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How To Deal With Corrosion Caused By ACQ-Treated Timber

October 11, 2018Olen Murriel

Pressure-treated lumber has been in use for the best part of half a century. However, there has been a shift in the preservative used to treat the wood to increase its longevity. Before 2002, the preservative used was arsenic-based. The solution was known as Chromated Copper Arsenate. This solution, though effective, raised concerns due to the potentially poisonous nature of arsenic.

This prompted the United States’ Environmental Protection Agency to intervene and direct companies to adopt a safer method of treating lumber. Companies, therefore, adopted a new formula known as ACO (Alkaline Copper Quaternary).

This new solution contains a high percentage of copper without arsenic. The solution solved the poisoning issue but it brought about another problem. Copper is a highly conductive metal. This causes corrosion for most metals in contact with the ACO treated lumber. This means that it has the potential to corrode the metal fasteners (nails and screws) that hold the lumber together.


Possible Solutions

The best thing about science is that it almost always produces a solution to a problem that it creates. The solution is in the element used make the fasteners that you will use with the treated lumber. You should only consider fasteners that do not corrode when used with ACQ-treated lumber.

Different types of fasteners

Stainless Steel/Copper

Stainless steel and copper do not suffer from corrosion. However, their main disadvantage is that they are very expensive. You might be forced to sell something substantial to afford these fasteners.

Galvanized fasteners.

You have to look for a special type of galvanized fasteners that does not suffer from corrosion. The special type of galvanized is marked as “G-185”. This refers to how thick the galvanization is Anything less will still be susceptible to corrosion if used with ACQ-treated lumber.

Galvanization can also be done with a special type of material that looks like it been painted on to the fastener It appears in a variety of colors depending on the manufacturer. You can easily identify these fasteners since they are specifically marked for ACQ use. You can also use lifetime guaranteed deck screws. Such deck screws usually have a corrosion resistant coating that doesn’t corrode when used with ACQ-treated lumber.

Additional information

Avoid Aluminum

Aluminum is highly prone to corrosion. It should not be used as a bracket when dealing with ACO treated lumber. The best option would be a G-185 rated bracket. For added safety, you can consider incorporating a plastic barrier between the treated lumber and the bracket.

Use similar metals

When different metals come into contact with each other they might trigger corrosion. You have to ensure that you uniformly use one type of metal throughout construction. For example, it would be pointless to use a G-185 bolt and a normal washer The washer will be susceptible to corrosion and it is very likely that it will spread the corrosion to the galvanized bolt.

How to spot dangerous corrosion

Even when you use galvanized metals, you might find some whitish corrosion. This should not worry. However, you should be worried if the corrosion is red in color. This indicates that the steel beneath the galvanization is corroding. This is a major issue and you should consider having the entire unit inspected by professionals. You should also ensure that all affected metals are replaced immediately.

Exercise extreme caution

You can never be too sure when it comes to metals and treated lumber. It is safer for you to exercise extreme caution when it comes to the type of metal used when working with treated lumber. It will not only ensure that your unit is safe but it will also ensure that you have peace of mind regarding the safety of your unit.

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