Some fence posts rotten, others fine

[WalksWithTurkeys]

Last winter some of my rear side fence came down, and a few weeks ago I started replacing it. I’ve put up five panels, five to go. Six 3” by 3” wooden posts have been in place for 18 years or more, buried in heavy clay, and show no signs of rot. 18 years ago my neighbours replaced four panels, with new ones and 4” by 4” posts. All these posts rotted at ground level. They were set in concrete, but each post was surrounded at ground level by soil. The posts rotted at soil level. The part in the concrete was in each case solid. Clearly the wood was in contact with wet soil and rotted. But why did the posts set only in soil (clay) not rot?

My neighbour suggested that the older posts were better. He might have a point, maybe a better form of preservative.

As an aside, wood buried in clay does not rot as air is excluded. Venice was constructed in the middle of a marsh and each building is built on wooden stakes driven into a clay subsoil. Some of these wooden stake foundations are over 1,000 years old.

 

[JohnD]

Wood rots at the point where the wet from the ground, meets the dry from the air.

There will always be a point where the dampness and air mixture is ideal for rot.

You can make the junction higher or lower, but there will always be one. It is usually worst a few inches above the ground.

Concrete posts and spurs do not rot. Unless you make a living out of replacing rotten posts, you may decide concrete is worth it.

 

[WalksWithTurkeys]

The question was about why one set of posts set in heavy clay soil are still solid, whereas those partially in concrete are rotten.

Concrete is out because I cannot lift 8 foot concrete posts, and I cannot lift into place 6 by 6 foot panels. Wood posts set in concrete are easy to set, look good, and are easily replaced. Plus when a panel fails, replacement is simple, not requiring me to hire trades. Oh and panels fixed to concrete posts rattle in the wind, which is really annoying. Plus according to various sources concrete posts have a life expectancy of 25 years. And lastly, concrete is environmentally very bad, wood is good.

 

[JohnD]

Concrete spurs are manageable, and you can bolt wooden posts to them, clear of the ground.

At my previous house, concrete spurs were still sound after 80 years.

 

[WalksWithTurkeys]

They are manageable, but expensive and ugly.

 

[camerart]

Hi W,
Where posts are set into concrete, the concrete is a water trap, and so stays wet.
How about steel post holders concreted into the empty old concrete, with an upstand up from the ground for the new posts.
Seal the posts first.
C

 

[WalksWithTurkeys]

Hi W,
Where posts are set into concrete, the concrete is a water trap, and so stays wet.
How about steel post holders concreted into the empty old concrete, with an upstand up from the ground for the new posts.
C

Are you saying the concrete absorbs water, or the water lies on top of the concrete? I assume the latter.

The fence is nearly done now, six panels in, four to go, woodennposts in concrete, with the top of concrete exposed to the air, and domed to shed water.

 

[camerart]

Are you saying the concrete absorbs water, or the water lies on top of the concrete? I assume the latter.

The fence is nearly done now, six panels in, four to go, woodennposts in concrete, with the top of concrete exposed to the air, and domed to shed water.

Hi W,
If you scoop the old posts out of their concrete bases, the hole left 'cups' will fill with water.
Water runs down the posts, and seeps down into the concrete 'cups' and can't drain out.
Water needs to be shed away from the seal.
C

 

[Munroast]

The question was about why one set of posts set in heavy clay soil are still solid, whereas those partially in concrete are rotten.

Rot needs a certain level of dampness to flourish, too wet or too dry and wood won't rot as quickly. The posts set in concrete in your garden must be providing a better environment for the fungus to thrive

How was the top of the concrete finished off ? does rain pool round the wood or run off ?


So many variables it is difficult to guess - I have a line of 10 posts in one part of our garden all set in concrtete 24 years ago, 3 have rotted quite quite badly, the others seem perfect.

I noticed the rot in these posts maybe 5 years ago, and I poured a lot of old engine oil in - they have not deteriorated since.

It is amazing how far the oil has worked up the post (rising damp)

 

[Stuart981]

Rot needs a certain level of dampness to flourish, too wet or too dry and wood won't rot as quickly. The posts set in concrete in your garden must be providing a better environment for the fungus to thrive

How was the top of the concrete finished off ? does rain pool round the wood or run off ?


So many variables it is difficult to guess - I have a line of 10 posts in one part of our garden all set in concrtete 24 years ago, 3 have rotted quite quite badly, the others seem perfect.

I noticed the rot in these posts maybe 5 years ago, and I poured a lot of old engine oil in - they have not deteriorated since.

It is amazing how far the oil has worked up the post (rising damp)

Never had a post treated with engine oil fail. I mix it 50/50 with kerosine and paint it onto the lower half of new posts.

 

[Munroast]

Never had a post treated with engine oil fail. I mix it 50/50 with kerosine and paint it onto the lower half of new posts.

I know a farmer has posts he is going to use stood in a 45 gallon drum of a mixture like that, lets them soak in it for weeks beofre knocking them in - they don't rot - the oily nature of themm makes them easier to knock in too

What a mess though

Used engine oil is a fairly toxic unpleasant chemical, it will kill any life around it,

as for the one's I did above, I drilled a hole down, fitted a pipe and then set up a drip allowing the oil to slowly soak in. that could have been 5 years back and they don't seem to have got any worse - and the plants either side didn't die.

 

[WalksWithTurkeys]

Hi W,
If you scoop the old posts out of their concrete bases, the hole left 'cups' will fill with water.
Water runs down the posts, and seeps down into the concrete 'cups' and can't drain out.
Water needs to be shed away from the seal.
C

You’ve lost me.

The new posts are set in fresh concrete which ends above ground level and slopes downwards away from the posts. So basically the post emerges from the top of a small mountain.

I discovered Durapost recently, basically metal equivalents of concrete posts. But they are easier to erect, as a panel can be screwed into one post, then the second post screwed on. And of course they are light.

 

[WalksWithTurkeys]

Rot needs a certain level of dampness to flourish, too wet or too dry and wood won't rot as quickly. The posts set in concrete in your garden must be providing a better environment for the fungus to thrive

How was the top of the concrete finished off ? does rain pool round the wood or run off ?


So many variables it is difficult to guess

Indeed. The top of the concrete was pretty much flat and covered with a few inches of soil. Also I noticed my neighour has a gutter with a downpipe hole, but no downpipe. That hole is approximately above the first postpost, and the garden slopes downward. So it it is possible that there is an excess of water around the first posts, favouring rot. Certainly the soil around the last five or six posts, which are solid, is currently much drier. I asked him to direct the water away from the fence, goodness knows what he will do. He built a small workshop behind his garage, and the water used to land on his patio and drain away.

 

[robinbanks]

It only takes one litre of oil to contaminate a million litres of water, and you pillocks are wilfully pouring it into the water table

 

[Munroast]

It only takes one litre of oil to contaminate a million litres of water, and you pillocks are wilfully pouring it into the water table

No - I was pouring the old engine oil into the rotten fence post, the fence post is encased in concrete so any that escaped the timber would be contained by the concrete

as for the farmer I mentioned, the oil will have been absorbed by the wood - no one is pouring oil into the ground