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Old 02-05-2006, 11:18 AM
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Re: Concept to Completion - Diary of a Sculpt

Hi Jo,

It is such a treat watching you have so much fun!

A thought on mixing resin in hot weather: If you were to refridgerate the two parts before using them it would slow down the reaction time. Make sure you close containers of resin as soon as possible so as not to get moisture in them.

As for repairing the mold: Perhaps you could experiment on the tab that you have made under the arm. Make a short cut there and try to patch it and see if it will delaminate. No loss if it doesn't work.

When I spray release into a mold, I just pry open the mold so I can see inside; give it a couple of shot of release; brush it around into the crevasses, and then leave the mold held open for 15 minutes or so to dry the release. Really quite simple and worry free.

Thanks for the great information on slush casting. That was a great tutorial. For a small piece it is probably not necessary but it is great to know how for a larger piece.



Here is a picture of a large piece that was roto cast for an outdoor public art project. It is only about 3/16 inches thick and yet very strong. You can imagine what it would have cost to cast it solid.

You are doing a fantastic job. The more of these you do the easier it becomes and the better your quality is. Learning how to fix problems is just as important as doing the work in the first place. (In my humble opinion!)

Gerard
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Old 02-06-2006, 11:44 PM
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Re: Concept to Completion - Diary of a Sculpt

Wow!!! Gerard,

That is such a totally impressive piece... you and Roger, you're both something else aren't you!! ... (that's actually a compliment just in case that doesn't translate well outside Aussie culture).

Great tip on putting resin in the fridge for a while in hot weather ... such a simple thing, yet it never occurred to me ... thanks for that!

Thanks for telling me what you do when spraying in the release ... it's good to know. When I do the further cut of the silicone mold to the hairline, it's quite possible that I will get to see inside the upper parts a lot more readily, in which case I will use a release agent ... I really would like to make the mold as durable as possible ... if I can't, though, I'll have to forgo it ... I definitely don't want a repeat of the last cast.

Gerard, with regard to the little experiment that you suggest that I do on the flange under the arm, I'm not sure what you mean by the word "delaminate". Would you be able to explain further?

"Learning how to fix problems is just as important as doing the work in the first place. (In my humble opinion!)"
... I absolutely agree with you!
...and shhh!!! no one is supposed to know how much fun it is!!

So I'm off now to do a few chores in the city, see family & ferret out some fibreglass tape (I can't get it locally) ... but when I come back in a few days ... I'll be ready to go!

Thanks,
Jo :>
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Old 02-07-2006, 10:21 AM
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Re: Concept to Completion - Diary of a Sculpt

Hi Jo,

By delaminate I meant that the new rubber you add may not bond with the old and come apart. This would do you no good. If you have not used a mold release on the rubber yet and you cleaned the area with alcohol, I should think it would stick. If you can't get the tape used in dry wall, regular fiberglass from an auto body shop would work too.

We are all waiting for your next piece, Jo!
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Old 02-14-2006, 04:26 AM
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Re: Concept to Completion - Diary of a Sculpt

Hi Roger,

Bit of a disaster, yesterday, I'm afraid ... everything was going reasonably well ... I had cut the silicone mold to the hairline ... found that I could not see her face ... and so cut to the top of the head.

I didn't reinforce the top of the cut as I don't have any fibreglass tape yet, but maybe I don't need it ... I'll just wait and see. It's a bit of a zigzaggy line on the arm ... however, without the sculpt inside, the scalpel was a little harder to use.

Anyway, so far, so good! It took a while to work out my plan of attack on how to cast and minimize the air bubbles ... I decided that my main priority was to save her face from bubbles as much as possible ... a few bubbles in the hair, I could live with! So I decided to cast the face first and then fill in the rest later.

I did all the right things ...shook both parts of the polyurethane ... let them settle so that no bubbles were there ... added part B to part A ... stirred four times in both directions and then poured it into the face, all within about 45 seconds.

I hovered over it with my sharpened matchstick ready to pop any bubbles but none came ... yahoo ... this is easy ... closed it up ... came back half an hour later to see ... yes it had bloomed, but why the hump in the middle ... didn't bode well.

So I popped the face cast out ... while the top of the cast had bloomed, the face part was still a sack of very bubbly liquid ... and it took the rest of the night to go completely white. In the interests of the experiment, I took it apart ... yep, the face was mostly bubbles, and really big ones too! ... took me over an hour to clean out the silicone mold with D'Limonene.

I think I really should have done a small test cast before going ahead ... I opened the resin kit a few weeks ago to do my first cast ... it was a very hot, moist day ... and even though I closed the containers immediately after pouring them out, I'm guessing that they attracted moisture from the air layer above them ( each container was about three quarters full of air) ... either that or I popped it out far too early ... what do you think, Roger?

Anyway, I started to feel a bit tragic ... not a sight for the faint hearted, so I had a party instead! ... no wine, just some good home brew beer!

Tomorrow, I'll open a new kit of procast and try again ... hmmm!! Maybe I better test it first.

Thanks Gerard for clarifying what you meant by delamination. You talk about using regular fibreglass if I can't find fibreglass tape ... I thought that fibreglass tape would be safer to use than the regular fibreglass (woven/knitted), or am I wrong in my thinking, there?

Jo :>
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Old 02-14-2006, 10:21 AM
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Re: Concept to Completion - Diary of a Sculpt

Hi Jo,

I should think that one kind of fiberglass is as safe as another except for a breathing hazard of the fine stuff.

Looking at my shelves of several brands of polyurethane, I can see on none of them instructions to "shake" the product. Only one of the two parts needs to be "stired".
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Old 02-14-2006, 03:12 PM
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Re: Concept to Completion - Diary of a Sculpt

Hiya Jo,

It's difficult to advise on Polyurethane casting because you are in a very different climate to me and I don't know what the gel time is on your resin but this is what I would do if I were casting a figurine like yours without a vacuum tank, bearing in mind it is generally cold and damp over here.

I would put the RTV part of the mold in my oven and warm it very gently and so that it is warm to the touch but not hot (recommended is around 20 Degrees C). I would do this even if the instructions said I didn't need to. When ready, strap it up in the back-up ready for casting

I would then take a mixing bucket with a very large diameter flat bottom and I would run a hair dryer around the inside a couple of times to make sure it was dry but be careful not to warm it up. I would then carefully weigh out the two parts of the polyurethane (enough for a "slush coat" - ideally you need a scales with an accuracy of +/- 2%) and then thouroughly but gently stir it with a wide blade spatula or palette knife ensuring that it was totally mixed. I don't think 4 times each way is enough except for very small quantities.

The resin I use has a 4-6 minute gel time and because I have that time available, I would leave it settle for a minute or so - but keep an eye on it and if unfortunately, it starts to bloom, cast it quick

I would then pour it in and constantly keep turning the mold at as sharp an angle as I could without losing too much resin out of the top. As soon as the resin gels I would then mix up some more and fill up the mold.

I think the problem you had was to do with not mixing the resin enough - I know you followed the advice given elsewhere and I'm sorry if mine above is conflicting. Sometimes you can have too much advice

By the way, I always shake the cans as well. Like you, I was advised to by the vendor, which in my case was the manufacturer's rep', although I have to admit it doesn't state this as a requirement in the data sheets.

As always good luck and let us know asap how you get on

Roger
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Old 02-21-2006, 01:25 AM
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Re: Concept to Completion - Diary of a Sculpt

Hi Roger,

Bet you thought that I got lost up a drainpipe or something ... hehehe! ... not so!! On the day that I had planned to open up my new Procast kit, it started raining ... and since I do the casting outside ... well, I just didn't want any moisture problems.

So when the rain and the humidity died down a couple of days later, I did a few little test casts to start me off ... I used a mold I'd made way back ... I think I told you ... anyway, it was pretty well a complete write-off for various reasons... but the face was intact, so I used that to cast in.

Doing those little casts told me that the polyurethane was useable, gave me a bit of practice in slush and solid casting, ... and slowed my fast beating heart to a tad below high anxiety.

Roger, I was really happy that you gave me those suggestions in your last post ... thank-you very much indeed. I agree that there is always a risk of receiving conflicting advice and that sometimes following that advice can run into headaches ... but I am quite prepared to accept that risk, particularly when the advice is genuinely given.

I've cast my net wide through books, research on the net and a couple of excellent but fairly basic workshops at my supplier's place, "Arms Model It" (www.armsmodelit.com.au)... but the science of moldmaking and casting is extremely complex and I've found that some of the intricacies of these processes are still a mystery.

Frankly, if it wasn't for lovely people such as yourself and Gerard who are willing to share knowledge with the rest of us cyberspaceniks, out of the goodness of your hearts ... and if it wasn't for people such as Al, my supplier, who wants to sell me product, but who also wants to see me succeed ... well, those kits might have just stayed in my cupboard to way past their use-by date ... and yes, I am making mistakes, but I'm making mistakes that I can build upon ...so a really big thanks!

Jo :>
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Old 02-21-2006, 04:02 AM
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Re: Concept to Completion - Diary of a Sculpt

Hi Roger,

Back again!

The day dawned when I could *****foot no longer!!!

I pretty well followed your suggestions for my second cast with a few minor variations such as ... I warmed the silicone mold in the sun instead of the oven ... I used a tongue depressor to stir, instead of a spatula ... I sprayed Stoner's Rocket Release into the mold.

Slush casting (hollow casting) such a big thing like this was a bit of a fun adventure ... messy too! As I was dumping out the excess after rotating the mother mold for a while ... boom! ... it started to gel and turn white ... oops! ... I think I had it in a bit too long. As the excess flowed out, it turned into a long thick piece of taffy ... I pulled at it and then thought better of it, but cut it off at the rim. The process left quite a bit of resin on the mother mold base rim, so I mopped up as best I could with paper towels.

I measured out the rest of the Procast kit and realized ... shock! horror! ... that I wouldn't have enough to finish the cast. I decided to use the new kit first, and then fill up the rest of the base with the remains of the last kit (you know, the one that I used in the trial cast in post #64, where the face was a bubbly mess) ... I was none too keen to use it, given that I still wasn't too sure if the faulty cast had been due to moisture contamination of the kit. In the end, I reasoned that if that part didn't cure, I would cut that part of the base off.

I managed to fill the mold with 60 gms to spare ...phew!! Lucky me!! Four and a half hours later, I opened the silicone mold up. With the seam now cut to the top of the head, the cast was a piece of cake to pop out. I don't think that I need to reinforce the top of the seam on the head of the mold for the moment, as the demolding process didn't make it vulnerable to further splitting. Here is what she looks like.




I was really excited when she came out, Roger ... although there is still finishing work to do on her body, the seam lines are so much better than the first cast ... the shim, as you can see, is barely there ... and the cut up to her head has produced very little waste ... now how is that?

I reason that the slush cast provided a hard shell, so that when I filled her up with the next pours, the weight of the resin material didn't put pressure on the seams. Also, you said that putting vaseline onto the mothermold would help the fit as well.

If you notice above her belly button, there is a lumpy bit ... when I pulled the taffy bit after slush casting, and then left it alone, I think that my action pressed it into the silicone mold, where it hardened. I think this, because when I inspected the mold after demolding, their were no holes in the belly area.

She was solid all the way to the base, so you were right, Roger, when you suggested that the botched trial cast from #64 was more likely a problem of mixing rather than moisture.

And behold! ... this time she doesn't have a "ravaged, pitted, scarred and beaten face" ... yahoo!



All in all, I was really very excited with the whole "slush cast then fill in solid" process. There were a couple of tricky bits though, that you might be able to comment on ... I'll put them in the next post.

Thanks a lot, Roger, for putting me onto this process.

Jo :>
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Old 02-21-2006, 05:57 AM
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Re: Concept to Completion - Diary of a Sculpt

Hi Roger,

Actually, there was a tricky bit and a sticky bit that occurred during the process ... first the tricky bit!

Do you know how to clean the hardened resin off the plaster mothermold?


When I put the vaseline all over the mothermold as you suggested, I thought that it might act like a release agent between the resin and the plaster ... if it was meant to, maybe I didn't "butter" it on enough ... I
brushed it on, and being hot weather, it was fairly runny (like oil) ... what do you think, Roger?

I eventually prised it all off with my trusty scalpel but it took a long time ... here's me hard at work on it ... the bottom of the base wasn't so bad ... but where the polyurethane seeped into the corners of the mother mold (ie.between the silicone mold and the mother mold), it was very difficult.





Now for the sticky bit, which you might like to comment on ... if you noticed on the face of the cast, she has a sheen to her ... well, that sheen is over most of her body. It's quite sticky and so even though she's a fine cast, I think that it is uncured resin, particularly since it was yellowing as the hours passed.

On that assumption, I searched the net for a possible answer to my dilemma ... the best I could get was to remove it with a solvent first, followed by rubbing with a dry cloth. So I tried white vinegar first, because it seemed the most benign ... but it was taking such a long time, so I switched to D-Limonene which is a citrus solvent. Overall, the stickiness was getting less, but it was still sticky.

It has since been suggested to me that I back off on the solvent and instead, put it in the sun or under a lamp ... and in this way, it might have a chance to cure ... so that's what I'm doing now ... I'll tell you if it works ... it's all good fun, learning how to rectify a mistake, but it's even better fun to avoid them.


So why was it sticky ... well, if you remember, I sprayed Stoner's Release into the mold in preparation for the cast. Anyway, my supplier suggested that it is possible that if the propellant in the release agent didn't have a chance to dissipate, then it could have interfered with the curing of the resin.

It seems like a feasible explanation ... I may have been a bit heavy handed with the spray because I really don't know when enough is enough ... and I had a lot of trouble keeping the silicone mold open to air it out, so it may not have dried out ... also, the mound out of which the lady is rising, and which is big and open to the air, was totally cured.

Also, Stoner's Release may not be the best for the job ... I originally bought it to release hydrostone, but since it was all that I had on me at the time, I used it. I think I'll use a release agent designed more specifically for polyurethane as suggested by Gerald, and perhaps I'll only use it on open-faced molds until I get a bit more experience under my belt.

Jo :>
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Old 02-21-2006, 07:24 AM
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Re: Concept to Completion - Diary of a Sculpt

Oops!! Sorry Gerard ... my fingers slipped to an "L" by mistake.

Jo :>
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Old 02-21-2006, 07:05 PM
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Re: Concept to Completion - Diary of a Sculpt

Hi Jo,

At long last well done, I can now relax in the sure and certain knowledge I haven't led you to disaster.

It looks pretty good in the photo, I think the stickiness you describe is due to not letting the release agent dry thoroughly before casting. I have rarely ever used a release agent with RTV molds. Even with polyester, which has a very high exothermal characteristic, I get a good life and with polyurethane casts it would be much better.

I don't know much about 'urethane moulding rubber but I think release agent is more important in their case, Gerard would know a lot more than me about it.

If you let the cast dry in the hot sun you have there it would probably have cured eventually. When it has hardened off you can clean it up with abrasive cloth.

One advantage of using plaster for back-up molds is that you can use heat to clean up stubborn bits of resin. I use a Cook's blow torch to soften up the resin and it peels off like butter. Although the vaseline should have made the job easy? Maybe as you say the heat affected it.

So once again well done and congratulations on a great job it's been a lot of fun working with you on this and I look forward to seeing more of your work in the future.

Best wishes
Roger
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Old 02-23-2006, 06:30 AM
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Re: Concept to Completion - Diary of a Sculpt

Hi Roger,

Well, it keeps raining at the moment so I can't put the cast in the sun ... so I have her between two lamps and she is drying nicely ... such a good thing to see.

I'd rather not have that happen again and although I want the mold to last as long as possible, I won't be using it again in this mold. The fact that you don't bother with a release agent in your molds and still feel that you a get a satisfactory life out of your mold is really nice to know ... and helped me to feel more comfortable with that decision.

A blow torch! ... that is such a good tip! Thank-you so much for telling me that ... I would never have worked that one out.

Roger, you have been really fabulous the way you have worked through this with me ... I have had just the best time! ... and I can't begin to tell you how much progress I've made ... all I can say is ... it makes me feel like dancing!!

And also a big thank-you to Gerard who gave me some really great info too.

Best wishes to both of you ...
Jo :>
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Old 02-23-2006, 11:16 AM
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Re: Concept to Completion - Diary of a Sculpt

Hi Jo,
Congratulations on your successful pour!

Thought I would submit a couple of things I learned about casting (maybe the only things). The first time I used mold release I had the same problem as you. I used too much. It takes only a light spray; brush it into all the crevasses; and then let it dry with the mold propped open for at least 20 minutes. A can of this stuff lasts a long long time. If you don't use it with a urethane mold you will end up with a solid mass that can not be separated.

Vaseline and wax don't work really well with urethane. As the product cures it generated a tremendous heat. (this is the main reason urethane molds fall apart early) I try to demold as soon as possible to let this heat disipate and not fry the mold. This heat also causes a meltable release to (guess what?) melt. The wax flows around and the urethane attaches to the mold. If wax, or vaselilne is used it is a good idea to spray it and the mother with mold release anyway (just lightly).

I have found that when roto casting it is best to pour enough resin into the mold to coat the mold and no more. Rotate this around until it sets up. One doesn't need to pour out any left like is done with slip casting clay, this is just a waste and it tends to pull the still soft cast away from the mold.

When casting with resin, as soon as the pour is done hold a hand held vibrator of some sort against the mother and this will help the little bubbles to rise away from the surface.

This is all I know about casting and you have learned the same thing through your trials. Next time I cast I will expect help from you! Thanks for shareing your experiences with all of us.
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Old 02-27-2006, 06:31 AM
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Re: Concept to Completion - Diary of a Sculpt

Good one, Gerard! ... me knowing as much as you! ... but I must admit, I feel so very much more confident now and it's a really ecstatic feeling! ... and who knows, maybe this time next year, I might be able to offer you assistance.

Thank-you for the additional tips ... all great stuff! ... I've noted them down in my rapidly expanding moldmaking folder, and will have fun experimenting with them.

me knowing as much as you! ... you really crack me up, Gerard!

Jo :>
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