TheKingaSwing
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Registered: 09-2004
Location: Midlands, England
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Question about latex shrinkage.
So we know latex shrinks but I was wondering HOW it shrinks, or better put, which way it shrinks.
My cowl is big enough to shrink and still fit but I was about to do the scallops when this question hit me. I know I need to sculpt them thicker than they need to be but do they also need to be longer too? My idea was to cut the scallops but leave the emblem cutting until after casting so I know it will fit but it's not something you can do with the other areas. Any help would be appreciated!
Nat.
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7/11/2009, 9:01 am
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youngbat
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Registered: 02-2004
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Re: Question about latex shrinkage.
what dicates shrinkage in SLIP cast latex.(not foam latex).
1. the brand, cheaper more calcium carbonate fillers.
2. how thick the wall thiceness is. i.e. the more contained mass the greater the shrinkage. a 1/8" wall will shrink less than a 1/4" wall.
3. it does not shrink evenly either. Foam latex Does shrink evenly. Usually, or historically when slip shrinks it distorts, areas with deep curves, become flattened, sculptures can literally change quiet a bit.
The trick is to get a casting that retains it original shape. some say it's best to make the wall thickness, really thick, so the piece stands up more or less on it's own. that WILL cut down on the elasticity. However slip is THE most durable rubber on the planet. Used to a certain percentage on car tires.
based on my experience from years ago, there may be others who have expereiences with more upgraded products, that are different.
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7/11/2009, 11:08 am
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efarrell4
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Re: Question about latex shrinkage.
I've heard (and even quoted) 15 to 20 % but in really thinking about it I don't know how accurate that really is. I'd go out on a limb though and say that if your sculpt (assuming cowl) is say 26" around it should be a tad loose on someone with a 24" head. Of course as Bob said wall thickness and how you work the latex makes a huge didfference. Some folks fill a mold and dwell it for 1 hour to 3 hours then pour it off. This will resulpt in more shrinkage than pouring several thin coats to get the same thickness. and the thicker it is the more shrinkage you will see.
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7/11/2009, 12:31 pm
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Lrcrow
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Re: Question about latex shrinkage.
WHEN does latex shrink? During the molding process, or after? I mean, if I get a 24 in. cowl today, is it eventually going to be a 22" cowl?
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7/11/2009, 1:30 pm
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Eopie Herder
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Registered: 06-2009
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Re: Question about latex shrinkage.
It's when it is curing, so your cowl should be fine.
---
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7/11/2009, 1:46 pm
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TheKingaSwing
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Re: Question about latex shrinkage.
Thanks guys. I know the cowl will fit, maybe even be a little loose but thats ok. My main concern was sculpting the scallops to be the right length only to have them shrink when cured and look like Returns scallops instead of 89s. See what I mean?
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7/11/2009, 2:05 pm
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bat texan
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Registered: 11-2007
Location: DFW Texas
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Re: Question about latex shrinkage.
Quote: Lrcrow wrote:
WHEN does latex shrink? During the molding process, or after? I mean, if I get a 24 in. cowl today, is it eventually going to be a 22" cowl?
From what I've seen with the cowls I've made, the shrinkage takes place in the first day or two after it's pulled from the mold. They're pretty stable after that.
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7/11/2009, 4:12 pm
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youngbat
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Re: Question about latex shrinkage.
when the water evaporates, you loose mass. that simple. ALWAYS WEAR AN AMONIA RESPIRATOR WHEN USEING SLIP LATEX. THE AMMONIA THAT'S PUT IN THERE IS A CLASS A CARCINOGEN. NOT KIDDING.
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7/11/2009, 4:35 pm
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efarrell4
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Re: Question about latex shrinkage.
Quote: youngbat wrote:
when the water evaporates, you loose mass. that simple. ALWAYS WEAR AN AMONIA RESPIRATOR WHEN USEING SLIP LATEX. THE AMMONIA THAT'S PUT IN THERE IS A CLASS A CARCINOGEN. NOT KIDDING.
EXACTLY!! You REALLY don't want to be breathing that stuff in. Bob here told me exactly what filter to get a few years ago and IMO he saved my life (I'll get even with you for that some day Bob, LOL). You want the green one made for ammonia. This cartridge on your 3M respirator mask will do the trick.
http://www.coopersafety.com/product/3m-6004-ammonia-methylamine-cartridge-1515.aspx
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I do NOT accept PM's, EVER!! If you need to contact me use my email [email protected] , it hasn't changed since 1996. ALL PM's will be ignored!
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7/11/2009, 7:55 pm
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sin03
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Location: Canada
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Re: Question about latex shrinkage.
Quote: efarrell4 wrote:
Quote: youngbat wrote:
when the water evaporates, you loose mass. that simple. ALWAYS WEAR AN AMONIA RESPIRATOR WHEN USEING SLIP LATEX. THE AMMONIA THAT'S PUT IN THERE IS A CLASS A CARCINOGEN. NOT KIDDING.
EXACTLY!! You REALLY don't want to be breathing that stuff in. Bob here told me exactly what filter to get a few years ago and IMO he saved my life (I'll get even with you for that some day Bob, LOL). You want the green one made for ammonia. This cartridge on your 3M respirator mask will do the trick.
http://www.coopersafety.com/product/3m-6004-ammonia-methylamine-cartridge-1515.aspx
Okay a bit of a newb question but here goes: is this why I've heard some bros say that doing a cowl in urethane just makes the cowl maker's life easier (pretty sure it was in a thread comparing urethane to latex a little while back)?
Jason.
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7/11/2009, 8:55 pm
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