Using Treated Lumber for Decks

New to the forum, but have seen numerous posts regarding the use of pressure treated lumber, and its potential corrosive qualities. I am in the pressure treating industry, and want to educate those folks who may not be clear on this topic.

About 4 years ago, a new treating chemical was introduced that was designed to eliminate the corrosive qualities of the chemical that was in current use. Any lumber purchased at the retail level with an end tag labeled ACQ or AC2 has corrosive qualities and is not designed to be used in direct contact with aluminum. With that, typical metal fasteners like deck screws, nails, joist hangers......had to be "hot-dipped" to protect against corrosion so that any structures being built wouldnt eat the fastener and jeopardize the integrity of the structure. If you tried to use a standard galvanized fastener, or attach aluminum flashing for a deck project, in direct contact with an ACQ or AC2 product, it would dissolve the fastener and aluminum over time.

So an new chemical was introduced; MCA-Micronized Copper Azole, that is approved for direct contact with aluminum. This is a much less corrosive chemical compound and is more similar in design to CCA that was the industry standard prior to the introduction of ACQ and AC2.

Bottom line.....if you want to use pressure treated lumber for your boat deck mods, you can do so by simply making sure that you purchase any product that utilized the micronized copper treatment. Check with folks at the lumber yard and ask them what treatment was used on their product. Most of the industry has moved to this newer chemical, but 1 of the big-box retailers still uses the old stuff.

Good luck with your projects!

you state the new chemcial is a "much less corrosive compound", but will it still have an adverse effect on aluminum? If yes, how much less? Just trying to get a bit more clariification.

Not to bash the store still using the old treating but which store is it?

Thanks for the informative post. There have been several interesting discussions on this forum and others debating the pro's and con's of using Pressure Treated (PT) wood. Personally, I found that there was a $10+ difference in price between the 2 sheets of plywood and the weight of the PT'd wood was really heavy, so I just opted for the non-treated one and bought some spar urethane. Long term, the PT'd wood will probably outlast the non-treated, but I think this is probably minimal. You sure have me curious to run home and look at the tags I have been peeling off my 2x4's though

Do you think there are any reactions between the steel Simpson Strong Ties (L-braces) and the aluminum in my boat? I have been riveting them directly to the hull, and I see that a lot of guys are putting EM5200 or rubber behind them before they rivet them to the boat. My understanding is that the reaction with the PT wood is the copper reacting with the Aluminum Oxide that is covering the aluminum of my boat and not the aluminum itself. Is there an issue with steel or whatever these things are coated with reacting with aluminum/oxide? (I think it's zinc). I think it will just turn white and oxidize over time.

Thanks
-House

The MCA treatment is approved for direct contact with aluminum.

I would rather not mention which store(s) stock the ACQ or AC2 products. These products are effective against rot, decay and termite infestation, which is what all pressure treated lumber is ultimately designed to do. Just ask which type of treatment they use and decide for yourself which is the best way to go. It is also very easy to tell simply by looking at the color of the pressure treated wood.....Dark Green is the old stuff. The lighter colored product has almost no green tint to it at all; which also makes it more appealing to home-owners who want to use a light stain to get a more natural wood look on their decks or fences.

As far as the copper reacting with the fasteners, you are correct. As the copper that is used during the treatment process leaches out of the wood, it reacts with the unprotected metal. Hot dipped galvanized or stainless steel fasteners are recommend with the ACQ and AC2 products. Not necessary with the MCA. Not sure about any conflict between the simpson fasteners and the aluminum. I do believe that some, if not all of the simpson products are actually hot-dipped galvanized rather than zinc.

Something totally unrelated......for anyone wanting to stain or paint pressure treated wood, you dont have to wait a year to do so. Once you have completed your project, give it a couple of good sunny days and then sprinkle a little water on the wood. If it absorbs the water within 15 seconds or so, then the wood is ready to be protected. If the water sits on the surface of the wood, then the moisture content is still too high, and staining or painting will not be effective.

Woodseller... Does the green treated wood affect fiberglass at all?

I can tell ya that Lowe's still carries the ACQ treated lumber because I work in the lumber department haha! Well in my neck of the woods they do.

The Menards in my area carries the new stuff. You can hardly tell that its treated.

The original post is misleading.

NOTE: ANY pressure treated wood that has the letter "C" in the type (which is ALL of them) is NOT approved for use in contact with aluminum. Especially nowadays with the newer types, that can actually contain 75-95% copper content causing expedited corrosion.

C = Copper, copper corrodes aluminum, that is the hard fact.

Regardless of what other chemicals they claim may counteract it, in reality there is little to nothing that can prevent corrosion caused by contact of such dissimilar metals.

This is why you buy NON-treated wood for aluminum boats and then soak or put a thick coat of something like Thompsons water seal on it.

Welcome to the site...woodseller10
It's not that I don't believe you but I'd like to read some more information on what you've discibed.
The words less corrisive still catches my eye.
I'll have to start googling.
Do you own a boat?

Woodseller, I noticed you completely ignored TNtroller's question.

You said the new product is "less corrosive". In my book that comment means its still gonna eat your boat, just not quite as fast. Care to clarify?

I'm also interested to find out if you own a tin boat or not.

screwballl said:

The original post is misleading.

NOTE: ANY pressure treated wood that has the letter "C" in the type (which is ALL of them) is NOT approved for use in contact with aluminum. Especially nowadays with the newer types, that can actually contain 75-95% copper content causing expedited corrosion.

C = Copper, copper corrodes aluminum, that is the hard fact.

Regardless of what other chemicals they claim may counteract it, in reality there is little to nothing that can prevent corrosion caused by contact of such dissimilar metals.

This is why you buy NON-treated wood for aluminum boats and then soak or put a thick coat of something like Thompsons water seal on it.

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^This.

I do believe that some, if not all of the simpson products are actually hot-dipped galvanized rather than zinc.

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Hot dipped galvanization is basically giving the piece of steel a zinc bath. Zinc and aluminum don't particularly like each other, so any form of zinc, be it plating, hot dipped galvinization, or whatever other form it is in, will still cause a dissimilar metals issue. Granted, with the zinc/aluminum combo, the aluminum is the cathode (where as it is the anode, when placed with copper), thus it will be the zinc that is eaten away the most, but in any case, having the protective coating on your fasteners removed, leaving exposed iron isn't a great idea.

uhya....and I can sign up on a gun forum and say that Hi-points are not really that bad, but... facts still remain :roll:

perchin said:

uhya....and I can sign up on a gun forum and say that Hi-points are not really that bad, but... facts still remain :roll:

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Come on now, you dont really think theres something wrong with guns that cost less than the ammo they shoot do ya!?! Lol

Screwball is correct about the "C" = Copper. However he is wrong about it not being approved for aluminum contact. See the attached link. OSMOSE makes MCA which IS APPROVED for direct contact with aluminum. Copper and Aluminum arent friends. However, Screwball, the FACT in the matter regarding Copper is this:

The Copper "leaches" (drains from) the wood after its been treated. All treated lumber does this. The MCA will still leach, but far less than the ACQ. Is Copper corrosive.....yes. Approved for Aluminum contact....MCA- YES ACQ- NO.

Check this site which compare the two types of chemicals I earlier described. https://www.deckmagazine.com/article/154.html

I do have a boat, 14' semi-v; about to begin the mods. This is my third over the past 15 or so years. Like many who modify their boats, I too used treated lumber for my deck on the previous two, and will certainly use it on this one.

As far being "less corrosive"; its just that less corrosive; not as corrosive as the ACQ.

I dont work for either of these two chemical companies. My only goal was to share some information about the newer chemical and its approval for direct contact with aluminum.

Check out the two major chemical manufacturers for yourself. OSMOSE and VIANCE. You will see for yourself which is approved for aluminum contact and which isnt.

I have no clue if the chemicals will create problems with fiberglass.

The problem with the linked story is:

The manufacturers claim that aluminum and standard G-90 galvanized hardware can be used in direct contact with micronized copper–treated lumber.

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Considering they are trying to get sales going, of course they will say whatever they want. The problem is that you cannot fight physics. that is obviously mentioned in that story as well by using phrases such as "less corrosive"... less corrosive still means it is corrosive. Less corrosive does not mean "not corrosive". That story and the manufacturers of MCA also have a very specific list of approved fasteners, which are very small contact points with the wood FOR FASTENING, not large scale high contact setups like what would be used with our boats...

MCA treated wood in direct contact with aluminum products should only be used in code compliant construction applications that provide proper water drainage and do not allow the wood to be exposed to standing water or water immersion.

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That pretty much means "not for boat trailer usage".


So with that at hand, it is still not recommended to use any treated lumber that contains copper that has any contact, direct or indirect, on our aluminum boats. You cannot fight physics, NEVER mix copper and aluminum.

I did some googling earlier on and couldn't find out to much more then whats in this article.
Most of the talk has to do with decks,fences or chicken coups.
They were complaining about the weight of it plus when it dries the twisting.Probably not really fair as they were using planks/boards and not plywood.I also seen where they still suggest using stainless or galvinized hardware.

Still having copper and the words less corrisive would make me lean away from using it in boating applications.
Just an opinion...
I hope you stick around,post some pictures of your boat and fishing/boating reports.

perchin said:

uhya....and I can sign up on a gun forum and say that Hi-points are not really that bad, but... facts still remain :roll:

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Ever own one or even shoot a Hi-Point? I bought a 9 MM to have something to shoot with my buddy. He's shooting a new GlocK. His Glock is a lot prettier and cost 4 times as much. The Hi-Point had a few FTE the first 100 rounds, but the Glock had 2 FTE as well. Also Hi-Point has a lifetime (yes, lifetime) guarantee. You can be the first owner or the 10th and they'll still fix it if for free if something breaks. My buddy liked mine so much he bought one and says he doesn't worry about scratching up the big ugly "brick". Made in the U.S.A. too! =D>

Oldgeek said:

perchin said:

uhya....and I can sign up on a gun forum and say that Hi-points are not really that bad, but... facts still remain :roll:

Click to expand...

Ever own one or even shoot a Hi-Point? I bought a 9 MM to have something to shoot with my buddy. He's shooting a new GlocK. His Glock is a lot prettier and cost 4 times as much. The Hi-Point had a few FTE the first 100 rounds, but the Glock had 2 FTE as well. Also Hi-Point has a lifetime (yes, lifetime) guarantee. You can be the first owner or the 10th and they'll still fix it if for free if something breaks. My buddy liked mine so much he bought one and says he doesn't worry about scratching up the big ugly "brick". Made in the U.S.A. too! =D>

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calm down... It was just a joke... on the other hand tell your friend to tighten up his wrist, cuz a glock wont FTE unless limp-wristing...just sayin' :mrgreen:

Would be curious to see if anyone out there that has used pressure treated lumber in their boat mods had has any issues with fastener failures or had holes eaten in their boats by the less-corrosive MCA?

That's the great thing about forums like this.....full of opinions, backed up with real-world applications, and an occasional reference to technical data provided by a manufacturer. OSMOSE says their product is approved for direct contact with aluminum. So Screwballs opinion is just that, an opinion.....his opinion. I personally tend to side with the manufacturer on this issue. Seems to me that they, like most companies, are in business to make money via "sales", any will make claims based on research and results accumulated from that research. Show me a company that claims their product sucks......

Once again, really anxious to see pics, not just words, regarding this "less corrosive" MCA, where this chemical, NOT THE OLD, MORE CORROSIVE ACQ, has caused ANY issues with direct contact with aluminum boats.

A few years back, I saw some a slide-show of the corrosion comparison between three chemicals used during pressure treating. It was an outdoor, third-party study that used unprotected aluminum flashing; a 20' x 12" section, commonly used when attaching a stringer to home for a deck. They sandwiched the aluminum between 2 pieces of 2x10x20 CCA, 2 pieces of ACQ and 2 pieces of CCA. They used several different fasteners, some coated, hot-dipped, stainless steel in each of the three types of pressure treated lumber; CCA, ACQ and MCA. The study lasted 2 years and the results were pretty clear. Of the 3 different chemicals, the ACQ was the most corrosive. It was visually apparent from the pics that the ACQ has caused color change to many of the fasteners, and when the fasteners when the fasteners were being removed for further study, it was very apparent that the corrosive qualities of the copper in the ACQ were wicked. The CCA and MCA showed no visible signs of discoloration on any of the fasteners used. These nails, screws, ledger bolts and joist hangers were in DIRECT CONTACT with the lumber. If I can find the source of that power point presentation, I will certainly post some slides for all to see what I saw, and base a big part of my comments on.

On my previous ALUMINUM boat projects, I wrapped the pressure treated plywood in an outdoor carpet, so it wasnt in direct-contact with the aluminum. The copper still will leach out of the wood, but I, personally had no issues with the ACQ eating holes in my boat. I also used fasteners recommended for use with ACQ. So if the more corrosive ACQ didnt present any problems for me, and knowing what I now know about the less-corrosive MCA, I will continue to use pressure treated lumber on this new boat project and all future projects WITH CONFIDENCE.

Bottom line is that you should each do your own research before making any decisions. We all have opinions to share.

I am not a chemist and dont pretend to be an all-knowing source for this thread. I get the feeling that that there are people on here that cant help but feel like they need to be right about any topic they see posted........again....just my opinion.

Im just a poor man livin' in a rich mans world, who's only real focus is that next cooler full of crappie!

woodseller10 said:

I am not a chemist and dont pretend to be an all-knowing source for this thread. I get the feeling that that there are people on here that cant help but feel like they need to be right about any topic they see posted

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:roll: ...any yet you took the time to join a forum, just to re-visit the beating of a dead horse.

woodseller10 said:

Im just a poor man livin' in a rich mans world, who's only real focus is that next cooler full of crappie!

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ya... me too, but perch :mrgreen: