What is Caustic Soda?

A friend just suggested using caustic soda to clean the paint off a plastic model kit that I want to repaint *. What I want to know is, what is the stuff, and how toxic is it? Can’t be too bad, as the stuff I used was sold as Espresso maker “shampoo”.

*It worked fantastic! One tbsp/pie plate of warm water, soaked 10 min, paint came off like magic. Only had to scrub panel gaps lightly with a toothbrush. Didn’t harm the model plastic at all. Paint was Tamiya Acrylic.

Caustic soda is sodium hydroxide or NaOH. Read all about it here. It’s pretty nasty in high concentrations, but when it is very dilute it seems fairly innocuous if you’re careful. I managed to get a dilution of NaOH mixed with sand in my eye while I was at work a while back. Not fun… Anyway, the link goes to an MSDS for NaOH, which would be a good thing to read if you plan on using it more.

Sodium Hydroxide is fun, fun, fun…if you don’t get it on your hand. Mix it with just about anything and add water and you’ve got yourself a nasty fire. Use it to amaze your friends. I used to make water mortars with it in high school.

Sodium Hydroxide + fat/oil = soap. Hooray for chemistry!


Let me echo that: What?
I’ve literally handled thousands of pounds of NaOH in aqueous solution, and I’ve never had one fire.

KidCharlemagne might be thinking of sodium, which of course does react pretty violently with water… forming sodium hydroxide.

Sodium hydroxide can be pretty nasty stuff… it comes in little pellets, which, when left out in the open, absorb water from the air and deliquesce, forming a nice strong pool of aqueous NaOH.

It is comonly known as lye, trade names are Drano, Liquid Plummer, It disolves organic items.

Lovely, lovely, stuff. But I’m a soapmaker, so I’m biased. I used to buy it in 50 pound bags, but I’ve downsized, so now I keep maybe 10# on hand.
You know you’re a true soapmaker when you get mad at your husband for using the lye to–can you believe?–CLEAN THE DRAINS. Honestly!

No I’m thinking of sodium hydroxide. Mix a spoonful of those pellets with some sugar (or just about anything for that matter), add a few drops of water and it will ignite. That’s why your cautioned to use “flooding amounts” when working with water. I’m not sure, but I think it’s what they use to determine the caloric content of food. Try pouring some on cereal and add a little milk.

Even fairly dilute concentrations of sodium hydroxide can cause serious damage to the eyes, such as blindness. It is worse than most acids of the same concentration.

You should always wear eye protection and if you do ever get a splash in the eye - wash you eye with lots of water.

Read the MSDS.

kid - you arent thinking of chlorine tablets (sodium hypochlorite) are you?

I thought chlorine tablets only when boom when you mixed them with automotive transmission fluid.

Nope, sodium hydroxide. This only works with solid sodium hydroxide, not an aqueous solution, because the heat is generated upon the addition of water.

Well, this is a new one on me, so I had to look it up, and sure enough…
From here:
http://www.ccohs.ca/oshanswers/chemicals/chem_profiles/sodium_hydroxide/working_sod.html#_1_2 :*

Sodium hydroxide solutions will not burn or support combustion. However, reaction of sodium hydroxide with water and a number of commonly encountered materials can generate sufficient heat to ignite nearby combustible materials. *

I ran across this statement on a couple of other sites as well; all are quite close in wording.

Interesting. Adding water to sodium hydroxide certainly generates heat in the near-boiling range…but if that is enough to ignite nearby materials, it seems that boiling water would be similarly risky, wouldn’t it? (Aside from the caustic effect, of course.)

I gotta try this next time we have a nice sunny day…

I’m actually surprised the warning is this tame because a “number of commonly encountered materials” seemed to be really just about anything. and “can generate” is more like “will generate.” The ignition is rather furious as well.

Caustic is a 1 on the PH spectrum.
Water being 7.5
and Acid being 14


Er… when I was at school, low pH was acidic and high pH was alkaline… I recall NaOHsub[/sub] coming in at around 12 or 13.

Oh, and pure water should be pH7.

Pure, distilled water is neutral. Therefore, its pH is 7.

Were you to read the Foxfire Book, you would learn how our ancestors created ash running troughs, and extracted lye (NaOH) and then combined same with tallow or other fatty renderings over fire to make soap.

From a Hazardous Materials standpoint, I’ll take an acid over a base any day. Acids will cause tissue damage, but tend to be neutralized by the liberated fluids. A base or alkaline product causes saponification by dissolving the fatty layers of human tissue, such that it will run to the bone.

Nasty stuff-don’t go there. We HazMat guys don’t like bases.