QUESTION

What should I take into Consideration in Selecting a Granite for an Exterior Countertop?

ANSWER

ANSWER - First of all let me give you some background info to consider.  Not all granite, or stones in general, are made equal by mother nature.   Being a natural material the physical properties can vary substantially within the same geological category and type of stone from source to source.  So not only can its physical properties vary from quarry to quarry, they can vary from one spot in the same quarry from another even if they are in close proximity.

True granites are one of the most durable materials in terms of wear, low absorption, chemical resistance, and stain resistance.

Although many of the stones sold as granite today may not be a true granite.  They call this a commercial granite.  Many of the Brazilian granites that are more colorful and have much more movement in the veining and color variation of the stone tend not to be true granites.  They may be more absorbing so they may be more susceptible to staining and less chemical resistant. They could have imperfections that are filled with resins and may be reinforced with a fiberglass back to stabilize them during transportation and the fabrication process.  They could have a resin coating over its surface to enhance the color of the stone that can become smudged if solvents are used over them.  Of course as in all things in life there are always trade-offs.

That said, it is better to go with the 3cm (1-1/4”) thick material.  You can avoid having to add an adhered apron to the edge of the stone and you can just route the edge to your desired look/configuration.  It is more stable being thicker and will look better.  They don’t have to add the plywood base with the 3cm thick stone if the counter top frame is constructed correctly in terms of being structurally stable.

You want to make sure they set the top so there is a slight slope towards the outside edge so it will drain when subjected to rain or washing down with a hose.  You don’t want it sloped towards the back where water will sit causing staining and potential deterioration called spalling.

The transition from the countertop to the backsplash,  if there is one, or any transition around sinks or wherever, should be filled with silicone sealant that meets ASTM C920 over a polyethylene back up foam if there is room.  Not latex or acrylic or siliconized sealants.   This allows movement without causing anything to crack and will last a long time.

I always recommend sealing the stone counter top with a breathable penetrating sealer.  It will help keep the granite from staining and will make it easier to keep clean.  Sealers on an exterior application needs to be redone every 6 months to a year.  As soon as water doesn’t bead up off the surface it needs resealing.  Also plan on wiping it down when it gets wet.  If you take care of it, it will last forever.  After all it is already millions of years old so there is a lot of intrinsic value.