This is the kind of question that makes me miss Robert Pavlis.

I wonder about the use of concentrated white vinegar for tough de-scaling? It would be an alternative to hydrochloric acid for scale too hard for citric acid or normal 5% vinegar. 25% white vinegar is readily available as a supermarket shelf item here in Austria.

Any experience or opinions?

Thanks!

Jim

Just an opinion, Jim. Why not? It's common to use higher strength acid with more intense scaling. Vinegar is low-risk compared to some of the alternatives. I would think that you'd want to take similar precautions to using any acid at greater strength, which is to monitor closely so you're not leaching metal out of your machine and not exposing chrome plating to descaling solution.

25% acetic should work faster than the usually recommended 2.5% to 5% acetic. It would be harsh - 25% acetic would have a pH of about 2.1, whereas 5% acetic would be closer to 2.4. For comparison, a 0.1 Mole/L citric acid solution (appx 1 tablespoon of citric acid monohydrate per liter of solution) would have a pH of around 2.1.


Dr Pavlis always favored the milder 5% acetic, sometimes diluted that by half and using a hot solution and allowing more time. For heavy scale you'd need to repeat with fresh descale solution. If it's CaCO3 you are removing, the lower strength acid will get the same job done more slowly giving you a better chance of keeping an eye on it. One thing he was adamant about was not using HCl in copper or copper alloys: Descaling copper boilers--something NOT to do!!!

All of this descaling is destructive of the boiler. How much destruction and how fast it happens is a function of the acid concentration and exactly which acid is being used. The proper approach is to prevent the formation of mineral deposits by eliminating the minerals from the feed water. This is a point Dr. Robert Pavlis made multiple times but very gently so it is usually missed. This is why he recommended distilled water buffered with potassium bicarbonate.

Yes, but when you're facing a restoration, this is often what you get. Jim, what are you restoring? If it's a commercial machine the boilers are usually quite robust. When I restored my Conti Prestina, it required descaling to just get to the point where I could polish off what remained. I used muriatic acid. The boiler is heavy, cast metal -- bronze, I believe. I was left with a very heavy, cast boiler that has held up as I've used proper water in it since, and I have looked inside a few times. There has been no further degradation at all, and no scale buildup.

The boiler material and any braised connections etc have to be considered as to what will perform best with the least damage. Sulphamic acid is a better bet for the casual user as it is less reactive with the base metals. Using common hardware store muratic/hydrochloric acid requires some knowledge as to what you are getting into as the vapor is corrosive and hard on everything it touches including your lungs so use outdoors with a breeze is recommended.

A 1 time restoration is a different situation than the periodic descaling, they are not equivalent. Copper and brass are common older boiler construction materials.

drgary wrote: ... I used muriatic acid ...

May be worth pointing out here that muriatic acid is another name for hydrochloric acid (HCl) and is the strong acid that Dr Pavlis recommended against using for copper/brass/bronze. As a last resort in a restoration, maybe - but use it already diluted and sold as a descaler, and follow safety and disposal instructions to the letter. You should never handle concentrated HCl/muriatic acid unless you have the proper safety equipment and are well versed in the safety of handling/storing/disposing it. ( https://www.msdsonline.com/2014/09/10/h ... fety-tips/ )

Of course this is why I like the idea of using potent vinegar. There was a discussion in my Conti Prestina thread about what descaler to use before I chose muriatic acid. Nasty stuff that I used outside, but it worked.

hankbates wrote:Robert Pavlis also pointed out that distilled water (+ small amounts of KHCO3) is in itself a very mild descaler, and could be used in mild cases of scaling.
The presence of chlorides of any type, including but not limited to hydrochloric acid, in our machines, was strongly discouraged. Even stainless steel offers very little resistance.

Chlorides in long term contact are the issue, not the quick short term acid bath that is properly neutralized. And that espresso machine boiler will never be impacted by chloride stress corrosion cracking either. Chlorides just taste very bad on a good day. Pure distilled water without the buffer will slowly remove this hard water scale.