Selecting the Right Grout for Your Hearth
Hearths are typically constructed from brick, block, or stone because these materials resist fire. Grout serves to bind these units together and fill gaps. Selecting the appropriate grout requires understanding the hearth's purpose and the material's characteristics.
By Sam Mitchell
The proper hearth grout prevents the early deterioration of the unit.
Hearths are commonly built from brick, block, or stone, as these earthen materials possess fire-retardant qualities. Grout is used in such construction to bind the pieces together and fill the gaps between them. When selecting grout for a hearth, the hearth's primary function should guide your choice.
Preparing the Hearth Surface with a Sealer
Some hearth materials may require sealing before grout is applied. Porous materials like slate present challenges because their uneven surfaces can interfere with grouting. Tim Carter of Ask the Builder notes that applying a grout-release sealer to the hearth materials before grouting produces a flat, non-absorbent surface. This allows grout to be applied uniformly and makes it easier to wipe away excess grout from the slate.
When to Apply Grout
Just like any masonry project involving stone or brick, grout is applied after the mortar or adhesive that secures the material has dried. Most adhesives take about 24 hours to dry, but you should check the manufacturer's instructions. Once the adhesive is dry, apply grout generously across the surface of the bricks, blocks, or stone, pressing it into the gaps to fill them. Before the grout dries, remove any that gets on the surface using a damp cloth. If grout dries on a porous hearth surface, removing it can be difficult.
Grout Options for Hearths
Because a hearth's grout is exposed to continuous heat and sometimes direct contact with flames, the grout must be able to withstand these temperatures. Grouts labeled "heat-resistant" are designed for this specific use. According to Carter, fireclay is a heat-resistant material that can be used like grout and performs well under the heat conditions found in a hearth.
Repairing Cracks in Hearth Grout
Regardless of maintenance, the grout in a hearth may eventually crack. Once cracks appear, the only way to repair them is by replacing the grout. To do this, you must first remove the existing grout. Use a chisel or screwdriver along with a hammer to take out the grout from the hearth, then brush the surface clean. After that, reapply grout following the same procedure described earlier.
