Silicone Rash Questions

[Tammyfarms]

I made two small batches of soap yesterday to compare tallow, which is new to me, and lard which is in most of my soap recipes. I will most likely end up with a combination of the two but for experimentation wanted to start separately. For each recipe, I used 75%lard or tallow, 20% coconut and 5% castor. No fragrance in either batch. Lye concentration was 35%. Both batches were poured, swirled and CPOP’d using a heating pad in an insulated box. (Thank you @AliOop, for the recipe suggestion.)

Both batches had significant pitting along the edges and bottom. From what I have read, that sounds like silicone rash? I was able to cut most of it off using a potato peeler (I don’t yet have a planer).

Are some silicone molds more prone to rash? These are new molds that I bought from Temu and I’m thinking that my good deal was a waste of money. I bought them as they are just the right size for test batches at 350 grams.

 

[not_ally]

Hi Tammy, that does sound like silicon rash to me, and it seems (at least in my case) to turn entirely on the mold being used and to be somewhat random. I remember several years ago Irish Lass having difficulty with her Essential Depot loaf Molds and silicone rash, while my ED molds turned out a really nice, smooth surface. I stopped soaping for a number of years, lost all my soap stuff, bought new ED molds (I've been using my same recipe all along, one very similar to yours.) And these new ED molds ones produce a rash, unlike the old ones. I love using these molds - they produce the perfect size shape for me when I use designs that require dividers - so I just plane the sides.

Re the Temu molds, I have bought a bunch from there and none of them have produced rash on the soaps. Since they are so cheap they are often not the most durable, but I've been pretty happy with them all things considered.

 

[Tammyfarms]

Thank you @not_ally. In addition to the rash the sides of the molds bowed significantly. I may use them again but will need to reinforce the sides if I do.

I usually use much less lard, 35%, so I’m wondering if that has something to do with it. I have been soaping for 7 years but it’s just for myself and friends so I wasn’t making a lot. Once I found a recipe I liked I mostly stuck with it. Now I’m interested more in experimenting with ingredients and having fun with colors and some fragrance/EO’s.

 

[Tammyfarms]

Oh, here’s a picture of the soap, the orange and purple is lard and the black and brown is tallow. I noticed there are some air bubbles in the tallow but that’s probably because it was firming up quickly. I tried banging it on the counter but without a support it wasn’t cooperating. The second picture is a piece I planed off the tallow soap.

 

[AliOop]

I have to concur that certain cheaper molds (from Amazon or the local craft stores) seem to create either silicone rash or heavy ash, while others (like those from Nurture) never have that issue. Same recipe, same temps, same heating pad process - the only difference is the molds. I ended up getting rid of the worst offenders because I hate planing soap.

 

[not_ally]

I don't know if it's the lard, for me the only molds that make the rash are the ED ones, and I use the same recipe with all my molds. Plus I've always used the same-ish recipe (60-65% lard, 5% castor, 20% coconut, the rest usually olive or avocado.) I've never been good at fixing bowing in molds, it seems like they always have that plastic ribbing on the sides which (a) is supposed to eliminate the bowing (and doesn't) and (b) makes it really hard to make something that you can get flush with the sides of the mold to fix the bowing! I have read about people just putting heavy cans on the sides of the mold to address it, worth a try?

These are the Temu loaf molds I bought, they are actually pretty sturdy (do not bow) and do not produce any problem surfaces. I'll try to find a bar that shows how straight/unbowed the sides are if you decide you want to replace yours. ETA: added the picture, ignore the speckles (that is an unrelated problem/not silicone rash), just wanted to show you the sides were unbowed using the mold in the link.

https://www.temu.com/goods.html?_bg..._1694997378708_4wbsjd4v2a&refer_page_sn=10045

 

[Tammyfarms]

Thank you @not_ally and @AliOop. This morning I realized that at least part of the issue was probably my fault. I normally have my molds in a wooden box when I sit them on the heating pad. These molds I sat straight on the heating pad which was on high for 3 hours. I’m guessing that is what caused the rash. I still have the bowing problem but should be able to address that as the molds do not have support ribs and I can make a box pretty easily. Here’s a picture of one of the molds. I do like the size for test batches and will give these another try with modifications. Thanks again for your help!