mattking

I need to try and clean up the corrosion on this dash. Been seeing a lot of videos on evaporust. Does it leave a black oxide like the phosphoric acid products.

Any suggestions would be appreciated. I just about have the dash out of the car but not quite.

joe_padavano

You have two different problems. The rust on the chrome speaker grill will come off in Evaporust, Rust911, and similar products. The problem is that the chrome is still deteriorated and it won't be perfect. The only way to fix it correctly is to have that part replated.
The rest of the dash is cast pot metal. There is no way to remove those pits short of grinding them out and filling the metal. No chemical dip will do anything about them. Plated pot metal parts like the heater control head can be repaired by stripping the plating, hand grinding out the pits, copper plating the part, and hand filling the pits with solder. You can imagine that this is not an inexpensive process.

mattking

Thanks for the info, Joe. I was afraid of exactly what you mentioned on the heater control. I'm going to work on finding this last mystery bolt and getting the dash on out. Ill try the evaporust for now..

72442conv

I just used this Permatex rust dissolver product last week on my master cylinder and calipers, it took away the rust and did not convert it to a black oxide finish. It was extremely effective at removing rust and just leaving the parts in the natural cast iron finish. You may want to give it a try for the upper part of the dash. I bought it at Auto Zone, here is a link to it:
https://www.oreillyauto.com/detail/c...over+gel&pos=2

joe_padavano

All of these water-based rust removers (yeah, I just typed "water-based rust removers") are pretty much the same. They vary by concentration. I buy the Rust911 in concentrate form and mix it myself. Why pay for the water? That's like buying the pre-mixed antifreeze.

Vintage Chief

In reality you're paying for the water, as well. You aren't going to buy H3PO4 dissolved in anything but water (H2O). The fact is, you're paying nearly twice the price for Rust911 than you would for another more common and concentrated product. Rust911 is ~40% H3PO4 (phosphoric acid - by weight) at a cost of $37/gallon; while, most home centers sell 75%-85% H3PO4 at a cost of $37/gallon. Less water in the H3PO4 than in the Rust911, but twice the concentration for the same money. The solute (being the phosphoric acid salt) is dissolved in the solvent (water) to form the H3PO4 solution.

joe_padavano

Norm brings up a really good point, which led me down a Google rabbit hole about phosporic acid and rust removal. I stumbled onto this academic paper about The Treatment of Rusted Machinery in Preparation for Surface Coatings, which has direct applicability to motorheads with rust issues. The whole document is interesting, but scroll to Chemical Rust Removal on the ninth page of the document (it's actually the page numbered 30 at the top). Interesting stuff.

joe_padavano

I should add that one interesting passage in that article points out that food grade phosphoric acid is an ingredient in soft drinks, which is why Coke removes rust.

Vintage Chief

H3PO4 is a very passive acid - very much unlike HCL, H2SO4 & HNO3 (which are very aggressive acids). The inclusion of restrainers (into H3PO4) further weakens the H3PO4. Essentially, and fundamentally, H3PO4 (like the other acids I mentioned) are all inorganic acids (phosphoric acid being quite passive). When you add an organic acid (restrainer) to phosphoric acid this slows the Rxn even further but also rapidly neutralizes the resultant solution - yielding it far less toxic than HCL, H2SO4 & HNO3. The most common inorganic acid (restrainer) added to H3PO4 is (you may have guessed it) - simple water (which is in and of itself a carboxylic [organic] acid).

Vintage Chief

Hears (LMAO) Here's a queer recollection of chemistry from years gone by: "Plants have no appetite for apatite". Apatite being the greatest geologic rock formations containing the highest yields of P (Phosphorous). Plants utilize the phosphates (which are dissolved in water i.e. fertilizers). The phosphorous cycle is probably the most difficult cycle to study since there are significant changes to the orthophosphates derived from Phosphorous. TMI

mattking

I have used the home depot "prep and etch" which is phosphoric I believe. I never really have great luck knowing how long to leave it on the metal or how strong to mix it. Sometimes it will leave a gummy wet residue and sometimes it leaves a chalky white residue. I have not had good luck top coating it either. I know a lot of people that use it, but my success has been mixed at best To Joe's point about it being in coke, I have grabbed a pen or something out of my mouth only to realize i had some one my hands . it does taste kinda citric me

Tedd Thompson

You might try 4/0 or 5/0 steel wool with a oil chaser and see if it helps or not. Probably the best solution would try and find a better dash if you could.... Tedd

oldolds88

i used a sos pad on my dash plate,looks perfect

mattking

Thanks for all the replies and insight. I’m definitely going to give some a try.

It will be nice to see it looking nice for a change.

ive seen one new dash pad for sale maybe at year one. But it is not in stock and doesn’t ship until next year. But. One step at a time