Stripping paint from Cast iron radiators using a lye bath

branimal

I've got a few a 1-way steam radiators that sorely need a new paint job. I've read here and elsewhere that I can give them a lye bath prior to painting. I have some large plastic cement mixing bins. One for lye solution, one for a clean rinse.

I can plug the air vent (1/8 brass plugs) and main valve with black plugs. And drop them into the lye bath.

One issue is I have to do this indoor b/c two of the four radiators are absolute monsters. I can't get them down safely even with a handtruck.

Can I do this indoors on a job site? The floors are subfloors and I can leave them in a room that is well ventilated. And setup fans to exhaust the fumes.

Thanks!

PC7060

I don't have any experience with lye bath. I had my radiators sandblasted and powder coated, came out great. These were heavy monsters too, used movers to get them them in and out. The movers use lift straps and were very efficient.

mattmia2

Lye will remove the paint. If there is any rust it won't remove that. Powder coat will be a lot more durable than any paint you can apply in the field. I would be as concerned with spilling or dripping lye indoors as with the fumes. If you spill it, you need to clean it up so you don't get chemical burns or burn other things. It might be something better left to someone with the equipment and space.

Jamie Hall

Allow me to be a bit more forceful than @mattmia2 . Lye is flat out dangerous to work with. You must -- no shortcuts -- wear heavy chemical resistant gloves, a water repellent if not waterproof bunny suit, and at least splash proof goggles (though I would recommend a full face respirator).

Back in the bad old days the mafia used it to get rid of bodies they didn't want to ever turn up. For all I know, they still do. It works fast.

Further, as @mattmia2 mentions, it won't take care of any rust.

I have painted a number of radiators -- quite successfully. Wire brush to get rid of all the loose rust. Use a top quality primer (Benjamin Moore makes one) and then use a top quality acrylic paint (again, I use Benjamin Moore, but Sherwin-Williams makes a first class product, too). Don't skimp. Quality paint costs more -- and is well worth it. You don't want to do it over 10 years down the line.

ethicalpaul

Do you use a chemical rust converter for such tasks, @Jamie Hall ? Does it help to delay the rust from returning?

branimal

Jamie Hall said:

Allow me to be a bit more forceful than @mattmia2 . Lye is flat out dangerous to work with. You must -- no shortcuts -- wear heavy chemical resistant gloves, a water repellent if not waterproof bunny suit, and at least splash proof goggles (though I would recommend a full face respirator).

Back in the bad old days the mafia used it to get rid of bodies they didn't want to ever turn up. For all I know, they still do. It works fast.

Further, as @mattmia2 mentions, it won't take care of any rust.

I have painted a number of radiators -- quite successfully. Wire brush to get rid of all the loose rust. Use a top quality primer (Benjamin Moore makes one) and then use a top quality acrylic paint (again, I use Benjamin Moore, but Sherwin-Williams makes a first class product, too). Don't skimp. Quality paint costs more -- and is well worth it. You don't want to do it over 10 years down the line.

I have everything you listed in terms of safety (chemical gloves, goggles, and a respirator with vapor filters). Unfortunately I don't have the tyvek/bunny suit. Going to see if my local HD got some back in stock. If not, there is a contractor safety equipment shop nearby.

I'll pick up some rust remover.

How soon after I strip one and clean it do I need to prime it? I take it you're not a fan of rustoleum primer. I have some on hand I was going to use with my HVLP spray gun. Will look around for a Ben Moore dealer near me.

I've read guys aren't using high heat paint on radiators b/c of the off-gassing. With an acrylic paint should I use an oil based paint?

Thanks!

Hap_Hazzard

I've used Rust Oleum high heat paint on a bunch of radiators and never had any "off-gassing" problems. I think the automotive paint for engine blocks smells bad when it gets hot, but the regular high heat paint is fine.

branimal

Started the lye bath. took 6 gallons of water to get the water level to the halfway point on the radiator. I poured in 1lb of lye to start. Wondering if more lye is required.

Going to check the water temp with a temp gun.

Beer o'clock.

Will keep you posted.

EdTheHeaterMan

If we don't hear from @branimal by Friday, someone should contact his Next-of-kin.

Jamie Hall

He's a braver man than I am...

Big Ed_4

branimal

Things went great. I didn't add more lye b/c it was working within 30 minutes. Flipped the radiator after 5 hours and let it sit overnight. It looks like the rad is down to bare metal. It kind of looks like hot rolled steel. Greying and bluing. Part of me wants to clear coat it and call it done.

There is some minor rusting in certain areas. I've got rust remover spray and wire wheels, rust remover discs for my grinder etc. Electrolysis is another option I'm considering to remove the rust.

I'm going to transfer the clean rad to a washing bin and drop another rad into the used lye bath. Hopefully it still has some punch.

My local HD only had 2 decent rustoleum colors. Flat black and hammered black. I like the gun-metal color. Will keep looking for it. Or maybe I'll clear coat it.

What can I do to prevent new surface rust before I paint it?

Here are some before & after pics.

mattmia2

Spray it with a metal primer, the gray rustoleum should be fine for metal in that condition. Could also use automotive primer.

EdTheHeaterMan

if you don't want a color, you can spray with lubricating oil. This will retard the rusting process, but you will need to thoroughly clean the oil off the metal before you start to paint or clear coat. Store the oiled metal indoors out of the weather. A garage or basement is fine. moisture is a problem, temperature not so much.

dopey27177

nice job. Dan has an article about painting radiatore and color combinations, read before you paint.

Jake

branimal

dopey27177 said:

nice job. Dan has an article about painting radiatore and color combinations, read before you paint.

Jake

Interesting article. I'm going either satin black or metallic black.

With the cost of used radiators now, I wonder why people don't downsize their radiators if they're overheating vs building a radiator cover. I suppose it could cause issues b/c now the boiler is becoming too large for the radiator's it is supplying.

Here's the painting link for others to check it out:

https://www.supplyht.com/articles/101777-dan-holohan-metal-paints-and-radiators

Joe_Dunham

If you want to shrink the radiators, You'd be surprised how easy you can separate the sections with hardwood a wedge top and bottom. Thats if you want to make the radiator smaller. You just have to hope the push nipples wind up where you want them. If you heat the section top and bottom where you want the nipples to come out of you have a better chance. Then use a light smear of red RTV to re-assemble.

ethicalpaul

The easiest way to shrink a radiator is to put a blanket on it.

But to address @branimal 's query about people getting smaller radiators, I have done it. My massive living room one failed and I replaced it with a smaller one from Craigslist. But it's a hassle and a backbreaker that very few homeowners are willing to take on. And it doesn't seem to be something that many of them think is worth putting money into.

mattmia2

You can always add a thermostatic valve to the vent to keep it from heating if the room is too hot, possibly more expensive but certainly much easier and less risky than trying to resize the radiator.

SteamCoffee

Lye is great stuff, use it properly! It’s a wonderful paint stripper, use Phosphoric Acid on rust (Ospho is a good product). You’ll need about a 1lb per 5 gallons min. Heat will make it work much faster, about 4 times, as will agitation. After you remove it, it needs a ton of rinsing. The it will start rusting, use cold water for this, seems to give me more time. Afterwords, I use Acetone Rinse as it cleans everything thing up nice and absorbs water. Flash rusting can be quickly treated with Phosphoric, let it dry overnight. I prefer oil based primers and top coats, Benjamin Moore makes great primers and Impervo topcoat is top shelf stuff. I have safely used Lye for cast iron engine blocks, gear boxes, Pans and a host of other things. It’s a do all chemical. PLEASE exercise caution and follow basic safety procedures, your eyes will be the most vulnerable, I use swimming goggles as I’d lose my job AND my eyesight if I screw it up! I use white vinager to neutralize. Ps, don’t use on aluminum etc. take some pics of the finished product.

branimal

I’m preparing to strip my larger radiators for which I bought 1 1/2” black plugs. The size seems close but not quite right. Do these old rads use a slightly different thread size?

(My smaller radiators were plugged with 1 1/4” plugs.)

mattmia2

is that the tapping in the radiator or the spud for the union on the valve?

branimal

I’m trying to thread the plug into the union pictured below. Is there an easier way to seal the rad?

Thanks

EdTheHeaterMan

can't use a plug on a union! you need to remove the spud. here is the tool needed.

try heating with a torch before removing the spud.

branimal

EdTheHeaterMan said:

can't use a plug on a union! you need to remove the spud. here is the tool needed.

try heating with a torch before removing the spud.

Ah a spud wrench. I read a lot of bad reviews on the HD version of the tool. What are my chances of breaking it free without a) breaking the tool inside the radiator & b) cracking my radiator?

I'll heat it up first.

Another option is trying a test plug like this:

https://www.homedepot.com/p/Oatey-1-1-2-in-Gripper-Plastic-Mechanical-Test-Plug-33400/100342630

Thanks Ed.

mattmia2

I think the most likely adverse outcome is shearing the lugs off of the spud that it grabs on to or otherwise damaging the spud.

mattmia2

If you can find the right kind of synthetic rubber to be compatible with lye, you could just seal it up with a rubber expansion plug.

branimal

SteamCoffee said:

Lye is great stuff, use it properly! It’s a wonderful paint stripper, use Phosphoric Acid on rust (Ospho is a good product). You’ll need about a 1lb per 5 gallons min. Heat will make it work much faster, about 4 times, as will agitation. After you remove it, it needs a ton of rinsing. The it will start rusting, use cold water for this, seems to give me more time. Afterwords, I use Acetone Rinse as it cleans everything thing up nice and absorbs water. Flash rusting can be quickly treated with Phosphoric, let it dry overnight. I prefer oil based primers and top coats, Benjamin Moore makes great primers and Impervo topcoat is top shelf stuff. I have safely used Lye for cast iron engine blocks, gear boxes, Pans and a host of other things. It’s a do all chemical. PLEASE exercise caution and follow basic safety procedures, your eyes will be the most vulnerable, I use swimming goggles as I’d lose my job AND my eyesight if I screw it up! I use white vinager to neutralize. Ps, don’t use on aluminum etc. take some pics of the finished product.

Finally getting around to posting some pics.

I used a Rustoleum rust remover spray on gel (phosphuric acid). and followed the directions - to wash it off fairly quickly 10-30 minutes after application. The stuff did not want to wash off. I ended up using wire wheels on my drill to get it off. I might setup an electrolysis tank for the next set of radiators.

The bedroom radiators were primed with a Rustoleum primer and painted with oil based satin black. I used thinned the paint 5:2 with acetone. They came out ok. Wish they weren't so shiny but I'd be complaining if they were matte black as well. So overall happy with the results.

For the next set of rads in my living space I might venture out and try BM or SW paint for the wider selection of colors. Maybe a gun metal grey. I'll also add some enamel hardener to the mix to get the paint a bit more durable and decrease drying time.

ethicalpaul

branimal said:

EdTheHeaterMan said:

can't use a plug on a union! you need to remove the spud. here is the tool needed.

try heating with a torch before removing the spud.

Ah a spud wrench. I read a lot of bad reviews on the HD version of the tool. What are my chances of breaking it free without a) breaking the tool inside the radiator & b) cracking my radiator?

I'll heat it up first.

Another option is trying a test plug like this:

https://www.homedepot.com/p/Oatey-1-1-2-in-Gripper-Plastic-Mechanical-Test-Plug-33400/100342630

Thanks Ed.

The odds are zero that the spud wrench will successfully remove the spud. I wouldn't even bother, but the wrench is good for installing a new spud. Like @mattmia2 said, what will happen is the spud's little ear things will shear off. They can't handle the force of removing an ancient spud.

Here is how to get a spud out of a radiator:

https://www.youtube.com/watch?v=NpaezIzl3hg

Note that he is removing a nipple, but it's just the same as removing a spud. Cut off the end just like he did, then get in there and make 2 cuts, definitely avoiding the threads!

It's better to not cut all the way through than it is to hit the threads, but I will tell you that anyone who has done this has definitely hit the threads a little. But when you do, don't panic. Unless you really cut through them the cut will seal up when you tape and/or dope it. I've removed 4 spuds in my house this way and I've never FUBAR'd it yet.

Also don't have your radiator on a rolling cart like he has when you are pounding on it!

Joe_Dunham

Before you cape it out like shown in the video, first try striking the spud with a hammer. hit it hard (dont be afraid) several times as if driving it into the radiator. Then either push the nut back and grab the end of the spud with a small pipe wrench (or use a spud wrench) and a helper. This has always worked for me. If you decide to heat it, heat the radiator not the spud.

mattmia2

Note that if you damage the spud you will have to replace the valve unless you can find an identical replacement, they are not standardized, they are specific to the valve they mate to.

Alan Welch

Cut off the nut , then use a wrench to back out the remainder from the radiator.

branimal

Stripped my 2 large radiators down to the metal using a custom sized bath. 2x10s with an old piece of shower liner. Had to enlist a buddy to move the radiators around.

I ended up pumping the lye water out into buckets. I'm hoping the solution will maintain it's alkalinity so I can use it on the next set of radiators 2-3 months from now. I know that sounds cheap but that was about $35 worth of lye. My buckets are free (paint, joint compound buckets) and so is storage.

I removed most of the accessible rust with a wire wheel on my drill.
Was considering using a wire wheel grinder attachment, But I think that might mar up the surface of the radiator.

Going to paint them today with Benjamin Moore Satin Impervo oil -alkyd paint. Gunmetal. Pretty excited. Ben Moore says not to thin the paint coming out of the spray gun. Anyone have experience thinning this paint?

Canucker

If you can store your solution in an airtight container it should be able be stored without much degradation for a long time

SteamCoffee

You should use BM’s oil based primer, (024?) first. The statement about not thinning is because BM is getting around regulations concerning VOC emissions. Dulamel (sp) enamel was BM’s best enamel ever, but banned by VOC REGS. Use Ospho LIGHTLY and rinse with acetone. Other stuff leaves a residue. Electrolysis is better than lye, if your imaginative enough, you could get de rusting of the inside of the rad.