Chemical Rust Treatment Comparisons

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all.jpg (79294 bytes)

This page compares chemicals commonly available in the United States which are intended to treat rust corrosion on steel.  It is primarily directed toward the use of such treatments on automobile sheet metal and specifically split screen vintage (1967 and earlier) Volkswagen busses, since that is my hobby which lead me to do this comparison. 


Page Contents

Corrosion of Iron (electrochemical cell, cathode, anode, electrolyte, road salt)
Excluded Treatments (POR-15, Corroless, Enrust, H402, Miracle Rust Remover and Metal Prep, OxiSolv, Rass-O-Nil, Ospho, Neutra-rust )
Types of Treatments (these are color coded throughout this page):

Electrolysis

Friendly Acids

Ecotec
Simple Solutions Rust Remover

Plain Phosphoric Acid Based

Rust-Mort
MP-7
Naval Jelly
Dupont 5717S
Mirachem 250

Phosphoric Acid with Zinc

Dupont 5718S
Metal-Ready

Other Acids

Envirosolve 1000
CLR - Calcium Lime & Rust Remover

Conversion Coatings

Extend
One-Step
Rust-X

Testing Method
Comparison Results and Organization 
My Conclusions


Corrosion of Iron

VW bus sheet steel is formed primarily of iron.   The corrosion of iron is a complex electrochemical reaction in which the iron combines with both oxygen and water to form iron oxides such as magnetite Fe3O4 (black rust) and ferric oxide Fe2O3 (brown or red rust) among others. The reaction  occurs when there is a difference in the electromotive potential of metals in the presence of a conductor.  This creates a electrochemical cell which has the following parts:

Electrons flow from the anodic area to the cathodic area causing the metal to corrode by forming soluble positive ions at the anode.   The overall reaction for the formation of ferric oxide:

4Fe + 3O2 2Fe2O3

may be written as two separate equations:

4Fe 4Fe3+ + 12e- and 3O2 + 12e- 6O2-

The iron loses electrons (e-), so it is said to be oxidized. The oxygen gains an equal number of electrons and it is said to be reduced.   For more information on the process of iron corrosion see: http://naio.kcc.hawaii.edu/chemistry/everyday_corrosion.html, and for a chart of the electromotive series of metal see: http://www.britannica.com/bcom/eb/article/single_image/0,5716,304,00.html or http://www.mtgloans.com/~thelen/1galv.html

Such an electrochemical cell can form between different metals, between different pieces of the same metal, and even within the same piece of metal for the following reasons:

This last point is also closely related to destructive nature of road salt.  Road salt mixed with water will accelerate the formation of rust by increasing the conductivity of the electrolyte in the cell and specifically as follows:

At the surface of the more noble metal (the cathode) negatively charged hydroxide ions are formed:

2H2O + 2e H2 + 2(OH)-

These hydroxides combine with sodium ions from the salt water to form sodium hydroxide:

Na+ + OH- NaOH

At the surface of the less noble metal (the anode) positively charged ferrous ions are formed:

Fe+ - 2e F+2

These ferrous ions combine with chloride from the salt water to form ferrous chloride:

Fe+2 + 2CI- FeCl2

The sodium hydroxide and ferrous chloride yield ferrous hydroxide where they meet:

FeCl2 + 2NaOH Fe(OH)2 + 2NaCl

In the presence of oxygen, a secondary reaction further oxidizes the ferrous hydroxide to form hydrated ferric hydroxide (red-brown rust):

4Fe(OH)2 + O2 2H2O + 2Fe2O3 H2O

If oxygen is limited, this secondary reaction is modified to form hydrated or black magnetite:

Fe3O4 H2O H2O + Fe3O4

Of course, the subject of electrochemical corrosion of iron is vast, and this has just highlighted the subject.  Some of the information here comes from Basic Methods of Conserving Underwater Archaeological Material Culture by Donny L. Hamilton, Nautical Archaeology Program, Department of Anthropology, Texas A&M University, Spring 1997.


Excluded Treatments

Paints and coatings which are intended to be applied over a rusted surface to encapsulate the rust but not chemically change the rust,  are not included in this comparison.  Some of these products are:

POR-15; Resto Motive Laboratories, Inc.; PO Box 1235, Morristown NJ 07962, phone: 800-457-6715 http://www.por15.com

Corroless; Eastwood; phone: 800-820-9042 http://www.eastwoodcompany.com

Zero Rust; www.zerorust.com

Enrust; P.O. Box 1165 / 800 S. Acadia Road, Thibodaux, LA 70301; Phone: 504-449-0730 or 800-325-3407; Fax: 1-504-449-0740; email: Customer Service@NAPASCO.com; web: http://www.napasco.com/enrustreat.htm

In addition, the following products were not included due to lack of time and money:

H402 Sodium Metasillicate pentahydrate and IGAPAL mixed with the baddest solvent around. Mike West mwest@cdsnet.net Said to desolve steel

Miracle Rust Remover and Metal Prep; Bill Hirsch Automotive; phone: 800-828-2061; $14.00 / 20oz; Manufacturer's Description: Removes rust and leaves gray phosphate coating on the metal to provide an excellent base for painting and welding conductivity.

OxiSolv; Eastwood; phone: 800-820-9042; $10.00 / 16oz; Manufacturer's Description: Dissolves iron oxide rust completely leaving a gray, zinc phosphate coating. Non-toxic!

Rass-O-Nil; web: http://www.icpi.net/rassonil.htm a phosphoric acid solution with zinc

Ospho;  Skybryte Co. 3125 Perkins Ave Cleveland, OH 44114; phone: 216 771-1590; supposedly available from True Value hardware stores

Neutra-rust (no information)


Types of Treatments

Electrolysis basically reverses the electrochemical reaction which created the rust in the first place.  It does not restore the oxidized iron to its original state, but rather removes the rust from the surface of the unrusted metal below.  The iron that rusted in the first place was an anode in the electrochemical cell.  Electrolysis reverses the reaction by making the rusted object into the cathode and some other piece of metal into the anode.  An electromotive difference is created between the cathode and anode with the use of a direct electric currant.  Just as in the original reaction which created the rust, the anode and cathode must be bridged with an electrolyte.  The anode is the positive terminal of the electrolytic cell, to which electrons, negatively charged ions, travel when an electric current is passed through the cell. Oxidation occurs at the anode and oxygen is evolved. The cathode is the negative terminal of the electrolytic cell to which positively charged metallic ions travel. At the cathode, reduction takes place and hydrogen is evolved.   For some good resources on how to do electrolysis, see http://www.bhi.co.uk/hints/rust.htm by Ted Kinsey or http://www.oldengine.org/members/billd/electrol.htm.   Full immersion is required and rust is more effectively removed from the cathode when the surface is in a direct "line of sight" with the anode.

electrolysis

 

Friendly Acids are ones which are not as caustic as the others in this comparison.  Full immersion works best for these products: 

Ecotec
Simple Solutions Rust Remover

 

Plain Phosphoric Acid Based rust treatments are used for two main reasons:

  • It dissolves rust at a much faster rate than it dissolves iron, and
  • It leaves a iron phosphate coating on the clean metal surface.

The phosphate in the acid converts ferric oxide (Fe2O3) into iron phosphate (FePO4) and water in a faster simple exchange reaction:

Fe2O3 + 2 H3PO4 2 FePO4 + 3 H2O

The water is removed when the part is cleaned but the iron phosphate will adhere due to surface effects so that it does not wash away.

The hydrogen ions in the acid will attack the iron and convert it into iron phosphate (FePO4) and hydrogen gas (the bubbles) in a slower reduction-oxidation reaction:

Fe + H3PO4 FePO4 + H2

Unless the metal is exposed to the acid  for a extended period and in sufficient concentrations, the effect of the acid attacking the steel will be negligible. 

Some of the above information comes from Lee M. Daniels,  Laboratory for Molecular Structure and Bonding, Texas A&M, daniels@tamu.edu [email updated July, 2001]

Since phosphoric acid works well for rust treatment, there are numerous products in this category:

Rust-Mort
MP-7
Naval Jelly
Dupont 5717S
Mirachem 250

 

Phosphoric Acid with Zinc works like plain phosphoric acid with the addition of leaving a zinc residue on the treated surface.   The zinc is intended to protect the metal from further corrosion in the same way galvanizing protects steel through passive cathodic protection.  The iron originally rusted since it was the anode (or more reactive) in an electrochemical cell.   Cathodic protection introduces a metal more reactive than iron (in this case zinc) into the cell.   Thus the iron becomes the cathode and the zinc becomes the anode.  The result is that the zinc will now be more prone to oxidation and corrosion and the iron will be protected.  If the conditions are right, the zinc will eventually be consumed.  However, zinc is consumed slower than iron.  This is true, even though  zinc is less noble and more reactive than iron.  Zinc oxide created in the corrosion process, forms a protective barrier on the surface which prevents further corrosion.  Iron oxide formed when iron corrodes, does not form such a protective barrier, but rather the familiar flaky and brittle rust.  Products compared in this category include:

Dupont 5718S
Metal-Ready

 

Other Acids (besides phosphoric acid) can be used in rust treatments including hydoxyacetic acid, sulfamic acid, and hydrogen chloride.   Hydrogen chloride (hydrochloric or muriatic acid) gives the same two reactions as phosphoric acid with Cl in place of PO4, but in this case both of the reactions are relatively fast, so  the actual metal is lost at a rate similar to the rust.   Also, the FeCl3 produced does not adhere to the metal surface as well, so you get little protection of the treated metal surface.  Products compared in this category include:

Envirosolve 1000
CLR - Calcium Lime & Rust Remover

 

Conversion Coatings are applied over the surface of rust and, unlike the other treatments in this comparison, are left in place.  These products claim to covert the underlying rust to an inert substance and leave a black primer for further coatings.  I have found little chemistry to explain these products:

Extend
One-Step
Rust-X

 


Testing Method

One half of a rusted steel bar was wire brushed (with an power angle grinder) and cut into squares to produce pieces which looked like this:

untreated dry.jpg (15833 bytes)

This was done to compare each treatment's effect upon both "raw" rust and rust which was has been wire brushed. 

Typical Testing
Other than conversion coatings, each piece was full immersed for about 30 minutes.  Results were then photographed both dry and after wetting with water to improve clarity.  Each piece was then further immersed for about 2 hours and each piece was brushed manually with a small wire brush.  Results were then photographed dry.

Conversion Coating Testing
For conversion coatings, two coats were applied.  Half of the finished surface was scrapped to reveal the condition of the rust below.  This scrapping was done perpendicular to the original division of "raw" and wire brushed rust, to reveal the condition of the rust both in the "raw" and wire brushed areas.

all treating.jpg (52868 bytes) Click on this picture of testing underway to view full size

treated.jpg (225239 bytes)Click on this picture of final results of all products to see full size.


Comparison Results and Organization

A large table is used to organize information for each of the products compared.  The products are listed across the columns of this table.   The following information is listed down each of the rows:

Product Name
Manufacturer / Source
Cost
Cost per oz
Active Ingredients
(CAS numbers are included for reference elsewhere)
Characteristics
(pH and specific gravity)
Other Information (including manufacturer's description)
Product Name (repeated for reference)
Results after short treatment and no brushing- photographed dry
Results after short treatment and no brushing - photographed wet
Results after long treatment and brushing - photographed dry
Product Name (repeated for reference)
Untreated Comparison (right side was wire brushed before treatment; left side was left "raw")

My apologies, but the reader will need to do a bit of scrolling to see all the information. 

ELECTROLYSIS "FRIENDLY" ACIDS PLAIN PHOSPHORIC ACID BASED PHOSPHORIC ACID WITH ZINC OTHER ACIDS CONVERSION COATINGS
electrolysis.jpg (9659 bytes) Ecotec.jpg (7504 bytes) no picture
(comes in bulk crystals)
Rust-Mort.jpg (9016 bytes) MP-7.jpg (8807 bytes) Naval Jelley.jpg (11536 bytes) Dupont 5717S.jpg (7034 bytes) Mirachem 250.jpg (9764 bytes) Dupont 5718S.jpg (7025 bytes) Metal Ready.jpg (10554 bytes) Envirosolve 1000.jpg (7902 bytes) CLR.jpg (12725 bytes) Extend.jpg (13524 bytes) One Step.jpg (8483 bytes) Rust X.jpg (8551 bytes)
Product Name electrolysis Ecotec Simple Solutions Rust Remover Rust-Mort MP-7 Naval Jelly Dupont 5717S Mirachem 250 Dupont 5718S Metal-Ready Envirosolve 1000 CLR - Calcium Lime & Rust Remover Extend One-Step Rust-X Product Name
Manufacturer /
Source
homemade Singerman Laboratories
4091 Saltsburg Rd.
Murrysville, PA 15668
phone: 800-798-7986
web: http://www.essex3
.com/slabs/metlmain.htm
Simple Solutions 
R.R.5 Box 283G
Gravois Mills, MO 65037 phone:  573-374-1746
fax: 573-374-4972
SEM Products, Inc.
651 Michael Wylie Dr.
Charlotte, NC 28217
phone: 704-522-1006
Must for Rust Co.
PO Box 972
Cedar Ridge, CA 95924
phone: 916-273-8283
Loctite Corp.
(as Permatex)
phone: 800-loctite
Dupont, local distributors Mirachem Corp.
1045 S. Edward Dr.
PO Box 27608
Tempe AZ 85285
phone: 602-966-3030
fax: 602-966-0890
Dupont, local distributors Resto Motive Laboratories, Inc.
PO Box 1235
Morristown NJ 07962
phone: 800-457-6715
DHS Distributing Inc.
2602 Ryder Court
League City TX 77573
phone: 713-334-3959
fax: 713-334-1069
Jelmar
6600 N. Linciln Ave.
Lincolnwood, IL 60645

available at local hardware stores

Loctite
(as Permatex or Duro)
phone 800-loctite
Mar-Hyde Corp.
4677 Devitt Dr.
Cincinnati OH 45246
phone: 513-874-5151
phone: 888-MA-HYDE
Integrity Industries
PO Box 5342
Kingsville, TX 78383
phone 512-595-5561
iii@trip.net
Manufacturer /
Source
Cost very inexpensive $11.00 / 32oz
$25.00 / 128oz (gallon)
$110.00 / 5gallon
Company took my money, did not send product, and does not return calls. $10.6 / 16oz $6.00 / 24oz $3.50 / 8oz jelly unknown $6.40 / 32oz unknown $13.00 / 20oz $14.00 / 16oz $5.25 / 28oz $4.85 / 4oz liquid unknown unknown Cost
Cost per oz very inexpensive $0.34375 /oz $0.6625 /oz $0.25 /oz $0.4375 /oz unknown $0.2 /oz unknown $0.65 /oz $0.875 /oz $0.1875 / oz $1.2125 /oz unknown unknown Cost per oz
Active
Ingredients
Negatively 12VDC charged rusted object submersed in a bath of 1 tabelspoon household lye (sodium hydroxide HNaO (CAS 1310-73-2)) or washing soda (sodium carbonate CNa2O3 (CAS 497-19-8)) per 1 gallon water with a positively 12VDC charged sacrificial iron electrode. No ingredients listed on MSDS. Active ingredients said to be:

monosodium citrate C6H7NaO7 (CAS 18996-35-5); used elsewhere as buffer in solutions, emulsions, berverages and foodstuffs. [This information updated July 15, 2001]

citric acid C6H8O7 (CAS 77-92-9)

I assume citric acid based 40-45% phosphoric acid H3O4P (CAS 7664-38-2) ; used elsewhere in softdrinks, welding agents, semi conductors; pickling agents

isopropanol C3H8O (CAS67-63-0) 1-5%; used elsewhere in solvent and deicing agent

17.5% phosphoric acid H3O4P (CAS 7664-38-2) ; used elsewhere in softdrinks, welding agents, semi conductors; pickling agents

 

25-30% phosphoric acid H3O4P (CAS 7664-38-2) ; used elsewhere in softdrinks, welding agents, semi conductors; pickling agents

1-3% sulfuric acid H2O4S (CAS 7664-93-9); used elsewhere in batteries, leather delimer, metal leacher

1-3% isopropyl alcohol (CAS 67-63-0)

31% phosphoric acid H3O4P (CAS 7664-38-2) ; used elsewhere in softdrinks, welding agents, semi conductors; pickling agents

15% ethylene glycol monobutylether (CAS 111-76-2)

phosphoric acid in undisclosed concentration; H3O4P (CAS 7664-38-2) ; used in softdrinks, welding agents, semi conductors; pickling agents 7% phosphoric acid H3O4P (CAS 7664-38-2) ; used elsewhere in softdrinks, welding agents, semi conductors; pickling agents 

3% zinc oxide OZn (CAS 1314-13-2); used elsewhere in white pigment, photocopier sensitizer, drugs

nickel phosphate H3O4P32Ni (CAS 10381-36-9); used elsewhere in yellow pigment

phosphoric acid in undisclosed concentration; H3O4P (CAS 7664-38-2); used elsewhere in softdrinks, welding agents, semi conductors; pickling agents

zinc phosphate in undisclosed concentration; O8P2Zn3 (CAS 7779-90-1); used elsewhere in dental cements, white pigment

octylphenoxy polyethanol ethanol triphenol methane (scintillation surfactant) in undisclosed concentration (CAS 9036-19-5)

hydrogen chloride (hydrochloric acid) in undisclosed concentration; ClH  (CAS 7647-01-0); used elsewhere in steel pickling, swimming pools, rodenticide

proprietary blend undisclosed concentration

12-14% hydoxyacetic (glycolic) acid C2H4O3 (CAS 79-14-1); used elsewhere in household cleaners

3-5% sulfamic acid H3NO3S (CAS 5329-14-6); used elsewhere in swimming pool disinfecting and cleaning

3-5% citric acid C6H8O7 (CAS 77-92-9)

2-4% alkyl alcohol ethoxylate-acetate (CAS 68478-93-3)

2-4% proprietary detergent mixture

35-40% proprietary vinylidene-arcrylic copolymer 

5-10% barium sulfate (sulfuric acid) BaO4S (CAS 7727-43-7); used elsewhere in filler and whitener

1-3% 2-Butoxy ethanol  (CAS 111-76-2); colorless liquid used elsewhere in cleaners and as solvent

1-3% proprietary organic acid

45-50% acetone C3H6O (CAS 67-94-1); used elsewhere in solvent

40-45% dimethyl ether C2H6O (CAS 115-10-6) ;used elsewhere in solvent, aerosol propellant

5-10% 2-butoxy ethanol  (CAS 111-76-2)

proprietary mixture  undisclosed concentration

mineral acids

Active
Ingredients
Characteristics   pH = 3.7 to 3.9
specific gravity = 1.11
pH = no data
specific gravity = no data
pH = 2.5 - 2.8
specific gravity = 1.19
pH = no data
specific gravity 1.13
pH = 1.5-2.5
specific gravity = 1.2
pH = no data
specific gravity = no data
pH = 1.0 - 2.0
specific gravity = 1.105
pH = no data
specific gravity = no data
pH = no data
specific gravity = 1.115
pH 0.= 1 - 1.0
specific gravity = 1.060
pH = 1.45 - 1.6
specific gravity = 1.05 - 1.07
pH = 1.95
specific gravity = 1.202
pH = no data
specific gravity = no data
pH = no data
specific gravity = 1.08
Characteristics
Other Information Manufacturer's  Description: Surface of rust is left black Available in crystalline concentrate which costs less. Full immersion required unless cream form is used.

Manufacturer's   Description: Biodegradable; Contains no hazardous or highly corrosive mineral acids or toxic volatile acids, such as muriatic acid or phosphoric acid. Will not harm plastic, paint, glass, aluminum, copper, brass, nickel, chrome, ceramics, or glazed tile. Will, however, attack zinc, lead and tin alloys. Heat will speed process.

full immersion required

Manufacturer's   Description: bio-degradable, non-toxic

200.jpg (679 bytes)
Manufacturer's  Description:
Converts rust through an exclusive chemical process to an insoluble black coating
Manufacturer's  Description: MP-7 is designed to dissolve rusts and oxides from metal surfaces. Chemically, it reverses the rusting reaction and cleans away all oxidation from the metal. Also, minute crystals are formed that become integral with the surface molecules of the base metal, inhibiting further oxidation. These deposits are completely inert and do not change the tolerances or the conductivity of the metal. After the rust is dissolved and MP-7 has dried, the surface is ready for the next step, whether it be painting or welding Manufacturer's  Description: Neutralizes rust. Gently etches metal while simultaneously leaving a zinc phosphate film to promote chemical bonding. Available from
TAIOWA
1704 E. Main St.
Endicott NY 13760
phone: 607-785-6170
fax: 67-785-0520
email: taioa@spectra.net
web: http://www/spectra.net/~taiowa

Manufacturer's   Description: a serious, industrial-strength chemical, which, because it is chemically buffered, is safe, fumeless, and harmless to your kin when used according to all directions and your common sense

Recommended by Thom Fitzpatrick

Manufacturer's   Description: As seen on TV

Per John S. Henry johnshenry@sprintmail.com, liquid better than aerosol. Converts rust to black, inert substance which includes magnetite (Fe3O4) Manufacturer's  Description: Completely passivates the rust, chemically preventing it from participating in further corrosion. Each molecule of RUST-X can attract and incorporate several iron atoms, and each single iron atom can be linked to three different molecules within RUST-X. The result is that RUST-X envelopes the rust at the molecular level, developing into a neutral layer which exists between the steel surface and the atmosphere. The neutral layer prevents the migration of ions so that no chemical reaction can occur. Dispersible in water Comments
Product Name electrolysis Ecotec Simple Solutions Rust Remover Rust-Mort MP-7 Naval Jelly Dupont 5717S Mirachem 250 Dupont 5718S Metal-Ready Envirosolve 1000 CLR - Calcium Lime & Rust Remover Extend One-Step Rust-X Product Name
Results after short treatment and no brushing- photographed dry electrolysis big.jpg (34369 bytes) Ecotec 1 dry.jpg (18810 bytes) Simple Solutons 1 dry.jpg (15805 bytes)

no picture

 

MP-7 1 dry.jpg (18580 bytes) Naval Jelley 1 dry.jpg (20818 bytes) Dupont 5717S 1 dry.jpg (18498 bytes) Mirachem 250 1 dry.jpg (18494 bytes) Dupont 5718S 1 dry.jpg (18738 bytes) Metal Ready 1 dry.jpg (19528 bytes) Envirosolve 1000 1 dry.jpg (20273 bytes) CLR 1 dry.jpg (20681 bytes) Extend 1 dry.jpg (17459 bytes) One Step 1 dry.jpg (22497 bytes) Rust X 1 dry.jpg (12650 bytes) Results after short treatment and no brushing- photographed dry
Results after short treatment and no brushing - photographed wet Ecotec 1 wet.jpg (19000 bytes) Simple Solutons 1 wet.jpg (16176 bytes)

no picture

MP-7 1 wet.jpg (17018 bytes) Naval Jelley 1 wet.jpg (22538 bytes) Dupont 5717S 1 wet.jpg (19232 bytes) Mirachem 250 1 wet.jpg (14632 bytes) Dupont 5718S 1 wet.jpg (18689 bytes) Metal Ready 1 wet.jpg (17775 bytes) Envirosolve 1000 1 wet.jpg (21349 bytes) CLR 1 wet.jpg (20356 bytes) Extend 1 wet.jpg (13965 bytes) One Step 1 wet.jpg (21644 bytes) Rust X 1 wet.jpg (16152 bytes) Results after short treatment and no brushing - photographed wet
Results after long treatment and brushing - photographed dry electrolysis 2 dry.jpg (20286 bytes) Ecotec 2 dry.jpg (16836 bytes) Simple Solutons 2 dry.jpg (21069 bytes) no picture MP-7 2 dry.jpg (11850 bytes) Naval Jelley 2 dry.jpg (16140 bytes) Dupont 5717S 2 dry.jpg (14305 bytes) Mirachem 250 2 dry.jpg (17325 bytes) Dupont 5718S 2 dry.jpg (11558 bytes) Metal Ready 2 dry.jpg (14855 bytes) Envirosolve 1000 2 dry.jpg (13420 bytes) CLR 2 dry.jpg (16518 bytes) long duration treatment
not applicable
to conversion treatments
long duration treatment
not applicable
to conversion treatments
long duration treatment
not applicable
to conversion treatments
Results after long treatment and brushing - photographed dry
Product Name electrolysis Ecotec Simple Solutions Rust Remover Rust-Mort MP-7 Naval Jelly Dupont 5717S Mirachem 250 Dupont 5718S Metal-Ready Envirosolve 1000 CLR - Calcium Lime & Rust Remover Extend One-Step Rust-X Product Name
Untreated Comparison - right side was wire brushed before treatment; left side was left "raw" untreated dry.jpg (15833 bytes) untreated dry.jpg (15833 bytes) untreated dry.jpg (15833 bytes) untreated dry.jpg (15833 bytes) untreated dry.jpg (15833 bytes) untreated dry.jpg (15833 bytes) untreated dry.jpg (15833 bytes) untreated dry.jpg (15833 bytes) untreated dry.jpg (15833 bytes) untreated dry.jpg (15833 bytes) untreated dry.jpg (15833 bytes) untreated dry.jpg (15833 bytes) untreated dry.jpg (15833 bytes) untreated dry.jpg (15833 bytes) untreated dry.jpg (15833 bytes) Untreated Comparison - right side was wire brushed before treatment; left side was left "raw"

My Conclusions

The following are my conclusions and recommendations for treating rust that I use in my shop (no powdercoating, plating, or galvanizing facilities).  These are listed in order of my preference:

1 Sandblast - Sandblasting is by far the best method for treating rusted metal.  It leaves the metal very clean, although some micro rust my be left embedded deep in the surface.   It is also very easy.  There are some drawbacks including:
  • The surface has to be accessible to the blasting nozzle (not inside a door panel, or an inaccessible cranny for example).
  • The abrasive is very intrusive and will get everywhere.

A wire brush (either power or hand) will compliment any of the rust treatments, but will won't get all the rust.

 

2  Electrolysis - Electrolysis seemed to work just as well if not better than other chemical treatments, and since it is so inexpensive, it may be the way to go.  There are drawbacks here also:
  • The part must be full immersed, which can be a problem with large objects.
  • The surfaces you want to remove the rust from must be in direct line-of-sight with the anodes (again won't get inside a door panel unless you can put an anode in there without shorting the electrolyte).
  • I have tried electrolysis since conducting this comparison, and have ended up with a layer of black magnetite on the surface.  This is easily brushed off, but makes me wonder if I have something wrong or why sandblasting is not just as easy.

 

3  Friendly Chemicals - When I need to use acid treatments, I like to use the Ecotec.  It is a little more expensive, but it works very well and is friendly to use and dispose of.  In my experience, Simple Solutions is not a trustworthy business.

 

4  Plain Phosphoric Acid Based treatments - These all seemed to work pretty well.  Naval Jelly is useful where a jell is needed to cling to surfaces.  Dupont 5717S comes in a concentrated solution which should be diluted according to the manufacturer's directions.   I have used 5717S undiluted on though rust and it works very well, but it is nasty to work with.

 

5  Phosphoric Acid with Zinc - I would not use these as a rust treatment alone, since the concentration of phosphoric acid is less than the plain phosphoric acid based treatments.   However, when used after treatment with the plain phosphoric acid based chemicals, the zinc in these treatments may do some good.  The scary part is that directions indicate that the parts be cleaned with water after treatment.  Cleaning raw steel with water is not something that thrills me.  The steel seems to oxidize immediately, but this might just be the zinc that is oxidizing.

 

6  Other Acids - CLR seems to work okay and is pretty inexpensive.  I prefer the phosphoric acid since it leaves the iron phosphate residue.  I found no benefit for the Envirosolve 1000 (expensive and no residue).

 

7  Conversion Coatings - I do not "believe" in these treatments, and you must have faith to believe the manufacturer's claims.  They are supposed to "convert" the rust, but after using them, I have scrapped them off and found rust still there underneath.  If you think about it, these products dry in a matter of minutes.  How can this provide enough time for the product to penetrate into and convert the rust?

 


Nothing on this page should be construed as following scientific method.  These comparisons were done pretty much off the cuff in my shop.  Any conclusions or recommendations are purely my subjective opinion.

This page was found at the site http://EcologicArchitecture.com/SoloHobbit/ and was last updated on May 24, 2000 (and slightly revised since)by me,SoloHobbit@EcologicArchitecture.com