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These foams come in an aerosol can, which will give you the required pressure to inject the sealant. The sealant will then expand to fill the void and then cure to a solid. Don’t be discouraged if you remember using these foams several years ago when they foamed excessively. Several “low-foam” versions are now available that should give you the right amount of controlled foaming for your application. If you need to remove the wood flooring in the future, the urethane will almost certainly have a low-enough cohesive strength to break rather easily under a minimum force.