Ethical Concrete Use
05/09/19 13:53
The most ethical way to use concrete is not to use concrete unless there truly is no alternative. This is because concrete has an enormous environmental cost that is absolutely not reflected in the money we pay to acquire it. It takes a lot of energy to make the cement portion of concrete. Concrete includes sand and small rock fragments. The sand is actually becoming short in supply - beach sand doesn’t work because it has rounded edges. Concrete needs rough edged sand. But making the cement that gets mixed with sand and rock... that takes a lot of energy. And we make a lot of cement. That is in part because concrete is used more than any other human-made material, and is the second most consumed substance in the world, right behind water. (http://concretehelper.com/concrete-facts/)
About 10 billion tons of concrete are produced every year, and it takes between 3.3 and 3.6 Gigajoules of energy to produce each ton of concrete. (https://en.wikipedia.org/wiki/Concrete#Cement). That works out to be between 33,000,000,000 and 36,000,000,000 Gigajoules spent making concrete. In 2013 it is estimated that the world produced 5.67x100,000,000,000 gigajoules, or 567,000,000,000 (https://en.wikipedia.org/wiki/World_energy_consumption). You can see where this is going.
The world uses about 33/567 of its energy it produced just to make concrete. That is 5.8% of the energy used on the entire planet!
It puts almost a pound of CO2 into the atmosphere for every pound of concrete produced. (https://www.cement.org/docs/default-source/th-paving-pdfs/sustainability/carbon-foot-print.pdf)
More on concrete and CO2 here: http://www.nrmca.org/greenconcrete/concrete co2 fact sheet june 2008.pdf
I believe it is my responsibility to reduce the carbon footprint of my business. I want to make choices that improve the carbon footprint of my projects without reducing the quality of my work. My lower-carbon approach cannot cost so much more that my clients will reject my proposals, because someone who charges less will probably also care less about the carbon footprint of their approach. The environment has no advocate if it isn’t us.
Fortunately in my business at least there are often alternatives. Most of the rest of this blog entry is about those alternatives. I am providing them for my clients who want to know why I work the way I do, and for other people who make fences, as a resource for their use in reducing the carbon footprint of their business.
First, I must repeat that the best use of concrete is no concrete at all. Meaning that if you can find a solution that doesn’t require adding any new concrete, that is a superior solution so long as it meets all relevant needs.
In this category falls:
For new fences either without any existing post bases or where they are not in useful locations I use Sika Post Mix, an expanding polyurethane foam. (https://retail.usa.sika.com/en/products/specialty/sikar-postfixr-fence-post-mix) It costs about $12 for the equivalent of 120 lbs of concrete. Not only is it not backbreaking to carry, it requires no cleanup like concrete equipment does. In my time-and-materials business this is a win for my client. The foam cures in a couple hours so if I start posts in the morning I can be building a fence in the afternoon. It is fine for fence posts. I don’t use it for gate posts (on which the gate hangs). It isn’t designed for structural applications like decks and or gate posts. But I spoke with someone who observed a new telephone pole which was secured in its hole using a durable foam instead of concrete. Here is one such product: https://rainbowtech.net/products/pole-setting-foam/
If there are already concrete post bases then I try to re-use them. To reuse the post base I dig out the remains of the original wooden post. It is usually rotted. People don’t tend to replace fences that don’t have a problem, and the most common problem I see by far is rotted posts, right at the base. Fence posts rot at the top of the concrete when the wood comes in contact with soil there. When the fence was made there was no dirt there, but years of accumulated leaves turn into dirt and that rots the post below the new soil line. Once the rotting begins gravity pulls water into the post base through the rotted collar around top of the post base. Over time the post decays and the fence begins to lean. It might not fall over because plants and trees might be holding it up. One service I provide is to replace only the posts and reattach the fence to the new posts I install. I replace one post at a time. It is best to get the most life possible from a wooden fence - there is no need to replace the pickets and laterals if they aren’t rotted. And, if someone is considering it both ways, the first job would be to replace the posts either way, so building the new fence is what takes the additional time and materials.
I use tools like crowbars, a demolition hammer and a hammer drill to dig, break up, pull and pry out the old wood of the original post. The worst cases are where the wood isn’t fully rotted yet. In the best of cases the old post has turned into dirt and I can dig it out with my hands.
Once the post base has been cleared of the old post, to at least 14” deep, I plane the end of a new post so that it will fit. Occasionally the original post had a defect (such as a shaved corner) that was cast in concrete. I have to match whatever shape the original post was, but it isn’t usually difficult. Since the bottom of the post base is sometimes covered in dirt, I will put in gravel or rocks so the new post doesn’t contact the dirt at the bottom. I treat the bottom 2’ of the post with a water seal and then drive the post into the original post base.
Sometimes the new post is perfectly plumb (vertical) and if I am just replacing posts it fits neatly back into the original fence. But sometimes it isn’t plumb. I can tell using a long level how plumb it will be. When it isn’t plumb there are a few choices:
The first option requires a bit more wood and woodworking, but it can look beautiful, depending on one’s aesthetic taste. I tend to mount a 2x4 vertically and attach it to the post with short blocks or 2x4 ties on the side of the post to the plumb face. Wood isn’t too expensive and the time would have been spent cracking and removing concrete.
To accomplish the second I use a hammer drill to drill a line of holes from a corner straight to the perimeter of the post base. If I am removing 1/4 of the post base these two lines of holes will be at right angles to each other. To remove half the post base these lines of holes are aligned on opposite sides of the post base. Once the holes are drilled I use a demolition hammer with a 3” wide bit to break the concrete along the line of holes. Once it is cracked I use the demolition hammer to break up the section to be removed. I try not to damage the soil around the concrete I am removing. Once the concrete is removed I mount the post plumb and fill in the gaps around it. If the post base is leaning toward the fence break away the part away from the fence. If the post leans left break away the right side. If it leans in two directions you’ll have to break away half of the post base and then it might be worth replacing the whole thing with a new Sika Post Mix base.
Why not just dig out the old post base and pour a new post base? You could, but in my opinion it is better to reuse an existing concrete post base if possible. Reuse is superior to recycling is superior to single use. Concrete really is an amazing material that makes wonderful post bases. By all means, if they are already there, don’t waste them! If you take used concrete to the dump you’ll probably find it costs about twice as much to throw away as to purchase! Or more...
You can dig a post base out, but the hole will be bigger than the concrete that filled it. So, you’ll end up needing more material to fill it - either more Sika Post Mix or more concrete. The math for the volume of a cylinder is straightforward.
If you change a 6” radius hole into a 7” radius hole that are both 24” deep, you’d end up needing an additional 80 lb bag of concrete to fill it. For 18” deep post holes you’d need an additional 60 lb bag of concrete. Even if you use Sika Post Mix you’ll still need more of it. What if you need a little more than one 33oz package? I keep squirt bottles of parts A and B so I can mix up a bit more, or fill cracks, etc. But it is not good to have a lot of the post mix left over as it will still expand hugely and it sticks to and will ruin everything it touches. You should have a plan for how to deal with the excess before you ever begin to use it. The foam gets very hot too.
Concrete is dangerous to use as well. The cement dust is very bad for people’s lungs, causing the same kind of disease that breathing asbestos can cause. And it takes a lot of water to clean up after using concrete. Failure to use that water to clean up leads to damage to the equipment which must then be replaced, increasing the carbon footprint of the project. Whereas, there is no water cleanup involved in using polyurethane foam.
I replace posts in existing fences and make new fences, all without using new concrete. I make gates and unless the post supporting that gate is braced with diagonals in orthogonal directions I have no choice but to use concrete for a gate post base. But, more often I replace an existing gate post with a new one and reuse the post base. So, I have nearly eliminated the use of concrete in my business.
Just to be clear, a 100’ fence would use about 1100 lbs of concrete. That is a lot to haul around and carry to the fence line. The equivalent in Sika Post Mix would be about 20lbs. In my time-and-materials business carrying 1100 lbs of concrete costs my client a lot more than the increased cost of the post mix. And, in terms of how much of my own energy is expended there is no comparison at all. It is trivial to transport and use the polyurethane foam and utterly exhausting to move and mix and use concrete. I get to spend more of my time working with wood if I use the polyurethane foam. I get to spend more time working with concrete if I don’t. My own quality of life on the job matters to me - when I am done for the day I like to have enough energy to make dinner and work on estimates for clients. A day working concrete is daunting.
I’ll finish up by pointing out that making fences is a niche. Perhaps there are some unique opportunities to reduce the carbon footprint of fences that don’t apply to other kinds of projects. But regardless of the project you can try to determine what are the worst parts of the project from a carbon footprint perspective and look for lower carbon alternatives. You are (hopefully) not alone in seeking lower carbon solutions for the problems you solve. You can and I think should value lower carbon solutions over low-cost solution, especially when lower carbon solutions are not too much more expensive. There is more than one way to meet your needs and some of them are better than others. Find options and make choices to reduce the carbon footprint of whatever you do.
While your own actions seem insignificant, the collective effect of demand for low-carbon solutions changes the economics of higher carbon solutions so they aren’t as attractive to sell. For example, I go to my nearby big-box home improvement store to buy materials for making fences. They sell a lot of concrete. And by I lot, I mean that often I see a forklift loading a pallet of sacks of concrete into someone’s truck. I’m only there for half an hour but more days than not someone buys that much while I’m there. Sometimes there are multiple pallets loaded while I’m there. Inside the store there are commonly 10 or more pallets of sacks of concrete waiting to be purchased.
Meanwhile over in the Sika products like epoxies and sealants there is one box with a single bag of Sika Post Mix. The stock says they have a dozen, so they haven’t ordered more. But they aren’t on the shelf. Just another day where the physical inventory doesn’t match the database.
They don’t treat the only viable alternative to concrete as an important thing to keep in stock. They should reorder when there are fewer than 100 bags left on any day, not 12. They should have cases in reserve, exactly the same way they have pallets of concrete in reserve, ready for sale in case there is an extra demand that day. But they don’t. It seems like it doesn’t occur to them how important it is to keep lower carbon footprint products in stock. They aren’t more important to the store’s management. Apparently they plan to expand to other planets after ours becomes a smoking hulk.
I don’t run that store. I run my own business. In my business it does matter that lower carbon solutions are available when they are ready to be used. It is my business to provide them.
Addendum: here are step-by-step instructions for reusing a post base, with photos by Greg Sandoval.
About 10 billion tons of concrete are produced every year, and it takes between 3.3 and 3.6 Gigajoules of energy to produce each ton of concrete. (https://en.wikipedia.org/wiki/Concrete#Cement). That works out to be between 33,000,000,000 and 36,000,000,000 Gigajoules spent making concrete. In 2013 it is estimated that the world produced 5.67x100,000,000,000 gigajoules, or 567,000,000,000 (https://en.wikipedia.org/wiki/World_energy_consumption). You can see where this is going.
The world uses about 33/567 of its energy it produced just to make concrete. That is 5.8% of the energy used on the entire planet!
It puts almost a pound of CO2 into the atmosphere for every pound of concrete produced. (https://www.cement.org/docs/default-source/th-paving-pdfs/sustainability/carbon-foot-print.pdf)
More on concrete and CO2 here: http://www.nrmca.org/greenconcrete/concrete co2 fact sheet june 2008.pdf
I believe it is my responsibility to reduce the carbon footprint of my business. I want to make choices that improve the carbon footprint of my projects without reducing the quality of my work. My lower-carbon approach cannot cost so much more that my clients will reject my proposals, because someone who charges less will probably also care less about the carbon footprint of their approach. The environment has no advocate if it isn’t us.
Fortunately in my business at least there are often alternatives. Most of the rest of this blog entry is about those alternatives. I am providing them for my clients who want to know why I work the way I do, and for other people who make fences, as a resource for their use in reducing the carbon footprint of their business.
First, I must repeat that the best use of concrete is no concrete at all. Meaning that if you can find a solution that doesn’t require adding any new concrete, that is a superior solution so long as it meets all relevant needs.
If you can find a solution that doesn’t require adding any new concrete, that is a superior solution so long as it meets all relevant needs.
In this category falls:
- New fence posts using Sika Post Mix
- Replacing fence posts in existing concrete post bases
For new fences either without any existing post bases or where they are not in useful locations I use Sika Post Mix, an expanding polyurethane foam. (https://retail.usa.sika.com/en/products/specialty/sikar-postfixr-fence-post-mix) It costs about $12 for the equivalent of 120 lbs of concrete. Not only is it not backbreaking to carry, it requires no cleanup like concrete equipment does. In my time-and-materials business this is a win for my client. The foam cures in a couple hours so if I start posts in the morning I can be building a fence in the afternoon. It is fine for fence posts. I don’t use it for gate posts (on which the gate hangs). It isn’t designed for structural applications like decks and or gate posts. But I spoke with someone who observed a new telephone pole which was secured in its hole using a durable foam instead of concrete. Here is one such product: https://rainbowtech.net/products/pole-setting-foam/
If there are already concrete post bases then I try to re-use them. To reuse the post base I dig out the remains of the original wooden post. It is usually rotted. People don’t tend to replace fences that don’t have a problem, and the most common problem I see by far is rotted posts, right at the base. Fence posts rot at the top of the concrete when the wood comes in contact with soil there. When the fence was made there was no dirt there, but years of accumulated leaves turn into dirt and that rots the post below the new soil line. Once the rotting begins gravity pulls water into the post base through the rotted collar around top of the post base. Over time the post decays and the fence begins to lean. It might not fall over because plants and trees might be holding it up. One service I provide is to replace only the posts and reattach the fence to the new posts I install. I replace one post at a time. It is best to get the most life possible from a wooden fence - there is no need to replace the pickets and laterals if they aren’t rotted. And, if someone is considering it both ways, the first job would be to replace the posts either way, so building the new fence is what takes the additional time and materials.
I use tools like crowbars, a demolition hammer and a hammer drill to dig, break up, pull and pry out the old wood of the original post. The worst cases are where the wood isn’t fully rotted yet. In the best of cases the old post has turned into dirt and I can dig it out with my hands.
Once the post base has been cleared of the old post, to at least 14” deep, I plane the end of a new post so that it will fit. Occasionally the original post had a defect (such as a shaved corner) that was cast in concrete. I have to match whatever shape the original post was, but it isn’t usually difficult. Since the bottom of the post base is sometimes covered in dirt, I will put in gravel or rocks so the new post doesn’t contact the dirt at the bottom. I treat the bottom 2’ of the post with a water seal and then drive the post into the original post base.
Sometimes the new post is perfectly plumb (vertical) and if I am just replacing posts it fits neatly back into the original fence. But sometimes it isn’t plumb. I can tell using a long level how plumb it will be. When it isn’t plumb there are a few choices:
- Add additional wood to form a plumb face - good when the post leans away from the fence line.
- Crack away 1/4 or 1/2 of the concrete base so the post can sit plumb, and add new concrete or Sika Post Mix to fill what was removed
- Destroy and remove the old post base entirely and use Sika Post Mix to make a new post base that holds the post plumb
The first option requires a bit more wood and woodworking, but it can look beautiful, depending on one’s aesthetic taste. I tend to mount a 2x4 vertically and attach it to the post with short blocks or 2x4 ties on the side of the post to the plumb face. Wood isn’t too expensive and the time would have been spent cracking and removing concrete.
To accomplish the second I use a hammer drill to drill a line of holes from a corner straight to the perimeter of the post base. If I am removing 1/4 of the post base these two lines of holes will be at right angles to each other. To remove half the post base these lines of holes are aligned on opposite sides of the post base. Once the holes are drilled I use a demolition hammer with a 3” wide bit to break the concrete along the line of holes. Once it is cracked I use the demolition hammer to break up the section to be removed. I try not to damage the soil around the concrete I am removing. Once the concrete is removed I mount the post plumb and fill in the gaps around it. If the post base is leaning toward the fence break away the part away from the fence. If the post leans left break away the right side. If it leans in two directions you’ll have to break away half of the post base and then it might be worth replacing the whole thing with a new Sika Post Mix base.
Why not just dig out the old post base and pour a new post base? You could, but in my opinion it is better to reuse an existing concrete post base if possible. Reuse is superior to recycling is superior to single use. Concrete really is an amazing material that makes wonderful post bases. By all means, if they are already there, don’t waste them! If you take used concrete to the dump you’ll probably find it costs about twice as much to throw away as to purchase! Or more...
You can dig a post base out, but the hole will be bigger than the concrete that filled it. So, you’ll end up needing more material to fill it - either more Sika Post Mix or more concrete. The math for the volume of a cylinder is straightforward.
cubic inches = π * r2 * height
If you change a 6” radius hole into a 7” radius hole that are both 24” deep, you’d end up needing an additional 80 lb bag of concrete to fill it. For 18” deep post holes you’d need an additional 60 lb bag of concrete. Even if you use Sika Post Mix you’ll still need more of it. What if you need a little more than one 33oz package? I keep squirt bottles of parts A and B so I can mix up a bit more, or fill cracks, etc. But it is not good to have a lot of the post mix left over as it will still expand hugely and it sticks to and will ruin everything it touches. You should have a plan for how to deal with the excess before you ever begin to use it. The foam gets very hot too.
Concrete is dangerous to use as well. The cement dust is very bad for people’s lungs, causing the same kind of disease that breathing asbestos can cause. And it takes a lot of water to clean up after using concrete. Failure to use that water to clean up leads to damage to the equipment which must then be replaced, increasing the carbon footprint of the project. Whereas, there is no water cleanup involved in using polyurethane foam.
I replace posts in existing fences and make new fences, all without using new concrete. I make gates and unless the post supporting that gate is braced with diagonals in orthogonal directions I have no choice but to use concrete for a gate post base. But, more often I replace an existing gate post with a new one and reuse the post base. So, I have nearly eliminated the use of concrete in my business.
Just to be clear, a 100’ fence would use about 1100 lbs of concrete. That is a lot to haul around and carry to the fence line. The equivalent in Sika Post Mix would be about 20lbs. In my time-and-materials business carrying 1100 lbs of concrete costs my client a lot more than the increased cost of the post mix. And, in terms of how much of my own energy is expended there is no comparison at all. It is trivial to transport and use the polyurethane foam and utterly exhausting to move and mix and use concrete. I get to spend more of my time working with wood if I use the polyurethane foam. I get to spend more time working with concrete if I don’t. My own quality of life on the job matters to me - when I am done for the day I like to have enough energy to make dinner and work on estimates for clients. A day working concrete is daunting.
I’ll finish up by pointing out that making fences is a niche. Perhaps there are some unique opportunities to reduce the carbon footprint of fences that don’t apply to other kinds of projects. But regardless of the project you can try to determine what are the worst parts of the project from a carbon footprint perspective and look for lower carbon alternatives. You are (hopefully) not alone in seeking lower carbon solutions for the problems you solve. You can and I think should value lower carbon solutions over low-cost solution, especially when lower carbon solutions are not too much more expensive. There is more than one way to meet your needs and some of them are better than others. Find options and make choices to reduce the carbon footprint of whatever you do.
While your own actions seem insignificant, the collective effect of demand for low-carbon solutions changes the economics of higher carbon solutions so they aren’t as attractive to sell. For example, I go to my nearby big-box home improvement store to buy materials for making fences. They sell a lot of concrete. And by I lot, I mean that often I see a forklift loading a pallet of sacks of concrete into someone’s truck. I’m only there for half an hour but more days than not someone buys that much while I’m there. Sometimes there are multiple pallets loaded while I’m there. Inside the store there are commonly 10 or more pallets of sacks of concrete waiting to be purchased.
Meanwhile over in the Sika products like epoxies and sealants there is one box with a single bag of Sika Post Mix. The stock says they have a dozen, so they haven’t ordered more. But they aren’t on the shelf. Just another day where the physical inventory doesn’t match the database.
But they never seem to run out of concrete.
They don’t treat the only viable alternative to concrete as an important thing to keep in stock. They should reorder when there are fewer than 100 bags left on any day, not 12. They should have cases in reserve, exactly the same way they have pallets of concrete in reserve, ready for sale in case there is an extra demand that day. But they don’t. It seems like it doesn’t occur to them how important it is to keep lower carbon footprint products in stock. They aren’t more important to the store’s management. Apparently they plan to expand to other planets after ours becomes a smoking hulk.
I don’t run that store. I run my own business. In my business it does matter that lower carbon solutions are available when they are ready to be used. It is my business to provide them.
Addendum: here are step-by-step instructions for reusing a post base, with photos by Greg Sandoval.
