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Pressure-treated wood and concrete are two commonly used building materials for exterior applications. However, setting the wood in concrete may create a situation that speeds wood rot.
Pressure-treated wood will rot in concrete when exposed to wet conditions such as trapped water. In optimal conditions, pressure-treated wood set in the earth may last as long as 40 years. However, when vertically set in a non-draining concrete base, pressure-treated wood may last only a few years.
Despite pressure-treated wood subjected to a solution of chromium, copper, and arsenic, the treated wood will still rot in time. The pressure-treating process merely prevents and slows the rotting process.
Wood, whether treated or not, will absorb moisture. The moisture will carry along the wood like a wick carries hot wax. And the wood can also swell from the added moisture.
The moisture that wicks along the wood will continue to do so into the cavity where the portion of the wood is embedded.
The moisture is then trapped inside the concrete, causing an accelerated rotting effect on the wood. Think of it like a cup holding water. Although concrete will allow a certain amount of water to soak through, it is nowhere near porous enough to count for a drainage effect.
How To Put Pressure Treated Wood In Concrete And Avoid Rotting
If completed correctly, several simple practices may extend the life of any pressure-treated wood embedded in concrete. Let’s take a look at some successful steps to marry with wood and concrete.
Install a gravel base first.
After digging your post hole, for example, or forming footings, ensure that before any concrete or wood is poured or set in place, a coarse gravel base of at least several inches is set at the bottom of your hole or formed area.
Before pouring concrete, set the wood in place directly on top of the gravel.
Concrete Around The Wood.
Never pour concrete, then place the pressure-treated wood. Always pour concrete around wood, never under the wood. If a proper coarse gravel bed installation is complete as per step 1, then the wood sitting on top of the gravel will be able to drain any moisture collected in the concrete due to the coarse gravel layer beneath. The concrete will not be under the wood, merely around it.
Slope The Surface.
After the pour, gently slope the surface of the concrete away from the wood. This practice will help direct any water away from the wood, helping to prevent pooling at the base that could seep into the void between wood and concrete or wick and the wood itself.
The Steel Bracket Solution
If you’re thinking that adding a gravel base, ensuring the wood is directly on the gravel with concrete around, and sloping the surface are tedious additions in a vain attempt to prevent the inevitable, you’re not alone.
There is an entirely different approach to installing wood to concrete that may prove to be the best solution of all – the use of an anchored steel bracket.
Whether it’s a post-installation or you’ve got loftier ambitions for your build, utilizing steel brackets embedded in concrete, elevating the wood off the concrete’s surface, is a much more resilient solution.
The steel bracket can be pre-painted for maximum durability and longevity, preventing oxidation. And the fact that the wood will never touch the concrete means that we have effectively solved the issue of water pocketing inside the concrete, accelerating wood rot potential.
Wood and Concrete Connection – FAQ
Is It ok To Put Pressure Treated Wood In Concrete?
Setting pressure-treated wood in concrete is ok with the awareness that unless proper installation techniques are employed, the wood will face an accelerated rotting situation.
Following the recommendations mentioned earlier in this article will help reduce the concrete’s potential for wood rot. However, the sound solution is an installation using some form of bracket embedded in the concrete, rather than the wood.
Does Wood Rot In Concrete?
Wood embedded in concrete will rot over time. Wood exposed to the elements and embedded in concrete will allow moisture to build within the concrete around and permeating the wood.
Over time, as the wood dries, it tends to shrink. Conversely, as wood becomes wet, from rain, for example, it tends to swell. This shrinking and swelling from moisture levels allow the wood to move within the concrete, creating a void between the wood and concrete itself. This void, combined with the wood acting like a wick, can allow moisture deep inside the concrete.
Whether the wood is pressure-treated or not, having moisture inside the concrete, keeping the wood wet, will cause an exaggerated rate of rotting of the wood within the concrete.
How Long Will Pressure Treated Wood Last In The Ground?
Pressure-treatment of wood is a sure-fire way to improve the longevity of the wood and prevent rotting. It isn’t a perfect silver bullet to our werewolf of rot, though. The length of time that pressure-treated wood can survive rot free in the ground has more to do with the wood’s preparation and installation than installers would like to admit.
Under normal conditions, without proper treatment and installation, pressure-treated wood will typically last around 8-10 years before facing catastrophic rotting failure when the wood is in the ground.
According to the Forest Products Laboratory and other research groups, properly treated and installed pressure-treated wood may last as long as 40 years rot-free.
Why is this disparity in the length of time pressure-treated wood can survive rot free in the ground? Well, a lot of this has to do with myth, believe it or not.
Many homes currently built with the fast-turnaround time in mind don’t account for longevity. The builders are playing a numbers game, and the longevity of the homes and installations are not at the forefront of most builders’ minds. With that in mind, a common practice is to rush installations and avoid incidental costs. It may include properly treating pressure-treated wood before it hits the dirt.
Even pressure-treated wood can absorb and shed moisture, dependent upon local climate conditions. With this in mind, knowing the wood will swell and shrink due to moisture makes us aware of how the wood fibers are being ripped apart over time – all by water.
Painting or staining pressure-treated woods with a water-repelling agent allows the wood to survive much longer without being destroyed by water.
Likewise, any holes drilled into the wood for inserting screws, bolts, or similar metal fasteners will allow water to seep in and accelerate the rotting or warping process. Sealing these sorts of drilled or cut locations will help prevent rotting, especially if the wood is in the ground.
How Do You Keep Pressure Treated Wood From Rotting?
As mentioned above, using techniques like keeping wood moisture-free is a sure-fire way of protecting the wood from rot.
Utilizing treatments that cause water to be repelled from the wood’s surface, dissuading soaking and leaching into the wood, will vastly expand the potential for rot prevention. Think of those greased railway ties sitting in a gravel bed for train tracks. The treatment is so good at repelling moisture that the ties last for generations.
Installing wood apart from any moisture-holding substrates like the ground or installing above concrete via a bracket will help prevent rotting.
What Should I Put Between Wood And Concrete?
Using a bracket such as the Sturdi-Wall Plus wet-set bracket mentioned earlier is an excellent way to marry wood to concrete in a structural build. A bracket such as this can be used for form or post-hole installation as the bracket accommodates a 6×6 in the vertically mounted position.
There are multiple similar brackets available. And many to accommodate different lumber sizes, and these solutions are some of the best options for installing between wood and concrete.
What Is The Best Glue For Wood To Concrete?
There are several different products on the market, claiming to work well for bonding wood to concrete.
In independent testing, we found that epoxy products tend to work very well for adhering wood to concrete or cement.
One of the best products on the market is the LePage PL 9000 heavy-duty construction adhesive. This stuff can hold a steel commercial garage door opener on a block wall with no other anchors – we’ve tried and tested this, it’s true!
Another highly rated product for adhering just about anything to concrete or cement, including wood, is the Gorilla Heavy Duty Construction Adhesive product.
Why Should Deck Posts Not Be Set In Concrete?
Setting deck posts in concrete is a sure-fire way to ask for a lot of work. And in as little as a few years, depending on local conditions.
Using the techniques mentioned above for wood to concrete installation when embedding the wood is the least one can help prevent wood rot. Wood rot will most definitely occur when installing deck posts in concrete; it is inevitable and only a matter of time.
If one doesn’t install a draining gravel bed at the base of each post, then water collecting ‘cup’ of sorts is created when installing wood in concrete or cement. This act will accelerate wood rot within the concrete, which is why wood deck posts should not be set in concrete.
Using an anchoring system to marry wood deck posts to concrete is a more suitable solution for the wood’s longevity.