A. T1-11 plywood is designed to be an economical way to cover the exterior of a house or other building. Because of that, the top layer is usually made from woods that do not hold up too well unless they are finished with good quality exterior paint or stain. There are often blemishes that may have been repaired with football shaped plugs.

If the T1-11 you are using has a quality top layer and you are ok with the appearance, you could use a semi-transparent or clear finish. I have often used a product called CWF made by Flood. I have not used it on T1-11, only on cedar shingles and trellises.