Fireplace surrounds and hearths

Clearance to the firebox opening

The first thing we look at is the distance from the firebox opening to the tile that goes around it. Most wood burning fireplaces have a manufacturer spec that says a minimum clearance from the firebox edge to any combustible material. Tile is not combustible but the thinset and the substrate behind it can be. We measure that gap and if it is too tight we can use a noncombustible backer board or a metal trim piece to bridge the space safely. Gas fireplaces have different rules and we check those too before we set any tile.

On a job like this we are working with the firebox opening as the starting point. We do not guess at clearance. We measure from the firebox edge out to where the face of the tile will sit. That distance determines how much of the surround we can tile and what material we use for the first row. If the opening is inset we sometimes need a metal strip or a thin band of stone to keep the heat path clear. Every fireplace is different and we treat it that way.

Heat rated setting materials

The thinset and grout you use around a fireplace have to handle the heat. Standard thinset breaks down when it gets hot and the tile will pop loose. We use a modified thinset that is rated for temperatures up to the range a typical fireplace produces. The same goes for grout. We use a cement based grout that can take the expansion and contraction without cracking.

If the surround is going on a wall that has a firebox behind it we sometimes use a furring strip to create an air gap behind the tile. That air gap keeps the heat from building up behind the tile and damaging the substrate. We also use a metal lath over the furring strips to hold the mortar bed. That is not something you see on every tile job but for a fireplace it is the way to keep the tile in place over years of heating and cooling cycles.

Stacked stone versus a flat field

Stacked stone is the most common look for a fireplace surround. It is small stone veneer pieces that sit tight together with thin grout lines or no grout lines. The tile setter has to lay each piece by hand and work the layout so the seams do not line up in a bad way. The finished look is a natural stone face that does not look like a grid. The downside is that stacked stone has a lot of small joints that can collect dust and soot over time. A flat field of large format tile is easier to clean but it does not give the same texture.

If you want a flat field we usually run the tile from the hearth up to the ceiling or to the mantel. We cut the tile to fit around the firebox opening and we miter the edges where the tile meets the wall. A flat field needs a straight wall to start or the tile will show every dip. We check the wall with a straightedge and if it is off we skim coat it flat before we start. That adds a day to the job but the tile sits flat and the grout lines stay even.

The hearth edge

The hearth is the ledge that sticks out in front of the firebox. It takes more abuse than the surround because people stand on it to reach the mantel or set tools on it. The edge of the hearth is where tile can chip if it is not supported right. We use a solid substrate under the hearth tile. That is usually a cement board or a mortar bed that is thick enough to carry the weight.

The front edge of the hearth we usually finish with a bullnose tile or a trim piece. Bullnose is a tile that has one rounded edge so it looks finished without a metal strip. We cut the hearth tile to fit flush with the bullnose edge so there is no step. The joint between the hearth and the floor is caulked with a color matched silicone because hard grout will crack where the hearth meets the wood floor or the carpet. That caulk joint is part of the job and we clean it up tight so it does not look like an afterthought.

Mantel interaction

The mantel sits above the firebox opening and the surround tile has to fit around it. Most mantels are wood or stone and they have their own weight that the wall has to carry. The tile surround stops at the mantel edge or we run the tile up behind the mantel if it is installed after the tile. We have to know the order of installation. If the mantel is already in place we cut the tile to fit tight against it and we leave a grout joint that matches the rest of the field.

The gap between the tile and the mantel is caulked with silicone. Wood mantels move with changes in humidity and hard grout will crack. Silicone moves with the wood and keeps the joint looking clean. We use the same color silicone as the grout so it blends in. If the mantel is stone we can grout that joint because stone does not move the same way wood does. We look at the mantel and make that call on the job.

• Clearance from the firebox opening to the tile is measured before any tile is set.
• Heat rated thinset and grout are used on every fireplace job.
• Stacked stone is set by hand with thin joints. Flat field tile is mitered at the edges.
• The hearth edge gets a bullnose tile or a trim piece. The hearth to floor joint is caulked.
• Wood mantels get a silicone joint. Stone mantels can be grouted.
• We use a metal lath and mortar bed on firebox walls that need an air gap.