Denatured vs 90% isopropyl alcohol for prep work/cleaning? (2024)

I’ve heard people specify “denatured alcohol” in discussing boat repair prep work. But I’m still unclear about any advantages or disadvantages between the two, especially for cleaning/prepping different surfaces. Not intended for cleaning electronics, antiseptic or glug-glug reasons if I run out of beer, but for boatwork and other small repairs.

Beyond the usual boat materials, polyethylene hulls, Royalex/T-formex, composites made with Vinylester or epoxy or polyester gel coat, I use 90% isopropyl alcohol (or, once upon a time, higher-test lab alcohol) to clean other surfaces prior to repair; when cleaning and G/flexing separated soles to shoes and boots (yesterday), or fixing broken household doohickies (today, separating aluminum skin on French doors).

Even 90% isopropyl has yet to dissolve the pump gasket in my spray bottle, the additives in denatured alcohol might eat that gasket.

https://www.canoetripping.net/threa...d-on-my-denatured-alcohol.124771/#post-124792

I’ve done a lot of Googling and studying, sort of on my own.

(That PSA freaked me out as young guy. It wasn’t true)

But the choice of which, denatured or isopropyl, for what and why, is still clear as mud.

https://www.chemicals.co.uk/blog/isopropyl-alcohol-vs-denatured-alcohol

https://survivalfreedom.com/denatured-alcohol-vs-isopropyl-alcohol-for-cleaning/

I ask because I have a $5 off coupon for the local hardware that expires tomorrow, and I’ll be up that way.

scoutergriz said:

The only alcohol I use is 99% ethyl alcohol (it's denatured by leaving 1% methyl in from the distilling process) it burns excellently in my alcohol stoves and lamps and is an extremely good solvent, especially on organics, and even removes permanent marker, dry latex paint (but not cured), and most paint markers. I water it down to 70% for most general cleaning/first aid/disinfection tasks (a quick spray after paddling in contaminated waters), and 50% for deicing windshields and bug removal. If alcohol won't do the job I reach for the acetone...

Click to expand...

Where are you finding 99% ethanol in Canada?

I order it online. Here's one place- https://sculpturesupply.com/product...74563&pr_ref_pid=7366519718051&pr_seq=uniform

Y’all convinced me. It helped that I had a soon to expire True Value hardware $5 off coupon. There were a couple varieties, “For Fuel” and “For Glass”. I don’t use an alcohol stove and it’s time for spring cleaning; we have a lot of windows, so I bought the latter and will try some there.

Nowhere on the can does it list the chemical composition. A little post-purchase Google shows that the “For Glass” is 65-75% methanol, 20-30% Ethanol, 5% Isopropanol an 1% Methyl isobutyl ketone. Tastes yucky.

The 91% Isopropyl alcohol I mentioned came from Walmart, and lacking the methanol I know it doesn’t eat the pump gasket in my sprayer bottle.

P5160014 by Mike McCrea, on Flickr

This is difficult to answer because denatured alcohol formulations differ so much. Usage matters too.

The deciding factor for me is toxicity. Isopropanol is the less toxic of the commonly used alcohols. If I'm doing lots of prep cleaning I'll use isopropanol.

Denatured alcohols with lots of methanol are best avoided because of the toxicity.
Many of the other denaturing agents are toxic too. It's kind of the point.

Denatured alcohol may contain things that are chemically different than ethanol, different enough to cause problems, like attack plastics.

Finally, ethanol is more reactive than isopropanol. So for cleaning isopropanol is the clear winner.

The real issue with using any denatured alcohol (IMO), is usually the lack of details on what was used to denature the solution. If it was something like benzene or methanol, that increases the handling risk and precautions needed ... if it was something like castol oil, then you might have a residue issue ..... so using denatured products for cleaning purposes requires some additional legwork to get a product that uses a compatible denaturing additive.

During the production of Isopropyl Alcohol (IPA), it will get distilled from water, the end product of this distalation is a solution that is 91% IPA and 9% water. This is a physical property of IPA and water, it is called an azeotrope and as long as there is IPA and water in a solution that is being distilled, the product will come over at 91% IPA and 9 % water (by volume).

So the bottle Mike posted is basically the end product of that distillation process and If you use that for cleaning, it won't leave residual water when it evaporates, the water will all go with the IPA. However, if you use that on a water wetted surface, there will be residual water left over.

I have a jug of 99% IPA that is pretty good for cleanup, it doesn't attack very many materials, will dry a wetted surface and contains no denaturing products, so no residue. Given the rise of IPA use for hand sanitizing, it isn't too hard to get the 99% product and it gets rid of concerns over denaturing agents and provides both cleaning and drying when used.

The 3 basic alcohols used for cleaning purposes (methanol, ethanol and IPA) all require care in handling as they can be absorbed through the skin or by inhalation. Methanol is by far the most dangerous to use, it evaporates the easiest (inhalation) and you can absorb toxic quantities directly through skin absorption .... so use it with ventilation and skin protection and caution ... it has the worst potential health effects of the three.

Brian

I used Spirytus Rektyfikowany to make and polish varnishes for many years with success. It’s a 192 proof grain alcohol from Poland that’s easy to find in liquor stores near me. Everclear at 190 proof is the domestic equivalent. Probably has some water content but is free of the toxic stuff and other additives.

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