Pressure treatment is a process that forces chemical preservatives into the wood. Wood is placed inside a closed cylinder, then vacuum and pressure are applied to force the preservatives into the wood. The preservatives help protect the wood from attack by termites, other insects, and fungal decay.
Some pressure treated lumber is already dried and ready to stain. Dry treated wood is ideal because you can confidently stain it right away. To recognize it, look for a tag or stamp that says KDAT (kiln-dried after treatment) or ADAT (air-dried after treatment).
Allow treated wood to dry thoroughly before staining or painting. It is recommended that you allow the wood to dry for at least 6 months prior to staining. Test dryness by sprinkling the wood's surface with water. If the water beads up, the wood is too wet and you must wait before applying a finish. If the water soaks into the wood, then it's dry and ready for stain.
Over time, most treated lumber will shrink slightly across its width as it dries out. Take this small amount of shrinkage into account when laying decking or fence boards. After being outdoors for six to 12 months, treated lumber will develop cracks, called "checks," along the surface of each board. These hairline cracks are a normal part of the drying process.
TWP Stain is a penetrating stain which means that it needs to penetrate the wood in order to provide protection, which is why you need to wait for the wood to dry thoroughly prior to staining.
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