below ground bitumen paint for wooden posts in concrete. Will it trap moisture ?

[Neilornoneil]

I have some sign posts made from sapele hardwood. Its like a goal post arrangement . 2 posts (3"x"2") with the sign panel bridging the top.
I've been advised to apply bitumen paint to the bottom of the posts up to just above ground level. I am worried that if the post is sealed it will accumulate moisture and rot out anyway, The ground is quite clayey so I need to do something. Will painting with bitumen do a good job? What do you suggest?

 

[Neilornoneil]

I read a previous post which suggests waterproofing a band of 6 - 8 inches which is the sweet spot for fungus decay which is less likely below this. I will use bitumen primer and bitumen paint to protect this area only.

 

[Burnerman]

Neil, have a look at postsaver.com
In particular, fence post rot protector sleeves. Just the job!
John

 

[JohnD]

A wooden post in the ground will rot, at the point, usually just above ground level, where the gradient of damp and air reach the perfect proportions. If you apply a band of waterproofer the perfect level will probably be a bit higher.

Setting them in concrete makes it a difficult and laborious job to remove them.

To repay the effort of digging the initial hole and filling it with concrete, use a precast concrete repair spur, and bolt your wooden post to it, above ground level and not in contact with the ground.

 

[StephenOak]

A wooden post in the ground will rot, at the point, usually just above ground level, where the gradient of damp and air reach the perfect proportions

But only if the post is allowed to have sufficient water & oxygen. And that can only happen in a relatively narrow height band.

The OP's second post refers to a thread, which may well be the one where I posted this

What can I replace this wooden stake railing with that wont rot so often?

I have a small walkway on the edge of my steep garden which is stake posts and handrails, with soil and chippings in a kind of trough. I have to replace them from time to time and I have also treated them regularly. I also don't really like the look of them but don't want to spend a fortune...

www.diynot.com

As I said there I have not used them but John (@Burnerman) recommends them and he knows what he is talking about.

 

[JohnD]

But only if the post is allowed to have sufficient water & oxygen. And that can only happen in a relatively narrow height band.

If you put a cover on part of the post, the ideal point will just move somewhere else.

It happens at the level where water rising by capillary action matches the rate of evaporation..

the same thing happens in a wall.

Too wet below, too dry above, perfect in the middle.

 

[StephenOak]

If you put a cover on part of the post, the ideal point will just move somewhere else

On that basis, a cover that extended 6 foot up the post would mean that it would rot c. 6'6" in the air.

Will capillary action take the water up that far?

Have you ever used these protector sleeves? I doubt that John (@Burnerman) would recommend them if he had not done so.

 

[JohnD]

On that basis, a cover that extended 6 foot up the post would mean that it would rot c. 6'6" in the air.

No, it will rot at the point where the "too wet " section meets the "too dry" section to form the "just right for rot" section. Which is "somewhere else"

Is there one of these sections you think does not exist?

 

[Burnerman]

I’ve used the heat shrink sleeves on 3x3” posts, on a diy fence around my septic tank.
8 posts in total, 7 are wrapped and set in postcrete, 1 that isn’t as it was too close to a salt glaze pipe.
I can’t say how things are going, but the wrapped ones show no capillary attraction, the unwrapped one looks wet and has developed a large shake.
Time will tell, but rot proofing at the timber yards is not what it was, probably due to green issues so every little helps I think.
The posts are capped and heavily coated in a creosote like solution.
I would recommend this product!
John

 

[Neilornoneil]

Thanks to you all
The posts had to go in this week, so I have used black jack primer and paint. Hopefully it will deter rot for a few more years than if I did nothing.
The post saver product does look to be a worthwhile option, which I will consider next time I erect posts. I have tried to copy the principle by applying the band of 'primed' bitumen to the same area as the post saver is positioned. I had not considered leaving the bottom section untreated , but it seems to make sound sense to seal just that area. I'd always wondered why the very bottom of an old post seemed better than the few inches around ground level.

 

[StephenOak]

No, it will rot at the point where the "too wet " section meets the "too dry" section to form the "just right for rot" section. Which is "somewhere else"

So evading rather than answering the question.

Is there one of these sections you think does not exist?

That is a meaningless question, so I will ignore it.

Someone, correctly, said "A wooden post in the ground will rot, at the point, ... where the gradient of damp and air reach the perfect proportions" (emphasis added). It is not just a matter of "too wet" meeting "too dry".

Sealing the air out, part of the purpose of these protectors, means that there will not be sufficient air at the height where there is the right level of moisture.

 

[JohnD]

Sealing the air out, part of the purpose of these protectors, means that there will not be sufficient air at the height where there is the right level of moisture.

That's an interesting suggestion.

So what else do you imagine will be in the cells of the timber, when they are partially, but not entirely, filled with water?

 

[JohnD]

Let's try another tack.

You have a piece of wood which is completely wet at one end, and completely dry at the other end.

There will always be a section, somewhere along its length, that is "a bit damp"

Do you think there is anything you can do to avoid having a section that is "a bit damp?"