Abstract: A method and apparatus for measuring the porosity or density of a porous structure surface is disclosed. A controlled quantity of volatile liquid is applied to a porous surface and is allowed to evaporate. The temperature at the surface reaches equilibrium at the point necessary to supply the latent heat of vaporization of the liquid. This equilibrium temperature depends on the evaporation rate, which has been found to be a function of surface porosity. The porosimeter substantially eliminates other factors influencing evaporation rate, and measures and records the temperature at the surface. Once calibrated with samples of known porosity, this system is capable of making rapid, accurate surface porosity measurements.