we use caustic soda (NaOH) in our vats to strip paint off furniture. it is a solution in water so it is very runny.
i have a big dumb thing i have to strip the paint off that cannot be put in the vat. i need the caustic to sit on it a while to eat on the paint for a period.
so my idea is to mix the caustic into a paste.
my question is:
will flour, baking soda or cornstarch neutralize the effectiveness of the NaOH?
caustic (NaOH) has ph around 14…baking soda/flour/cornstarch are all around 5-7 (right in the neutral zone).
if those thickening agents are all wrong for what i want to do, what is a good solution for making a more vertically-clingy paste?
we full-on neutralize the caustic with vinegar or other acids. the caustic solution is rather weak as it is so i don’t want to neutralize it too much, and i sure don’t want to mix some pasty slurry that is chemically neutral and wait all day for something to happen like a dummy.
The baking soda will. Starches (cornstarch or flour) aren’t directly water soluble; they will dissolve eventually, specially if aided by strong acid or base, but they don’t dissolve anywhere near as easily as the baking soda - if they did, we wouldn’t be able to cook pasta, rice or potatoes in water.
I’d pour the soda solution slowly into one of the starches, to make a paste that will still have a strong pH and which will be… nor so different from cake batter, when it comes to consistency and sticking ability. I figure you already know this, but remember to protect the work area and yourself - using that paste with your bare hands would be as bad as putting your hands into the cleaning solution.
It isn’t a matter of looking for pH neutral components to mix with your caustic. They need to be nonreactive. Also keep in mind that anything “organic” such as cornstarch or flour will have a tendency to decompose and that might leave an undesirable finish.
Baking soda is a very weak base. It might actually work with your caustic soda.
I’d suggest making some test pastes in small quantities and put them on a hidden area. Wash off the pastes at different times, to see which one does the best job, and how long it takes to work.
Trial and error is probably your best bet.
Could soaking rags or paper towels and slapping those on the surface be a possibility? The fabric/paper will probably disintegrate in the process, so don’t use anything of value, like the antique linen tablecloth or your grandmother’s wedding dress.
~VOW
Solids like NaOH and flour don’t really have a pH; that refers to a solution of it. And the pH is going to depend on concentration. I’ve never heard of using hydroxide to strip paint. Can you not use toluene or something like that?
NaOH is otherwise known as caustic soda, which is used as a furniture stripper. my art studio operates out of an antique warehouse, so the strip shop is mainly for antiques.
the situation is this: i have this big art piece i am commissioned to repaint. it’s a fiberglass form that seems to have been painted with household bucket paints but has sat in the sun and the paint has started to flake. it appears they put several re-coats just over the old ones.
nothing was ever primed.
methaleyn chrloride (in most industrial paint strippers) will eat the fiberglass.
there exists a fiberglass specific stripper, but it is special ordered and costly and messes up my time deadlines.
the caustic works, but it’s runny and will not cling. it works over time, so i need it to adhere and sit a while.
i got all three items (cornstarch, plain flour and baking soda) to try on an inconspicuous area but i figured there was a way to chemically understand if they work or not before embarking on all this tomorrow.
Baking soda will dissolve - it will take a ton of it to make a paste! The insolubles is what the OP wants, because he doesn’t want a lowered-pH solution, he wants a paste.
thanks nava. i plan to mix both starches and test them on two areas.
if there’s any other ideas for mixtures let me know. i considered salt but i don’t think it will get very pasty. i dont know about powdered soaps or anything else.
i wish our NaOh didn’t come as an aqueous solution, but in flakes or pellets or granules. oh well.
If you want granulated lye, look for cans of “Red Devil” where the drain cleaners are located. It’s probably right next to the cans of Drano. Drano has other additives, Red Devil is pure lye.
WARNING! The granulated lye WILL react with plain water. ALWAYS add lye to water, not the other way around! Use goggles and gloves and other safety equipment. Keep your vinegar nearby to neutralize splashes.
~VOW
thanks again. i do use all precautions. bear in mind we have a standardized furniture stripping facilities and employees. the case is such that we buy aqueous solution NaOH, is all. nearly every project that comes this way can be fitted into the swimming-pool size tank and soaked, submerged, so this is a bit of an “odd duck” as far as local projects go.
this fiberglass buffalo is just too monstrous. not just that–but i do not want to soak it since i am unknowing if 1. the fiber will melt in similar time that it will take to eat whatever the painting layers are and 2. if there are holes that will allow the caustic entrance to through the vacuum molded body in places i cannot see, like the space between the feet and the steel plate it is affixed to. that sounds like asking for trouble.
caution will be employed, which is why i asked: we didn’t doubt the neutrality of Baking soda; we simply feared the explosive possibility. i’m not much into dangerous experimentation, and since we are dealing with an aqueous but still industrial strength NaOH solution i wanted to err on the side of caution.
thanks for all advice.
Caustic sprays (oven cleaners) or drain cleaners maybe too concentrated for your needs and may do other things you didn’t want. So check it out on a sample piece first.
I would recommend that you wrap the furniture neatly with paper towels (or maybe scotch tape it carefully) and use your normal caustic solution.
Bases will catalyze the hydrolysis of carbohydrates into component sugars, which are probably quite soluble. A above, sodium bicarb is quite soluble. Drain cleaners use polymer-based thickeners like Acrysol. A google search for sodium hydroxide paste confirms that poly acrylic acids are used there as well.