Can Soap Flakes Go Bad? - Popular Woodworking Magazine

Can Soap Flakes Go Bad?

 In Chris Schwarz Blog, Woodworking Blogs

I’m a big fan of a soap finish for certain projects. It doesn’t provide a lot of protection to wooden objects, but it is completely safe, easy to apply and quick to repair. But this week I encountered some difficulty with the finish that caused me to ask: Can soap flakes go bad?

First off, if you want to read more about how to mix and use a soap finish, check out this free article I wrote for Popular Woodworking a few years back. It will answer most of your questions and dispel a few myths about the finish.

Back to the soap opera: I finished building a maple stick chair this week and decided to mix up some soap finish for it. Because I wanted the finish to have a little sheen, I mixed up some soap flakes with boiling hot water in a 50/50 solution.

This mixture is supposed to produce a thick, waxy-like substance. But when I poured the hot water into the soap, a weird thing happened. The flakes didn’t dissolve. Instead, they clumped up in a yellowish ball that looked like a weird animal brain when it cooled.

Vexed, I tried again with the same results.

Double-vexed, I tried again with a different brand of soap flakes. Same result (but not as yellow).

So I started to dig around and do some research. Soap flakes are a natural product made with natural oils. So I suspected that these three-year-old flakes were expired (for lack of a better word). While I couldn’t find anything definitive from the manufacturers, I found several claims that most natural soaps should be discarded after a couple years. (Want to read more from the soapmaking community? Start here.)

I tried making the finish a fourth time, this time with newer soap flakes. They dissolved beautifully and the finish worked out great.

Despite this hiccup, I still am a big fan of soap as a finish. We have several tables and chairs in my shop and home that are finished with the stuff. I resoap them every few months (or when they start looking dingy) and they are easily renewed. They aren’t going to stop coffee or red wine from staining the wood, but that’s the price of using the finish.

— Christopher Schwarz

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  • Longfatty

    Soap is made of fats and oils which can go rancid. Sunlight speeds this up but oxygen from the air is the main driver.

    Tropical oils like palm are more stable because they are saturated. Hydrogenated oils (like the old Crisco) are also more stable and will have a longer shelf life. Olive oil is mono-unsaturated, so it won’t last as long as palm but it should hold up on the shelf fairly well. Castile soap is made with Olive oil. Flax seed oil is poly-unsaturated and has a high potential to go bad if you don’t keep it out of the sun, or if it just gets old.

    There are a few different ways that the fat molecules can go rancid. In linseed oil furniture finish, oxygen from the air starts a process that causes the unsaturated fat molecules to link to each other which is why it seems to “dry.” Worse things can happen. An oil can degrade into smaller molecule like butyric acid. Butyric is a big part of that old-oil smell you may detect in rancid cooking oil, or old soap that starts to get brown around the edges.

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