Nicolock PA- TF 18X18 BS Thermal Finish Flagstone Bluestone 18" x 18". Make foot traffic areas clean, safe, and gorgeous with these Thermal Finish Flagstone paving stones. We have engineered them to have a smooth, consistent texture with a thermal finish. Six different sizes let you make the layout as simple or complex as you want. The spacer lugs allow you to snug the blocks together with a sand joint. You can also lay them down in a grid pattern, letting the grass peek through for natural beauty and drainage