Building a deck or porch: choosing material and finishes

When building a porch or deck, major considerations include whether or not to use a finish — and if so, which one. Another is whether or not to use pressure-treated wood. Here's what you need to know to make the right choice.

Building a deck or porch: choosing material and finishes

Choices for finishing

You can be taken aback by the variety of deck-finishing products that you'll find at the hardware store or home centre. But just like the 30 varieties of yogurt you find in the supermarket diary case, there really aren't many variations in suitable wood finishes. In fact, you really only have three choices:

Apply no finish. This is a perfectly valid choice if you live in a relatively dry climate and you don't mind the deck turning grey.

Choose a sealer. The most popular finishes for decks are clear penetrating wood finishes, sometimes called sealers. These usually darken the wood's natural colour in a way most people find pleasing. Clear finishes contain a water repellent — usually paraffin wax — as well as a mildewcide and ultraviolet stabilizers to slow deterioration from the sun.

Clear finishes need to be reapplied each year. It's easy — just use a paint roller attached to a pole for the deck boards and a natural-bristle brush for the railings and anyplace else the roller can't reach. Use a roller designed for textured paint finishes — it holds the most finish.

Semitransparent stain. If you want to change the colour of your deck, you can use a semitransparent stain. The major difference is that the pigment in the stain provides more protection from the sun than a clear finish can provide. You'll need to recoat only about every two or three years. To apply, use the same technique as for a clear finish.

When to use pressure-treated wood

Wet-site projects.

  • It's a common belief that pressure-treated wood is the most durable word product you can buy for outdoor use.
  • Depending on the application, that's not always the case. In the pressure-treatment process, chemicals that are toxic to termites and fungi are forced into the wood under pressure.
  • This means the critters won't eat the wood. Keep in mind, though, that termites and fungi also need a moist environment — they won't eat wood that doesn't stay damp.
  • So if you are building something that will remain damp or will be in contact with the ground, such as the frame of a deck or porch — nothing will last longer than pressure-treated wood.

    Dry-site projects.

  • For a deck or porch floor, pressure-treated wood may not be the ideal choice. Water can't collect on a well-designed and well-maintained deck, so fungi and termites won't come to dine anyway.
  • Plus, pressure-treated wood is usually made with southern yellow pine, which is denser than lighter woods like redwood and cedar.
  • This means southern yellow pine is more likely to warp and splinter from humidity changes and the effects of wetting and drying — an especially important consideration for decks that get rained on.
  • Porch floors are usually covered by a roof, so rain shouldn't be a problem. Choose tongue-and-groove mahogany porch flooring, which looks much better than pressure-treated boards.
  • The mahogany is more durable, too, and you will be pleased to discover that it costs no more than pressure-treated wood.
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