How to protect fence posts from ground rot and frost damage
You might be wondering why I'm going to talk about protecting brand new fence posts from ground rot and frost damage? I build my fences to last 30 years, and in 15-20 years time, if you haven't gone the extra mile to add this crucial step, then getting 30 years out of the fence is going to be difficult. Time will take it's toll on any timber which is in the ground, it's just a fact, but if you do this, you can maximise the life you will get out of that timber.
If you can see my photo there, the black stuff all around the foot of the post is bitumen. It comes in a tin and you literally paint it on.
If we didn't do that, when the soil is spread even along the base of the fence, that soil would be in direct contact with the timber, and that's not a good idea.
Timber is porous, and like a wick, it will draw up moisture. Why is that a problem? In winter, that moisture is going to freeze, and when water freezes, it expands, and just the same as it will burst your pipes, it will, believe it or not, burst all the timber fibres apart every time there's a hard frost. Now it doesn't have the dramatic and catastrophic effect of a burst pipe. Your fence doesn't suddenly fall over during it's first winter. This process happens slowly over time, little by little, one layer at a time, until eventually there's not much left to hold the fence up, and over she goes.
So that's problem one.
Problem two is the soil itself. Timber is an organic material. If you put a piece of timber on the compost heap, nature will break it down and turn it into more soil, and that's exactly what happens, albeit slowly in treated timber, when soil is in direct contact with it. Mother nature simply says "thank-you very much, I'll have that". Much like the frost damage, it doesn't happen fast, but we're looking ahead here past 10 and 20 years down the line, when the potency of the timber treatment has faded. That's when the added protection of the bitumen really comes into play here.
There's one more issue which I'm betting most fencers and gardeners have experienced at one point or another, and that is Woodlice. Those little pre-historic critters will be put off initially, when the foul taste of the treatment is still strong, but give it a few years and their hunger for wood fibres will kick in and they will set up a huge banquet on your fence posts, down at ground level, just under the surface of the soil, out of sight and out of mind. They will literally mine a cavern out of the fence post and have a nice dry and cosy cave inside to build a new colony and raise the future generations of woodlice. They are just another division of mother nature's army constantly fighting to bring the whole place down lol.
The hard shell of bitumen will act as a strong barrier. Woodlice won't typically climb, they like to stay low, so I cover about a foot at the bottom of each post in the bitumen and make sure it's overlapped onto the concrete to completely seal the timber off from attack.
I'll get you a link to the stuff I use. It's Black Jack, for sealing leaky roofs, but it does this job equally as well. There's no way I know of to wash this off a paint brush so I would just buy the cheapest throw away brushes in the pound stores and use them once and dump them. Wear gloves too, and don't get it on you. If it gets on you, you'll need commercial wipes to get it off or about an hour in the shower with a nail brush lol
Here it is here: (I get about 10 posts done from each litre tin and I really lather it on thick.)