Pressure Treated landscape timbers

The last ones I bought at Walmart were not pressure treated, they were dipped. Went to Lowes and they had the same dipped timbers. I would not have known but I happened to look at the tag that was stapled to the end. I would give the dipped one just a year.
 
If they are ground contact PT you can get 20 years, it does help if the grade doesn't let water puddle on them.
 
When I need pressure treated I never buy anything thicker than 1 1/2 inch then double or triple them up. Seems the thicker stuff rots from the middle like the treatment doesn't reach center.
 
I have not ever seen real pressure treated landscape timbers.
Yes they may dip them or pressure treat them to a chemical retention level of .01 lb per cu ft with MCA but that is not real pressure treating.
Any cut or scrape will revel untreated wood.

In comparison box store 2x4's are pressure treated to a chemical retention level of .15 lb per cu ft with MCA and at that level it barely meets ground contact levels.
 
I don't have any confidence in ACQ pressure treated lumber for ground contact. CCA (copper chromated arsenate) is a much better preservative, just not so easy to get, but is allowed for Ag and Industrial applications. Also depends on your ground conditions.
I used CCA lumber for sill plates onto compacted gravel for a set of front porch stairs I built for a neighbor in '96, they are still there today, stairs and sill plates.
 
The have already "STARTED? to rot. When will the exceed their useful life depends on how many wet/dry cycles they are exposed to.
 
(quoted from post at 17:01:52 01/12/20) How long before landscape timbers will start rotting.

They start rotting the minute you expose them to the weather. To many variations come into play to give an accurate time frame for in which the rot to become noticeable.

Not many people here use treated post any longer for pole barn type construction. Laminated pressure treated 2 bys have taken over.
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I have always thought that there could be a market for plastic landscape timbers, boarders etc by recycling all of the plastic bottles, bags and such products. I know some places have been testing rail road ties made from recycled plastic.
 
It depends a lot on climate, but in my experience, the cheap landscape timbers are only good for a couple of years. I think they're actually a byproduct of plywood manufacturing; they're the cores of logs after the useful veneer has been cut off. Having used landscape timbers once, I'll never use them again.

If you want something that's in contact with soil to last, it needs to be constructed of pressure-treated wood that's rated for GROUND CONTACT. Check the label on the end of the board; most treated lumber you'll find at a big-box store will not be rated for ground contact. Ground contact-rated lumber should last for decades in even the most severe conditions.
 


There are some options out there. Thirty years ago I installed some actual oak railroad ties as a retaining wall. It is still retaining the dirt.
 
Ground contact is commonly called "foundation grade" and is labeled .60 as opposed to your everyday big box store .40 PT, which is near worthless and also usually SYP, which is garbage wood to begin with. Untreated larch or locust will last much longer.
 
I heard/read years ago that "off the shelf treated lumber for ground contact has to be 4 x" I'd still look at the label on 4x4s for preservative content.
 

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