Cracks in Urethane Resin

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LandfillLumber

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I poured a few slabs of Urethane resin worthless wood and got cracks in one slab.It was as if I dropped it and it was brittle enough to crack???Urethane resin is not brittle in anyway at all it will bounce before it cracks.What gives anyone have an idea.Nothing was any different from slab to slab except the colors of resin,HMM???Please any info. would help,Victor
 
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Victor,

IF Urethane resin is the proper name for the casting resins we use, the dye will affect the curing rate. So, a red may take forever and a black set instantly.

If it sets fast, it also may achieve a higher temp and get cracks from the heat it generates.

Just a theory, certainly NOT a definitive answer!!
 
Sounds look like that could be it,I have poured many Urethane blanks and have only had issues with bubbles due to moisture.But this slab had many deep cracks like the end grain of a log checks.Thanks,Victor
 
Does the stuff you're talking about need a catalyst? If it's anything like polyester resin, adding too much catalyst will cause it to heat up, cure really fast and potentially crack. Did your casting heat up a lot? My first attempt produced white fumes...
 
I agree with Ed. (Don't let that go to your head Ed!)

I think you may have had a cure that was too rapid. I have had the same thing happen based on colors. Or too large of a pour. When I pour my pendant blanks in a 2.5" round mold by 3" tall, it creates some massive heat...
 
The answer to your question is "sort of."

Have a look at what I just learned.

So, I think it would be dangerous to make the assumption "black makes resin heat up." It appears that your current batch of black may be ONE OF the influences making your current batch of resin heat up!

The funny thing is this: I would expect the addition of pigment to cause the cure to slow down rather than speed up. Conversely, the addition of pigment I suppose reduces the quantity of resin pro rata and by extension, you're increasing the amount of catalyst without knowing it!

I've been advised several times to make a log book. I thik you should, too. Make notes of quantities used, stirring times, settling times, brand names. Also make a note when you start to use a new batch of a substance. I reckon my log book has saved me a small fortune.
 
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