Uniformity of color is essential for a high quality concrete finish. Variations in color may be due to several factors: the materials and proportions of the mix, the form material and the release agent, and the placing and curing techniques. It is essential, if color variation is to be avoided, to recognize the probable sources of trouble before work begins, and to guard against them accordingly. Inherent color variations is the difference in color between two lifts. It is caused by using cements form different plants. A similar effect is obtained if the water/cement ratio is different for each lift. Aggregate transparency is when the dark areas of the mottled effect correspond with pieces of coarse aggregate near the form face. This is caused when, during vibration, fine particles, including cement, form a very thin layer over the aggregate in the narrow gap between the particles and the form face. Hydration discoloration can take many forms. A common problem is when water leaks through joints between boards. The dark discoloration is due to a concentration of fine particles, including cement , drawn towards the joint. Joints between boards must always be adequately sealed. Other causes are grout loss between boards resulting in a sand textured strip, moisture loss into unsealed plywood, a more absorbent board being used to replace a damaged board in formwork panel, or pressure during placing. Variations in the shade of concrete is due to segregation discoloration. This is caused by variation in water content over the surface resulting from segregation. Dye discoloration is caused by rust being washed down by rain from reinforcing bars on to the soffit form face. When this happens, the position of each bar will be clearly marked on the concrete. Another cause can be nails left to rust and stain the formwork. Oil discoloration occurs when an excessive application of oil on a soffit form results in the continuity oft he mortar surface being broken and in the sand and coarse aggregate being exposed.