Joints can be topped up with the same mass used when installing the slate slabs. For joints with a large width, gravel or single grit 2-4 mm can be used. Narrow joints can be topped up with a dry and fine-grained grouting sand. Weeds in joints can be removed using chemicals, be burned with a propane burner, or removed using boiling water, which is the easiest and most environmentally friendly method.