Chinese Drywall and Copper Wiring


Copper has proven over the last century to be a very reliable material for household wiring. With copper prices continually rising, other materials such as solid core aluminum wiring have been tried on a large scale, but after complications were discovered (see our popular article on solid core aluminum wire) copper wiring has become the norm again in household wiring.

With 100 years of copper wiring dependability, it is a very big surprise as a home inspector to open an electrical panel to see large scale black corrosion on the copper wires but based on inspector reports around the internet and our own first hand experience, this is a rare yet existing concern discovered in home inspections.

Copper Wire Corrosion

If you ever owned a ‘rust bucket’ car in your youth, you are well aware of the effects of corrosion on metal. Steel and iron when exposed to water will ‘rust’ and the material will erode commonly with an orange colour.

Black corrosion visible on copper wires at breakers.

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Notice the black corrosion where the wire is exposed from the insulation at the breaker connection.

Copper is quite resistant to corrosion but when allowed to naturally rust, it turns a green colour. Corroding (or oxidizing) cooper sheets are what give many iconic buildings such as the Parliament Buildings in Ottawa or the Statue of Liberty in New York their green colour.

So what then causes copper to turn black? Well, thanks to some beginner chemistry (the type I understand), copper can form different types of oxides depending on the chemical process happening to it. The chemical process involved with exposure to water creates a visible green rust, however, other chemicals in reaction with copper can create a visible black corrosion. Small traces of these chemicals in the air such as can be found in swimming pools, photo labs, or stored in garages, can cause a black corrosion and can be easily explained (but not necessarily desired).

In some cases however, black corrosion is visible and there is no readily explainable reason nearby. For example, the sample photos on this page were taken in a 2002 condo unit, nowhere near a pool or other obvious air contaminants. This is where inspectors and home owners now need to consider an issue known as ‘Chinese drywall’.

Chinese Drywall Issues

First, the Chinese take a lot of abuse for the quality of imports into North America, and while some of that is well earned, many great products are made in China (e.g. iPhones) and many bad products are made in North America. It is a little unfortunate that the term ‘Chinese Drywall’ has become a negative keyword around the building industry but in lieu of any other phrase for the issue, please forgive the non-political correctness of it.

Black corrosion on exposed electrical wires in recently inspected panel.

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Ground wires on panel ground bar.

In the early 2000’s, there was a major building boom in North America which has local suppliers of drywall products running at maximum capacity. When some serious hurricanes rolled through the American south during the decade, massive rebuilding efforts caused shortages in supply and building supply companies turned to factories in China to supply drywall to fill the local shortage.

It didn’t take very long after the installation of this Chinese supplied drywall and some home owners began to experience mechanical and health concerns in their homes. Researchers have determined that when some drywall samples are exposed to high humidity, they can produce off-gassing which reacts to create corrosion on copper wiring and other copper in the home such as with air conditioning and fridge coils.

Based on reports around the internet, it seems that coal dust in the Chinese air from coal burning power plants may have made its way into the gypsum wallboard during manufacturing and this combined with the gypsum and humidity levels creates the off gassing and damages. To be fair, samples of North American supplied drywall in some cases exceeded the Chinese products in producing off-gasses in the same testing so there is still some debate over who is really to ‘blame’ for this problem.

Health Complications

First, another disclaimer, professional home inspectors DO NOT cover environmental or air quality issues in their inspections, there is a whole separate industry devoted to this area.

That said, there are reports tied to the Chinese Drywall issues that may suggest some negative health impacts particularly relating to respiratory issues. If you think you may have Chinese Drywall in your home, it would be prudent to conduct additional research on this topic and consult with air quality professionals.

I Have Black Corroded Wiring in Home Inspection Report, What Do I Do?

If your home inspection report highlights black corroded wires, it is important to call in an electrician to review the safety and functionality of your electrical system. In some cases, such as when stored chemicals have been removed by previous occupants, the electrical system may be under no more future stress. In other cases, incorrectly wired electrical panels have been known to oxidize themselves with no outside contaminants. However, this cannot be conclusively diagnosed by your home inspector which is why additional review is needed.

Home inspectors have the ability to save home buyers thousands in unexpected costs; however, we are generalists, not specialists. As home inspectors, it is our job to identify the existing conditions discovered, and to recommend further review if needed. In the case of observed corroded black copper wires, your next call should be to a professional electrician to look at potential causes.

By James Bell - Owner Solid State Inspections Inc.