These are pressure treated 4x4 posts supporting my fresh water dock. There are 15 of them and they're about 20 years old. Do I need to start worrying?
Dock pilings deteriorating at the waterline
- Thread starter Joe Blizzard
- Start date
You may want to be pro active with changing them. At very least the worst looking ones this year and then the same each year until they are all done.
I would test to see how much good wood is there by pushing a knife or thin bladed flat screwdriver into the rotting part. If you have less than 3" of good wood.... Change them while you can do it from the dock. If you wait it's a bit more work.
About pressure treated wood; Don't use it in water. The chemicals leach out. Fish don't like that. I would suggest a metal post such as galvanised.
I would test to see how much good wood is there by pushing a knife or thin bladed flat screwdriver into the rotting part. If you have less than 3" of good wood.... Change them while you can do it from the dock. If you wait it's a bit more work.
About pressure treated wood; Don't use it in water. The chemicals leach out. Fish don't like that. I would suggest a metal post such as galvanised.
Worse
I have seen worse here at docks in Florida and we have round like what you
have and in salt water and yes some have concrete pole and concrete dock pads.
I would say looking at them that they look pretty good and fresh water is maybe less harm than salt water and just keep a look out at them every year
.
The ones at my dock have lots of growth on them and even loss of wood and
one day will need to be replaced but I don't own the dock and I am sure the home owner is not going to replace until really need to and so far they are doing
a good job and not really worried.
When the dock repair guys put in new poles they seem to wrap the part in the water with some king of plastic wrap to keep growth off the wood.
Nick
I have seen worse here at docks in Florida and we have round like what you
have and in salt water and yes some have concrete pole and concrete dock pads.
I would say looking at them that they look pretty good and fresh water is maybe less harm than salt water and just keep a look out at them every year
.
The ones at my dock have lots of growth on them and even loss of wood and
one day will need to be replaced but I don't own the dock and I am sure the home owner is not going to replace until really need to and so far they are doing
a good job and not really worried.
When the dock repair guys put in new poles they seem to wrap the part in the water with some king of plastic wrap to keep growth off the wood.
Nick
Lots of them in my neighborhood
All the docks in my neighborhood were built between 1970 and 1980 using pt 4x4s. The few still standing are beyond repair. A few owners extended the life of their docks by replacing posts, but that was a band-aid at best. It wasn't long before the decking also needed replacement and the entire docks had to be rebuilt. We're in Florida, hot sun and brackish water on a river that feeds into the Gulf. Most folks are wrapping new and good posts that are in the vinyl protective wrap. Another note, all posts do not rot out at the same rate. I had 8 installed at the same time. 7 are like new, I recently had them wrapped. The other is nearly rotted through.
When you take the worst ones out take a look at condition of wood submerged in the bottom muck/soil/?? depending on the flora and fauna this can degrade as well.
I like the idea of PVC encased concrete which should be easy to pour especially in fresh water.
If you can add a reinforcing rod down the center you'd then have reinforced concrete.
Good idea to paint the PVC escpecially top and down a ways into the water. Lots of PVC doesn't stand up to sunlight and will crack. Is dock subject to much torque from wind and such pushing on a boat tied up to dock? If so you'll need to drive deeper into the bottom. Driving a PVC pipe might prove troublesome.
I like the idea of PVC encased concrete which should be easy to pour especially in fresh water.
If you can add a reinforcing rod down the center you'd then have reinforced concrete.
Good idea to paint the PVC escpecially top and down a ways into the water. Lots of PVC doesn't stand up to sunlight and will crack. Is dock subject to much torque from wind and such pushing on a boat tied up to dock? If so you'll need to drive deeper into the bottom. Driving a PVC pipe might prove troublesome.
As has been stated, pressure treated wood is not all that resistant to decay anymore. Also not a lot of experience to draw on with the new treatment chemicals. I have a floating pier in 4 to 8 ft of fresh water with four steel post near the corners that appear to be in reasonable condition after 17 years. Under normal conditions, water is at the pier about nine months each year. The posts do have a layer of corrosion on them but appear to be solid under surface.
CCA treated wood
Since 20 years ago CCA treating was still available I will presume this posts were CCA treated. CCA treated was suppose to last 20 years and in practice it will last longer but not indefinitely.Today they use other products to treat wood with equivalent results regarding the duration of timber in different different environments. All the procedure was and still is standardize. The biggest decay will be in the zone you have exposition to air and water, under the water the wood will last a life time especially if it was CCA treated. the whole structure will not collapse, you will eventually see one post or another giving in, warning you in advance. I would gradually replace the most affected ones but only the top part making sure to include the water line zone. Always remember pier posts must be flexible to absorb lateral loads.
Since 20 years ago CCA treating was still available I will presume this posts were CCA treated. CCA treated was suppose to last 20 years and in practice it will last longer but not indefinitely.Today they use other products to treat wood with equivalent results regarding the duration of timber in different different environments. All the procedure was and still is standardize. The biggest decay will be in the zone you have exposition to air and water, under the water the wood will last a life time especially if it was CCA treated. the whole structure will not collapse, you will eventually see one post or another giving in, warning you in advance. I would gradually replace the most affected ones but only the top part making sure to include the water line zone. Always remember pier posts must be flexible to absorb lateral loads.
I know a guy down in Lafayette LA who plumbed the top of his pipe so he could pump water into the pipe while he drove it. He sucked water out of the bayou with a pump he got at norther tool. The water jetted out of the bottom of the pipe while he pushed it down with a chain attached to a through bolt (and the bucket from a backhoe).
AND the crazy thing is his goal was not to drive the pipe.... he had attached the pipe to a big telephone pylon.... and the pylon went down with the PVC (like a knife through butter).
He had suspended the pylon with a chain using his backhoe, turned on the water and then lowered the backhoe bucket. It sunk about 10' in about 5 minutes.
If you got a soft bottom without much rock.... I think this same technique would work very well. Get some 4" pipe, and a high volume pump... Put an end cap on the pipe and plumb it so you can get a lot of water into that pipe. Push it down in the muck until it is at the depth you want and then cut off the end cap, fill with concrete and recap it. Maybe a good idea to run your through bolts before you pour the concrete...
And I like the idea of ramming a long piece of rebar through the center when you are done.
I like the way you're thinking. Also Missy's suggestion of replacing just the tops sounded interesting, but I don't know what kind of joint would be appropriate. Concrete would be nice, but the water is about twelve feet deep off the outside of my dock, so I don't know if that would be practical.
If I ever do a major refurb, I'll probably switch to a floating dock. There are several newer ones up river from me that I like the look of. They use a pair of moorings high up on the bank with long metal beams to hold the dock out and a diagonal pair of wires that act kind of like spring lines.
I am an engineer and have poured concrete pilings. Facts....
1) The bigger the diameter (pipe or wood) the more that dock weight is "distributed" to the earth bottom.
2) Concrete weighs more than wood. So "tall" pilings of concrete my sink slowly if not on hard bottom earth.
3) You can hydraulically drive a pile with a pvc pipe on a simple garden hose by flushing the soft bottom until you hit hard bottom (like in "rgranger"'s post). It is call "hydraulic jetting".
4) I would use 6" pvc at the "corners" and 4" in the middle. Concrete will flash set in salt water, so when you pour, ask your local "Ready Mix" company for an expert, which is normally free of charge, to make a "Through water pour". You can pour into a fresh water filled PVC pipe since the concrete will sink and displace the water.
5) Rebar is used to "holds concrete together and distribute loads". It doesn't resist loads. So rebar will help with lateral pounding of the posts and docks.
6) Use bolts through the pipe-concrete at top to connect the dock beams.
Galvanized metal needs air to "oxidize the zinc" and make the protective coating of zinc oxide. Submerged zinc dissolves away like your sacrificial zinc anodes on most boats.
Lastly... none of the treatment chemical ever hurt fish or environment (designed to kill rotting bacteria). Creosote was always the best, but looked ugly. The plastic wrap perhaps prevents barnacle, but doesn't stop bacterial rot.
Use PVC for longevity.
Jim...
1) The bigger the diameter (pipe or wood) the more that dock weight is "distributed" to the earth bottom.
2) Concrete weighs more than wood. So "tall" pilings of concrete my sink slowly if not on hard bottom earth.
3) You can hydraulically drive a pile with a pvc pipe on a simple garden hose by flushing the soft bottom until you hit hard bottom (like in "rgranger"'s post). It is call "hydraulic jetting".
4) I would use 6" pvc at the "corners" and 4" in the middle. Concrete will flash set in salt water, so when you pour, ask your local "Ready Mix" company for an expert, which is normally free of charge, to make a "Through water pour". You can pour into a fresh water filled PVC pipe since the concrete will sink and displace the water.
5) Rebar is used to "holds concrete together and distribute loads". It doesn't resist loads. So rebar will help with lateral pounding of the posts and docks.
6) Use bolts through the pipe-concrete at top to connect the dock beams.
Galvanized metal needs air to "oxidize the zinc" and make the protective coating of zinc oxide. Submerged zinc dissolves away like your sacrificial zinc anodes on most boats.
Lastly... none of the treatment chemical ever hurt fish or environment (designed to kill rotting bacteria). Creosote was always the best, but looked ugly. The plastic wrap perhaps prevents barnacle, but doesn't stop bacterial rot.
Use PVC for longevity.
Jim...
Joe:
Regarding joints in the treated wood posts there are many solutions. I will describe what we did. We decided only to overlap the damaged part, with two pcs. of treated 2x4 on each side of the post, always making sure to reach the not damaged zone, and there we placed two 1/2" galvanized bolts on each end, with washers of at least 1"dia. this to make sure neither end of the bolt would sink into the wood when tightened. The bolts in each end are offset (not in the same section) this, so not to weaken the original post with two 1/2" holes and at the same time increasing the leverage of the joint in case of lateral loads. When the lake was low an electrical drill was used but since this was done through the years some times the "tide" was high and then a hand drill was used. The whole repair was randomly done by inspection through different seasons. the last being 3 years ago, since then no problem. I guess you can also use brackets to embrace the 2X4 ´s, but eventually, some drilling has to be done to bear the vertical loads in case the decay advances towards the center of the original post.
One last thing on pressure treated lumber. Codes specify different concentrations regarding the final use, dock post are among the most severe uses, thus high concentrations are required, but this is difficult to get in the ordinary market, thus a common treated lumber for exterior use in housing has proven to me to be enough.
Regarding joints in the treated wood posts there are many solutions. I will describe what we did. We decided only to overlap the damaged part, with two pcs. of treated 2x4 on each side of the post, always making sure to reach the not damaged zone, and there we placed two 1/2" galvanized bolts on each end, with washers of at least 1"dia. this to make sure neither end of the bolt would sink into the wood when tightened. The bolts in each end are offset (not in the same section) this, so not to weaken the original post with two 1/2" holes and at the same time increasing the leverage of the joint in case of lateral loads. When the lake was low an electrical drill was used but since this was done through the years some times the "tide" was high and then a hand drill was used. The whole repair was randomly done by inspection through different seasons. the last being 3 years ago, since then no problem. I guess you can also use brackets to embrace the 2X4 ´s, but eventually, some drilling has to be done to bear the vertical loads in case the decay advances towards the center of the original post.
One last thing on pressure treated lumber. Codes specify different concentrations regarding the final use, dock post are among the most severe uses, thus high concentrations are required, but this is difficult to get in the ordinary market, thus a common treated lumber for exterior use in housing has proven to me to be enough.