Wood Posts Set in Concrete
Here in the Raleigh / Durham area of North Carolina, the industry standard is to set wooden posts in concrete. I am well aware of pros and cons of doing this, and maybe at another time I will post on that subject. In the area I live in, the standard is to set the posts in concrete, and having signed a contract to install a fence this morning in Holly Springs, NC., the customer questioned our practices for doing this. I immediately thought this would be a great topic for the blog.
Retention Level:
Retention level may or may not be something you are aware of when it comes to having your fence installed. Retention level refers to the amount of preservative that remains in the wood after the treatment process is complete. It is measured on a weight basis and is typically expressed as pounds of preservative per cubic foot (pcf) of wood. There are a number of typical retention levels available. Generally, the harsher the condition the wood is exposed to, the higher the retention level must be. Typically, the pcf for above ground use (wood not in contact with soil) is .25, and the rating for ground contact (wood in contact with soil) is .40 or higher. The wood we use for our posts is rated at .40.
How Far in the Ground Should the Posts Be?
This question comes up often, and surprisingly, you will get different answers from different contractors on this one. Typically, we set posts 24″ in the ground for five and six foot tall wooden fences, and 18″ in the ground for a 4′ fence. Now, there are instances where this is completely impossible to achieve. Some examples are: close to the building you can run into the footing, the terrain you are digging in has very large rocks under the soil, and there are other instances where this happens. In these situations, we try to go at least 18″ and make a wider hole to add more concrete to add to the stability of the post.
Digging the Holes:
Typically, we use a gas powered, two man auger to dig the holes for our posts. When that is not possible (underground utilities present) we hand dig with post hole diggers. Obviously, the gas powered auger is the most efficient way to dig the holes, but there are other important reasons for this. When digging with post hole diggers, it is very easy to dig a hole which is more narrow at the bottom than at the top, this could create issues of the posts rising during extreme weather where the ground freezes. Using the auger allows more of a uniform hole to work with.
The Concrete Has to Set!:
After we have laid out the line of the fence, and dug the holes, we set the posts in wet concrete. Typically, 40lbs of concrete per hole on line posts, and up to 80lbs for the corners and gate posts (we use 6×6 posts for ALL gates). Here is where my customer from this morning questioned our policy. He told me the neighbor behind him recently had a fence built, and the contractor came and finished in one day. At Carolina Custom Fences, LLC., we ALWAYS let the posts set in the concrete overnight, allowing the concrete the time it needs to properly set up. If this is not done, the chances of the fence becoming “shaky” or developing a “lean” are much greater.
Conclusion:
As we are constantly trying to set ourselves apart from the “typical” fence contractor, here is another example of something that may take a little longer but achieves a much higher grade of installation. So, when you decide to choose to hire a fence contractor, ask some questions about their installation methods, and choose accordingly. It may cost you a little more now, but it will save you much more later!
Keith R. Bloemendaal
