Drip a couple of drops of clean water onto the surface of the lumber. This might not be a good comparison but some cedars turn a similar grey colour over time as well. Choosing 4 4 Treated Lumber Diy Woodworking Woodworking Projects Wood Check it to find the type of preservative used. How to tell if lumber is pressure treated . Ground Contactand Above Ground. Some differences between cedar and pressure-treated wood are readily apparent. It can have a green or brown color from the treating process. The numbers depend on the chemical preservative used in the treatment. Look for Stamps. Sprinkle some water on the wood if the wood absorbs the water within 10 minutes stain your wood as soon as possible. PT lands in two basic camps. As the treated wood ages it can turn a grey colour. As you should know every wood is cut in a specific way. The preservative retention for both CCA- and ACQ-treated lumber is 25 for above-ground applications and 40 for ground contac...