The Ford Barn

Charles Reese · 01-03-2011, 10:31 PM

Don’t have ready access to media blasting so am considering degreasing with solvent and then soaking some small cast iron pieces (i.e. water inlet/outlet, etc) in acid prior to painting. Am I correct that muriatic acid is more aggressive than phosphoric?

marc hildebrant · 01-03-2011, 10:49 PM

Muriatic is an unrefined version of HCL or Hydrochloric Acid. It is stronger than phosphoric. Check the label on Coke...contains phosphoric acid.

HCL will not attack copper and some other metals.

Marc

Craig Lewis · 01-04-2011, 01:45 AM

Charles in my opinion I wouldn't use the muriatic because it's difficult to flush away and nautralize... an even bigger problem given the porous nature of old cast iron. You'd likely end up with the pieces turning very rusty over the ensuing weeks, right through the paint... as that nasty muriatic leachs out!

Phosphoric will clean the cast well and is more forgiving, although getting a good "etched" surface that will promote adhesion to primer & paint takes some experimenting.
Basically I would use phosphoric and a stiff brush to clean...flush with a thinner diluted mixture & blowgun dry. Next, get them in front of a heater & watch the cast dry up as it warms. Do a final scower with a fine bristle brush(wire) to remove any residual acid powder...a scotbrite pad works OK too...then dust on a very thin coat of etching primer, let primer dry & then paint while still warm so as it flows out nice and thin ...2 coats would be good ...then let it bake for a while and set up.

I sometimes lay a cardboard box on it's side and point a ceramic cube heater inside, then line up all your little pieces on "the stage" and let er cook with the box as a backstop.

Mike V. Florida · 01-04-2011, 02:13 AM

How about http://www.evaporust.com

Bick in New Zealand · 01-04-2011, 02:17 AM

Charles, watch out with the phosphoric, I used to use a phosphoric tank very successfully to remove rust etc. I did however have a couple of disasters, one was with a carb. and the other with an inlet manifold. I think I left them in the solution a little too long. Both became so soft you could scrape the metal with your fingernail and leave a mark. Someone told me afterwards phosphoric removes the carbon from cast iron.

pooch · 01-04-2011, 05:02 AM

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If you cannot blast, I would suggest wire brush and paint.

Cast iron does not get black rust like steel does.

Wire brush will see you out and your grandkids.

Acid will leach into the cast pores.

Kevin in NJ · 01-04-2011, 06:59 AM

Muriatic acid leaves behind chlorine atoms that will recombine into hcl. This will cause rust to form later even under paint.

You are much better off looking up electrolytic rust removal and try to get some carbon electrodes. Other choices include molasasis and evaporust type products. These methods are safe and hard to mess up.

Electolytic rust removal will also fully remove the cl ions left behind from muriatic acid.

Richard Lorenz · 01-04-2011, 10:30 AM

Ditto Bick's experience with softening the cast iron if left in HCl too long. A short time might be O.K. Neutralize the acid remaining in the part. Give it plenty of time. There should be no odor if fully neutralized.

RonC · 01-04-2011, 11:05 AM

soak greasy parts in simple green pro HD from homedepot. http://www.simplegreen.com/products_pro_hd.php. Them wash in bucket filled with hot soapy water (dish detergent). If you have rust soak in evaporust (available at harbor freight). Wire brush clean and paint. You can buy a wire brush for a drill at homedepot.

Cool Hand Lurker · 01-04-2011, 11:44 AM

Don't use muriatic acid on cast iron. I did, but only once! After a couple of days I took the cast iron out of the solution and it literally crumbled in my hand. I also tried muriatic acid on a 1" hot rolled square shaft and when I took it out of the solution there were channels eaten away in the shaft. It looked like termites were at work. Now I only use phosphoric acid or the electrolytic method, but mostly the electrolytic method with a final wash in phosphoric just to take care of any surface rust.

Richard in Anaheim CA · 01-04-2011, 01:43 PM

Phosphoric acid is safer and also leaves a deposit of phosporus on the metal which is similar to Ford's original bondorizing process.

I buy mine in the Home Depot paint department. It is labeled "metal prep". It leaves a deposit you may think is rust but it isn't. Leave the coating on and paint right over it. Don't let it sit around. I'm sure it would rust eventually. Never had a problem with it "yet".

Richard
Anaheim CA

01-03-2011, 10:31 PM	#1
Charles Reese Senior Member Join Date: May 2010 Location: Richmond, VA Posts: 882	Acid Cleaning of Cast Iron Don’t have ready access to media blasting so am considering degreasing with solvent and then soaking some small cast iron pieces (i.e. water inlet/outlet, etc) in acid prior to painting. Am I correct that muriatic acid is more aggressive than phosphoric?

01-03-2011, 10:49 PM	#2
marc hildebrant Senior Member Join Date: May 2010 Location: Cape Cod Posts: 1,128	Re: Acid Cleaning of Cast Iron Muriatic is an unrefined version of HCL or Hydrochloric Acid. It is stronger than phosphoric. Check the label on Coke...contains phosphoric acid. HCL will not attack copper and some other metals. Marc

01-04-2011, 01:45 AM	#3
Craig Lewis Senior Member Join Date: May 2010 Location: Parksville B.C. Canada Posts: 880	Re: Acid Cleaning of Cast Iron Charles in my opinion I wouldn't use the muriatic because it's difficult to flush away and nautralize... an even bigger problem given the porous nature of old cast iron. You'd likely end up with the pieces turning very rusty over the ensuing weeks, right through the paint... as that nasty muriatic leachs out! Phosphoric will clean the cast well and is more forgiving, although getting a good "etched" surface that will promote adhesion to primer & paint takes some experimenting. Basically I would use phosphoric and a stiff brush to clean...flush with a thinner diluted mixture & blowgun dry. Next, get them in front of a heater & watch the cast dry up as it warms. Do a final scower with a fine bristle brush(wire) to remove any residual acid powder...a scotbrite pad works OK too...then dust on a very thin coat of etching primer, let primer dry & then paint while still warm so as it flows out nice and thin ...2 coats would be good ...then let it bake for a while and set up. I sometimes lay a cardboard box on it's side and point a ceramic cube heater inside, then line up all your little pieces on "the stage" and let er cook with the box as a backstop.

01-04-2011, 02:13 AM	#4
Mike V. Florida Senior Member Join Date: May 2010 Location: South Florida Posts: 14,054	Re: Acid Cleaning of Cast Iron How about http://www.evaporust.com __________________ What's right about America is that although we have a mess of problems, we have great capacity - intellect and resources - to do some thing about them. - Henry Ford II

01-04-2011, 02:17 AM	#5
Bick in New Zealand Senior Member Join Date: May 2010 Location: Napier New Zealand Posts: 931	Re: Acid Cleaning of Cast Iron Charles, watch out with the phosphoric, I used to use a phosphoric tank very successfully to remove rust etc. I did however have a couple of disasters, one was with a carb. and the other with an inlet manifold. I think I left them in the solution a little too long. Both became so soft you could scrape the metal with your fingernail and leave a mark. Someone told me afterwards phosphoric removes the carbon from cast iron.

01-04-2011, 05:02 AM	#6
pooch Senior Member Join Date: Sep 2010 Location: South Coast NSW Australia Posts: 2,596	Re: Acid Cleaning of Cast Iron Sponsored Links (Register now to hide all advertisements) If you cannot blast, I would suggest wire brush and paint. Cast iron does not get black rust like steel does. Wire brush will see you out and your grandkids. Acid will leach into the cast pores.

01-04-2011, 06:59 AM	#7
Kevin in NJ Senior Member Join Date: May 2010 Location: South East NJ Posts: 3,398	Re: Acid Cleaning of Cast Iron Muriatic acid leaves behind chlorine atoms that will recombine into hcl. This will cause rust to form later even under paint. You are much better off looking up electrolytic rust removal and try to get some carbon electrodes. Other choices include molasasis and evaporust type products. These methods are safe and hard to mess up. Electolytic rust removal will also fully remove the cl ions left behind from muriatic acid.

01-04-2011, 10:30 AM	#8
Richard Lorenz Senior Member Join Date: May 2010 Posts: 447	Re: Acid Cleaning of Cast Iron Ditto Bick's experience with softening the cast iron if left in HCl too long. A short time might be O.K. Neutralize the acid remaining in the part. Give it plenty of time. There should be no odor if fully neutralized.

01-04-2011, 11:05 AM	#9
RonC Senior Member Join Date: May 2010 Location: Rhode Island Posts: 1,868	Re: Acid Cleaning of Cast Iron soak greasy parts in simple green pro HD from homedepot. http://www.simplegreen.com/products_pro_hd.php. Them wash in bucket filled with hot soapy water (dish detergent). If you have rust soak in evaporust (available at harbor freight). Wire brush clean and paint. You can buy a wire brush for a drill at homedepot.

01-04-2011, 11:44 AM	#10
Cool Hand Lurker Senior Member Join Date: May 2010 Location: So Minn Posts: 1,565	Re: Acid Cleaning of Cast Iron Don't use muriatic acid on cast iron. I did, but only once! After a couple of days I took the cast iron out of the solution and it literally crumbled in my hand. I also tried muriatic acid on a 1" hot rolled square shaft and when I took it out of the solution there were channels eaten away in the shaft. It looked like termites were at work. Now I only use phosphoric acid or the electrolytic method, but mostly the electrolytic method with a final wash in phosphoric just to take care of any surface rust.

01-04-2011, 01:43 PM	#11
Richard in Anaheim CA Senior Member Join Date: May 2010 Location: Anaheim California Posts: 551	Re: Acid Cleaning of Cast Iron Phosphoric acid is safer and also leaves a deposit of phosporus on the metal which is similar to Ford's original bondorizing process. I buy mine in the Home Depot paint department. It is labeled "metal prep". It leaves a deposit you may think is rust but it isn't. Leave the coating on and paint right over it. Don't let it sit around. I'm sure it would rust eventually. Never had a problem with it "yet". Richard Anaheim CA