Not Every Concrete lifting Foam Is the Same
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There are special characteristics you need to look for when deciding what polyurethane foam to use for lifting and leveling concrete. Expansion is important, but what about set-up and cure times or adhesion? In this blog, we are going to explore the truth about polyurethane concrete lifting foam and what questions you need answered before purchasing a foam for this special application.
Foam Reaction Time
Reaction time is an important property to consider when choosing the best polyurethane foam for the job. Too quick of a reaction time can create foam pillars under the slab leaving a large percentage of the slab unsupported and making the contractor more susceptible to a call back due to resettling or even worse the slab cracks from being voided when weight of a vehicle is on it. Too slow of a reaction time can lead to the foam escaping outside of the slab being raised and possibly underneath an adjacent slab, leading to a lift on an unintended slab. It’s also important to consider the project that will be completed. Is it a sidewalk project with small slabs that will require a foam that sets up fast enough to not escape beyond the slab? Or is it a large roadway panel where a slow reaction time is ideal to let the foam spread and fill as much void underneath as possible while minimizing the need for numerous holes? The proper reaction time in the polyurethane foam being used is crucial to maximize efficiency and success.
Polyurethane foam for concrete raising should lift the concrete without sticking to it. This is why it is important to have a foam that skins over quickly, preventing it from sticking to the slab or the surroundings. For example, if raising a slab along a concrete foundation without a foam that forms that tough exterior skin quickly, the foam will stick to the slab and the foundation, effectively locking that slab into place. A foam that skins over quickly will not adhere to the foundation wall and will allow that slab to raise freely. This eliminates the need for repeated saw cutting to free the slab, saving the contractor valuable time.
HMI offers a variety of concrete raising foams in varying densities and reaction times. While these varying foams have their own ideal uses, there is a great amount of crossover between them allowing our customers to tackle a wide variety of projects without having to carry multiple densities of material. Our 2 lb. per cubic foot foam is our quickest reacting foam and also has the lightest density. This makes it ideal for manipulating smaller slabs such as sidewalks and driveways, while also providing the highest yield. Our 4 lb. per cubic foot foam has a higher density and slower reaction time than the 2 lb. foam. This is often used on projects with heavier lifts, such as roadways and warehouse floors. We also offer a Fast version of the 4 lb. foam, providing our customers with the density of the 4 lb. foam with a reaction time very similar to the 2 lb. foam. This gives our customers the ability to raise everything from sidewalk slabs to roadway panels without having to change foams, making it our most popular selling foam! A 6 lb. per cubic foot foam is also offered with a slow reaction time, designed to raise heavy highway panels and withstand heavy truck traffic, while also being able to spread well under the large slabs with its slow reaction time to fill the space and support the slab.
The density of the foam is determined by the amount of material it requires to fill a one cubic foot box at free rise, without any compressive force upon it. Therefore, one can see the variance in yield of these foams as 6 lbs. of our highest density foam is required to fill the same space as 2 lbs. of our lowest density foam. However, on a typical concrete raising project the foam is being pumped into a confined space with the force of the concrete pushing down on it. This allows more of the material to be pumped into the same space, thus increasing its density to what is required to raise and support the slab. For example, 2 lbs. of a 2 lb. per cubic foot foam will fill a one cubic foot box, as mentioned earlier. However, if a lid were to be placed on this box and another pound of foam were to be installed, the foam will either expand to lift the lid or build upon the density of the existing foam, now creating a 3 lb. per cubic foot foam. This is how a 2 lb. foam is able to lift much larger and heavier slabs than the sidewalk slabs it may be designed for. However, as more material is being injected to increase the density of this foam the high yield of the 2 lb. foam is being sacrificed. This goes to show why the varying foams are designed with specific uses in mind, but also provide for a large amount of crossover.
The ideal polyurethane foam for concrete raising does not fully cure immediately. This gives the foam pliability until it is fully cured, allowing the contractor to continue manipulating slabs into place after the foam has fully expanded. Concrete lifting contractors know that by raising one corner of a slab the opposite corner can be brought down if there is a void underneath that corner or if the foam is still pliable. This allows for better fine tuning of the concrete for the best end result. The ideal foam will stay pliable after fully expanded for approximately 15 minutes. This allows for that continued manipulation, but still cures fast enough so that by the time the contractor leaves the jobsite the foam is fully cured and the concrete is available for full use.