Slab Jacking With Polyurethane Foam – How Strong is Strong Enough?
Published June 12, 2013 | By Andy Powell
Raising Concrete with Confidence
When pumping a light-weight material beneath a slab, you need the confidence that it is strong enough for the application. How strong is strong enough? This is a commonly asked question by contractors that are new to slab jacking with polyurethane (poly lifting). Alchemy Polymers structural foams only need to be as strong as dirt, but they’re actually stronger than crystalline bedrock.
The Right Strengths for Concrete Lifting
Slab lifting foams are rated on density (weight per cubic feet) and compressive strength. This testing and rating is based on the foam in a free rise state; the parts A and B are mixed together and allowed to expand freely. Our AP Lift 430 and AP Lift 475 structural lifting foams, for example, will weigh 2.75 – 3.25 lbs (AP Lift 430) to 4.75 – 5 lbs (AP Lift 475) per cubic foot. But they have a compressive strengths of 50 psi and 100 psi in a free rise state. That’s equal to 7,200 to14,000 lbs per square ft of support, just in a free rise state.
Polyurethane Slab Jacking Compared to Clay and Bedrock
To put that into perspective, the National Home Builders Association and the International Building Code lists stiff clay at 4000 psf and crystalline bedrock as having 12000 psf of load bearing capacity. Consider the job site conditions where the foam will be injected into a confined area. Testing data in the lab shows that our lifting foams will increase in compressive strength: In a space confined 25% by volume there will be an increase of 31% in psi and in a space confined by 75% there will be a 79% increase in the psi.
Slab Jack for Any Job with the Right Foam
Today polyurethane lifting foams are used to level airport slabs supporting jumbo jets, equipment and building slabs supporting tremendous loads, and even railway sleepers that support the heaviest freight trains. So don’t let the word “foam” fool you. These resins cure to strengths beyond what is needed to support any structure.