Should you Pressure-wash under Your Deck?

It’s expensive, messy and labor-intensive to pressure-wash and fungicide under a deck. Is it worth it? When should you do it? This short video helps you decide.

Holding down Deck Boards with Screws: a Simpler Method

The funny thing about decks is that, by just walking on it, the nails are caused to rise up and get in the way! In this short video, we talk about how to overcome that problem by inserting a screw between the nails. This is a much more effective solution than the usual technique of pulling out all the nails…….and a lot faster, too!

Look out for Deck Destroyers: Guarding against pests and rot on your deck

Look out for “Deck Destroyers”


The two principal deck destroyers are surface damage (like mold) and deep damage (like rot and pests). Let’s look at them in turn:


Dealing with Surface Mold

There are four types of mold under the deck to look out for:

1. Black mold. This is mildew and can be seen as lots of black spots. It is fairly normal to see this.  Sometimes, if the deck is very wet, the whole bottom of the deck boards is black. A spray of dilute bleach under the deck is a simple treatment to keep this under control.

2. White mold. This is a fungus called Mycelium and it is a sign that the deck is wet and staying wet. Often you see this where water “stands” where deck boards meet the joists. This indicates that a problem will appear in the next ten years. If you can reach it, it is best to pressure wash off the fungus and then kill it with dilute bleach.

3. Green mold. This is the worst rot and needs immediate attention. Usually it is a thin film of green mold, but it can get far worse within a few years. I have seen a deck covered in thick green mold under and on the deck; you could barely walk on it without your feet going through. Best to pressure wash off the green mold and apply chemicals to stop it coming back.


Dealing with Deep Rot and Pests

There are four types of deck board damage to look out for:

1. Dry rot. You will be familiar with this. This is rotting, usually first seen at the ends of deck boards as a softness and brown discoloration, often dampness. Replace the board when the end starts to get springy. Or you can use Copper Green chemical (very toxic, respirator needed).

2. Brown rot. This is quite rare, and is a cubic break-up of the wood. Treat with chemicals or replace the board.

3. Termites. When wood gets damp (such as, when the stain no longer keeps the water from entering the wood), termites can burrow into it. They tend to enter at the ends of boards and munch their way down the grain, then they find another board. Many people think they are like piranha but they are not that fast. Every house has termites; you just don’t realize it. There are different types of termites. Some fly around and then drop their wings and enter the wood. Others can make their own “ladder” and climb vertically upwards towards your deck! Look out for discarded wings, small brown wood particles pushed out of holes in the wood, or distinctive fungus-like vertical tubes under your deck. Treat with “Orange Oil”, tent the deck and house with chemicals for 3 days, or have a pest-destroyer come along with their microwave wand.

4. Beetles. Fairly rare, they leave a single pinprick entry point about 1/32 inch in diameter. Easy to miss. Usually not that destructive. Apply killing chemicals to entry point.


You can find more information and pictures in our handy pdf called “Deck Destroyers” from our website.

Avoiding Physical Damage to Your Deck

Avoid Damage to the Deck


Mechanical damage caused by your furniture and other contractors can be an issue worth looking out for before it happens as they are hard to fix.


Put feet on bottom of chair legs.

Metal furniture and all forms of metal-to-wood contact are always a problem. With metal furniture, I suggest you check that none of the plastic feet have come off. You can get replacements at Home Depot or Ace Hardware.


Don’t drag stuff across deck.

Several times year we get calls from people where they, or their landscape or interior contractors, have dragged something across the deck and scored the wood. This obviously goes through the stain and leaves the wood exposed. Look out for: gardeners rolling planters across the deck, furniture movers dragging filing cabinets over it, window washers not having soft feet on their ladders, contractors working inside taking in heavy materials, and the golfer in the family walking on the decks in golf shoes!

Keeping Water Damage on a Deck Under Control

Keep Water Under Control


It’s water and UV that really damage decks. Moisture is one thing, water itself (in large quantities!) is quite another. Here are a few suggestions for you.


Put feet under planters.

“Standing water” (water that never quite dries out and can’t easily escape anywhere) is the number one enemy of decks. Most people overwater plants and the planters sit directly on the surface, leaving a wet patch underneath. If you can elevate the planter, the wood has a chance of drying out. You can get plastic or ceramic feet, or cruciform wood structures with wheels, or planters with wheels at your local hardware store (try the gardening section). You can also see if you are overwatering and can adjust your watering or irrigation system.


Fix leaky gutters.

Not only will a leaky gutter cascade vast amounts of water onto the deck, leaving it damp all winter, but the impact will probably rip off the stain and leave a line about 6” wide across the deck. We have seen this in a fair number of decks, and now I know what to look out for (and you do, too!) The most obvious point is right under the corner of a roof, where the water cascades around so fast it overspills on the corner and deluges down. Or, if you have a tall wall that faces into the wind, water can hit the wall and cascade down the wall, and then drop where a patio door is and damage your deck right there; a small deflector strip above the door can be enough to solve this issue.


Avoid irrigation spray on the deck.

Make sure that your lawn sprinklers do not douse your deck as they will leave precipitated minerals (i.e. a white mark) as the water evaporates. Water can also soften the stain, making it vulnerable to being scratched off. I suggest you make sure your landscape contractor (or you!) use 180˚ sprinkler heads facing away from the deck, not 360˚ heads, close to the deck.



Keeping Mold on a Deck Under Control

Keep Mold Under Control


Mold is the harbinger of much more serous damage. It’s best to keep an eye on it. Here are two things you can do.


Spring and Fall scrub.

During the winter, fungus and moss can grow in wet dark corners under trees and in the shade of your house. Sometimes these areas never dry out and they can get slippery. The answer is to put some dilute bleach/deck cleaner onto the deck. I recommend first wetting the deck with a pressure washer or garden hose, then gently applying deck cleaner liquid through a pressure washer on its lower pressure setting and scrubbing it in. Or pour bleach into a 5 gallon bucket and fill up with water then brush on.  I advise against a more concentrated mix than 10%. You want to be careful not to let droplets of concentrated bleach fall on your deck – you will get distinct spots of discoloration.


Scrape between boards before the rains.

Deck boards should be spaced at 3/16” or ¼” spacing when they are new, to allow tree debris to fall through. Contractors in the old days didn’t do this (they prided themselves on tight boards) and many decks today are suffering because of it. What happens in the winter is that the wood swells as it gets wet. Amazingly a 5.5” wide board (the actual size of a standard “2 by 6”) will swell 1/8” each side. If there isn’t a ¼” space then you will gradually get warping and lifting boards. Especially if there is debris stuck in the gap. The answer is to keep those gaps empty before the rains come. The best way we have found to do this, is to use a paint scraper, a hooked handled device you can buy at Home Depot or Ace Hardware. You gently drag it along the gaps and you can pull out the debris, and then blow it off the deck. To avoid hurting your back, most people tape the handle to a broomstick and stand up while using it. I have heard people using a Skilsaw to clear the gap or widen it but this leads to big problems at the end of the cut when you can’t get the saw in, and it is easy to wander off track a bit and end up with very uneven edges.