It specifies a method for determining the staining of porous substrates (e.g. marble, limestone, sandstone or granite) by sealants used in building construction. The method evaluates the likelihood of a sealant causing an early stain on a porous substrate due to exudation of materials from the sealant. The outcome of the test is specific to the tested sealant and tested substrate and cannot be extrapolated to other sealant formulations or other porous substrates.