We talk a lot about soil stabilization underneath existing structures, but what about new construction? Before construction can begin on any new structure, stable ground underneath is obviously an essential prerequisite.
Unstable soil can be defined as soil that will not stay in place on its own, and therefore requires extra support. It should be noted that unstable soil can threaten the stability, security, and safety of any potential new construction projects, such as buildings, bridges, and roads. There are a variety of factors that can cause unstable soil including erosion, poor compaction, freeze/thaw cycles and decomposition.
Soil can be stabilized with high strength polyurethane resins applied by skilled & experienced contractors. Once the bearing capacity of the soil has been increased, then the new construction can begin.
When choosing a polyurethane foam slab lifting contractor, it’s important to make sure they have a thorough understanding of industry best practices. There are a great number of details to be aware of, but they’ve become second nature to us over time. Why? Because we care about your property.
For simplicity’s sake, we’ll divide the best practices of slab lifting into three sections:
- Lifting the Slab
- Wrap Up
Let’s start with the very basics. When we arrive on the site, we double-check location of buried utilities and other underground infrastructure. We always make sure we have a thorough understanding of the subterranean layout before we begin. Another essential preparatory step to evaluating a job site is to document the existing conditions of the site. Aside from lifting your slab, we want to do our best to leave it as it was before we arrived.
Polyurethane foam, once cured, is VERY difficult to remove. That a testament to its strength and binding qualities, but can be quite a pain if a careless contractor accidentally splatters some on your property. That’s why we make sure to cover any critical property that can’t be moved out of the way. For example, if we’re lifting a warehouse slab next to heavy machinery that’s secured to the floor, we’ll cover the machinery in plastic.
Lifting the Slab
The first step in the slab lifting process is to make sure that the slab can be lifted. In other words, we check the joints around the edges, where the slab connects to walls or other slabs. We make sure they’re clear and the slab isn’t fused to those other objects. In many cases, we may need to either saw cut some joints or clean them out with a sawzall or a trowel.
Next, we’ll set up a measuring device that accurately indicates when and by how much the slab lifts. Now it’s time to lay out the drill holes. Each slab is different, so we consider very carefully where stress points may occur under the slab as we inject the expansive foam. A gradual, measured approach is always best.
Before we begin work on each section of the slab, we spray Spetec Surface Guard along joints and around the outside of drill holes to prevent foam from bonding to the concrete surface in case it ends up overflowing into those places. This is a critical step, since – as mentioned earlier – it’s very difficult to remove foam once it has cured. While injecting, we use longer shots to move the material out wide and fill voids, and use shorter controlled shots to get foam to cure right beneath drill hole area and lift.
While injecting polyurethane foam, we always maintain a 360 degree field of awareness. We never try to lift the entire slab from one drill point. Smaller injection amounts, spread across many drill points will lift the slab smoothly and gradually.
After leveling and/or stabilizing the slab, we trim all excess foam that has eased out from underneath the slab. We sweep up any cured foam bits, concrete dust, etc. Our goal is to leave every site in better shape than we found it!
When choosing slab lifting contractor, make sure they care enough to follow these industry best practices and you’ll be one step ahead in your decision process!
On large projects, the first question any engineer will ask is “Does the solution fit the needs of the application?” When it comes to structural foams used for slab lifting repair projects, we can confidently answer “yes.”
Light Weight & Enduring Strength of Polyurethane Foam
Concrete, a mixture of cement, sand and aggregates, weighs on average 150 pounds per cubic foot, and high-density concrete can weigh in at 300 pounds or more. Any material used to serve as an elevating cushion of support between concrete and soil is literally caught between a rock and hard place – the concrete and the natural soil on which it rests.
By definition, structural foams need only be strong enough to heft sinking slabs back to level ground and durable enough to stop them from sinking again once cured. But polyurethane foams are actually one of the most resilient foundation repair solutions ever innovated.
Rated on density and compressive potency, the strength-to-weight ratio of lifting foams is staggering. Successful applications include airport runway and railway bed repair projects – in other words, structural polyurethane slab lifting foams like the products we use are heavy-duty enough to support the lift-off and landing of a 747 or the constant travel of a freight train.
Demo and rebuild or rethink and repair – these are, generally speaking, the two available resolution options when shifting soils give way under structural foundations and existing slab work. When possible, remediation repairs for settling concrete require far fewer resources than reconstruction.
Traditional mud jacking, which requires hydraulic pressure to inject mud into the void or weak soil beneath the slab, can’t hold a candle to the power of expanding, high-density polyurethane foam. Lifting foams are injected in bursts and rapidly expand 15-25 times or more the original volume, filling voids or strengthening soil in the affected space and creating comprehensive support. These stronger-than-bedrock polymers also subdue the kinds of stress points that mud jacking applications can create, eventually causing cracking and a second round of expensive repair work.
Another contrast with traditional mudjacking materials is the fact that polyurethane does not shrink or wash out over time, saving property owners the extra cost of re-treating the problem at a later date.
Slab lifting foams don’t just save money, they save time. Because of their expansion properties, they can be applied quickly to lift slabs, and curing doesn’t require the same amount of time as other solution applications, such as mudjacking with cement slurry. That means a seasoned slab lifting technician can deliver project completion – with drive-on capability – in a much more efficient manner. Depending on contingencies and project timelines, that savings alone can be worth its weight in gold to potential customers.
We have pumped, shot, spilled, splashed, sprayed, poured and injected polyurethane foam into every imaginable type of concrete structure known to man. 99.9% of it has ended up where it was supposed to go.
But there are those rare occasions when a small amount may end up ON the concrete we are trying to fix. Luckily that’s NOT a problem at all, because we use Spetec Surface Guard to prevent staining from polyurethane resins!
Spetec Surface Guard is a concentrated product that we mix with 3-5 parts water. It can be sprayed onto concrete, wood, metal, or plastic and creates a barrier layer that prevents polyurethane foam from sticking to and staining the surface.
Not all two-component polyurethane lifting and stabilizing foams are specifically designed for wet environments. In most situations when a contractor is injecting polyurethane foam into the ground underneath your structure, there is a high probability that the soil is going to be wet. You need to be confident that the foam will react and retain the desired properties in these wet environments. If the foam your contractor is using is not specifically designed for wet environments, then you may be getting cheated out of the best possible results.
All polyurethane foams are going to undergo a density change when introduced to water. This is precisely because the isocyanate (A component) in polyurethane reacts faster with water than it reacts with the polyol (B component). Some will undergo drastic changes and some minor changes. It is important to feel confident that the foam your contractor is using will only undergo minor changes. The density of the foam is very important because density correlates to foam strength, and you are relying on that strength to support your valuable structure.
All the Alchemy-Spetec lifting products we use are formulated to achieve minimum density changes when introduced to wet soil.
In countless regions around the world, many structures we build start settling or sinking sooner or later. Sometimes they sink very gradually with the evidence and damage showing up after a long period of time. In other cases, entire homes and roadway sections are swallowed up in minutes. These situations create serious problems for property owners and property managers.
Concrete Lifting is Often the Solution
Certainly, if your house or building has disappeared into a sinkhole, you will need a lot more than slab jacking. But if the issue is uneven concrete slabs, settling foundations, roadways, railways, or sidewalks, then these solutions may be for you.
Raising Concrete: Technology + Experience = Knowledge to Share
Ground Consolidation Services uses high strength polyurethane lifting foams for slab jacking and structure lifting. In addition to that, our staff has extensive experience fixing problems just like the one on your property. For immediate assistance, call us at 678-337-8374.
So, you have a sunken concrete slab that could be repaired via replacement or lifting. How do you know which option to choose? Here are a few things to think about.
Raising Concrete is More Cost Efficient Than Replacing
If the slab is in good shape, and is of a reasonable enough size and thickness, it is usually going to be more cost effective to lift it back into place with structural polyurethane foam. The PMC pumps we use can deliver the AP Lift series of foams we use as far as 400 feet away through heated hoses. And remember, whenever you have new concrete installed, you have to haul away old concrete.
More Environmentally Friendly with Polyurethane Concrete Lifting
Everybody wants to be green and take care of the environment these days, because it’s the right thing to do. There is an environmental impact every time concrete is replaced. The cement manufacturing process is the second largest cause of greenhouse gas emissions in the world. Additionally, there is the issue of what happens to old concrete once it is removed. One would like to think it is recycled, but more often than not it ends up being dumped. Hopefully that would be in a landfill, but we’ve all seen piles of concrete rubble in places where it would be considered trash or pollution. It’s worth considering. Meanwhile the AP Lift 430 and AP Lift 475 foams we use are so environmentally friendly they are NSF approved for contact with drinking water in their cured state.
Polyurethane Slab Jacking Requires Less Downtime
How long can you, as a property owner or manager, afford to have that area out of service? Consider a busy warehouse, an airport taxi way, or a bridge approach on a highway. There is an economic impact when those locations are out of service for replacement. It can be a couple days before new concrete is traffic ready. Wouldn’t it be better to have it lifted in a few hours, and then back in service 15 minutes after the slab jacking is done?
Though there are many reasons for sunken slabs, we have identified the three main conditions that cause the settling issues we like to fix. These include erosion, poor compaction, and biological decay.
Erosion Often Leads to Concrete Slab Settlement
Erosion is the most common cause of settling and the most common reason for slab jacking. Poor drainage, improperly placed downspouts, leaking drain pipes, and broken water lines are common culprits. Water can either slowly erode soil over time, or very quickly erode away the soil beneath a concrete slab or structure causing it to settle.
Poor Compaction Can Cause Settlement & the Need for Raising Concrete
When backfilling on a new construction site, the builder is supposed to walk in backfill (drive over it with heavy equipment) and compact it in small lifts. However, this isn’t always done properly for one reason or another (inexperienced operators or people taking shortcuts). The result can be soil that will continue to compact itself and settle over time. A great example of this is bridge approach slabs. These slabs are found on roads and highways all over the world. Bridges typically sit at a higher elevation than the roads that approach them. During construction, the final section of road (typically a concrete slab) is built on backfill to raise the elevation to meet the bridge. Over time, the slabs can settle due to poor or improper compaction. Compounding the problem is the fact that when a slab settles a little, the expansion joint opens up and allows water to get underneath the road, adding erosion to your compaction problem.
Biological Decay Can Result in Sinkholes and Sunken Concrete Slabs
Construction trash pits, buried trees, and other biodegradable materials all eventually break down. Sure enough, there always seems to be some corner of a building or a separate parking area or driveway that ends up right over it. These situations can range from slight settling to very severe. Sometimes you have a combination of factors that cause settling. As we discussed in the bridge approach slab issue, poor compaction can lead to settling which will open a joint and allow water to compound the problem with erosion. Property owners and managers should not ignore these problems, or they will become more expensive to fix over time.
Any successful slab lifting job begins with a thorough site evaluation. A site evaluation is not limited to, but should include Identifying the Cause of Slab Settlement, Gathering Information, Identifying Potential Hazards, and Visualizing the Mobilization.
Cause of Slab Settlement
Determining the cause of settlement is usually the first step in beginning our evaluation. The cause can be any number of things such as erosion, ground water, sink holes, poor compaction, and buried debris that breaks down over time. Correctly identifying the cause will help us determine if slab jacking alone will solve the problem or whether a combination of lifting, stabilizing, and / or void filling will provide the permanent solution.
The next phase should include gathering information from multiple sources. This includes dimensional information such as length and width of the slab; but also, the amount it has dropped, to help determine the volume of structural foam needed to lift the slab back into place. We also gather information from the property owner; finding out about any known irrigation, electrical, water, or drain lines. Specifically, we find out from the owner about any areas or features that need protecting around the injection site, the location of our rig, and all points in between where our crew may be working.
Identifying Potential Hazards
If the job is outside of a building, we find out where the utilities are and have them professionally located. Additional information that may be available could include a soil engineering report, a structural engineering report, and reports from the builder of the structure. We also consider other issues that might create problems like slabs binding (concrete saw?), bent rebar from a settled slab, etc.
Visualizing the Mobilization
After the data gathering is complete, we visualize the job site as a whole and consider any challenges to mobilizing and physically reaching the areas that need lifting. We consider the size of the rig we’re using on the job compared to the site size, the amount of pump hose we’ll need to reach the lifting points, the power we’ll need, etc. Some of the above seem obvious, but it’s often the obvious things that get overlooked by the common contractors out there. Mistakes can drastically affect the cost to the property owner, in terms of both time and money. There’s a reason why highly skilled airplane pilots go through the same checklist prior to every flight. Sometimes you only get one chance to choose the right contractor.