How to Stop Timber Rot

You’ve thought of everything for your new deck: a curved design, a perfect colour board, a beautiful railing, and sophisticated lighting. 

The only thing you did not think about is the long-term life of the timber you used to build your deck. If not protected, your deck’s timber substructure is prone to damage due to moisture over time.

Moisture content is the number one enemy of your deck, as it creates the perfect environment for mildew, mould, and fungus. Dry rot fungus, such as serpula lacrymans, can wreak havoc on your timber. Mycelium secretes enzymes that break down the timber.

If continuously exposed to condensation or water, your deck may succumb to dry rot or wet rot — both are dangerous and involve different moisture levels. As you might guess, wet rot fungus grows at a higher water level. With wet rot or dry rot, the structural integrity of your deck timber can be compromised.

The Rot Stopper

To stop rot, you must prevent or limit your deck’s exposure to the elements. Over time, this will involve regular sweeping and cleaning to avoid damp leaves or debris buildup. It will mean sealing any exposed timber board and flashing and caulking where needed.

However, the best time to prevent moisture exposure is during construction. You can find peace of mind with Trex Protect.

To protect an average size deck measuring 3.5m x 7.5m will require approximately 5 rolls of Trex Protect Joist Tape and one roll of Trex Protect Bearer Tape. For less than a $130 investment, your deck substructure can last as long as the decking it supports.

Trex Protect, a butyl flashing tape, acts as a moisture barrier and prevents timber decay and rot. Unlike asphalt-based tape, Trex Protect’s butyl tape endures through high temperatures and has a wider temperature range for installation.

It comes with a 25-year warranty that guarantees you will get the most life out of your deck.

The materials you use in building your substructure also matter. Use rot-resistant timber such as cypress or cedar. You might also treat the timber with a fungicide (like borate) to kill or slow harmful fungi growth.

Consider composite decking made of recycled plastics. Composite boards are low-maintenance and don’t require regular sealing like timber. Most composite decking materials come with a lengthy manufacturer’s warranty.

Spot Dry Rot

Untreated timber will decay over time if exposed to moisture and mould. The most common and serious rot issues involve an incorrectly installed ledger board that allows water to penetrate the house wall. Because the house framing is not treated, it is much more likely to rot. According to Decks.com, if your ledger board is infected with rot, you will likely need to replace the entire deck. You may also need to repair portions of the house wall. If a few joists or some decking is rotting, you may be able to remove and replace only the affected pieces.

While this article focuses on decks, be sure to inspect all the timber on your house regularly for rot. An inspection includes window sills, roofing, and siding.

How to Identify Dry Rot on a Deck

How do you spot rot? Symptoms include spongy and discoloured timber that may flake off and fall apart when wet. You can use a screwdriver to test the timber for soft spots. You can also tell if timber is rotten by checking for these likely problem areas:

• Anywhere timber contacts the ground
• Long sheets of greyish mould or darker-looking timber  
• Pest damage, those spots could be a combination of insect damage and dry rot since dry rot attracts termites and other timber-eating pests
• Leaky plumbing, gutter failure, sprinkler system issue, and any and all other water pooling possibilities
• Not sure if it’s dry rot? When in doubt, call a professional to come to inspect your deck and give you an estimate for repair.

How to Treat Timber Rot

Discovering areas of dry rot on your deck requires immediate action. When replacing rotten deck boards, thoroughly inspect the compromised areas.

Be sure to inspect all areas directly adjacent to the rotten timber, as even early signs of decay will eventually contaminate your recent repairs. If you’re unsure how to identify or fix areas of rot on your deck, call a professional. This is one home improvement project you must get right to keep you and your family safe!

If you feel competent to DIY a repair, follow these general guidelines:  

• Remove nails and screws. Use a pry bar, screwdriver, or drill. If the fasteners refuse to come out, chop the board into pieces and pry them up.
• Inspect bearers and joists. Remove any rotted timber. Repair and reinforce any timber that is soft or discoloured with timber hardener or rotted timber putty.
• Protect the bearers and joists. Before replacing the deck board, cover joists and bearers with butyl tape. If there are areas you cannot reach to apply tape, use a clear sealer to prevent further rotting.
• Reinforce the joist. Be sure to cover all damaged timber with tape or sealer. Position a reinforcing bearer tightly against the damaged timber. Attach it with galvanized nails or galvanized deck screws.
• Secure reinforcing joist. Attach the reinforcing joist to the ledger and header by toenailing with nails or screws.
• Prepare and install deck boards. Cut the replacement boards from matching timber or composite decking. If using timber, seal the new deck boards.

Just as you wouldn’t skimp on a home’s foundation, don’t take chances with your deck’s substructure. Be proactive so you can enjoy your outdoor living oasis with a reliable and safe substructure today and tomorrow.