Introduction
The true strength of a building lies in its foundation. A good foundation is crucial during construction as it holds up the structure above it and keeps it standing. It's the "base-is" for everything.
Horrific puns aside, a poorly constructed foundation means a poorly built building. With that understanding, we can't overstate the importance of a good void form or concrete underlayment in ensuring a foundation stays sturdy.
It's essential because your building's foundation faces numerous risks, such as heave, subsidence, or even frost/moisture damage. With the groundwork laid out, let's dive in.
** This article is provided for informational purposes only.
Understanding Construction Foam
There are so many types of foam that explaining them all would be an entire series of articles. So, let's cut to the heart of the matter and discuss foams used explicitly in foundations. There are many types of foam we can discuss:
● Polyethylene
● Polystyrene
● Polypropylene
● Polyurethane
That's a lot of "polys…". This article will shed some light on the foam type that arguably stands head and shoulders above the rest in terms of quality: polyethylene foam or PE foam!
A key reason PE Foam is considered a top foam choice for construction foundations is its outstanding dimensional stability and recovery characteristic, which provides optimal cushioning protection against impact. Basically, it can take a punch, a squish, or a crush and come back swinging, so to speak.
PE foam is used throughout the construction industry as a joint filler, between or underneath concrete slabs, and as structural insulation. Its closed-cell properties, which we'll touch on in a second, make it so favorable.
However, if used underground, PE foam also boasts resistance to mildew and chemicals, heat transfer, and repelling vermin or insects.
What are Some of the Principal Features of Polyethylene foam?
One of the most critical factors we touched on briefly is that polyethylene foam is a "closed-cell" foam. This means its structure is made of millions of tiny bubbles sealed off from each other. These millions of isolated compartments fused to resist water while also providing great strength and rigidity that isn't present in open-cell foams.
In addition to water, PE foam punches above its weight class in resistance to solvents, petroleum products, and as we mentioned earlier, the growth of mold, mildew and bacteria.
PE foam is forged from heating polymer compounds and pressed into shape, which means additives can be added to the formula when creating the foam to give it certain characteristics, like increased R Values. This means a PE foam sheet made with insulating additives will have consistent R value rating throughout the form.
Like other foams, PE foam is available in varying densities for different applications. The higher the density of polyethylene, the smaller and potentially thicker the cell walls are, which creates a more robust material.
How Does Polyethylene Foam Help with My Concrete Foundation?
PE Foam has excellent strength and rigidity, which helps resist creep. No, we're not talking about creepy crawlies here; construction "creep" is the term for increased strain or deformation of a structural element under a constant load.
Essentially, if you've poured a concrete foundation, the concrete's "load" will be placed on top of your underlayment for as long as the building stands, so you need a material tough enough to sustain that load and fend off the prolonged effects of compression creep.
PE foam compresses and recovers against the foundation's load while also resisting vibrations and being shock-absorbent.
The Go-To Void Form for Concrete Underlayment
Construction managers and engineers must be efficient and select only the best materials for their projects. Building a structure on a weak foundation only invites problems.
As we know, PE foam measures up to this because of its resistance to phenomena like compression creep. Many engineers and building owners elect an underlayment foam as their go-to lightweight fill material because of its structural strength,
It's consistently a top selection also because of how lightweight it is. PE foam is super easy to manage and also helps by cutting costs through limiting labor and resources needed for installation. At the same time, the closed cell structure of PE foam creates moisture resistance by providing continuous insulation.
What Else About Polyethylene Foam Waterproofing
Waterproofing your foundation can be a critical part of the process because it helps prevent mold and other build-up from accruing under the foundation slab.
This can cause many issues, so it's important to have a durable fill material that can withstand the test of time and resist the build-up of harmful mold, mildew, or other contaminants.
PE foam resists mildew and mold because it doesn't sponge up water, which can cause the underlayment to deteriorate and expose the foundation to climate factors and soil swell.
Why is Polyethylene Construction Foam Good at Insulating?
PE foam is excellent for insulating objects. One of the reasons is because it's so flexible. PE foam is able to bend without compromising on insulation value at the same time, following the contours of the foundation or even subterranean pipes.
PE foam sheets can also be doubled up and stuck together with an adhesive and cut to fit the exact size of the shape needed to double up on insulative properties. Circling back to earlier comments, you can use PE foam to insulate an area exposed to solvents and other petroleum products that can cause deterioration or disintegration of the insulating barrier.
Importance of Foam Compression
Now that we understand construction foam and some of its capabilities, it's important to hone in on one of the most valuable features of void forms: its ability to compress and support the load of the foundation upon it.
The insulated foam layer "carries" the foundation and, therefore, must be able to hold a certain level of load. We know that PE foam excels in this area, and part of the reason it remains a top choice for contractors is that some areas will have certain codes or engineering specs that construction underlayment needs to meet in order to be used. Always ensure your construction underlayment is rated for the job being done.
The strength and compression ability of the foam depends on its density. However, structural-grade foam underlayment is resistant to the stresses on structural loads. The greater the foam density, the higher the load capacity it can carry. Typically, PE foam has an impressive resistance rating (around 10 - 60 psi, depending on density).
Coupling the compression resistance with the foam resiliency is also a key focus point when dealing with construction foam. Resiliency is the ability of the foam to recover its strength when the load is applied.
A good way to think about it is that the compression rating of a foam is how well the foam receives the load, while resiliency is how much the foam is able to "push back" against the load of the foundation and maintain its shape. High-quality foams can have a resiliency or recovery percentage of 90% of the original dimension after the load is applied.
Are High Compression Strength and Resiliency Recognized in Industry?
Many organizations that test and set construction practice standards value compression strength and resiliency ratings. A few such organizations that have set standards for this include:
● American Society for Testing and Materials (ASTM)
● Underwriters Laboratories of Canada (CAN-ULC)
● Canadian Construction Materials Centre (CCMC)
Due to the higher densities of closed-cell polyethylene foam, it not only passes structural grade requirements but also meets insulation requirements for geographical areas that endure sweeping climate cycles and adjusting soil conditions.
So, not only do the higher compressive and resistant foams protect the slab/foundation structure, but they can also protect against different soil phenomena and load stresses due to temperature fluctuations above and below the slab.
This brings us to the largest environmental factor acting on the foundation: soil expansion. Let's examine it.
Fighting Compression Creep and Soil Expansion
Soil Swell: Are We Shrinking or Swelling?
Shrinking or swelling are changes to volume that occur as moisture content shifts in clay-rich soils. Swelling pressures can cause something called "heave," which is lifting structures. Subsidence or "shrinking" is the settlement of a structure.
This shrink-swell phenomenon is the most damaging geohazard in most northern climates, especially those with varying freeze-thaw cycles. In the United States, the estimated damage to buildings and infrastructure exceeds $15 billion annually. The American Society of Civil Engineers estimates that one in four structures or buildings as some damage caused by shrink-swell soil issues.
Fine-grained, clay-rich soils can absorb large quantities of water after rainfall, becoming sticky and heavy. At the same time, soils with an abundance of clay can become very hard when dry, which results in shrinking and cracking of the ground. This process of hardening and softening is what we know as 'shrink-swell' behavior.
Buildings in many parts of the Northern Hemisphere are affected by shrink-swell-related subsidence. In some areas, shrinking is caused by the movement of the ground with changing weather conditions. A few examples of this would be a place like Alberta with dry summers or, conversely, a place like the west coast of British Columbia with wet winters.
The amount by which the ground could shrink or swell could also be determined by:
● Water content near the surface
● Type of clay in the soil
● The likelihood of the clay to shrink or change volume
Shrink or swell can also be linked to a natural/seasonal occurrence and can be enhanced by factors like:
● Normal seasonal movement of soil with changes in rainfall and vegetation growth
● Enhanced seasonal movement with planting, severe pruning, or removal of trees or hedges
● Changes to surface drainage and landscaping, including concrete or asphalt
● Short-term, unseasonal movements as a result of leaks from water supply pipes or drains
● Long-term shrinkage from water deficits (droughts, diminished rainfall)
● Long-term heaving as water volume increases (heavy rain, monsoons, etc.)
Heave
Aside from being a fun word to yell when moving something heavy, heave happens when the soil beneath the foundation is pushing the ground upwards. This phenomenon can cause damage, so it's vital to have a good foundation layer to fight against it.
What exactly causes heave?
Heave is usually the result when the clay-rich soil we've discussed increases in moisture levels. If it's summer and you notice a lot of rainy days, not only is that bad for your chances of enjoying the outdoors, but it can mean the risk of heave goes up around your building's foundation.
Clay itself is called "expansive soil." When you soak clay with water, it expands, like applying water to one of those little sponge bricks, which then expands and grows.
Are only natural factors affecting it?
No, don't make this mistake. Natural factors like the death of a nearby tree or high precipitation can cause soil expansion. Tree roots suck up lots of water, so when the tree in the above example dies, the water will remain in the soil. Excess water will soak into the ground and increase the water table volume, leading to a higher heave potential.
However, construction work or problems with buildings can also cause heave. Excavating topsoil can cause something called "stress relief," which means the lower levels of soil will expand due to removing the pressure of the ground above, which causes heave.
Even something like a nearby broken drain can lead to excess moisture in the soil and an increased risk of heave. This is why a PE foam void can be crucial in helping fight against heave. When the water saturation and expansion press up, the foam underlayment helps by absorbing the expansion during freezing or soil swell to help prevent cracking and minimize shift.
Subsidence (or Shrinking)
Subsidence sounds like a severe word, and although it can be a serious problem, we can also refer to it as "soil shrinking" for ease of understanding! Essentially, it's a lowering or collapsing of the ground.
As opposed to heave, which pushes up and lifts structures, subsidence is the settling of ground and lowering of structures. It can be triggered by artificial disturbance, a change in drainage patterns, or even water reduction in the soil.
Shrinking soil can cause engineering problems such as damage to foundations, buildings, or infrastructure just as much as heave. Subsidence events can sometimes be connected to water loss (aka abstraction) through soluble rock or even collapsing soil in areas caused by events like mining or mass excavation jobs.
Overall, dry weather and high temperatures can trigger the shrinking of clay-rich soils. PE foam underlayment helps keep that void space filled despite contracting soils, can prevent negative or positive pressures on pipes, and can help prevent shifting.
What Part Will Climate Change Play in Soil Shrinking Going Forward?
Every summer can be completely different from the last. For instance, summer 2018 in North America was one of the hottest on record, while June 2019 was one of the wettest on record.
However, we must take the time to analyze all we know about shifting climates and their impact on concrete foundations in terms of soil conditions. If future predictions of warmer, drier summers continue and increases in annual temperature and rainfall levels are correct, we can expect many properties to experience an increase in subsidence or heave due to climate change.
This fact alone shows that having the proper underlayment is essential, with the future of construction anticipated to face these challenges. A closed-cell polyethylene product delivers on this by resisting the effects of soil swell and helping to prevent damage to your structure's foundation.
Frost Heave in Colder Climates
Frost heave occurs in places with colder climates, like Canada or the northern United States. When it gets bone-chilling cold in the winter, the top layer of soil freezes. As a result, water underneath the top layer can't be released and freezes.
It creates a cause-and-effect situation because the frozen topsoil prevents water underneath from escaping, and therefore, the trapped water freezes up, which can cause the ground to swell. This phenomenon is called first heave, and it is where your problems can really begin.
As ice freezes beneath the soil line in colder climates, it can build up into thick sheets. The trapped water beneath the frost zone will still try to diffuse upwards but run into the frozen soil (sometimes called an "ice lens"). What you get is somewhat of a snowball effect. Like a cartoon character rolling down the hill in a snowball that gets bigger and bigger, the diffusing water underneath rises and freezes to increase the size and pressure of the frozen ground.
All of this underground phenomenon happens with you none the wiser. You will notice it when it's too late, and the ground heaves against your driveway or basement foundation. Over time, this expansion and the freeze-and-thaw process can create voids between the soil layer and your foundation centimeter by centimeter until cracks and shifting cannot be ignored.
Is This Where A Polyethylene Void Form Comes In To Play?
You should almost be expecting this by now!
Whether it's excess water in autumn or winter, lack of water during a dry summer, or a constant freeze-thaw cycle, soil swelling, shrinking, or frost heave creates gaps and voids that lead to costly damage and cracks over time.
A PE foam underlayment anticipates this movement from the soil, acts as a buffer or cushion against the effects of frost and adjusts soils. Its highly durable nature means it is designed not to biodegrade over time or collapse under foundation weight.
Summary
Polyethylene construction foam is why modern foundations are built more efficiently. They handle the pressures of soil swell, heaving, or shrinking while also absorbing the compression of the foundation load.
The high-density foam's increased structural integrity and flexibility allow for efficient fitting and adhesion along contoured surfaces and resist mold, mildew, vermin, and hydrocarbons.
Laying the groundwork for a project is extremely important as you build upon it. The rest of the structure on a solid foundation succeeds, and construction foam underlayment helps give the assurance that it will.
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