Dock repair, and telling repair from rebuild

Three kinds of problem

It helps to separate what is wrong with a dock into levels, because the cost and the urgency differ enormously between them.

Surface and hardware problems are maintenance. Cupped or soft boards, fastenings standing proud, a seized gangway hinge, float attachments working loose, corroded cleats. Annoying, visible, and comparatively inexpensive.

Framing problems are the middle tier. Stringers softening where they bear on piles, joist hangers failing, a section of pierhead with noticeable movement underfoot. Repairable, usually in sections, and the right moment to inspect everything else while things are open.

Pile problems are structural. Everything above depends on them, and they are the level at which a repair conversation can turn into a rebuild conversation.

What the environment does

Marine borers are the quiet one. They work below the waterline, which is where nobody looks, and they enter through damage to the treated envelope of a pile. A pile that looks fine at deck level can have lost significant section down where it matters.

Corrosion works on the hardware faster than on the timber, and dissimilar metals in contact accelerate each other. A structure that was built with a mixed and unconsidered hardware specification ages faster than one that was not.

The wet-dry cycle and the sun work on the deck surface, which is why decking is the most visible ageing and, misleadingly, rarely the most serious.

Storm loading is episodic rather than continuous, but it finds whatever was already weak.

Inspecting your own dock

1. Walk the whole structure slowly and feel for movement and soft spots rather than just looking.
2. Look at every fastening you can see. Standing proud, weeping rust, missing.
3. Look at where stringers meet piles. That junction is where framing trouble starts.
4. Check the gangway hinge and the lower bearing, and the float attachment points.
5. At low water, look at the piles below the usual waterline for damage, section loss and marine growth.
6. Look at guide piles for the float, which take repeated impact.
7. Do it once a year and after any significant storm.

When repair becomes rebuild

There is a threshold, and it is worth naming because owners often cross it gradually without deciding to.

If the piles are sound and the problems are above them, repair is almost always the right answer and the structure has years left in it.

If multiple piles have lost section or moved, the arithmetic changes. Replacing piles under an existing structure is more difficult and more expensive per pile than driving them on a clear site, because the work has to happen around what is already there. Past a certain number, rebuilding is both cheaper and better.

There is also a permitting dimension that surprises people: repairing a structure in kind and substantially reconstructing it are not always treated the same way. A project that started as maintenance and grew can find itself needing authorization it did not originally require. Worth raising before the work expands rather than during it.

After a storm

Look before using it. Damage from storm loading is frequently below the waterline or at connections rather than obvious on the deck surface, and a structure that looks intact can have moved.

Check pile alignment against how you remember it. Look for framing that has shifted relative to piles, and for hardware that has pulled.

Check the float and its guides, which take a beating, and the gangway, which can come off its bearing.

Photograph everything before anything is moved or repaired.

What a repair costs you in access

The thing that makes dock repair different from most building work is that the job site is over water and reached along the structure being repaired.

That constrains everything. Material has to be carried out or floated in. Waste has to come back the same way. Equipment that would be trivial to position on land may not be positionable at all, and on a long crossing or a compromised structure the safe working method changes.

This is why repairs sometimes carry a cost that looks disproportionate to the quantity of material involved. The material is rarely the expensive part. Getting people and material to the right point over a tidal marsh, in a working window set by the tide, is.

Sequencing repairs sensibly

If several things need attention, the order is worth thinking about rather than doing the most visible first.

Structure before surface, always. Replacing decking over framing that will need opening up within two years means paying for the same access twice.

Anything that requires the gangway or float to come off is worth grouping into one visit. So is anything below the waterline, because that work is tide-dependent and the windows are the scarce resource.

And if a pile assessment is due, do it before committing to the rest, because a bad answer there changes what the sensible scope is.

Dock repair, and telling repair from rebuild — common questions

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