Conti Prestina Espresso Machine Restoration 101 (Completed and Indexed) - Page 16

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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Clint Orchuk

#151: Post by Clint Orchuk »

If you really want to get the boiler and plate clean, go with muriatic acid. Oxalic acid will get rid of the rust on the other parts safely.

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drgary
Team HB

#152: Post by drgary »

Thanks, Clint. That's why I post these pictures, so after I stumble along I can get advice on how to really get the job done! :D BTW, what do you think of all those apparently bronze parts going copper?
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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Clint Orchuk

#153: Post by Clint Orchuk »

I think the acids (citric, oxalic, muriatic) cause some of the copper to to dissolve in solution and lightly coat the brass. It's easy to polish off the brass, and the copper will polish back to an orange color. I used some simichrome on a rag for for the pipes and a little buffer on a dremel for the fittings and a bigger buffer on a drill for the boiler and the plate. Easy process. Get some muriatic acid from a hardware store and use it on the boiler and the plate and anything else that's nasty like the heating element. I put about a half gallon in a cooler, added enough hot water to cover the stuff and in 3 or four hours it was spotless. Do it outside. It bubbles and fizzes and produces a lot of gas. The stuff is nasty. When it's done, dumpt it somewhere safe and refill the cooler with some water and a good amount of baking soda to neutralize any acid that might be left on the pieces. Oxalic acid is really safe. Same acid as in rhubarb. It's been a secret weapon for years for guys who restore old bicycles. Just drop the whole rusty frame in a bath and in a day or two it's spotless. Amazing stuff. Blows away any kind of commercial rust remover or mechanical way of doing it. Easy on the skin and very little fumes. You can find it as wood bleach in hardware stores or cheaply off of eBay. Works great on steel, stainless, or chrome, but not on aluminum. I brought an old Honda CT70 back to life with the stuff.

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drgary
Team HB

#154: Post by drgary »

Clint,

What concentration (how much powdered acid in how much water) do you use for oxalic and muriatic acids? I found some oxalic powder on my paint shelf. Wouldn't use it on guitars, though, unless the finish is in really bad shape!
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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Clint Orchuk

#155: Post by Clint Orchuk »

For the oxalic, try about a tablespoon per quart of hot water. You'll see if it's working or not. The acid gets used up as it works on the rust. If it looks like nothing's happening, add some more. When the water gets really gross, change it and do it again. The muriatic is way stronger than the oxalic and works fast. I was tired of screwing around with the boiler scale so I used a half gallon in 5 gallons of hot water. Just be careful with it. The fumes are brutal. But it will come out spotless.

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drgary
Team HB

#156: Post by drgary »

Clint Orchuk wrote:Get some muriatic acid from a hardware store and use it on the boiler and the plate and anything else that's nasty like the heating element. I put about a half gallon in a cooler, added enough hot water to cover the stuff and in 3 or four hours it was spotless. Do it outside. It bubbles and fizzes and produces a lot of gas. The stuff is nasty. When it's done, dumpt it somewhere safe and refill the cooler with some water and a good amount of baking soda to neutralize any acid that might be left on the pieces.
Warning: Use at your own risk!

I'm about to use the muriatic acid and have been warned by two people to fill the vessel with water first, then add the acid. Otherwise you risk splashing, and this stuff can burn you.

I'll let you know how it goes.

First report after adding about 1/3 gallon to about 8 gallons;it does emit nasty fumes but it doesn't bubble and fizz. That's probably because I started with water. I did this outside, was wearing heavy jeans, rubber gloves, snow boots and eye protection, and I was ready to jump in the pool if need be! :lol:
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

Warrior372

#157: Post by Warrior372 »

For anyone taking refurb notes. . . . For the record, Citric Acid at the proper concentration in water will clean any old rusty piece soaked for 24 hours, or so, along with steel wool will get the dirtiest boiler as shiny as it can possibly get. There is no reason / benefit to play with more aggressive acids. All that does is add unnecessary risk to the refurb equation.

As far as pH goes, Vinegar is about 3, Citric 2.2, Oxalic 1.3 and Hydrochloric / Muriatic Acid is about 1. Citric acid will irritate the skin, while hydrochloric acid is corrosive to skin.

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drgary
Team HB

#158: Post by drgary »

Hi Michael,

Living dangerously here ...

Aren't all highly concentrated acids hazardous?

One other thing I'll do before disposing of that muriatic acid is dissolve a large quantity of baking soda in a lot of water, add it to the solution first, then pour it down a drain and rinse. This should mostly neutralize it before it leaves the container.

Later add: Warning! If you add baking soda solution to a strong acid, expect the acid to intensely foam up. Fortunately I did this outside, on concrete, while wearing protective clothing, and I added the baking soda solution gradually, so there was no mishap.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!

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Clint Orchuk

#159: Post by Clint Orchuk »

The boiler on my machine sat for 18 years with water in it. Citric acid wouldn't touch it, unless I was prepared to wait for my next birthday before putting it back together. All acids are hazardous. Just use common sense and you'll be fine. If you have nasty scale, use a nasty acid. For regular descaling, citric works fine, but if you've got heavy, thick black concrete-like buildup, go heavy.

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drgary
Team HB

#160: Post by drgary »

Clint Orchuk wrote:Citric acid wouldn't touch it, unless I was prepared to wait for my next birthday before putting it back together. All acids are hazardous. Just use common sense and you'll be fine. If you have nasty scale, use a nasty acid. For regular descaling, citric works fine, but if you've got heavy, thick black concrete-like buildup, go heavy.
Yeah. Thick black concrete-like buildup here, and I don't want to wait until my next birthday or take a wire brush to that big boiler. The oxalic acid has already taken care of the rust on the group cylinder. Just upped the oxalic and muriatic acid concentrations (different buckets) and haven't melted any body or machine parts yet. I am taking precautions, though.
Gary
LMWDP#308

What I WOULD do for a good cup of coffee!