Questions? (kinda long)

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MarkHix

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Joined
Jul 6, 2007
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982
Location
Carrollton, Texas, USA.
Ok, I took the plunge and tried to cast my own blanks. The first two attempts were worse than a disaster. The third looked like it had a chance. I used the PR from Hobby Lobby, about 6-7 drps of hardener per ounce, poured it yesterday late in the afternoon. My molds were 1/2" pvc w/ caps. I vibrated them to get the bubbles out. I had to knock them out of the molds. They were pretty hard to get out. They looked good. They felt rubbery and soft. When I drilled them, they crumbled.

Does the resin brand make a difference?
Could I put in too much hardener? Is too little better?
I tinted one white and the other white w/ blue added. Can you add too much color?
I let it cure on the patio. Today it got to about 98 degrees. Would that effect it?

I would appreciate any ideas you have.
 
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I'm no expert at this but here is some of my experience. I've found that for me casting into tubes takes longer to cure than the flat molds. The fact that they felt rubbery and soft is to me an indication they had not fully cured.
It is possible that the resin or hardener was old.
Though some would say you used too much hardener I have often used that much with no problem. If anything too much hardener would make it hard and brittle not soft and crumbly.
What did you use to tint it? Different materials can effect how much hardener you need to use.
The temperature on the patio should have helped it cure faster. I live in So Ca where it gets hotter than that and cast outside with no problem. I usually do my casting in the evening and let it sit outside for 24 hours.
 
Mark,
There is not so much a diff in the resin brand as the resin type. Are you sure you had "casting resin"? Many use a resin categorized as "silmar 41". It is specifically made for casting in thick pours. And is usually known as "water clear" also.

More catalyst should not be a problem. I have added a "lot" to accelerate curing and not had any major problems.

The color issue is a funny thing. Powdered tints are less likely to be a problem as are liquid dyes. Liquids tend to alter the curing process. Slow it down most times. And some colors much more than others.

As far as heat, it should help if anything. The catalyst causes a chemical reaction and creates heat to accelerate the curing process. The only time heat is bad is when its so excessive that it interferes with the casting. As in damaging the media in the casting. (cactus, labels, snake skins, etc.)

The only time I have had a blank come out rubbery is when I used the incorrect type of resin. I have never had a blank crumble on the drill press.

Hope this helps.

PS: I don't use or care for PVC. I use mostly (95%) flat molds. Just my preference.
 
Thanks for the help. The tint was liquid from HL called Casting Craft..looks like thick paint. It was the same brand as the resin. I used the PVC so I could test in small amounts. I will try again and leave it longer before I remove it from the mold.

I have to admit, it was exciting to pull it out of the tube, kinda like my first turning. I see lots of expense in the future!
 
That is the same tint that I use so my guess is your cast wasn't fully cured. Like Steve I too prefer the flat molds. We don't have a Hobby Lobby here so I don't know their prices but you might check prices online. I know the cost of resin at my local Michael's is outrageous, fortunately I have a local plastics store that sells it much cheaper and about the same as I found online.



And yes it is addicting also[}:)]
 
Does the resin brand make a difference?
- I don't think the brand is important, but the age of the resin matters.

Could I put in too much hardener? Is too little better?
- This is a hotly debated issue. Personally, I only add 3 or 4 drops/oz. and let my resin cure a minimum of 12 hours.

I tinted one white and the other white w/ blue added. Can you add too much color?
- Yes, you can use too much tint and it will affect the resin.

I let it cure on the patio. Today it got to about 98 degrees. Would that effect it?
- The resin cures via heat. MEKP is a chemical way to produce heat. From your description you blanks were not fully cured. Let them set longer or put them in a non-food use oven @ 150 degrees for 15 minutes. They will finish curing.
 
Originally posted by Blind_Squirrel
I let it cure on the patio. Today it got to about 98 degrees. Would that effect it?
The resin cures via heat. MEKP is a chemical way to produce heat. From your description you blanks were not fully cured. Let them set longer or put them in a non-food use oven @ 150 degrees for 15 minutes. They will finish curing.
A few weeks ago, I made a batch of 'UT Orange' blanks and set them out in the sun on the porch to cure. I figured the heat of the sun would help them out and the shop wouldn't be as smelly.

A week later, my wife asked me why they were sitting out there. <Oops!> When bring them back in, I accidently dropped one on the shop floor. It cracked right in two. I'm not completely sure that the repeated exposure to sunny days caused the blanks to be more brittle than others because I don't generally drop them on the floor, but it seemed very brittle. We haven't gotten around to turning any of them to see if there were any issues.

BTW, I'm a 4-5 drops/ounce guy who generally let's blanks hang out for a day or so before popping them out of the molds and typically let them go several days before turning.
 
Thanks for the help. I keep trying to learne patience over and over and over....Batch number 4 is curing on the patio. I promise not to touch them until Friday..I promise not to touch them until Friday...I Promise...
 
Hi
Sounds like you didnt wait long enough for them to cure as for the amount of hardner i have used as little as 3 drops per oz to as much as 20 drops per oz and have noticed a small increase in brittleness (which i happen to like) with more hardner .
As for colorant I use coastal scents mica powders and pigments and have never had a problem (jcollazo here on this fourm has them now too).
And for resin I use Silmar 41 from mr fiberglass.com and always get fresh product from them (I am guessing but I've never had any problems with it) and they are much cheaper then HL and Michaels (aprox $33.00 a gallon w/hardner) .
 
Mark,
If you add a near correct amount of MEKP, it shouldn't take days to cure. The longest I have seen is 48 hours and that was because of liquid dye. I'm a little puzzled as to why this is taking so long to cure. Be sure to let us know what you come up with.
But do what you need, and good luck.
 
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