Q. I am planning to replace the porch floor on a 120-year-old Victorian home. Since cedar and redwood seem too soft for a porch floor, I am choosing between tongue-and-groove yellow pine, vertical-grain fir, and mahogany. Can you explain the advantages and disadvantages of these species when used for a porch floor? As for the finish, I’m considering a transparent oil stain, because deck paint is slippery to walk on, and the stain will allow the wood grain to show through. It’s also an advantage that a stain will not peel. What is your advice?

A.Wood finishes expert Bill Feist responds: The National Park Service often specifies vertical-grained Douglas fir for its decks and porches. This wood has a good combination of hardness, moderate rot resistance, dimensional stability (resistance to warping), and cost. This may be a special order item at your lumberyard.

A true mahogany would be the optimum choice for a deck because of its marked durability, its rot resistance, its hardness and wear properties, and its very good dimensional stability. The only major drawbacks are its high cost and limited availability.

Tongue-and-groove yellow pine would probably be the last choice. This wood tends to be less dimensionally stable than Douglas fir or mahogany, and it can be difficult to nail. Untreated yellow pine would have a high potential for rot problems. However, several commercial wood treaters offer 5/4 radial-edged yellow pine decking with dual treatment, using a water-repellent followed by treatment with CCA ( chromated copper arsenate). This lumber is marketed under brand names such as Ultrawood, Wolman Extra, MELCO, and Weathershield. These brands use a better grade of wood, with fewer knots or other defects, than is usually used for standard pressure-treated wood. The wood tends to have few warping problems, and is highly rot resistant.

I agree that paint is not a recommended finish for a deck or porch. Because the horizontal surfaces are exposed to the sun and collect moisture, and because the finish is subject to abrasive wear, a paint or a solid-color stain would be likely to crack, flake and peel. These film-forming finishes also tend to trap water, leading to a greater possibility of rot problems.

A penetrating water-repellent preservative or a semitransparent penetrating oil or alkyd-based stain may provide the best finishing solution. Special formulations specifically made for decks are available. These penetrating deck finishes are easily renewed and enhance the appearance and service life of both naturally rot-resistant wood species and pressure-treated wood.