# Rusted metal roof



## jacobs

I have three jobs coming up that are metal roofs, with rust, and all three customers made similar comments: "that roof was painted 6 years ago, but it looked like that a year after the guy painted it". My sales pitch was that I would wire brush the rust, coat it with SW KembondHS, and then use SW DTM. Claiming that it should last much longer than their previous paint job. The other option I offered was to use an elastomeric coating. So then I go back to my local network of painters and SW rep and I get ten different descriptions of what I could do, what I should use and how long I could expect it to last before re rusting/peeling off. I prefer to use paint instead of elastomeric but I also prefer to not come back next year. Any comments/advice much appreciated.


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## Epoxy Pro

I have not done any metal roofs. Would a rust converter work? I would think a rust converter or sand/soda blaster.


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## Delta Painting

Sand\ wire brush, then use penatrol too seal rust top with the coating of your choice...


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## straight_lines

cdpainting said:


> I have not done any metal roofs. Would a rust converter work? I would think a rust converter or sand/soda blaster.


I agree that looks like one that needs blasting to get any longevity out of a new coating. House also looks pre 73 and there is a good chance there is lead there.


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## mudbone

Similar situation awhile back and had sw rep take a look at it and what he recommended. Turned out the price for their products were higher then a new metal roof!


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## journeymanPainter

To do the job properly, yes the materials will probably cost more than getting a new roof (especially if you use BM, or SW). This is always something I've wanted to get into because there are probably 60-80 farms between me and the city.

Wire brush (go with a wire wheel on a grinder), rust inhibitive primer (or red oxide primer), then I personally would use a high build DTM primer, then your top coats.

I don't think an elastomeric coating will do anything for you or the owner.

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## jacobs

Thanks, I got two of the three jobs and have one more estimate to prepare today. On this last job its a metal shingled roof (not the picture above)that roofing companies already priced there solution out of his range which was about the same as my on site quote of $3500 which I thought was competitive. I told him if he wanted to drop the price a thousand I could just wire brush it and paint with DTM but it probably wouldn't last two years and that I try to do things to make my jobs last a good ten years (not warrantied for that long of course) but that I try to produce high quality work. Ive been pretty steady 4 years now so I don't really need to low ball or take slop jobs. Im starting to get more calls for metal roofs and am trying to learn some of the options, like when do I coat a roof with roofing products instead of DTM, what is the situation that makes the difference, for pitched metal roofs with rust, My big question is what do I use to make it last ten years plus? Is the three product method that you mentioned going to make it last that long if prepped and applied properly?


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## Lambrecht

Corotech 100% Solids Pre-Prime V155. This is a 2-part epoxy clear primer that encapsulates the rust and will not allow it to grow anymore. Coverage is approximately 1200 sq Ft per gallon. This is the only product I will use on heavily rusted exterior surfaces. I first used it on a heavily rusted scaling airplane hanger where the only prep work was pressure washing then topcoated with PPG industrial DTM. 3 years have past and no sign of any rust and the topcoat still looks freshly painted. I have also used it on many smaller buildings and have not had a single failure. Benjamin Moore carries it or can get it for you.


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## Jmayspaint

I have had the best luck on rusty roves using red oxide primer, and top coating with DTM. Rustolem Rusty Metal primer works really well, or Khem Kromic if you want something more heavy duty. 

Something to look out for on those old metal shingle roves is that some of them are made from passivated galvanized metal. A copper sulfate test will show if the metal is passivated or not. If it is, extreme measures have to be taken to get any coating to stick. 

This is a passivated shingle roof I ran into that was peeling horribly. The blue crystals are copper sulfate. On a regular galvanized roof, copper sulfate dissolved in water will cause a reaction than leaves a black residue on the surface. No black residue means the galvanized has been passivated.


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## jacobs

How have you applied the corotech ? have you ever sprayed it?


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## kentdalimp

You can either fix the problems (blasting the rust off) or try and cover it up. The Problem with fixing it is the price will be high.

Other have suggested encapsulation. We've had good luck with Amerlock sealer as a primer. Just make sure and coat everything. Then you can topcoat with almost anything. (Latex, etc.) Should hold up for 5+ years if you cover all the rust well.

Look into Noxyde by Rustoleum (mathys) haven't used it but have really been looking for an excuse to.

Good luck!


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## Paint it Now

Hand scrape, wire brush loose coating. Rinse. Two full coats non fibered asphalt aluminum roof coating. Highly reflective, attractive and will encapsulate the rust. Will not peel if the loose coating is removed and will Last.


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## journeymanPainter

jacobs said:


> Thanks, I got two of the three jobs and have one more estimate to prepare today. On this last job its a metal shingled roof (not the picture above)that roofing companies already priced there solution out of his range which was about the same as my on site quote of $3500 which I thought was competitive. I told him if he wanted to drop the price a thousand I could just wire brush it and paint with DTM but it probably wouldn't last two years and that I try to do things to make my jobs last a good ten years (not warrantied for that long of course) but that I try to produce high quality work. Ive been pretty steady 4 years now so I don't really need to low ball or take slop jobs. Im starting to get more calls for metal roofs and am trying to learn some of the options, like when do I coat a roof with roofing products instead of DTM, what is the situation that makes the difference, for pitched metal roofs with rust, My big question is what do I use to make it last ten years plus? Is the three product method that you mentioned going to make it last that long if prepped and applied properly?


Epoxy

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## painter213

Journeymanpainter, epoxy on a metal roof would crack and make it leak worse than it was in the beginning. Epoxy coatings are too rigid and lack the elongation needed for a metal roof. Metal roofs have a lot of movement and would cause the epoxy to crack and sheer. Someone above mentioned aluminum asphalt roof coating. For a inexpensive repair that just cannot be beat. I've seen them last for many years. That's what I would suggest.


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## Paint it Now

Check it out http://www.karnakcorp.com/images/PDF/28.pdf


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## journeymanPainter

painter213 said:


> Journeymanpainter, epoxy on a metal roof would crack and make it leak worse than it was in the beginning. Epoxy coatings are too rigid and lack the elongation needed for a metal roof. Metal roofs have a lot of movement and would cause the epoxy to crack and sheer. Someone above mentioned aluminum asphalt roof coating. For a inexpensive repair that just cannot be beat. I've seen them last for many years. That's what I would suggest.


Sorry but you are 100% wrong (please note, all read was about how epoxy on a metal roof will crack). 

I know this because I sprayed epoxy on a METAL roof of the Best Western in Abbotsford BC, and Langley BC. The roofs went from green to black as well

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## mustangmike3789

i think that some epoxy coatings can withstand the movement of a metal roof depending on the type of epoxy but they will need to be top coated to keep it from chalking. I wouldn't put epoxy direct to the galvanized surface because the reaction from the alkaline levels in the zinc and the esters in the epoxy can cause saponification especially in humid environments.


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## painter213

journeymanPainter said:


> Sorry but you are 100% wrong (please note, all read was about how epoxy on a metal roof will crack).
> 
> I know this because I sprayed epoxy on a METAL roof of the Best Western in Abbotsford BC, and Langley BC. The roofs went from green to black as well
> 
> Sent from my SGH-T989D using PaintTalk.com mobile app


Spraying a true epoxy on a roof and it actually working is two different subjects. I know of a lot of people that have used different coatings on different substrates all the time. Do they actually work? I'll just say that I get paid a lot for performing consulting and failure analysis work. When we say epoxy, are we actually talking about a true epoxy "Polyamide Epoxy, Polyamine Bisphenol Epoxy or Novalac Epoxy" or are we talking about what I would call a Epoxy Hybrid such as a Epoxy Siloxane? A epoxy siloxane is labeled as an epoxy but it actually has an amount of polyurethanes in the chemistry. 

A TRUE Epoxy does not have good elongation nor is it UV stable. Just because it may be labeled as being a epoxy material, does not make it a epoxy material. Some people think that just because the material is a two component material, that it makes it a epoxy. WRONG!! 

Yes, there is roof coatings out there that claim to be epoxy's, but when you get down to the actual chemistry of the formulation, they are in fact a polyurethane elastomeric coating that has been labeled as an epoxy. The chemistry will have very little epoxy chemistry in fact. I do not know of any true epoxies that is UV stable. 

So, if you take a true epoxy, let's say a polyamide type epoxy and apply it to a metal roof. With the expansion and contraction of such said roof, in time the epoxy will begin to crack and fail in all of the joints and attachments "screws" due to the movement of the roof.

Benny "Benjy" Abbott
Abbott Consulting & Coating Inspections


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## painter213

mustangmike3789 said:


> i think that some epoxy coatings can withstand the movement of a metal roof depending on the type of epoxy but they will need to be top coated to keep it from chalking. I wouldn't put epoxy direct to the galvanized surface because the reaction from the alkaline levels in the zinc and the esters in the epoxy can cause saponification especially in humid environments.


 We specify epoxy over zinc all the time Mike. I've never heard of saponification between an epoxy and zinc. Now if you apply an Alkyd coating over a zinc or concrete substrate then yes, you will have saponification to occur, but I have never seen or heard of it happening between a zinc and epoxy coating before. Do you have any instance's of this happening? 

Benny "Benjy" Abbott
Abbott Consulting & Coating Inspections


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## mustangmike3789

painter213 said:


> We specify epoxy over zinc all the time Mike. I've never heard of saponification between an epoxy and zinc. Now if you apply an Alkyd coating over a zinc or concrete substrate then yes, you will have saponification to occur, but I have never seen or heard of it happening between a zinc and epoxy coating before. Do you have any instance's of this happening?
> 
> Benny "Benjy" Abbott
> Abbott Consulting & Coating Inspections


yes you are correct. we have done epoxy over galvanized metal also depending on the "type" of epoxy used, but as you said, some epoxy is more of a modified urethane and not a "true" epoxy. 

some epoxy esters used are basically an oil based paint with epoxy resins used which when applied over galvanized metal (zinc) will saponify. I have applied cycloaliphatic amine epoxy over galvanized steel several times without any problems but I don't think that it would hold up on a metal roof because of the reasons that you mentioned earlier.


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## painter213

Correct, epoxy esters are not real epoxies. Basically an alkyd with a hint of epoxy resin added. Not much better that a plain alkyd system and not a true epoxy either and should never be applied to an galvanized or concrete substrate.


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## mustangmike3789

just to clarify, we do the zinc, epoxy, urethane systems on bridge coating all of the time. even some polyurethanes can not be applied directly to zinc because of the type of oils used, this is why an epoxy tie coat or intermediate coat is sometimes specified. 
saponification can happen with all types of coatings such as epoxy esters, linseed oil paints, alkyd esters and some PVA latex can be affected. some modified alkyds have been designed to resist saponification even when applied over zinc or hot concrete with a high pH level.


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## eligoldman

First remove the rust with sandblaster and then wash it with detergent.Then paint the roof and then coat it with corrosion resistant lubricant.This method has been shared by a roofing contractor a few months ago.I hope you will surely like this method.


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## DEK Painting inc.

1. first clean the roof 2. cover everything down below with old drop cloths especially if their is concrete , ospho will eat through it . 3. apply ospho to all rust 3. wait 3-4 days and sweep roof to remove any white residue 4. apply rustoleum heavy rust primer 5. coat with zinsser 123 primer 6. topcoat with elastomeric roof coating !


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## christysk

You can consult with your roofer friends.


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## mDUB562

I think it is important to remember that there are plenty of systems that work 70% of the time. However, as professionals we have to maintain systems that work 99.9%, if not 100%, of the time. Just because epoxy worked in one situation doesn't mean that it will hold up in another.
Having said that if you are willing to try the CoroTech V155 a similar product made by Sherwin Williams is called Macropoxy 920 PrePrime (B58T101) 100% solids penetrating primer designed for use over marginally prepared steel or concrete surfaces.


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## PaPainter724

http://www.ppghighperformancecoatin...RD®-Direct-To-Rust-Epoxy-Mastic-Coatings.aspx


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