Here's my .25 cents worth, after conducting research into wood treatment and successfully filing a claim against Georgia Pacific for insufficient treatment of about 1/2 mile of 4" fence posts.

There are published standards for wood treatment that you can find online; they go up to marine grade (the highest percentage of residual preservation chemicals of course) which is for constant immersion in water and protection against plants/algae /bacteria and also worms/borers/etc. You can't achieve that level of protection by just "painting" on; it requires pressure treatment to the core. I had many, many posts that rotted from the core out because of lack of sufficient penetration and this was in earth---not even water.

If I was to fabricate a dock, deck or anything that I didn't want to have to take apart and redo in the near future it would be with treated lumber suitable for the application from a reliable supplier. And on that note, the next time I purchase lumber by the load I am going to spend $50 to send some samples to a lab for analysis of the treatment (penetration and residual) before I invest a ton of labor only to have to redo in a year or two. They put whole bundles of lumber at a time into the pressure treatment vessel so if you don't break a bundle you can be pretty sure they were all treated identically. During the drought last year I watched a neighbor down the street build a new dock with treated lumber (fence grade) from Lowe's. Oh well.

If you have a dock/deck that is deteriorating and you are trying to stop the decay then IMHO you are probably forestalling the inevitable and this, or other, products may help for a while.

Good luck!

Last edited by CypressTx; 08/17/12 03:50 PM.