Repairing Broken Ceramics Patty Storms

Appears in the Jul/Aug 2016 issue of Pottery Making Illustrated.

The best way to restore a broken ceramic object is by using a cold-materials process. With modern adhesives, fillers, paints, and cold glaze, it’s possible to perform seamless repairs to damaged ceramic objects. A basic ceramic repair happens in two steps, first mending the broken pieces and second, filling and sanding the visible break lines, chips, and gaps using the best commercially available materials. This basic process applies only to non-porous or slightly porous materials such as porcelain and stoneware.

Note: When mending more porous materials such as terra cotta and plaster, heating the surface to 90°–110°F prior to the epoxy application on both sides of the object improves bonding. Be aware, heating also reduces workability and cure time. You have to achieve proper positioning twice as fast as you would with porcelain and stoneware.

Choosing Adhesive

Specific kinds of adhesives are generally used to mend ceramics. We recommend clear, five-minute setting, two-part epoxy. There are cases where a slower setting epoxy will work better. In order to choose the correct adhesive for a ceramic repair, you must first identify the type of ceramic involved. Because an exact fit is essential in repairing ceramics, you must adjust the pieces precisely before the glue sets. Five-minute epoxies and instant glues might cure too fast and are not recommended if you need longer time to match and adjust a precise fit. We use different adhesives for different applications.

Prepare the Surface

The most important step in repairing a broken ceramic object (1), is to make sure the pieces are clean. If the item has been fixed before, clean off any old adhesive, or the new adhesive may not bond. Goof Off removes stains, paint, oil, cements, glues, and cold glazes. Acetone or lacquer thinner does a good job of cleaning off surfaces with cured 2-part epoxy. Use rubbing alcohol for general cleaning of dirty surfaces.

Caution: Before cleaning, you may want to put on clean gloves to protect your hands from any sharp edges.

Fill a container that is slightly larger than the piece you want to prepare with plastic pebbles, rice, or sand. This will cradle and hold the repaired piece still and in place while it cures. Finally, do a dry run of how the pieces will fit together.

Mixing and Applying the Adhesive

Place even amounts of five-minute, clear, two-part epoxy on a paper or cardboard pad. Mix the epoxy well with a pin tool or a wooden stick (2). Using a wooden stick, paper clip, or a pin tool, apply the epoxy to only one of the broken edges (3). Use only enough adhesive to cover the edge. Too little will leave gaps, resulting in a weak repair; too much will make it difficult to achieve a tight joint.

Tip: Warming up the ceramic pieces to 90–110°F will thin the epoxy, creating a better fit, but will result in a faster cure time. Quickly join the pieces together while applying light pressure to squeeze extra epoxy out (4). Use tweezers to apply small pieces. You only have about 60–90 seconds from start of epoxy mixing to placement before the epoxy becomes gummy and unworkable. Use clay to hold the pieces together if gravity alignment is not possible (5). Any epoxy that oozes from the joint can be removed later using a razor blade (6).

Fixing an Item with Multiple Breaks

If you have a piece of ceramic that’s broken in more than a couple of pieces, plan the attachment sequence to avoid being left with a final piece that cannot be easily attached or fit in. Numbering the pieces after a dry run is a good idea and will assist in the actual implementation. Let each joint cure before repairing the next one.

Filling in for Missing Pieces

We use different products for different situations. PC-11 filler epoxy is a very good option for filling in smaller missing pieces and visible repair lines (7). What you’re looking for in a good filler is: exceptional adhesion; won’t shrink while curing; workable—can be drilled and sanded; paintable; water/oil proof; will tolerate a wide temperature range without shrinking or expanding. We let the filler epoxy cure at 110°F so it cures very hard, which is needed before sanding. Wipe all surfaces with a 91% alcohol solution to remove dust and oils prior to applying filler epoxy. Mix equal parts of PC-11 epoxy filler (8).

Tip: For ease of application, work in a room that is 75°F or warmer. Apply a thin layer of filler while pushing in to fill cracks and missing fragments (9, 10).

Allow filler epoxy to cure for 12 hours or more at a temperature of 75°F or warmer. Alternatively, place the filled object in a kiln heated to 110°F for eight hours. Placing the object under a lamp is another good option to optimize hardness for better sanding performance. Place the lamp at least 12 inches away from the repaired item to avoid overheating. Use a Dremel EZ-lock 120 grit sanding disc to sand down the extra surface epoxy (11). Caution: Wear protective eyewear and a dust mask when sanding. Use the Dremel tool on a low speed to avoid burn marks and apply only light pressure. If sanding by hand, start with 220 grit sandpaper and finish with 400 grit sandpaper (12). If you see missed cracks, repeat the steps above for the selected areas. Clean the entire piece with alcohol to prepare the surface for painting and cold glazing to hide the repair lines.

Filling in for Larger Missing Chunks

To fill in for a large missing piece, begin by repairing as stated in the previous steps and fill in any cracks. Once the piece is fully cured, fill in the missing gap with wet clay. Smooth over the clay so it matches the height and surface of the surrounding area. Let the clay dry in place. Once dried, carefully remove it and fire it to bisque temperature. Verify that the fired pieces fit (it will be smaller due to shrinkage) the ceramic object, then adhere them with 2-part epoxy, and let it fully cure. Sand the edges for a tighter fit needed. Fill in any remaining gaps with PC-11 and let the entire piece fully cure again before a final sanding. The restored piece is now ready for coloring.

Painting/Color Touch Up

If the repair lines are not acceptable to you, and a seamless repair is desired, the required skill is much greater. Color matching and re-creating an artist’s work and style takes time. We use high-end acrylic paints or coloring pigment powders and colored hardeners mixed with additives to create strength. Matching colors, texture, and sheen is the longest and the most difficult part of process to mastering ceramic restoration. The match must be perfect if it’s expected to be invisible. To make a color match perfectly, one must take into account the fact that the color could change as it dries and could change again once cold glaze (paints applied after the final glaze firing) is applied. The changes are sometimes making the color darker, sometimes lighter, and sometimes the hue is modified. The paints we use are acrylics,  oil, enamel, or mineral pigments depending on the projects. A good starting point for first time DIY job is to use water-based acrylics.

Lakeside Pottery, a nationally recognized ceramic and sculpture restoration studio owned and managed by the husband-and-wife team of Patty Storms and Morty Bachar, was established in 2001 as a ceramic art and pottery teaching facility. Lakeside Pottery focuses only on ceramic and sculpture repair and restoration in addition to custom made pottery and Kintsugi art. To learn more, check out www.lakesidepottery.com.