SV Pilgrim - 1979 Morgan 382 - Homeport: Beaufort, NC

Tuesday, September 16, 2014

Re-bedding The Chainplates

This is the third post in our chainplate series.  Here are links back to the first two posts:

Pilgrim’s six midship chainplates were all bedded directly atop the non-skid with 3M 5200.  To ensure good adhesion with the new sealant all the old 5200 needs to be removed.
Old 5200 residue.  The darker areas are indicative of water intrusion.
Round One: De-bond 2015 and a scraper.  I’m not partial to one brand of chemical 5200 remover or the other.  If possible I prefer to simply use a heat gun to soften the sealant and then scrape it off.  BUT –  heat guns can easily damage laminates, varnishes, etc.  Fearful of overheating the deck layup I went with the chemical remover for this project.
The chemical agent softens the old 5200 and makes scraping it off much easier.
When  using a de-bond type agent to soften old sealant, then be sure to thoroughly wash the area once finished.  Residual chemical can compromise the new sealants effectiveness.

During round one I used the pointed end of my scraper to work down into the thru deck holes.  This removed a counter sink shaped section of the old sealant stuck in the holes to a depth of about ¼”.   My preference would be not to have any sealant down in the holes.  If water ever makes it past sealant on decks, then I prefer it drip on through the deck and serve as a notice to re-bed.  If sealant below the level of the deck stops the water from exiting below decks, then that water will be seeking an exit latterly through the deck coring or the water will rest in a pocket alongside the mission critical stainless steel machine bolts /tangs.

Round Two:  Wire brush chucked into my cordless drill.  I derive great satisfaction from watching the wire brush fling tiny balls of 5200 away from my project area.
Using the drill with a wire brush is a very effective tool for removing old sealants.

Avoid using ferrous metal brushes if possible.  The bristles leave tiny metal particles that will appear as rust spots once exposed to salt water.   Stainless brushes are harder to find and more expensive, but are out there.  I’ve just discovered Dico Nayalox Brushes and have been impressed with their performance thus far.

Round Three - Hand sanding with 80 grit sandpaper.   If Pilgrim’s deck fittings were installed atop paint rather than non-skid, as most boats I encounter, then I would skip this step.   I feel mounting the deck fittings a smooth surface will result in a better seal.  So my intent with this round is to eliminate much of the texture of the non-skid.
Area under chainplate fitting after sanding down non-skid with 80 grit sand paper.  Note: Circular plug of solid epoxy in center of holes illustrates how Morgan filled the core of the decks to prevent water damage.
I realize that on multiple occasions my posts are critical of Morgan Yachts construction techniques and quality control standards.  Allow me now to praise Morgan  for filling the deck core with epoxy around the thru deck bolts.  This extra step prevents core damage when (not if) the chain plates begin to leak.  Each chainplate site matched the one pictured above.  My best guess is that Morgan fabricated the deck with voids in the areas to receiving chainplates.  Once the deck was assembled a 1” hole was drilled in the center of the void. Then thickened epoxy was injected into the void..  Once the epoxy hardened then the holes for the bolts were drilled through the solid epoxy.

For the re-install, Anne worked the topsides and I below decks.
Anne waiting on me to get back to work below decks.

What did we use to re-bed the hardware? 

Well… I am proponent of butyl tape for sealing fasteners, but when sealing one relatively large surface against another (e.g.  hatch flanges, port flanges, sail tracks, etc.) I’ve had buty tape disappoint on multiple occasions.  I loathe 5200 as a sealant.  Use 5200 for permanent bonding, but there are far better sealants available.  My current go to sealant for such an application…. 3M 4000UV.  On Pilgrim’s chainplates, we utilized a combination of 3M 4000UV sealant for the bases and butyl tape around the counter sunk fasteners.
Squish out of 4000UV around the base and butyl tape around the fasteners is a good sign.
We have experienced a couple hard rains since the re-bedding and so far so good.

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