Taking a short break from electronics to document an easy solution for the frustrating home repair of rotten fence post replacement. Here in Seattle, it is quite common for pressure treated 4×4 fence posts to rot from the ground level down after about 20 years in the humidity. Standard replacement method is to dig out and smash up all of the 24″ concrete base surrounding the rotten 4×4 and replace with new concrete. Two feet ( ~1/2 a meter ) down is a lot of digging ( especially in Seattle clay+rock soil ) and with 3 rotten posts ( and 27 more most likely to fail in the next 5 years ) – I set out on an engineering mission to find an easier – greener – way. This might not seem appropriate for a Black Mesa Labs post – but just like how BML does things very different in electronics from society norm ( example : soldering 45nm QFN FPGAs onto 2-layer PCBs using a $20 hot plate ) – the fence post removal was a full Thomas Edison obsession of doing something different through persistent experimentation. Going into this project I was told by countless people 1) That just isn’t how it is done, 2) It won’t work and 3) Just hire a guy to take care of it. Like all things at Black Mesa Labs, I was determined to do things different.
Through much trial and error – this is the Black Mesa Lab “Cork Popper” method of fence post removal and replacement without all the digging. This method supports removing the rotten section of 4×4 while retaining the majority ( 75%) of the existing concrete base in place. Keeping the existing concrete also means the new post will be in the same location and plumb as the previous post. Less waste, less effort, faster repair.
Step-1 ) Tear down the fence sections supported by the rotted 4×4 post. A Sawzall with a metal cutting blade that rips through nails makes quick work of this.
Step-2) Dig a hole 12 inches ( 1/3 meter ) down around just two side of the concrete base. This is only 1/2 the depth of the entire concrete base. Once exposed, this concrete will now be like an egg-shell ( assuming it has been in the ground for 20 years ). The packed earth is the only thing holding this structure together at this point in time. Using a wrecking bar and a small sledge ( or even just a hammer ) – pry off the exposed concrete. It should easily break off with very little effort.
Step-3) Post Extraction. With the concrete removed, the post is now much easier to extract as only the very bottom 12″ is applying pressure against all 4 sides. If the post is not entirely rotten, the easiest method is to drill a 3/4″ hole through the post above ground level and shove a segment of 1/2″ black iron pipe. For less than USD $40 total I purchased two matching 6 ton hydraulic bottle jacks which can then lift the iron pipe ( and 4×4 post ) slowly out of the ground.
Step-4) Is only necessary if Step-3 failed – the post is so rotten that it breaks into 2 pieces, a 6′ above ground section and a 2′ below ground section. Using a small hand saw ( such as this great little folding jab saw ) – or an awesome mini “Sawzall” such as this 12V Bosch reciprocating saw cut the rotten section away and leave a nice level 4×4 surface of fairly decent wood. A friend of mine says this 12V Bosch is actually made by Playskool , but I don’t care – it gets into really tight places. Trick is to have lots of 12V Lithium Ion batteries ( I have 5 ).
Step-5) Attach the extractor. I built this extractor for about $40 using these 12″ lag bolts and some eye bolts from Home Depot and this 5,000 lb 36″ trailer safety chain. I have 30 posts total in my fence – so money well spent. Extracting the old 4×4 in tact means I can reuse 75% of the existing concrete base. This is about 150lbs of concrete I don’t need to buy, haul and mix and old concrete I don’t need to dig out of the ground and toss into a land fill. Win-win.
Step-6) Screw the extractor into the remaining section of post using a ratchet and then lift it out using the bottle jacks.
Step-7) Insert the new post. I used Hem-Fir Severe Weather Standard Pressure Treated Lumber (Common: 4 x 4 x 8; Actual: 3.5625-in x 3.5625-in x 96-in) from Lowes for $10. The 4×4 post should go in easily assuming dry wood and should already be plumb ( but check with a level ). Pounding with a 4lb sledge from the top if necessary. I really like this 4lb sledge as it is small enough to wield on top of a 6-foot ladder like a normal hammer but still packs a punch. For the old/new hybrid base, surround the exposed 4×4 with some chunks of 4x4s or 2x4s as temporary spacers and then surround those with some cardboard. Fill in outside with packed dirt. Remove the wood blocks and pore the concrete between the post and the cardboard. I used a single 80lb bag of concrete for 2 posts. I think next time I will buy 50lb bags instead as the 80lb bag is just awkward to handle. While the concrete sets – remove old nails from the fence panels and then start rebuilding. I rebuilt using these Deckmate star drive screws and my Bosch Impact Driver. Very little effort and time compared to hammering and will make the next tear down job much easier. Hopefully this post will last another 20 years.
12 hours of work start to finish and the Job is done!
I hope you found this short tutorial on a quick and easier method of fence post extraction and replacement helpful.