How to Finish a Slate Hearth

What You'll Need
Tri-Sodium Phosphate (TSP)
Portable Electric Polisher
Sealer Sponge
Sealer Sponge or Brush
Natural Stone Sealer
Spray Bottle
Mild Detergent
Rubber Gloves

A slate hearth can be made more beautiful and functional by finishing it with a stone sealer. The sealer does not only protect the hearth from stains, it also enhances the color of the slate and makes it more attractive.

Step 1 – Choosing a Finishing Material

The best way to finish the stone is to seal it with a natural stone sealer. However, other homeowners have also tried varnish. Never use paint because it will just cover the natural color of the stones. Since the stones are at the fireside, select a sealer that can withstand heat.

Step 2 – Preparing the Hearth for Sealing

To ensure a good sealing result, clean the entire hearth with water. Use a spray bottle to spray the water and use a soft-bristle brush to scrub stubborn grime, dirt, soot and ashes. Add a mild detergent to the water to remove greasy stains from the stone surfaces. If mild detergent does not remove the stains entirely, make use of a stronger cleaner like tri-sodium phosphate. Follow the instructions carefully when using the product.

If there are any organic growths on the slate, use oxygen bleach. Allow the solution to dislodge the growth for about 10 minutes before scrubbing the growths. Wash the residue from the stone using water. Do not flood the entire hearth. Use a spray bottle and a sponge. Allow the hearth to dry completely. It will usually take about 4 to 6 hours, but that will depend on the climate during the time of sealing.

Step 3 – Trim the Edges and Remove Scratches

If there are uneven edges or scratches on the stones, now is the time to hone or polish them. Rent an electric wet polisher and use 100-grit disc initially to polish the surface. Increase the grit level gradually until the uneven edges become flat and the scratches become invisible. Dust off the stones afterwards with a paintbrush.

Step 4 – Applying the Sealer

Open the windows and the doors to provide good ventilation into the room. Use a respirator in case the room is poorly ventilated. Wear rubber gloves to avoid contact with the chemicals. Pour the sealer into a bucker first and shake it completely. Make sure to follow manufacturer’s instructions if the sealer needs to be prepared differently. Apply the sealer onto the hearth using a paintbrush or a sealer sponge. Apply the sealer thinly. Check to make sure that the sealer is spread evenly onto all surfaces. Apply several more coats. Give it at least 72 hours to cure completely.

Step 5 – Maintaining the Finished Slate Hearth

To ensure that the sealed hearth lasts long, take time to clean any stains on its surfaces, especially if the liquid spills are acidic. To clean dirt and grime, use soapy water with mild detergent. Do not scrub the surface with abrasive. Use a sponge or a soft-bristle brush. Reseal the hearth after 3 years or so.