What Is Pressure Treated Lumber?

• Untreated wood is subject to decay, rotting, warping and infestation. Treated lumber contains chemicals that prevent or delay this natural process. These chemicals are reverse-vacuumed deeply into the interior wood fibers.
  
  

Problems with Absorption

• Professionals know that moisture prevents wood from accepting any sort of new finish. Unfortunately, the same chemicals that protect treated lumber from decay also prevent the wood from absorbing stain and/or sealers. Unlike water, which evaporates from wood within hours or days, these reverse-vacuumed chemicals keep the lumber moist for a long period of time. If you attempt to add any type of oil stain or wood preservative to treated lumber before it's had a chance to dry out, flaking will prove inevitable.
  
  

Dehydration

• You can finish treated lumber if you've demonstrated adequate patience. Professionals wait at least six weeks for treated wood to dehydrate. If you want a lasting finish, do the same. In humid environments, six weeks may prove inadequate. To ensure that the lumber is ready for its finish, test it for absorption before beginning full-scale application. Add a small amount of stain or sealer to an inconspicuous portion of the lumber. If puddling, beading or dripping results, wait at least two more weeks for the wood to dehydrate further. If the lumber accepts the finish, you may proceed with full-scale application.
  
  

Choosing a Finish

• Though any type of stain will work on dehydrated treated lumber, some prove better than others. Avoid water-based stains and sealers that do not absorb into the wood fibers as well as oil-based ones. Thicker, gel-based stains are easier to work with and drip less than runny, liquid finishes. If you prefer a clear finish for your treated lumber, add a solvent-based polyurethane. Avoid two-in-one products, which don't tend to last as long. When choosing a specific brand of stain or sealer, disregard name recognition and opt for the one that boasts the longest warranty.