Soap shrinkage rates & soap bar size when made, unmolded, and cured.

[JuneP]

I'd love to know what your soap bar measurements after un-molding, and what your lye concentration is it to get to that size. And then, what is the size of your cured soap after your usual cure time of 4 or 8 weeks, or????

I'm trying to figure out how many oz of oils I need to fill the Essential Depot red silicone mold, and have it come out to be a proper size. Since I have been using a low water discount recently, changing from full water, and slowly trying to get to even higher water discounts, I don't know how much shrinkage I can expect at the various water levels, so I'm hoping those of you who are professionals who need to have your soap be uniform size have figured out the lye concentration level, to get the bar the size you want before and after cure.

Also,I'd like to be able to calculate my batch to give me consistent sized bars, using various lye concentration levels and I don't know if there's a chart some where showing shrinkage levels of the soap based on water content and cure times. Is there such a thing?

 

[lsg]

A lot depends on how much liquid was used in the recipe. If you use a water discount, the soap won't shrink as much because there is not as much moisture to evaporate. Soaps that I have found in drawers, that are a couple of year old have shrunk quite a bit. I always try to allow a little extra in each bar from what is the listed weight on the label. For instance if the label states the weight of the bar is 4 oz, I make sure that the soap alone weighs at least 4.5 oz. I know that I probably didn't answer your question, but here is a link with more info.:

http://www.soapmakingforum.com/showthread.php?t=7682

 

[KristaY]

Someone else asked about bar measurements the other day and I still don't have an answer on that. I have a line marked on my cutter so I know how wide I'll cut each bar. I know I get 9 bars from a 10" mold that average 5.3oz after cure. I also know my average weight loss from each batch is 6.9-8.0% using a 1.8:1 water/lye ratio. I've never measured each bar in mm before and after cure. I think it's going to be different for each soaper depending on ingredients, water/other liquid, environment when curing, etc.

 

[DeeAnna]

Regardless of water content, I figure 8% to 12% loss in weight and volume during a 4-6 week cure. Soap continues to shrink after that, just much more slowly, so I don't expect to ever be able to nail down a final size or weight for my soap, but these percentages will get you close.

http://www.soapmakingforum.com/showthread.php?t=35831

 

[kchaystack]

Yeah, I've used shrink wrap on my 6 week old soap, and then come back a couple months later, and the shrink wrap is loose.

 

[The Efficacious Gentleman]

One of the best ways to be sure is to make batches and measure them at those curing stages. A lot of factors will play in to it, so what your curing area is like, for example, will give you a different result than that of someone with a curing area with a different humidity

 

[JuneP]

Thank you everyone! I guess the best thing it to allow a lot of extra batter and figure the size of my molds in relation to the recipe, the amount of bars I can get and then keep track. It helps a great deal to know a general range of shrinkage, so I'll use that as my starting point.

i have a couple of four and five months old bars left,, so I'm going to see if I can look at the photo of it in the mold, a gauge how high I filled the mold, then check the batter, lye concentration, etc. and see what I wound up with.

It may not be too accurate since my cuts were made with a cheese cutter and not my new cutter; but I should get enough information to give me a general idea.

 

[DeeAnna]

I don't think you can nail this down real tight, June. Even 1/8" variation in the height of the batter in your mold is enough to add a fair bit of error. It's pretty easy to get that much variation and more unless you can always pour at super-thin trace, ensure your mold is dead level, and never swirl or decorate your tops.

 

[TeresaT]

I am curious about this question/issue. Why is it important? I'm not trying to be rude or argumentative; I genuinely want to know. I haven't been making soap very long and don't sell. My cuts are crazy-crooked and no two bars are alike. But I find that to be part of the charm of my hand made product. I always soap at 2:1 water:lye ratio because that's what I'm comfortable with; it's not too fluid, yet doesn't trace too quickly on me. I don't see any weird distortions in any of my CP bars of soap that have been sitting around for a while, however, all of the HP bars cut from loaves are oddly distorted. They are slightly triangular shaped; the tops of the bars have shrunk inward while the bottom of the bars have maintained their natural shape. The HP single mold bars are not distorted. It doesn't bother me. It is kind of odd looking, but it emphasizes the uniqueness of the handcrafted nature of the soap. Is this distortion something you are trying to avoid happen to your products? I don't really see it in my CP soaps and I'm guessing that is because I use so much less water during the CP method than the HP method. I wonder if the distortion could be avoided by rotating the soaps (switching sides/tops and bottoms) on a weekly basis during the cure? Does anyone do that? I would think not since so many decorate and do high tops, it would mess up your work. Anyway, like I said, I'm curious why it matters how much shrinkage occurs in actual size vs weight.

 

[JuneP]

I just checked the two bars I have left from the February challenge and they average 4.4 oz. My 1 lb silicone mold was pretty much filled to the top with maybe 1/8" from the top as near as I can tell from the photo.

That batch had a 28% lye concentration, and the water was 35.5%. So I'm guessing that a higher lye concentration would give me a slightly heavier bar after a six to 8 week cure, or I could cut the bars about 1 1/8" thick if I want them heavier.

I think I'd rather have the bar be a bit thicker than taller, because I think it would fit my hand better.

If I feel better in a couple of days (diverticulitis is back and bad at the moment), I'll hopefully be making an attempt at the wall pour challenge in the same 1 lb silicone mold, so I think I'll up the lye concentration to 29 for this challenge. I don't want to go any higher because of the nature of the wall pour design - don't want to risk it thickening up too fast.

 

[penelopejane]

Soap shrinkage rates & soap bar size when made, unmolded, and cured.

TeresaT
If you sell you need to be above a certain weight if your labels are printed.
If you don't sell but are a bit of a perfectionist and you want your bars to be consistent you need a multi-bar wire cutter.

JuneP
My bars are cut with a paint scraper and mitre box and the actual bars are so inconsistent (top 30mm bottom 27mm) that despite marking the size I cut my bars at I don't know which side is the "right" one.
Responses to my thread said bars shrink about 3-4mm (or 1/8 inch) over 32mm (or 1 1/4 inch) bar for a standard 30% lye concentration. If you go higher lye concentration it SHOULD shrink less. DeeAnna is right about the % if you are good at maths [emoji33]

When I get my beautiful multi bar cutter (being a happy micro manager) I will be able to tell you in about 3 months if you are interested. One slight spanner in the works is that no matter how beautifully made a multi bar cutter might not produce exactly the same size bars. But at least they will be straight.

I think that maybe soaping is trying to teach me that perfection is not a necessary trait and learn to let go and go with the flow. [emoji322][emoji322][emoji322] Difficult as that may be for some!

 

[JuneP]

Theresa, for those who sell soaps, sometimes I've read, their wholesale accounts want uniformity in the size of the soaps.

For me, it's just a matter of wanting the finished size to be consistent, comfortable in my hand, and looking well finished and pretty or interesting if possible. As a crafts person for over 40 years in another field, I just have the habit I guess of wanting to make the best product I can, not just in how it functions but also in presentation.

I only make soap for my family and a few friends, but I still want to give them the best soap I know how to make. And one of these days I'm going to figure out how to make a nice label for them as well. So far I only manage to put them in a shrink wrap bag and tie with a ribbon when I gift them.

 

[DeeAnna]

I wish I could find the thread where a person posted the water loss from higher water and lower water soaps. The rate of loss was almost exactly the same over the (I think) year of the test. Grrr. I think it might be helpful to this discussion, but I can't dredge...

Oh, oh! I found it -- http://www.soapmakingforum.com/showthread.php?t=38161 See especially Timber's posts #13, 18, and 30

 

[penelopejane]

I wish I could find the thread where a person posted the water loss from higher water and lower water soaps. The rate of loss was almost exactly the same over the (I think) year of the test. Grrr. I think it might be helpful to this discussion, but I can't dredge...

Oh, oh! I found it -- http://www.soapmakingforum.com/showthread.php?t=38161 See especially Timber's posts #13, 18, and 30

Timber said:
"I did the final weights today and the bar with more water at the beginning still has more water at the end. Interesting..."

Would this indicate that the soaps with more water in the beginning are softer even after a year?

This really doesn't show that the soaps have the same shrinkage rate after a year, though, does it? It is just measuring weight.

 

[DeeAnna]

"...Would this indicate that the soaps with more water in the beginning are softer even after a year?..."

I don't have a clue. The only way to know is to measure the hardness and Timber didn't do that.

"... This really doesn't show that the soaps have the same shrinkage rate after a year, though, does it? It is just measuring weight. ..."

Timber also didn't measure the dimensions, so yeah it's just measuring weight. Timber's info is not very helpful to the current discussion; I can see that now.

 

[JuneP]

Theresa, I'd love to have that information once you get your multi bar cutter.; and I'm sure other forum members would find it interesting and useful as well!
I recently got a Bud cutter to replace a cheese cutter, which worked OK, but not great. The reason I got the Bud, single bar cutter, was to have the flexibility to cut whatever size bar I wanted. And since I don't sell, and don't know if I ever would, it seemed like the best choice for me at this time.

TeresaT
If you sell you need to be above a certain weight if your labels are printed.
If you don't sell but are a bit of a perfectionist and you want your bars to be consistent you need a multi-bar wire cutter.

JuneP
My bars are cut with a paint scraper and mitre box and the actual bars are so inconsistent (top 30mm bottom 27mm) that despite marking the size I cut my bars at I don't know which side is the "right" one.
Responses to my thread said bars shrink about 3-4mm (or 1/8 inch) over 32mm (or 1 1/4 inch) bar for a standard 30% lye concentration. If you go higher lye concentration it SHOULD shrink less. DeeAnna is right about the % if you are good at maths [emoji33]

When I get my beautiful multi bar cutter (being a happy micro manager) I will be able to tell you in about 3 months if you are interested. One slight spanner in the works is that no matter how beautifully made a multi bar cutter might not produce exactly the same size bars. But at least they will be straight.

I think that maybe soaping is trying to teach me that perfection is not a necessary trait and learn to let go and go with the flow. [emoji322][emoji322][emoji322] Difficult as that may be for some!

 

[JuneP]

I would think the water would still keep evaporating. I guess you could always make two small batches with the exact recipe, the same day and then check the cut weight, and then check each every month for six months or even longer. I would take a guess and say that after a long period of time, both soaps would cease evaporation, which could be observe through weight comparisons, and then you could figure out the percentage of final shrinkage based on the various percentage water amounts used in the initial recipes..

Timber said:
"I did the final weights today and the bar with more water at the beginning still has more water at the end. Interesting..."

Would this indicate that the soaps with more water in the beginning are softer even after a year?

This really doesn't show that the soaps have the same shrinkage rate after a year, though, does it? It is just measuring weight.

 

[penelopejane]

"...Would this indicate that the soaps with more water in the beginning are softer even after a year?..."

I don't have a clue. The only way to know is to measure the hardness and Timber didn't do that.

"... This really doesn't show that the soaps have the same shrinkage rate after a year, though, does it? It is just measuring weight. ..."

Timber also didn't measure the dimensions, so yeah it's just measuring weight. Timber's info is not very helpful to the current discussion; I can see that now.

DeeAnna,
I wasn't sure if it weight was relevant to shrinkage or not. It seems like it should be. So very difficult to make definitive statements about all this because it depends on the recipe, the water, the scales, the ruler, the cure time, the cutter and the human involved in the cutting and measuring.

 

[penelopejane]

I recently got a Bud cutter to replace a cheese cutter, which worked OK, but not great. The reason I got the Bud, single bar cutter, was to have the flexibility to cut whatever size bar I wanted. And since I don't sell, and don't know if I ever would, it seemed like the best choice for me at this time.

June,
Do you like Bud's single bar cutter?

 

[DeeAnna]

Not June, but I really like mine. Bud does a good job and his single wire cutter makes consistent cuts. I'm a hobbyist and not in any hurry, so cutting one bar at a time is not a problem vs. cutting multiple bars with a multi-wire cutter.

I like the ability to adjust the bar thickness depending on what I'm doing -- for example, I cut pucks of shaving soap to 1 1/2" tall to make short, fat cylinders of the soap. I cut my usual bath bars a little thinner (about 1 1/8") to fit the hand better. I also made some 1/2" thick sample-size bars recently to use as gifts.

The single-wire cutter will let you split soap in ways a multi-wire cutter cannot. For example I could have laid the 1/2" thick bars flat on the bed of the cutter and split them into two pieces to make even smaller sample bars -- like cutting a peanut butter sandwich in half.

If you've never used a wire cutter, here's a thread about planing soap that might be useful: www.soapmakingforum.com/showthread.php?p=589486 I talk a little about the difference of a blade cut compared to a wire cut in Post 12.