Castin problem

[kf4knf]

So I am using some Castin Craft Poly resin I picked up at a local craft store. I used the ratio of resin/hardner suggested on the bottle but when I cast anything it doesnt harden all the way and comes out sticky and flexible.

I let it sit overnight before even checking on it - thats when I discoved this. How long do you let your casts sit for? Will it always be sticky, even after its cured? Help!

 

[DWK5150]

Length of cure time depends on the size of the casting. When I cast in small tubes I dont even try to remove them from the mold for about 3 days when I use the larger square mold I have I can usually knock it out next day. Set times can also very by temp and humidity. Im sure some others will speak up that cast more than me but that is just what I have seen personally.

 

[JimGo]

Cure time is also dependent on the amount of catalyst. Obviously, you need to stay within certain bounds, otherwise it comes out too brittle or too soft to be useful, but the (approximately) 7 drops per ounce rule that Anthony and Jay indicate in their tutorials has served me well. On warm, relatively dry days, if I cast in the morning (around 10:00 at the earliest - I don't like to get up early), I can some times knock the blanks out by 4:00 or 5:00 PM, even when using the ice cube trays. Some times, the outside of the blank is still tacky even though the inside is fully cured. A wipe-down with some Acetone will clean off the tackiness and help finish off the curing.

 

[DWK5150]

Originally posted by JimGo
<br />Cure time is also dependent on the amount of catalyst. Obviously, you need to stay within certain bounds, otherwise it comes out too brittle or too soft to be useful, but the (approximately) 7 drops per ounce rule that Anthony and Jay indicate in their tutorials has served me well. On warm, relatively dry days, if I cast in the morning (around 10:00 at the earliest - I don't like to get up early), I can some times knock the blanks out by 4:00 or 5:00 PM, even when using the ice cube trays. Some times, the outside of the blank is still tacky even though the inside is fully cured. A wipe-down with some Acetone will clean off the tackiness and help finish off the curing.

Jim you have actually been able to knock your out that soon? I have never been able to do that even using 7 drops on a warmer day. Now I have been using 5-6 drops per ounce seems to work better but yeah they cure slower.

 

[JimGo]

Don,
Yeah, I was actually surprised a few weeks ago when I had to wait 2 days - I had used a new coloring agent, and had used a LOT of it, which slowed down the curing process. I usually mix 2-3 oz at a time, and put somewhere in the neighborhood of 7-8 drops per ounce. When turned, they are a little softer than Lucite, and are about the same as the acrylic blanks I've gotten from Martin at Woodbin.

 

[its_virgil]

Every PR cast I've made has been sticky on the surface exposed to the air. It will eventually dry or can be wiped off as mentioned. The catalyst does strange things. As the ambient temp goes up the amt of catalyst goes down and at warmer temps it goes back up. I cast snake skins in a mold that holds 14-16 oz of resin and I use 3 drops per ounce. I cast in a pressure tank (which I don't think affects curing rate). My shop also has HVAC, and when casting, I have the AC on. I do not cast without the AC if the ambient temp is 90* or over. Heat + heat = hot and heat is one of the bad guys, especially when casting snake skins. I leave it in for 4 hours and it has always been hard. I have had a few casts, not clear, but with coloring, that were not hard in 4 hours...still kind of flexible...but are nice and cured the next day. Some colors cure differently than others. Seems that some titanium oxide white gave me some real problems. I have started using only pigments sold by the resin suppliers...which seems to work much better than other pigments. What works for me in N Texas may not work exactly the same in other parts of the country. So some practicing, keep good notes on what was done so you can duplicate the results (right Anthony), and you can figure out what works in your shop.

Casting Craft from a local store is expensive stuff to practice with. I get resin with catalyst for $28 per gallon plus shipping...total of (about)$35 per gallon shipped in. Buying from local craft stores is not too bad if you have one of their 50% off coupons.

Do a good turn daily!
Don

Originally posted by kf4knf
<br />So I am using some Castin Craft Poly resin I picked up at a local craft store. I used the ratio of resin/hardner suggested on the bottle but when I cast anything it doesnt harden all the way and comes out sticky and flexible.

I let it sit overnight before even checking on it - thats when I discoved this. How long do you let your casts sit for? Will it always be sticky, even after its cured? Help!

 

[kf4knf]

Yea buying at a local craft store is kinda $$. I just wanted a small can of resin to try it out with. Yea I was using about 5 drops per ounce and was casting about 3 onces in a platic container. I figured that would be to much cat for that small of a batch. I have heard it will crack the poly if it gets to hot. I assume if that happened you would see a visible crack before you turn it - correct? Has anyone ever cracked one?

I was also using the powder tempra paint pigment I posted on before. Maybe that had sometime to do with it... I will check on it tonight and see if its fully cured.

 

[PenWorks]

I have turned PR that appears to have surface cracks and it ends up being fine.
Also, don't be quick to judge what your casts look like from the outside, they are just
like wood. The beauty starts to come out when you turn them. Good luck.

 

[its_virgil]

The heat is a function of the cast thickness. Thicker = more heat whch can't dissipate quickly enough and it sorta builds up in the center of the cast. Heat cracks (that I have noticed) have usually looked like half moons...sorta like the old fashioned hand fans that we had to unfold...more like little fissures but they don't seem to run from one end to the other. Reading some of the casting forums or on the instructions, the catalyst is reduced as the cast's thickness increases. Keep playihng and you'll get it.
Do a good turn daily!
Don

Originally posted by kf4knf
<br />Yea buying at a local craft store is kinda $$. I just wanted a small can of resin to try it out with. Yea I was using about 5 drops per ounce and was casting about 3 onces in a platic container. I figured that would be to much cat for that small of a batch. I have heard it will crack the poly if it gets to hot. I assume if that happened you would see a visible crack before you turn it - correct? Has anyone ever cracked one?

I was also using the powder tempra paint pigment I posted on before. Maybe that had sometime to do with it... I will check on it tonight and see if its fully cured.

 

[ed4copies]

Re: cracks.

Turn down to 1/16 to 1/8 over finished dimension, bathe liberally in thin CA, let sit overnight. (Do try not to become permanently attached to your work in this process). When turned the next day, tiny fractures are healed.

 

[JimGo]

Originally posted by PenWorks
<br />Also, don't be quick to judge what your casts look like from the outside, [...] The beauty starts to come out when you turn them.

EXCELLENT advice. Some of my favorite blanks looked very plain and boring when cast.

 

[kf4knf]

Thanks for the advice guys. Yea I just turned my first cast into a slimline tonight. It was still sticky on the outside but hard on the inside. Turned out very nice.

What's that? You want a picture - hehe I know you all to well!

 

[kf4knf]

Sorry this is not a real good picture of it...

<br />

 

[johncrane]

for your first cast you should be very happy looks great.I havent tried it yet. I have all the resin/colours but it is winter here.I am waiting for summer before I try it out.