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Degree of shrinkage during cure?

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makemineirish

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I am planning to build some fun molds this weekend so I can try out a few interesting color effects. The problem is that I have specific dimensions that I would like to shoot for on my finished bars. Therefore, I would like to adjust my mold size to allow for a bit of shrinkage. I am not that OCD about it, but as long as I am going to the effort to build molds...I'd prefer to get them right the first time.

When using full water:

How much do the dimensions of your cured soap differ from your initial pour (mold dimensions)?

Responses are also appreciated from those of you taking water discounts, just give me a heads up, as it affects the result.

As always, thanks for any help. I will be happy to curse the ash gremlins for any who take the time to respond:wink:
 

makemineirish

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I appreciate the links, but I did research the topic and read each of those threads prior to posting my own query. Most of the replies are vague and contradictory: "not that much", "a whole heck of a lot", or "use a water discount".

The few that provide quantitative numbers do so by weight. I get that, but it makes it hard to translate into a dimension shift using math, as the density of fresh soap would be different than that of the cured bar.
Jcandleattic stated that her 5.5-6 oz bars lost 3 oz during cure. Carrebear highlights the mathematical improbability of this. Surely, they do not shrink to half their original size?
I had hoped that I could get a sense of the dimension change if I made it clear WHY I was asking about shrinkage. Once again, sorry to be so anal retentive about the process. I was trying to make a packaging idea work out neatly. I can always cut the soap down slightly, but wanted to ensure that I did not grossly undervalue shrinkage (ending up with tiny bars) or overvalue it (and chop it to bits).

At the moment, I am planning on adding 0.25" width, 0.25" height, and 0.5" length to a loaf mold that should hold 42oz of oils (based on the oils/volume sticky). I am planning to add a full 0.75" to a slab mold for 9 bars, under the assumption that each bar will loose 0.25" on each dimension.Does that sound sufficient to you to compensate for shrinkage of full water CP?
 
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jcandleattic

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I appreciate the links, but I did research the topic and read each of those threads prior to posting my own query. Most of the replies are vague and contradictory: "not that much", "a whole heck of a lot", or "use a water discount".

The few that provide quantitative numbers do so by weight. I get that, but it makes it hard to translate into a dimension shift using math, as the density of fresh soap would be different than that of the cured bar.
Jcandleattic stated that her 5.5-6 oz bars lost 3 oz during cure. Carrebear highlights the mathematical improbability of this. Surely, they do not shrink to half their original size?
I had hoped that I could get a sense of the dimension change if I made it clear WHY I was asking about shrinkage. Once again, sorry to be so anal retentive about the process. I was trying to make a packaging idea work out neatly. I can always cut the soap down slightly, but wanted to ensure that I did not grossly undervalue shrinkage (ending up with tiny bars) or overvalue it (and chop it to bits).

At the moment, I am planning on adding 0.25" width, 0.25" height, and 0.5" length to a loaf mold that should hold 42oz of oils (based on the oils/volume sticky). I am planning to add a full 0.75" to a slab mold for 9 bars, under the assumption that each bar will loose 0.25" on each dimension.Does that sound sufficient to you to compensate for shrinkage of full water CP?
The ones I was talking about surely DID shrink that much, regardless of how "mathematically impossible" it was. Everything I do, I do by weight. And yep, those ones shrunk in weight by about 3oz. I don't know why, I don't know how, but they did.

However, since I do everything by weight, I don't know how to answer your particular question.
 

makemineirish

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The ones I was talking about surely DID shrink that much, regardless of how "mathematically impossible" it was. Everything I do, I do by weight. And yep, those ones shrunk in weight by about 3oz. I don't know why, I don't know how, but they did.

However, since I do everything by weight, I don't know how to answer your particular question.
Thanks:D. I know you would not have measured your bars, but do you remember thinking, "Wow, those are tiny" or "They don't LOOK that much smaller"?

Either way, I am sending bad juju to your ash gremlins now ;-).
 

jcandleattic

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Thanks:D. I know you would not have measured your bars, but do you remember thinking, "Wow, those are tiny" or "They don't LOOK that much smaller"?

Either way, I am sending bad juju to your ash gremlins now ;-).
they were smaller, but no, not "half the size" and not tiny.
 

Marilyna

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I know that eventually over a long period of time, my soap loses all the weight of water and lye. So, what I'm left with is the weight of my oils and FO.

In my recipe for 16 oz fats, 1 oz fo, and 6.6 oz lye/water, it totals 23.6 oz, but will shrink eventually to 17 oz. So 17/23.6 = 72% HOWEVER, that calculation doesn't really work, since I've noticed that when I pour a batch it doesn't always weigh the total of all that added up. I'm not sure where the weight goes. You might check a freshly poured batch and see what you get.

So all I can tell you, and I'd help you more if I was able, is that eventually your soap weighs only the weight of fats and FOs, plus any solid additives, I suppose.
 

Nevada

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In my experience using a water: ratio of 2:1 the soap should loses 5-8% in mass.
Obviously the more water you use the more mass you will lose due to evaporation.
YMMV
 

Lotus

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Hey, OP, the problem with your attempt to mathematically foresee what size your bars are going to end up, is that, first of all every batch is going to be a little different. What might be so for one batch may not work for the next.

Most importantly, however, and the reason you're getting answers in weight, is because, while the weight might stay the same, the measurements won't necessarily shrink evenly on each side.

Bottom line, you're literally going to need a rocket scientist and even then, some controlled tests, to figure it out to a consistent degree.

Otherwise, your best bet, is trial and error, with proper logging of results.

One more thing. You have to remember to account for all sides. So if you find that each bar loses it's diameter by .25", you'll have to calculate the area of loss on all sides of one bar, and then multiply that by the amount of bars. But I really think the shrinkage amount is a bit of a bobble head.
 
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makemineirish

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Hey, OP, the problem with your attempt to mathematically foresee what size your bars are going to end up, is that, first of all every batch is going to be a little different. What might be so for one batch may not work for the next.

Most importantly, however, and the reason you're getting answers in weight, is because, while the weight might stay the same, the measurements won't necessarily shrink evenly on each side.

Bottom line, you're literally going to need a rocket scientist and even then, some controlled tests, to figure it out to a consistent degree.

Otherwise, your best bet, is trial and error, with proper logging of results.

One more thing. You have to remember to account for all sides. So if you find that each bar loses it's diameter by .25", you'll have to calculate the area of loss on all sides of one bar, and then multiply that by the amount of bars. But I really think the shrinkage amount is a bit of a bobble head.
I understand that. I comprehend the math.

I am not trying to get ridiculously specific on the dimensions. Rather, I am a complete neophyte when it comes to soap and and have no frame of reference for shrinkage. A 50% reduction in weight would not necessarily translate into a 50% reduction in size, as the density differs. When I tried to search the forum, the few threads devoted to the issue had widely different and subjective responses.

The degree of disparity would become apparent with experimentation. However, I am building molds to START experimenting and would prefer that they not become single-use items because I screwed up so badly in my first attempt.
As an unschooled novice, I am just trying to get a decent enough grasp on the size differential that I can make molds that continue to be useful.

Does your standard soap bar shrink by more or less than 0.25" on each side?
 

makemineirish

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For those novices like myself who stumbled onto this thread with the same concern:

I called Brambleberry and posed my question to the customer service representative. While she concurred that the specific size differential would be dependent on a number of variables, curing should only alter the finished bar dimensions by around 5%. Therefore, there is no need to alter my mold size. The disparity in actual size is negligible.

In the meantime, Nevada corroborated this with her designation of a 5-8% differential.

I am sorry to have bugged everyone with something that is apparently a non-issue. I simply did not want to waste my materials or time.

Thanks again for any and all help. I'm off to the garage to start sawing wood:D.
 
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Pims

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For what it's worth, 3 1/2 years later, I don't think your questions were unreasonable at all.

Would you now be able to speak from experience as to how much average shrinkage by weight there is?

Thanks in advance.
 

penelopejane

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In the meantime, Nevada corroborated this with her designation of a 5-8% differential.

I am sorry to have bugged everyone with something that is apparently a non-issue. I simply did not want to waste my materials or time.

Thanks again for any and all help. I'm off to the garage to start sawing wood:D.
Like you I find it an important question (esp when I was ordering a bud cutter and wanted to know how else my bars would eventually be after cure).

My bars shrink in all directions after a 3-6 month cure.
My mold is 87 mm wide and I cut at 31 mm thick (with a wire cutter so it is exact).

After a 5 month cure my 50% salt bars measure:
87 mm wide x 30 mm thick
ie: they barely shrink at all.

My regular recipe in the same mold after a 6 month cure measures:
82 mm wide x 28 mm thick
which is a 6.8% shrinkage in the width and 9.6% shrinkage in thickness.
 
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