How to Repair a Long Hairline Crack on Ceramic and Pottery with Strong Mechanical Integrity
When a ceramic vessel has a long hairline crack, typically, it is required to be broken completly before repair for proper reapir access. When the hairline crack goes through design details and breaking it will increase the required repair areas, the "pegging" method illustrated below can be used. The pegging technique ceramic repair requires the walls of the vessel to be thick enough to accept a peg. When pegging is done properly, it is an excellent way to restore durability to the repaired ceramic item with a hairline crack prior to continuing the restoration process. Below, we repair a cracked jar with some step by step illustrations and explanation. To see examples of a cracked bowl, cracked mug, cracked plate, cracked vase, cracked urn or a cracked jag, see our restoration examples page.
Step 1: The Crack and Grinding for Peg Insertion
Choose to grind the channels on the side with less details. In this example, we used a 5mm diamond rotary disk to create a channels across the crack to embed the peg. We also created a channel along the crack to allow the clear epoxy to pool so that it can penetrate through the crack's wall.
Step 2: Copper Peg Preparation for Cementing
In this case, we used 12 gauge copper wire. We textured the surface for better bond with the adhesive. The razor blade is inserted in the crack to widen the gap for better epoxy penetration to the walls of the crack.
Step 3: The Cementing Process
Heating the mug and the epoxy to 120-140 degree F will make the epoxy more liquid and enables it to penetrate through the crack. Warm the epoxy before mixing it and make sure the two parts do not touch each other to avoid cure time from starting (we use microwave oven to warm epoxy). 120-140 degrees however will reduce to epoxy cure time from 5 minutes to about 2 minutes so make sure all you need is near you.
Step 4: The Cementing Process - Two Part Clear Epoxy
Place the mug so that the crack and the grinded channels are on the bottom before placing the mixed 2-part epoxy. After applying the epoxy, inspect the other side of the crack to verify that the epoxy went through the walls of the crack. Remove the razor blade while the epoxy is still very liquid. Place the clamp before the epoxy hardens and put back in the oven (120-140 degree F) for optimum cure strength.
Step 5: Filling in and Covering Repair Lines
After cleaning the excess epoxy with a razor blade, fill all gaps with 2-part filler epoxy and sand with a Dremel and than by hand graduating to a very fine sand paper.
Step 6: Paint and Cold Glazing
If the glued seam shows or the filler is visible and this is not acceptable to you, color touch up is required and is not covered here due to numerous possibilities and the complexity of it. We use high end acrylic paints or coloring pigments powders and colored hardeners mixed with proper additives to create strength and the right light reflection to emulate the broken item's glaze affect as close as possible - see our tools and materials tutorial page. Note that this is the most difficult part to master and it is very time consuming especially when repairing objects with multiple colors.