Granite, Marble, or Stainless Steel – To kasher (for year-round and Pesach), clean the countertop, wait 24 hours after its last use, and then pour boiling water over each part of the countertop. You may need to refill the pot several times. (It is not sufficient to pour on one spot and let the water run over the counter.) Make sure the material is a pure granite or stone. Sometimes they are really “composites” and therefore CANNOT be kashered.
Wood may also be kashered as stainless steel if it has a smooth surface and no cracks.
Porcelain Enamel, Corian Solid Surfaces®, Zodiaq Quartz Surfaces®, Formica, Silestone – Star-K policy does not allow kashering of plastic or materials with plastic components.