What wears out a wooden piling?
Six things do most of the damage, and most of them work near the waterline.
| Cause | Where on the pile | Which water |
|---|---|---|
| Rot (decay fungi) | Above the waterline, the cut top, deep cracks and bolt holes | Fresh, brackish and salt |
| Shipworms | Inside the wood, below the waterline | Salt and brackish |
| Gribbles (Limnoria) | The surface, between low and high tide | Salt and brackish |
| Rubbing | Where boats, floating docks and debris touch | Any |
| Sun | The surface, above the water | Any |
| Ice | At the ice line | Water that freezes |
Why do pilings rot near the waterline and not under it?
Rot fungi need water, air and mild temperatures. Wood that stays under water gets too little oxygen, so it decays very slowly or not at all. Wood above the waterline gets wet from tides, spray and rain but also gets air, so rot takes hold there.
Treatment protects only an outer shell. Above the water, the wood keeps drying and can crack deep enough to reach untreated wood. Cuts, bolt holes and the sawn top of a pile open it up too.
Check the pile tops. Rot can grow inside a top that looks solid, and a wrap at the waterline does nothing up there. Ask a contractor about treating and capping them.
What are marine borers, and do I have them?
Marine borers are small sea animals that eat into wood in salt and brackish (part salt) water. In salt water harbors, they are the main cause of damage to wood piles.
Shipworms are mollusks, related to clams. They get in as tiny larvae and, when not crowded, can grow 1 to 4 ft long inside the wood. The surface can show a few small holes while the inside is honeycombed.
Gribbles (Limnoria) are shrimp-like animals about 1/8 in long. They chew shallow burrows that moving water wears away, mostly between tide levels. The pile thins to an hourglass shape, and gribbles can take 1 in a year off its diameter.
On the Pacific, Gulf and South Atlantic coasts, untreated piles can be destroyed in a year or less. Attack is slower in colder New England water, but it still happens. Treated piles last longer, but borers get in where the treatment is thin or broken.
Borers are rarely a problem in fresh water, but they sometimes turn up in rivers above the brackish zone. Ask locally.
How do boats, sun and ice wear pilings?
Rubbing: boats, debris and floating docks wear pilings, most of all a floating dock riding up and down with the tide. Wear through the treated shell leaves untreated wood open to rot and borers.
Sun: sunlight turns wood gray and rough and opens small cracks near the surface.
Ice: ice freezes onto pilings and pulls them up when the water under it rises. After several rises, this ice jacking can lift a pile out of the bottom. Moving ice also pushes sideways.
What does a piling wrap do, and what doesn't it do?
It covers one band of sound wood, up to 48 in tall per piece. Pier Protector is black HDPE, 30 mil thick, UV-stabilized and 48 in wide. For a taller zone, stack bands with a 6 in overlap, the upper band over the lower one so water runs off.
Each piece goes over at least 3 layers of stretch wrap. You tack one edge with 3 to 4 nails, pull the sheet tight around the pile, overlap the ends 6 in, then nail the seam every 3 to 6 in. In that band, boats and debris touch the HDPE, not the wood, and the wood is out of the sun.
It's a cover for sound wood, not a repair for a damaged piling, so a weak pile stays weak. It doesn't treat rot or borers already in the wood. The top and the wood above and below the band stay exposed.
Should I wrap the piling or replace it?
Wrap only pilings with enough strength left to be worth protecting. Check each one in and around the band you plan to wrap.
At low tide, push an awl into the wood, pry up a small sliver and tap the pile with a hammer. Probing opens the treated shell, so ask a contractor about treating those spots.
Then take tape readings around the pile where it wears, 2 ft above and 2 ft below. A sound pile tapers steadily, so the middle reading falls between the other two.
Example: 38 in above and 36 in below means a sound pile reads about 37 in between. A middle reading of 34 in is 37 − 34 = 3 in short, or about 1 in of diameter (3 ÷ 3.14 = 0.96).
| What you find | What it means | What to do |
|---|---|---|
| The awl sinks in easily, or the sliver breaks off short or crumbles | Rot near the surface | Call a marine contractor. Don't wrap. |
| A dull thud or hollow drum, not a sharp ring | Wet, rotten or hollow wood inside | Have a contractor core or test it |
| The middle tape reading is the smallest | Wood is gone | Have a contractor check its strength |
| Many tiny holes below the waterline in salt water | Possible shipworms | Have it tested. The surface can look fine. |
| Leans, moves when pushed, or sits higher than the rest | Lost support, sometimes from ice | Call a contractor. A wrap won't help. |
| Wood that splinters, a sharp ring, readings that follow the taper | Sound, even if the surface is scuffed | Good to wrap |
Tapping and probing can miss early rot. A contractor can core or test the pile.
If the contractor finds sound wood, wrap it. If not, repair or replace the pile first, then wrap the new wood if you want. A splice of treated wood or a concrete jacket can save a pile from replacement.
How do I get sound pilings ready to wrap?
- Check the rules. Work in navigable US waters can need a US Army Corps of Engineers permit, and your state or town may add its own rules.
- Write down each pile's condition and tape readings.
- Pick the band. Look at where your pilings show wear and how far the water rises and falls.
- Clean it. Scrape off growth and anything loose, so the stretch wrap lies flat.
- Measure. Cut π × diameter + 6 in for each pile, measured inside the band. See how to measure dock pilings for wrap.
One install kit covers about 10 pilings. See Pier Protector for prices, and how cut-to-length ordering works for the 5 ft steps and the 20 ft minimum. Then follow the Pier Protector install manual.
How do I check a wrapped piling later?
You can't see the wood under the band, so check what you can when you look over the dock.
- The wrap: look for tears and loose nails. Re-nail a loose seam every 3 to 6 in. Replace a torn piece with one cut to π × diameter + 6 in.
- The wood above and below the band, and the top: probe, tap and take the same tape readings. Compare them with your notes.
If that wood goes soft or thin, or the pile leans or lifts, call a marine contractor. Ask whether the wrap should come off so they can check under it.
Who is a piling wrap not for?
- Failing pilings: soft, hollow, leaning, cracked through or thinned where they wear.
- Concrete, steel or plastic piles. Pier Protector is nailed on, so it is for wood piles.
Common mistakes
- Wrapping before checking. Once wrapped, you can't see the wood in that band.
- Wrapping over soft or hollow wood. The wrap hides the rot and doesn't treat it.
- Skipping the stretch wrap. At least 3 tight layers go on first, under each piece of HDPE.
FAQ
What is the stretch wrap for?
At least 3 tight layers of stretch wrap go on first, under the HDPE. They seal the wood surface in the wrapped band as a layer against marine borers such as shipworms and gribbles. The HDPE on top takes the rubbing, sun and debris.
Does Pier Protector stop marine borers?
We don't promise that. The stretch wrap under each piece is there as a layer against marine borers in the wrapped band, and the HDPE on top takes the wear. For the best result, wrap sound wood and cover the band where your pilings show wear.
Can I wrap a piling that already has rot?
No. A wrap isn't a repair, and it doesn't treat rot already in the wood. It also hides the wood, so you can't watch the damage. If an awl sinks in easily or the pile sounds dull or hollow, have a marine contractor check it.
Do freshwater dock pilings need a wrap?
Marine borers are rarely a problem in fresh water. On a lake, the wear comes from rot above the waterline, rubbing, sun and ice. A wrap puts HDPE between the wood and the rubbing in one band. We don't claim it stops rot or keeps ice from lifting a pile.
How long do wooden dock pilings last?
It depends on the wood, its treatment and the borers in the water. The USDA Wood Handbook reports average lives of 22 to 48 years for well-treated Douglas-fir piles in San Francisco Bay. It estimates 10 to 12 years, often longer, for creosoted piles in South Atlantic and Gulf waters. We don't give a lifespan for a wrapped pile.