2.5 on this pour and still "crack" so I'll try 2 and keep the tank in the basement where its cool instead of upstair. Thanks
 
John, your pours have a lot of mass.... and....(OMG) I agree with Jeff on the PR!!! :eek::biggrin:
I'll send you something that might help.
 
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You stated you are not adding heat... What are the ambient temps for your workspace? Are you working in a heated or cold workspace? Are you leaving your casting to cure overnight in an unheated workspace?

How much resin are you pouring at one time?

Which supplier did you get your S41 from? What is the brand of MEKp? It will state on the MSDS. The dispensing bottles I get from US Composites don't come with holes in them, one has to hole them oneself.

Are the feathers coated with anything?

Have you done any 1 ounce pour tests to see if the resin reacts in the same manner while you are observing it?
 
Glass Scratcher said:
You stated you are not adding heat... What are the ambient temps for your workspace? Are you working in a heated or cold workspace? Are you leaving your casting to cure overnight in an unheated workspace?

How much resin are you pouring at one time?

Which supplier did you get your S41 from? What is the brand of MEKp? It will state on the MSDS. The dispensing bottles I get from US Composites don't come with holes in them, one has to hole them oneself.

Are the feathers coated with anything?

Have you done any 1 ounce pour tests to see if the resin reacts in the same manner while you are observing it?
Click to expand...

THAT sounds like a GREAT idea!!!
 
I appreciate all the help in the posts and pm's. I've been casting the same way for over a year now with over 500 successful feather blanks and now "Suprise", so the only thing that has changed is the weather and where I keep the tank when curing over night. Also, maybe I cut too much off the tip of the MEKP bottle than I thought. Im going to try and cut back to 2 drops per ounce and leave the tank in the unheated basement. Hopefully that will help. Thanks again, John
 
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I am another one for heat. I had this happen to me also. It turns out the room temp. is a critical factor. I learned in winter when it was cool I had times it did not set at all and in summer when it was hot it cracked. Also mass (not your problem) the more mass you have will create a LOT more heat. All these things need to be considered and the MEK needs to be adjusted accordingly. Now how much to adjust ???? I don't think anyone has the answer to that one time and $$$ will tell you.

Hey those blanks look great keep up the good work.

Now that my show season is over I am going to get back to work.

Isn't resin so much fun
.
 
Are the cracks always in the same place??? It looks like a clean break in a piece of glass. Did the pot get bumped as it was curing??? Something seems strange. I have changed my approach when using a pressure pot and that is I only leave my castings under pressure for no more than 2 hours and then let them cure for 24 hours. You may want to do some experimenting without the blanks to see if you are using too much catalyst. I use 5 drops per ounce and maybe my drops are smaller than yours but find that hard to believe that makes that much difference. You may need to look at anything different that you have been doing from previous pours.
 
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jttheclockman said:
Are the cracks always in the same place??? It looks like a clean break in a piece of glass. Did the pot get bumped as it was curing??? Something seems strange. I have changed my approach when using a pressure pot and that is I only leave my castings under pressure for no more than 2 hours and then let them cure for 24 hours. You may want to do some experimenting without the blanks to see if you are using too much catalyst. I use 5 drops per ounce and maybe my drops are smaller than yours but find that hard to believe that makes that much difference. You may need to look at anything different that you have been doing from previous pours.
Click to expand...

I would say you have been lucky.

Either you had no air in your resin to begin with or more likely the resin was fully cured before you released pressure. Because if you have just the tiniest amount of air and the resin is not completely cured and set. It WILL blow up like a balloon.

The whole reason we use pressure is to shrink the air in the resin. It does not get rid of the air just shrinks it to the point you can't see it. Trust me it is still there. I really don't think pressure has any thing to do with the cracking heat is the culprit and can be caused by a number of things mainly the ratio of cayts. and ambient temp.

Just my opinion & experience
 
I just poured my next batch with 3 drops per ounce from a new bottle of MEPK, making sure not to over cut the tip of the dropper. Im hoping the problem was my drops were too big since this problem started after I began using the last bottle of MEPK. Keeping fingers crossed..... If it continues, I'll just make sure to put the ugly ones to the outter edges. lol Thanks for all the help and info.
 
bruce119 said:
I would say you have been lucky.

Either you had no air in your resin to begin with or more likely the resin was fully cured before you released pressure. Because if you have just the tiniest amount of air and the resin is not completely cured and set. It WILL blow up like a balloon.

The whole reason we use pressure is to shrink the air in the resin. It does not get rid of the air just shrinks it to the point you can't see it. Trust me it is still there. I really don't think pressure has any thing to do with the cracking heat is the culprit and can be caused by a number of things mainly the ratio of cayts. and ambient temp.

Just my opinion & experience
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Not sure if it is luck Bruce. I was having all kinds of problems when I left the blanks under pressure for 24 hours. ( You can ask CaptG because he knows how many times I kept bugging him and he kept repeating the same steps I was doing and then I just tried this method and the rest is history) I switched to this method and have not had a failure in many many blanks. This was the only factor I changed in my method. I do heat my resin so that there is very little amount of air bubbles to begin with and the thinner resin is easier to mix as I found. What I found was the air pressure is just to rid the resin of air bubbles and after they start setting no air is getting in again. The blanks cure slowly with the use of Silmar41 as I mentioned in another thread about casting. I found after 2 hours my mix ratio starts to cure slowly. Maybe it is the mix ratio or not but I guess everyone has a formula that works for them. I have found mine. Who knows maybe someday I may be in the same position as John is in. Things do change.
 
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JohnU said:
I just poured my next batch with 3 drops per ounce from a new bottle of MEPK, making sure not to over cut the tip of the dropper. Im hoping the problem was my drops were too big since this problem started after I began using the last bottle of MEPK. Keeping fingers crossed..... If it continues, I'll just make sure to put the ugly ones to the outter edges. lol Thanks for all the help and info.
Click to expand...


How many ounces/mL of resin are you casting in a batch?
 
My vote is for either bad MEKP or a bad batch of 41. Yes, I have gotten a bad batch before. It was actually another U.S. Composites product with a 41 label. Does the resin look or smell different from other batches that you have used?

Fiberglass resin looks like 41, but smells different and doesn't really like MEKP.
 
John I would say it's the weather, I had the same thing happen to my feather blanks, I always drop the hardener by 10% in the warmer weather for my other pen blanks but on the feather blanks is to drop the hardener again another 10% I would put money on it that the warm weather conditions is causing this to happen, I think you just need to slow down the curing time this is what i have found John and it seems to work for me.

Merv
 
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