Sunday, March 25, 2007

Keep The Water On The Outside, Part 3: Stanchion Bases

Rebed Stanchion Bases, 3/18 - 3/25/2007

I was absolutely dreading this project, concerned that it would be a disaster. The bow railing includes vertical supports (stanchions), mounted to the deck in 8 locations. The stanchion bases are attached with bolts into the cabin below, and sealed against water intrusion. Two of the bases on the starboard side were not sealed properly, so water was getting into the cabin in heavy rain or heavy seas. My main concern was whether I'd be able to break apart the bases from the deck to remove the old sealant. If the prior job was done with a permanent adhesive like 3M 5200, removal would be very difficult and likely to damage the deck. Fortunately, they came up easily, so it seems the prior seal was done with something more appropriate.

Rebedding deck hardware is not a trivial task, but it is a manageable two-person task. The hardware is through-bolted into the cabin, so removal and reassembly requires two people: one on the outside with a screwdriver, and one on the inside with a wrench.

Here's a description of the process Michele and I followed. Hopefully it will be helpful to others who have to tackle the same project.
  1. Remove old fasteners, using a screwdriver on deck, and a wrench from below. Sometimes, just getting to the nuts on the underside is difficult, but Cape Dory provided reasonable access.
  2. Remove old adhesive with a scraper and/or sandpaper. Scuff the surface to provide some grip for new adhesive.
  3. Wipe up any dust or residue with acetone.
  4. Examine deck for coring issues. If the deck is soft, the coring must be repaired. Otherwise, it's generally considered best to overdrill the fastener holes (or just dig out some of the wood core around them), fill with epoxy, and then drill new holes through the epoxy for the fasteners. This way, the epoxy prevents any intruding water from getting in the wood core. In our case, it appeared that this had already been done -- the wood core looked sealed already.
  5. Place wide painter's tape over the area where the base will sit. Then place the base down on top of it, and score the tape (don't damage the fiberglass!) around the edge of the base. Lift the base, and remove the circle of tape from underneath the base, leaving an outline of the tape to protect the surrounding area.
  6. Apply a polysulfide sealant, such as 3M 101. Using a putty knife, spread a layer of sealant on both the deck and the underside of the stanchion base. Apply a small amount to the underside of the bolt heads as well.
  7. Gently set the base against the deck and insert the bolt. Be careful not to apply to much pressure, or all the sealant will squeeze out.
  8. Have helper place a backing plate over the screws from the inside, and thread on nylon locknuts. (At minimum, use big fender washers for the backing plate.) Snug the locknuts, but do not tighten. It's best to turn the nuts, not the bolts, so that the sealant under the bolt heads does not come out.
  9. Remove tape from around the base, lifting any squeezed out sealant.
  10. Wait a minimum of one week for the sealant to cure. Protect from rain if possible, but a good sealant will cure even if wet.
  11. Have one person hold the bolt heads firmly with the screwdriver, while the other person tightens the nuts from the inside. Again, turn the nuts, not the bolts. At this point, it is crucial not to break the seal under the bolt heads. The nuts should be tightened firmly and securely, but not so much that the deck compresses.
Once completed, there should be a nice layer of flexible, cured sealant squeezed down tightly between the base and deck.

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