Silestone is a composite material of quartz and resin used to create countertops. A clean crack can be repaired relatively easily, despite the difficulty of working with Silestone. The crack can be closed together in the same manner used to connect Silestone joints. Silestone does not need to be sealed after being repaired since it is non-porous. Shattered or heavily damaged Silestone counters need to be replaced. The hardness of the quartz makes larger repairs difficult, time-consuming and expensive. It is cheaper and easier to replace anything beyond a clean crack.
Clean the area around the crack with mild soap and water. Dry it thoroughly. There are usually small particles of material in any crack, no matter how clean it is. This could interfere with the adhesive.
Place masking tape along the top edge of the counter on the edges of the crack. The tape blocks excessive amounts of silicone from affixing to the top of the counter.
Apply silicone along the edge of the crack.
Press the pieces of Silestone firmly together. A little silicone usually is squeezed through the top of the crack.
Wipe away the excess amounts of Silestone using a putty knife.
Silestone has a 15-year warranty. Check with the manufacturer before attempting to repair a crack yourself. Depending on the cause of the break, the manufacturer may repair or replace the countertop for free. Attempting to repair the counter yourself voids the warranty.