One of the weak points on a fence post is the end-grain exposed top - water gets there and starts the decomposition process. So placing a cap on the post to shed water - just like a roof or a rain hat - makes sense.
There are boat loads of commercial options for your basic 4x4 post - copper, solarlights, mitered wood, etc. But they are expensive and I'm using round posts or variable diameter so options are needed. And since I'll need something like a hundred of them I'm not interested in crafting them.
Any suggestions/experience on post caps? Old pie tins? hubcaps? just slabs of wood? dessert plates and a blob of silicon? freakishly large jar lids?
After 40 + years of fixing fence. I can tell you that your posts will rot at ground level.
Lots of cheap options for capping. #10 cans from a restaurant will fit over most posts. Old pie plates, cowboy boots .
Squares of old roofing tin, rubber tire squares.
About anything you like, although most will look odd to your neighbors ...
You'll be that eccentric new guy that bought the old Smith place!
I think simply cutting the top so it's beveled like 15 or 22.5 degrees for example to shed rain is all that is needed, and buying or making things is unnecessary, unless an artful take is desired. As Thomas noted, the fence post will decay at the ground long before decay at the top of the post could compromise the fence post. I have driven by fences that had an upside down coffee can on every wooden post developing a rusty patina and giving things a certain rustic look.
"Study books and observe nature; if they do not agree, throw away the books." ~ William A. Albrecht
Whilst I am in agreeance with all advise, I also happen to disagree with it as well!!!
I too have been fixing domestic fences as a business for many years.
And sloping the top of the post is a great start, but is hard on farm pence posts to carry out.
I have installed house stump ant caps on many farm posts.
Posts will certainly rot in the area of the soil that changes from dry to wet over time, continually.
But often decks are built with no post in the soil.
I have seen many posts in poor condition because of water entry at the top.
In fact I suggested to somebody last week they should think about capping the post during the restoration they were undertaking.
Anything that does not blow away will work.
\ But, why is copper too expensive, compared with the cost of post removal?
John Daley Bendigo, Australia
The Enemy of progress is the hope of a perfect plan
Be careful using cans that leave space, I have found the hard way that bees, wasp and yellow jackets like to live in the extra space and when the can is disturbed those little stingy things get mighty angry. I have since gone to leaving them open and when they rot it is at the bottom at ground level.
When I installed my meter pole I capped it with tin can lids.
I'd nail the lid to the side of the pole and hammer it over and nail it to the top. I used several lids. The last nail was a roofing nail and went through the top. The nails had been dipped in silicon adhesive to seal them.
I got that idea from old piers. The posts were capped with metal sheets to preserve them. Looked cool anyway!
ETC(SW) US Navy, retired
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The Greenhouse of the Future ebook by Francis Gendron