Mending a broken hearth

When it comes to minor damage, fixing up your tiles is easy

By David ZimmerDavid Zimmer

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Amidst the orderly geometry of a field of ceramic tiles, just one damaged square can stand out like a sore thumb, immediately drawing eyes to its imperfect existence. And unlike drywall or solid wood — which everybody knows can be filled, patched, and sanded to erase signs of damage — there is a mystery to tile repair that keeps it off weekend warrior to-do lists. Some jobs should be left to the experts: If damage is extensive, like a fault-line crack that runs across a whole floor or an entire wall of bathroom tiles dropping by the dozen, you’ve got underlying structural troubles that may need the attention of a professional. But more common minor damage, such as that crack that appeared when you dropped a big chunk of maple on the tiles under the wood stove, is easily remedied.

1. Start by removing the grout from the perimeter of the repair area using a grout saw (available at hardware stores), a utility knife, a masonry chisel, or even a hacksaw blade. The idea is to isolate the repair from the rest of the tiles so they won’t be disturbed by what comes next. With a hammer and masonry chisel, chip out the broken tiles; you want to remove the bad tiles without transmitting the force of the blows to surrounding good ones. Once you get the tiles up, you’ll expose the setting adhesive, either organic mastic (which looks like hardened beige glue) or thin-set mortar (which looks like, well, mortar). Again, use chisels or scrapers or anything it takes to get down to the substrate, which might be concrete, plywood, or cement backer board. When every speck of old grout and adhesive has been scrupulously removed, vacuum thoroughly.

2. It’s important that your repair use the same type of adhesive as the original, or the new tiles may not sit flush with the old ones. Organic mastic is a premixed adhesive, usually sold in a can. Thin-set, a generic term for setting mortars, is usually sold in a bag, and mixed with water before use, but many stores now carry premixed thin-sets, convenient for small repairs.

3. Following the manufacturer’s recommendations, apply adhesive to the substrate using a flat trowel, then “comb” the adhesive with a notched trowel. (The U- or V-shaped notches in the trowel ensure that just the right thickness of adhesive is applied.) Set the tiles, pressing them down firmly or tapping with a rubber mallet; for a good bond, you want to see a bit of adhesive squeezing out from around the tile edges. Once the adhesive has set for a few minutes, remove any excess from both the face of the tile and from the grout joints in between (a utility knife works well for the joints). It’s important to do this before the adhesive has fully cured or it will be very difficult to remove.

4. Next day, to grout. If your joints are in the neighbourhood of 1⁄8″, use plain or “unsanded” grout. Wider joints require “sanded” grout, which has more strength over a wider span. In either case, look for grout labelled “polymer modified,” which indicates it has additives to make it more flexible and resistant to fading and moisture.

5. Mix up a batch of grout according to directions until it reaches a spreadable consistency, then let it rest, or “slake,” for a few minutes to allow it time to fully absorb all the water. Then remix. If it’s too dry, add a bit more liquid, but don’t overdo it. Dump a pile of grout over your repair, then use a rubber-soled grout float to spread the grout and work it into the joints. Holding the float at about 30˚ to the surface, pack the joints full and tight. When they’re nicely filled, hold the float at right angles to the surface and scrape off the excess, working diagonally so you don’t end up stripping grout from the joints. There will still be grout smeared over the surface of the tiles — leave it be for now.

6. After the grout has set for 10–15 minutes, clean the surface of the tiles with water and a sponge (you can pick up scratchy sponges made for just this purpose). The sponge should be very damp, but not dripping. Work it around, rinsing it in a bucket, until your tiles are shiny clean. If the original tiles were protected with a sealer, apply it to the repair, and you’re done. Let the repair cure for at least 24 hours before dancing, showering, or filleting fish and it will be better than new. But no more splitting kindling on that fireplace hearth. And absolutely no boat anchors in the bathroom.

This article was originally published on April 1, 2005

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David Zimmer