Pressure Treated Timber Still Needs Protection from Rot

Pressure Treated Wood protects against timber rot and insect damage, but it is not infallible.

Builder Tim Carter explained in this Washington Post article that there are several reasons pressure-treated timber can deteriorate quicker than expected. According to Carter, “The bottom line is that timber rots and many things can go wrong in the treatment process, causing premature failure.” Perhaps the chemicals didn’t penetrate deeply enough, so screw holes invite the possibility of water damage. Cracks in the timber also encourage rot.

Carter stated, “Any number of products are available to stop water from entering the treated timber. Last year, as part of my deck reconstruction project, I applied a special tape on top of my timber joists before I installed the decking. This tape has a butyl rubber adhesive and seals around the shaft of the screws used to attach the hidden fasteners for the decking.”

The British Standard BS 8417 (2014) and the WPA Code of Practice – Industrial Wood Preservation (January 2021) sets out the minimum standards for the treatment of wood. These standards give guidance on the loading and penetration of timber preservatives. While preservatives are essential in helping wood to last longer, they do not render timber fail-proof.  “But some failures continue to be reported, typically around poorly flashed ledger boards, where water collects on wide deck boards, and in the seams between built-up beams,” according to ProRemodeler.com.

Rot is a Real Threat for Any Timber

Pressure-treating can make timber water-resistant, but it’s not 100 per cent rot-resistant. Water can enter any time the timber moves, bends, or cracks. While this may seem worrisome, the key is to keep the water away.

On the Ask the Builder website, Carter endorses Trex Protect as the product he prefers. “I have faith in the product and have taken steps using modern new products to minimise water infiltration into both the new deck and the existing treated lumber,” he said.

Trex Protect’s butyl tape is easy to use and convenient to apply. Available in three widths – 50 mm x 20 m for joists, 100 mm x 20 m for bearers and 279.4 mm x 15.2 m for rim joists —Trex Protect is applied as a cap (vs wrapping) to horizontal and vertical surfaces, allowing the timber to breathe. It comes with a 25-year warranty that guarantees you will get more life out of your deck.

So, if you’re installing a pressure-treated timber deck, don’t skip the essential and low-cost step of protecting your bearers and joists. The small cost is well worth adding years to your new deck.