Special care urged for pressure wash, stain removal
Q: I am removing the screws from our 10-or-more-year-old redwood deck. At about 1,200 square feet, it’s a big job, and it’s taking a lot of time to remove the screws, inspect the boards, then flip them over and screw them back down, replacing boards as needed. I am about halfway through with this project.
When finished, I plan to power wash the deck, then stain and seal. A neighbor told me I’m too late because the decking has turned gray and no stain or sealer will cover the gray. We don’t really worry about the gray — that is a natural color for wood to turn when sun and weather get to it.
Do you have any suggestions on what stain and/or sealer I should use to level out the color? Some of the boards are gray and on many you can see lighter areas where they were fastened to the joists every 2 feet. The power wash may help a little, but I know it can also damage the wood’s softer grain.
A: Your plan is pretty much right on and your neighbor is dead wrong. Flipping the boards on a redwood deck the size of a small house will save you a ton of money and be worth the work you’re putting into it. With a few simple steps and some caution with the power washer you’ll have a deck uniform in color and ready for another 15 or so years of enjoyment.
You’re halfway there on the first step. Flipping the boards is the lion’s share of the work.
We suspect that the original decking contains most, if not all, heartwood. For that reason, use construction heart-grade boards for replacement. Also, as you replace the damaged boards, disburse them at different locations around the deck. If there is any color or finish variation when complete, they won’t all be in the same place.
Ultraviolet radiation from the sun breaks down surface fibers of the wood, causing graying and surface erosion. Moisture encourages surface mildew and causes stains. Tannins in redwood also can discolor the surface.
After you flip the boards, your next step is a good cleaning with a pressure washer. Ten-plus years of exposure to dirt, dust and cobwebs need to be cleaned out. You’re right — caution is the watchword.
Be gentle with the wand. Wear safety glasses; hold the nozzle about 6 inches above the deck’s surface and spray in line with the wood grain, overlapping your path. Make sure the spray is a fan shape and keep the wand moving. Leaving it too long in one place will dig at the soft wood fibers of redwood. You’ll find that much of the gray color and perhaps some of the joist marks are removed with the washing.
Once you’ve done the initial pass, give the deck a few days to let it dry thoroughly.
The first line of attack on joist marks is a light sanding. A palm sander and 80-grit sandpaper will work best. But a sanding block and 80-grit sandpaper will do the trick and build some muscles, too. Make sure you sand with the grain and remember that a light sanding to remove the joist lines is all you’re after.
Several products are available for dealing with any residual graying and stains. Commercially available powder or liquid concentrates have a base of non-chlorine bleach or oxalic acid. Bleach-based products eliminate mildew and acid-based materials handle graying and stains. Make sure you test any chemical in an inconspicuous place, as some products may darken the redwood.
Wear rubber gloves, eye protection and old clothes when working with these chemicals, and follow the directions precisely.
Leaching tannins or corroding hardware and nails cause non-mildew stains. For these problems, an acid-based deck restoration product is best. Pre-mixed oxalic acid deck cleaner and oxalic acid crystals can be purchased from a hardware store or home-improvement center. Make sure to follow manufacturers’ instructions for use. Allow the deck to dry, and then rinse with clear water.
Before finishing, allow the deck to dry for a week or two. The best finishes are those that penetrate and soak into the wood. If you want to add color, a semi-transparent stain is the way to go.
- There are three important characteristics to look for in a finish.
- The finish should be water repellent or waterproof, not just water resistant.
- It should offer UV (ultraviolet) protection.
- If mildew is a potential problem, the finish should contain a mildewcide, which a wood preservative does.
Regular preservatives should be reapplied once a year, but some newer and better products offer more UV protection and may last up to four years.
And, as always, buy quality materials and follow the manufacturer’s directions.
Copyright 2010 Bill and Kevin Burnett