Dress Up a Concrete Hearth With Slate

A roughed-in concrete hearth can be covered with slate, a durable natural stone that's easy to clean and comes in a variety of natural tones.
A roughed-in concrete hearth can be covered with slate, a durable natural stone that's easy to clean and comes in a variety of natural tones. (By Tim Carter -- Tribune Media Services)
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By Tim Carter
Saturday, September 6, 2008

Q: DEAR TIM: I have a concrete fireplace hearth. Is it possible to cover it with slate? If so, is that difficult? Instead of slate, should I just install a hearth pad?

-- Marianne C., Millis, Mass.

A: DEAR MARIANNE: You can cover the concrete hearth with slate, tile, stone or just about any non-flammable building product. If you had X-ray vision, you would see concrete just below many of the hearths in older and even modern homes. Builders install concrete hearths as an extension of the concrete pad that the fireplace is built upon.

Usually, the biggest challenge is planning ahead to create a clean transition between the finished floor in the main part of the room and the finished material on the hearth. Sometimes this is handled by creating a raised hearth where both the hearth and the firebox are higher than the finished floor.

I prefer when the top of the finished hearth is the same elevation as the underside of the room's hardwood flooring. This way, a beveled strip of hardwood flooring can overlap the finished hearth for a professional look. To achieve this, pour the concrete lower than the wood subfloor of the house. The distance you drop the concrete depends on the thickness of the material you are placing on the concrete and the thin layer of adhesive you will use to attach it to the concrete.

Slate will bond easily to your concrete hearth. I would use thinset adhesive, which is a blend of Portland cement, silica sand and chemical bonding agents. Thinset is fireproof.

Perhaps your biggest challenge in working with slate is that all cuts need to be made with a diamond wet saw or by hand using a carbide rod saw that fits into a standard hacksaw. You can't use a standard ceramic-tile snapper cutter with slate, as the stone will fracture along an uneven line. It is possible to lay out the slate and pre-mark all of the pieces to cut. Sometimes the slate store will cut the pieces you bring back. Not all stores offer this service.

Slate is a great material to use for a fireplace hearth for a number of reasons. It's a durable natural stone, it's attractive, it looks fantastic next to a burning fire, it's easy to clean, and it's available in a variety of natural tones, including red.

If you want to use a hearth pad, you may have a problem finding one the right size. Hearth pads are pre-made thin platforms that you set on the floor. Some come covered with tile, and I have seen some made with slate. Many of the hearth pads I have seen come in a few popular sizes. It may be hard to locate one that covers your existing concrete hearth and is also proportioned correctly for the room.

You can build your own custom hearth pad to cover the concrete, but I feel this effort should be concentrated on installing the slate you want in the first place.

If you have any trepidation about installing slate, I propose that you make your own test hearth pad in your garage. Purchase a small piece of cement board that is perhaps 30 inches by 36 inches. Get some discount slate and apply it to the cement board. Forget about making cuts unless you want to do it by hand with the carbide rod saw. My guess is that you will discover in short order that the slate goes down with little effort.

Tim Carter can be contacted via his Web site, http://www.askthebuilder.com/printer_Submit_Question.shtml.

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