What can I put on this wood to preserve it?

[Propflux01]

There is pressure treated wood and ground contact pressure treated wood. You should have used ground contact PT wood.

Nothing will prevent the decay but oil based deck stain will make it look better.

Termites are a possibility once it starts to decay.

I did not build the shop myself, I just watched the contractor guys do it. I saw the lumber when it was dropped off. It just said 'pressure treated pine' IIRC. it is the standard wood used around here for darn near everything.

 

[PimTac]

How about a copper based wood preservative? I think Rustoleum makes a paint type product with copper and there is Cuprinol and other brands if you don’t want a paint product.

 

[doitmyself]

What PimTac said ^^^^^^^^

 

[Pablo]

How about a copper based wood preservative? I think Rustoleum makes a paint type product with copper and there is Cuprinol and other brands if you don’t want a paint product.

This.

I don't know the Rustoleum product, but agree - really where that wood is and the exposure - nothing will stop the contact rot. Get the strongest brown one and soak it really well.

I made some short posts (varied from 5" - 8" long) by doubling up some 2x4's (to replace rotted posts). Because they were short and mucho exposed ends, I did not want to use 4x4 if I didn't structurally need to. 2x4 doubled up, plenty strong in compression PLUS face to face much better pressure treated near the core. PLUS I soaked each cut piece for a few days, let dry a bit for handling, then clamped and screwed them together. That was 20 years ago at that house. Porch is still solid.

That cuprinol (type) product works. Now when I do any sill type work, I coat exposed areas. Just out of caution. I even coated several lower rows of heart cedar lap siding when I replaced a patio door at the previous house. That siding will last a LONG time.

One caveat, it does take paint, but not immediately and may bleed through and need a coat later.