muriatic acid on table saw

[Mike O.]

We were working on a job the other day and the masons were cleaning the brick with muriatic acid. The guys doing the work were clever enough to remove a very expensive front door but in doing so, the wind blew in a fine mist of acid into the great room where a contractors saw was set up. Now we have a nice collection of acid "freckles" on the saw top.

The first thing we could think to do was to see how many finish nails we could shoot at the masons. After much discussion with my partner (it is his saw) we eventually decided against that.

Then, we tried cleaning the top with WD 40 and the wiped it down with Top Coat. The next day the freckles were still growing. Does anyone have any ideas on how we might neutralize the acid to at least stop any further deterioration of the top?

Any suggestions would be appreciated!

Thanks

Mike O.

[Frank Boettcher]

I would give it a good scrubbing with a baking soda paste to try to adjust the PH. Then follow up with 30 micron paper (that's 30 micron not 30 grit) on a RO sander. Then wax or topcote.

[fredfighter]

You didn't specify if the saw table was aluminum or ferrous metal but ferrous metal should not be eaten away by hydrocloric acid so I assume aluminum.

To neutralize an acid use a base. But don't leave any long-term residue on the saw because aluminum reacts with both acids and bases.

I suggest a mild base like baking soda, sprinkle it on, rub it in, brush as much of it off as you can dry, then wash with a damp rag.

Do not use sodium hydroxide, it reacts vigorously with aluminum.

[Mike in Arkansas]

baking soda solution?

[tom]

Neutralize acids with bases, like baking soda. "Battle scars" may result no matter what you do, but it'll still cut wood like always. Good idea, not shooting. Them masons are tough. ! Tom

[max]

You might shoot nails, but they can mortar you with bricks!!! max

[bridger]

the blood of a mason is supposed to work....

[Dr. Fu Man Chu]

You could go a little stronger than the baking soda by using ammonia. If the spots don't go away, you could get gutsy and wet the whole table down with an even coat of muriatic acid, let it etch its magic, and then neutralize again.

It would probably be prudent to run this on a sacrificial piece of metal first.

[BobS]

Ok!...That one made my day........;-)

Bob S.

[Mike O.]

Delta Contractors so the top is iron.

Mike O.

[Mike O.]

LMAO

This would be our preferred method!

I think we'll try baking soda as it seems to be the most common suggestion.

Thanks to everyone for your help!

Mike O.

[BillyBob]

Rust Free is a cast iron cleaner product based on Hydro-fluoric acid (nasty stuff!). Its sold by the same company that sells Boeshield T9 protectant. They sell the two together as a cast iron cleaner and maintenance system. Both are available at Woodcraft. I know that the Rust Free stuff does a good job of cleaning. But if you don't followup with T9 pretty quick, your table is guaranteed to rust overnight.

You might try some T9 or even clean the top with rust free and then followup with T9.

Bob

[John Martin]

How sure are you about that, Fred?

John Martin

[fredfighter]

Pretty sure. Muriatic (hydrocloric) acid can be used to clean scale and mineral buildup in iron pipes. It should not eat holes in iron overnight.

OP says the table top was cast iron. Perhaps the spots were discolored, but not pitted?

[Roger amd Missy Behnke]

Muratic acid (which is diluted hydrochloric acid) will damage iron and steel. In this case it also removed any protective coating that was on the table and allowed rust to form and keep forming. Phosphoric acid can be use to remove the rust if you don't want to use an abrasive method. Neutralize with baking soda or a detergent. Rinse with water then coat with paste wax.

Roger

[Roger amd Missy Behnke]

Just checked my Rust Free label. Phosphoric acid is listed as the active ingredient. Not so nasty. We use it in the janitorial industry to as an alternative to hydrochloric acid for removing water deposits from steel, chrome, tile, masonry etc. If it gets on your skin just rinse it off. No need to even hurry.

[Guess who]

That's right. It will take a lot less than overnight. It needed to be dealt with immediately. Used to remove scale, it is meeting the scale first, and is dilute. It will certainly react with the iron when it gets there and if continued, and will not take overnight.

When Muriatic [Hydrochloric] acid is spilled, the best solution is a ton of water ...applied immediately. Otherwise, it's too late. Applying soda is after the fact. One company kept a bucket of soda handy for sulphuric acid spills on workers. I advised them to replace it with a shower head. The acid would cause a sore wound, then they would rub salt into it. The solution is to flush it out ...quickly and thoroughly.

If someone is worried about their spoiled table top, it can be weld-filled, then machined again. There are at least four small businesses here who could do that easily.

[fredfighter]

OK. Iron exposed to air oxidises to form FeO which is a hard black oxide that adheres well to the underlying metal. It is that oxidation that causes shiny iron to fade to its familiar grey color. Muriactic acid will react with that:

2HCl + FeO -> H2O + FeCl2

So the acid has etched away the patina and left Ferric Cloride.

You will have to use water to wash off the FeCl. Leaving clorides on the surface will promote corrosion. By now all of the HCl will have either reacted or evaporated. Exposure to water will further oxidise the FeO to Fe2O3 the familiar reddish-brown flakey rust. That in turn can be (should be) rubbed off with fine sandpaper, steel wool, synthetic steel wool, or a brass brush like a pot brush.

[BillyBob]

I stand corrected. I had it confused with another rust removal product. The other one is nasty! I don't think its sold any more.

Bob