Subsurface micro-defects in rock and concrete-like materials, crucial for the integrity and durability of the epoxy repaired structures, which should be carefully treated during repair. In this study, a Resin Pre-coating (RPC) method was used to seal the subsurface micro-cracks by capillary action. The sandstone (the average grain size G = 0.5 mm) and granite (G = 2 mm) were selected to test the efficiency of RPC method. After the notched three-point-bending (3-p-b) specimens were loaded to fracture, the substrates were bonded together using epoxy adhesive or epoxy adhesive plus RPC. By comparing the peak loads, fracture energy, crack paths, micro-cracking activities before peak load and X-ray Microscopy (XRM) images of subsurface micro-structures of specimens repaired with different methods, the RPC method was proved to be effective for repairing the subsurface micro-cracks and strengthening the repaired structures, meanwhile the efficiency was confirmed to be relevant with the grain size.