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There are a lot of paint-on products for treating the cut ends of pressure-treated lumber. However all of the products that I can find are rated for above-ground use only.

PT lumber comes in "ground-contact" rated treatment, so you can place the lumber directly on the ground and it will take years to rot. It's expensive. But it really only works if you don't cut it and expose the untreated innards of the lumber.

Is there a product that is rated for ground-contact that I can paint on the cut ends of ground-contact-rated PT lumber?

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  • Think the old PT treatment was mainly a surface treatment, so paint on ends were needed. The new treatments I think soak into the wood and don't need end paint as much. Any way of turning the wood around so the cut ends are up?
    – crip659
    Feb 16 at 13:02
  • Cut ends up seems to be the best advice, @crip659
    – FreeMan
    Feb 16 at 15:58
  • Cut ends up doesn’t work for joist ends that will sit against the face of another PT ledger board or rim joist. Feb 16 at 17:38

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Pressure treatment was always a penetrating infusion. Granted, large timbers may have had untreated cores, but the whole point of high-pressure infusion was to treat the entire board volume.

If we're talking about two-by or 4x4 boards, no end treatment is probably needed. However, it should be visually apparent if the treatment doesn't penetrate fully. In that case an additional treatment might be wise. 6x6 posts tend to show weak treatment at the core, for example.

That said, end grain is very absorptive. You might consider isolating it from ground contact anyway as that's where your structure will probably fail first in the long term. Eventually the treatment leaches out and the wood rots.

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