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I'm doing a job in a plant. The job is inside of a cooling tower. We are changing out all of the girts(2x4's), but they don't want to change the columns(4x4's). The plant supervisor said that they expect what we are doing to this unit to last another ten years. In my opinion that would be ok if you were changing everything. My question to this dilemma and to ease my mind is does anyone know how long a new, treated 4x4 post last in constant water? I think they'll be coming back in another 2-4 and changing out the 4x4's. Oh well, it ain't my money they are wasting!!
 

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treated redwood lasts a long time submerged in water. its the fungus that gets it right above the water line where it is exposed to air
 

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If you get the old style treated pine (cca) that is rated for saltwater it will last quite a while, probably more than 10 years. It is still available, but in most cases is a special order item. The new stuff in water probably won't last a couple of years.
 

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In the sewer treatment plant where we are working right now they use a lot of redwood & engineered laminated lumber for their flights which are submerged almost constantly. I think all the new flights are either engineered or fiberglass now. They also use some south american stuff like ipe.
 

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I don't think PT will last very long submerged in water. Especiallyl if it is fresh water. It will last a lot longer in salt water. I'd say 3-4 years max in fresh water.
 

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I don't think PT will last very long submerged in water. Especiallyl if it is fresh water. It will last a lot longer in salt water. I'd say 3-4 years max in fresh water.

I have seen PT last over 20 years in salt water and even more so in fresh water.

here you go heres the listing for the different grades if you are gonna use it in water.

ApplicationRequired Retention* (pcf)LUMBER, TIMBERS and PLYWOOD Above Ground0.25Ground / Fresh Water Contact0.40Salt Water Splash0.60Wood Foundation0.60Salt Water Immersion2.50PILING and COLUMNSStructural Poles0.60Foundation / Fresh Water0.80Salt Water Immersion2.50
 
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