Deck Stain vs Sealer: Which One Does Your Deck Need?

The hardware store doesn't make this easy. Sealer, waterproofer, toner, stain, stain-and-sealer: the labels overlap so much it's hard to tell what you're buying.

The deck stain vs sealer question mostly comes down to one ingredient: pigment. A clear sealer keeps water out. A stain does that too, and its pigment also shields the wood from the sun. That difference decides how the deck looks next summer and when you'll be redoing it.

What a Clear Sealer Does

A clear sealer, often sold as a water repellent, soaks into the wood so rain beads up instead of soaking in. The boards keep their natural look for a while.

Its weak spot is sunlight. Consumer Reports says clear sealers have little or no pigment, so they generally don't deflect UV, and the wood turns grey anyway. Clear sealers earned the lowest scores in their testing, and they say you'll probably need to reapply every year. The USDA Forest Products Laboratory puts it at about a year on the exposed surfaces of a deck.

The upside is that with no pigment, there's no colour to match and no lap marks, so a sealer is the easiest finish to put back on.

What Deck Stain Does

Stain carries pigment, and pigment is what blocks UV. More pigment means more protection and less visible grain. Deck stains fall into three rough groups.

• Lightly tinted water repellents, sometimes sold as toners. A touch of colour and a bit more sun protection than a clear coat.
• Semi-transparent stain colours the wood while the grain still shows. It soaks in instead of forming a film, so the Forest Products Laboratory says it won't blister or peel. Consumer Reports expects two to three years from it on a deck.
• Solid stain looks and behaves a lot like paint. The best ones in Consumer Reports' tests should last three to five years on a deck, but the coats build into a film that can peel, chip and crack.

Deck Stain vs Sealer: Which Should You Use?

For most decks around here, we recommend a semi-transparent stain. It keeps water out, lasts longer than a clear coat, and since it doesn't form a film, it wears away instead of peeling, which makes the next coat simpler.

The Forest Products Laboratory leans the same way. It recommends penetrating finishes for deck surfaces and warns that paint and solid stain tend to trap moisture and fail by peeling. Railings are the exception, since they don't take foot traffic.

• Choose a clear sealer if you love the bare-wood look and don't mind recoating every year. If you can't decide, the lab suggests starting with a water repellent and switching to semi-transparent stain at the next refinish.
• Go semi-transparent if you want the grain to show and a coat that lasts a couple of years.
• Solid stain makes sense for boards that are blotchy, patched or mismatched. Going back to semi-transparent later generally means stripping it first, since a penetrating stain has to reach bare wood.

How to Tell When Your Deck Is Due

Thompson's WaterSeal suggests a splash test: sprinkle a little water on the boards, and if it soaks in and darkens the wood within about five seconds, it's time to reseal. Other signs:

• Grey, washed-out boards, worst where the sun hits hardest
• Worn paths in front of the door and down the stairs
• Peeling or flaking, if the deck has a solid stain

Timing: New Wood and Ontario Weather

Brand-new pressure-treated lumber is often too wet to take stain right away. YellaWood, which makes pressure-treated pine, uses the same drop test the other way around: if the water beads, wait, and if it soaks in, the wood is ready. Just don't leave a new deck bare for a year. The Forest Products Laboratory warns against leaving deck lumber unfinished for 6 to 12 months.

Weather matters too. Consumer Reports suggests staining when it hasn't rained for three days and the forecast shows at least two dry days ahead, with temperatures between 10°C and 32°C and low to average humidity. The can will list its own limits as well.

By late fall in Ontario, a dry, mild stretch like that is hard to find, and cool, damp air slows drying. If your deck failed the splash test this October, plan the work for spring instead of rushing it.

Having It Done

Our deck staining starts with a pressure wash to clear dirt, mildew and old stain residue. Once the deck dries we sand it to knock down raised grain, then apply one or two coats, taking care to avoid lap marks. If the old finish is peeling, we strip it first, because new stain over a failing finish won't hold up.

Cleaning plus staining on a standard 10x12 deck usually runs $400 to $800, depending on the deck's condition and the type of stain. A power wash on its own starts at $150. Bigger decks, or ones with railings and stairs, cost more.

Call (289) 928-5689 for a free written estimate.