Sealing Stone Surfaces

This is an an explanation of how sealers work on natural stone counters and flooring.
Perhaps nowhere is there more bad information about maintaining a building material than there is about stone sealers. If you stand in a stone dealer showroom you will hear sales people say to each customer "yes all natural stone needs to be sealed" The question is does it really.

Backing up a few steps I would like to mention briefly just what a sealer is. Stone sealers are at a basic level a polymers suspended in either water or a solvent. The invisible polymers fill holes in the face of the stone and increase the chance of removing a spill that could possibly permanently stain the stone. These sealers are then applied to the stone surface where ultimately they penetrate into the porous stone, filling microscopic (and some not so microscopic) holes. When applied correctly the desired outcome is a stone surface that has increased surface tension and decreased absorbency. The sealer then offers the stone some water and oil repellency.

Grout Cleaning



The variables involved in application of a sealer:

The suitability of the sealer for the job. Let’s say you apply an acrylic floor sealer to a stone floor. The stone wont even resemble what you picked out in the first place and you are going to have to speak with a guy like me to restore it. A proper stone sealer under all circumstances will be invisible on the stone surface.


The suitability of the stone for the sealer. Many stones, regardless of the finish (honed or polished) will not take a sealer and it will sit right on top of the stone surface. An absolute black granite with a honed finish will not take a sealer, nor will a polished creama marfil.

The condition of the stone immediately before application of the sealer. Many times sealers are used to cover scratches and grout haze from an instillation. What can I say, it happens. Call me.


Some sealers work better than others. A solvent-based sealer will work better than a water based sealer. There are also enhancer sealers that can add to the depth of color of some stones. They can change the way a stone looks, but applied properly you will not see the sealer or residue on the stone surface.

Sometimes because of the intended use of the stone, you really need a sealer (honed finish in a kitchen with lots of kids and a dog) and sometimes (a polished finish marble with two retired people who remove their shoes at the door) you don’t.


So the variables are the applicator, the sealer, the stone and the traffic.
Go over these carefully with your stone pro to be sure you are getting what you need. If you are a doityourselfer, follow the guidelines listed in this blog for proper sealer application.



Remember too, no sealer will keep the floor from getting dirty. Look to the maintenance guidelines listed on this blog for guidelines. Sealer objective is to give you a little time to wipe up an oil or water based spill before it penetrates into stone.

To test if your stone needs a sealer, drop some water on it and if it darkens, it probably needs sealing. The only rule I know that applies to all sealers and all stone is to test in an inconspicuous area to see how it will look. When you are satisfied you will be happy with the way it looks go ahead and seal away.

sealer applied to granite. notice water beading due to increased surface tension.
stone enhancer applied to slate. BTW we used respirators during this application.
water beads on sealed granite

sealer beads up on right, and lays flat on unsealed left