Nail Rot in timber on a Strip Built (or Strip Planked) boat. How To Cure It

What is Nail Rot?

A Boat constructed with strip timber, mahogany in this case, has been nailed together using galvanised nails. This is known as ‘Strip Building’ or ‘Strip Planking’. After many years the galvanisation on the nails is failing, and the nails have started rusting, presumably due to the twin evils of moisture and electrochemical reaction. The rust spots are spreading from the nails, and are visible through the paint on the hull. Furthermore they are causing softening of the timber around them, which is evident after the wood has been stripped of paint. These soft spots have not progressed to be so bad as to require replacement of structural timbers.

Nail Rot In a Wooden Boat
Nail Rot

What is the Cure for Nail Rot?

  • Strip the timber back to bare. Even if the nail rot is only evident in a small area, it is only a matter of time before it becomes evident everywhere
  • Dry the timber thoroughly
  • Repair any structurally damaged areas of the timber. By structural damage I mean anything that may cause the boat to leak or break. Entire rotten planks, or parts of a plank that are rotten half way through would be a prime candidate for replacement. If in doubt please just ask us
  • Treat the nails and the stained timber with ‘Jenolite’ or another proprietary phosphating solution. You can also use Phosphoric Acid, around 30% concentration works fine on timber., These preperations are commonly sold for the ‘curing’ of rust on steel for car bodies. The rusty fasteners will become phosphated, and the red or black iron oxide in the timber will be turned into grey iron phosphate, which is far less noticeable against the wood
  • Dry the timber thoroughly once more
  • Saturate the timber with Clear Penetrating Epoxy Sealer (CPES). It will consume lots around areas of soft timber by the rusting fasteners. Apply as much as the wood will take, and repeat the coats until the wood will take no more, and has a shiny surface finish once it has dried
  • Fill any surface imperfections caused by rotten wood around the fasteners with Fill-It epoxy filler. Apply one final coat of CPES to ensure the paint or varnish bonds firmly to the filler after sanding to profile
  • Paint or Varnish the timber once the CPES has dried, but before it has fully cured, to ensure that the top coat is strongly bonded to the primer for extreme durability. See here for full instructions

How does this cure Nail Rot?

  1. The fasteners have been coated in iron Phosphate to resist further corrosion
  2. The Iron Oxide in the timber has been turned into Iron Phosphate, which may allow the finished product to be varnished once more
  3. The CPES will act to resist corrosion around the fasteners
  4. The CPES will increase the electrical resistance of the timber around the fasteners to resist further electrolytic attack
  5. The CPES will harden the softened areas of timber attacked by the nail rot
  6. The CPES will bond the top coat strongly to the timber, reducing future maintenance requirements

The final finish may even be good enough to varnish if you desire, with far less unsightly marks around the rotten nails. The refinished surface should be good for many years to come. A photographic demonstration of phosphating nail rot on an old deck in my garden is shown here.

nail rot in oak before phosphating
Nail Rot in Oak Deck. Click to enlarge
nail rot in oak during phosphating
Nail Rot in Oak Being Phosphated Closeup. Click to enlarge
nail rot in oak during phosphating
Nail Rot During Phosphating. Click to enlarge
Nail Rot After Phosphating Drying
Nail Rot After Phosphating While Drying. Click to enlarge
finished oak boards cured nail rot
The boards after drying and varnishing. The Nail Rot is nearly invisible now. Click to enlarge.