Late last night an alarm bell went off and I remembered that there was an issue of copper reacting to concrete back in the 50’s when it was first used as radiant floor. (ruined a good nights sleep)
I had planned on using copper flashing to protect the black walnut timbers in my home when I infilled between them with bricks.
Now I’m not certain, should I consider aluminum flashing instead? What other choices do I have?
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Replies
Frenchy,
You may want to look at lead-coated copper as a possible alternative.
The lead coating does take reduce the temper of the copper, so order up one weight. Meaning that instead of using standard 16oz rolled copper, up it to 20oz lead-coated copper.
It's quite malleable, and solders well, though you should use a tin-heavy solder for better joint strength.
Do be careful with the lead coating. It's pretty durable, but if you damage the coating by scratching through it, you can introduce the dreaded galvanic reaction.
It takes paint well, too.
Frenchy,
Aluminum is not a good choice; wet portland cement products corrode aluminum. Copper would perform very well in the application you describe. It is my favorite metal for flashing chimneys. As I said in my article on flashing chimneys (FHB # 136): "Handsome, durable, exuding quality, copper is truly the Irishman of flashing metals." (I'm not sure but I think the fact that my editor was Tom O'Brien and his boss is Kevin Ireton had something to do with that sentence surviving the editing process.) The copper development association (http://architecture.copper.org/faq-faq.html) states: "A service life of over 80 years has been common to copper flashing". Lead coating does not extend the life of the copper flashing; it is applied for aesthetic reasons. Lead-coated copper, by the way, has been called the Frenchman of flashing metals.
That was my first thought, I have the copper, then why did copper tubing used as in floor radiant heat start to fail? I read where it was a reaction to cement and copper
Frenchy,
I'm not sure why copper tubing eventually fails in concrete slabs but I know it does. I've done just one radiant heating system and used Wirsbo tubing. In the masonry industry, though, copper flashing is generally considered to be good for the life of the structure.
Frenchy,
In Masonry Design and Detailing for Architects, Engineers, and Contractors, the author (Christine Beall) states that "copper and copper alloys are essentially immune to the corrosive action of wet concrete and mortar. Because of this immunity, copper can be safely embedded in fresh mortar even under saturated conditions. Galvanic corrosion will occur, however, if copper and steel items are either connected or in close proximity to one another. The presence of soluble chlorides will also cause copper to corrode."
From this, I surmise that copper tubing has corroded in slabs because it was close to or in contact with reinforcing steel and/or that additives to keep the concrete from freezing contained soluble chlorides. I also remember from the literature that I read from Wirsbo that copper tubing could be damaged during the pour by such things as concrete spreading tools and workers stepping on the tubing. To demonstrate how tough their tubing is, Wirsbo had a picture of a concrete truck backed over their tubing during a pour. I also vaguely recollect that Wirsbo claimed that their tubing was much better than copper at surviving movement and settling in the cured slab.
I would never use copper tubing in a radiant slab but copper is my first choice for flashing masonry. The one drawback is the green run-off that sometimes stains roofs and walls below. Lead coated copper has a gray run-off. Most people, including me, accept these stains. I think they even carry a certain status as they indicate that the material above is the real thing. This is analogous to the way people accept checks and other imperfections in large, exposed timbers.
Use copper flashing, Frenchy, and sleep well.
Edited 5/18/2002 9:27:17 AM ET by John Carroll
Edited 5/18/2002 9:59:57 AM ET by John Carroll
Thank you John,
Copper was my original thought, in fact the copper had already been purchased and used extensively so far. You know how certain things tend to recycle in your brain when you are worried, well that's what was going on, I had considered stainless steel and in fact had priced it out, gulp! I evan went so far as checking out the inventory of the scrap yard downtown where the price for new surplus was considerably cheaper than buying new.
I'm greatful for your knowledge and being able to set my mind to rest.
Thank you,
Frenchy
One of the two main upsides of lead-coated copper is the light gray staining (as John mentioned) it gives off vs the darker staining caused by uncoated copper. I thought that lead-coated would be preferable to rolled copper due to the inevitable staining, given the proximity of the timber in the structure to the flashing.
Rolled copper is typically the first choice for flashing. Lead-coated comes next, and is chosen usually because of either staining concerns or because of the desire to paint the flashing so it better blends with the rest of the structure. Either way, I feel it's preferable to stick with copper in one form or another.
I feel that for most applications there are two types of acceptable metal flashing...copper, and lead-coated copper. Most everything else is a usually a compromise.
I'll edit to add this:
Copper embedded in cured concrete is virtually immune to reaction with corrosive alkalies, even if the concrete gets wet or is exposed to moisture. Rainwater leaching may bring chlorides in contact with the copper, causing corrosion, seen as green staining from the runoff. If using copper, it helps to ensure that chloride admixtures are not used in concrete that will have copper embedded in it.Lead will corrode in fresh mortar becuase of the calcium hydroxide in the mortar. Cured mortar will not corrode or react with lead. The corrosion of lead results in a runoff of lead oxide, which is the light gray staining that you see. When lead is partially embedded in mortar, and partially exposed to free air, as most flashing is, and is exposed to constant moisture, the lead can become polar and can corrode from a process called differential aeration. To prevent this, or to slow it, some masons will coat the portion of the sheet-lead flashing that is tyo be embedded in the mortar with an asphaltum product.
All this talk about corrosion may sound scary, but it's all gradual, taking decades. Copper, and lead-coated copper, will preform quite well as flashing when embedded in mortar.
Edited 5/18/2002 9:54:46 AM ET by Mongo
Edited 5/18/2002 10:15:26 AM ET by Mongo
I find this discussion interesting tho I understand little of it.
An avant guarde builder here in Albuquerque built in-floor systems in the 40s and 50s. Some failed almost immediately, some not.
I was in one the other day. 50 years old. Original boiler still working. Original copper still in the slab. Heat still chugging away. Couldn't understand it. My husband spent several hours explaining batteries to me, zincs on boats and the like. I nodded as my eyes glazed over and my mind shut down. His theory was some thing or some event changes the environment and the reaction begins. But, it's only a theory.
Since I know the woman who bought it, I'm concerned for her. But if it's just proximity to steel, it may just be luck in this particular house. Is that right?
Shelley
Shelly,
If your friend's system has worked flawlessly for fifty years, she may well have many years of good service left. But one never knows and all she can do hope that her luck holds.
Frenchy,
As you're probably aware, you should use copper fasteners with copper flashing to avoid galvanic reaction.
Yup! been using them evan when I have to predrill into white oak! I wish there were a source for 1/2 long copper nails, predrilling a hole one inch long on the foot of a timber just to use the nails to hold everything into position while it's upended and put into place seems overly complex.
Heck once in place there is tons of house holding things down! I'd be happy with little 1/4 inch long copper nails!
Lead coating does not extend the life of the copper flashing; it is applied for aesthetic reasons.
John, I think I've got to disagree with you here. It has been our experience in the Northeast that the lead coating on the copper provides a protective layer for the copper base metal and allows it to last quite a bit longer. We have acid rain problems here which are corrosive to copper but have less of an effect on the lead coated variety. We especially find this to be true on terracotta roofs with open valleys.
carpenter in transition
Tim,
The link I provided in my first post above leads to the "frequently asked questions" section of the Copper Development Association web site. In response to the question, "What is the purpose of the lead in lead-coated copper?", they answered:
"Lead-coated copper is the copper industry's response for a strong, lightweight, durable, easy-to-install gray metal finish on a copper substrate. The material has been available since the early 1900s. Lead coated copper does not extend the life of a copper roof. Its purpose is to provide an alternate color to architectural copper applications. In addition lead coated copper runoff fulfills the objective of providing a metal whose runoff staining is compatible with light colored materials such as masonry, marble, limestone, stucco, and light painted woodwork. The stains produced range from light to dark gray in color and resemble the natural atmospheric weathering of masonry or paint."
I lived in New England (Hampton, N.H.) for three years in the late 1980s and I occasionally visit my sister, who lives on Cape Cod. In conversations with builders there and in reading comments posted here and in several building magazines, I've noticed a strong regional preference for lead flashing in New England. In some, this preference borders on religious belief in the qualities of lead. The reality is that lead is soft, punctures easily, and corrodes at a rate slightly higher than copper. Coating copper with lead does not extend the life of the flashing; it provides the look of lead with the performance of copper and it provides for runoff stains that might be more acceptable.
In most circumstances, uncoated copper that is exposed to the elements corrodes very slowly. As it corrodes, the corrosion shows up in the form of the green-brown patina that eventually covers the roof in wet climates. This thin layer of corrosion adheres tightly to the copper and eventually forms a protective layer against further corrosion. In New York, Boston and other cities in the Northeast, there are many copper roofs that are still going strong after 100 or more years. When I attended a workshop hosted by CDA in Raleigh a couple of years ago, the moderator showed a slide of a church in Quebec that was in the process getting a new copper roof. The old one, which was over 300 years old, was still sound. The problem was that the underlying timber structure had decayed.
The circumstance that you described can create problems for any metal, including lead or lead-coated copper. In CDA's "Copper in Architecture" manual, the problem is stated as follows: "...When (acidic) rain falls on a non-copper roof such as tile, slate, wood, or asphalt, the acidic water is not neutralized as it flows over the inert material. When water collected over a large surface, is diverted or collected by a relatively small copper flashing or gutter, the copper may deteriorate before it develops a protective patina." In other words, if you do an entire roof in copper in your area, there is a very strong possibilty that you won't have problems with corrosion. If you do just the valleys in copper, however, there is a chance of corrosion-related problems. In general, though, copper performs very well in coastal and industrial areas and I think the chance of corrosion leading to failure is fairly small. I have a feeling that the lead-coated copper you've used eventually developed a protective patina and that this, rather than the lead coating, has been the key to the long-term performance of your valleys.
John,
This is off the subject, but I just wanted to say that I enjoyed your article (FHB # 146) about shingling roofs from the top down. I remember reading in Breaktime about a year or so ago about that method and had the chance firsthand to try it out last summer. It worked really well.
The one thing about your article that amazed me, was the fact that you and your partner HAND NAILED the roof? What's up with that? You a glutton for punishment? Or just too stingy to fork out the dough for a case of coil nails? ( ha! ha!)
Please doooon't tell me that you can hand nail as fast as I can coil nail. I've heard that line before, and it doesn't hold water. I'm 43 yrs old , and the last time I hand nailed an entire roof was over 10 years ago. I'm impressed by your stamina!
Again, very nice article on the subject.
Davo
Nice article.
Davo,
Glad you enjoyed my article. I don't roof full time anymore but I always put the roofs on the projects I build. I actually enjoy these occasional roofs but, at fifty-two, I'm not looking for roofing work. I don't have anything against pneumatic nailers; in fact, we used a nail gun to frame the roof shown in the article. However, I don't do enough shingle work these days to justify the expense of a nail gun for roofing nails. I started roofing in the late 1960s and hand nailing is second nature to me.
John,
I appreciate your response, I'm just at a loss to understand how putting a protective coating on a product exposed to the elements won't extend its useful life. I find it hard to believe that two pieces of 16 oz. copper, one coated with lead, one not, are going to corrode at the same rate. Are you suggesting that eventually when the lead coating wears off that the copper base metal's corrosion is accelerated for some reason ? The paint we put on our cars today is there for more than just decoration.
carpenter in transition
Tim,
No, I am not suggesting that if the lead coating wears off lead-coated copper, the corrosion of the underlying copper will be accelerated. I am saying that the lead is there, not for protection, but rather for looks. That is what the Copper Development Association says in plain English.