Which treatment would be the least effective for preserving wood?

The least effective treatment for preserving wood is paint. While paint does provide a layer of protection by creating a barrier against moisture and fungal growth, it does not penetrate the wood fibers. This means that it can trap moisture underneath, leading to potential wood rot and degradation over time. Furthermore, paint may chip and peel, which exposes the wood to the elements and can compromise its integrity.

In contrast, treatments such as staining, sealing, and varnishing allow for better penetration into the wood structure. Staining not only changes the color of the wood but also can contain preservatives that protect against UV rays and moisture. Sealing provides a protective layer that can help with water ingress, and varnishing adds an additional layer of durability while enhancing the wood's appearance. These treatments generally offer longer-lasting preservation compared to paint, making paint the least effective option for wood preservation in the long run.