Hidden Rot

[Paul H (admin)]

Talking to my neighbour, leaning on my boat I noticed a crack in the white paint, which was soft under finger pressure.

45 minutes later I had scrapped away a scary amount of damp wood. No prisoners were taken as I hacked my way to dry wood:




I have treated it with Ronseal Wet Rot treatment. That will soon be fully dry in the hot sun, then I will flood the area with epoxy.

It's not clear where the water got in, but it certainly happened while it was covered in a tarp and not from sailing at all. Condensation runs inside the tarp and might have touched the wood. Pin holes in the paint may have let water in, but it's a mystery.

This is the fore-deck extension, 2 layers of 6mm ply. The lower layer is perfect with a good coating of epoxy, internally it is strong and dry. But the top layer may not of been sealed well with epoxy or the Jotun 2-pack paint. I can't figure out if the water has moved up or down, but the area slopes out towards the gunnels.

Paul

[Timmo]

Ouch.

But at least you've found it before it got worse and you've a solid base to fill back in on!

Tim.

On 14 Jun 2018, at 17:19, Paul (admin) [via UK HBBR Forum] <[hidden email]> wrote:

Talking to my neighbour, leaning on my boat I noticed a crack in the white paint, which was soft under finger pressure.

45 minutes later I had scrapped away a scary amount of damp wood. No prisoners were taken as I hacked my way to dry wood:




I have treated it with Ronseal Wet Rot treatment. That will soon be fully dry in the hot sun, then I will flood the area with epoxy.

It's not clear where the water got in, but it certainly happened while it was covered in a tarp and not from sailing at all. Condensation runs inside the tarp and might have touched the wood. Pin holes in the paint may have let water in, but it's a mystery.

This is the fore-deck extension, 2 layers of 6mm ply. The lower layer is perfect with a good coating of epoxy, internally it is strong and dry. But the top layer may not of been sealed well with epoxy or the Jotun 2-pack paint. I can't figure out if the water has moved up or down, but the area slopes out towards the gunnels.

Paul

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[Chris Waite]

I think Paulie

That this is where (the Tesco's finest polycotton sheet) sheathing prevents such problems.

It's quite possible my mind is playing tricks on me, but I cannot remember having this happen with any of my sheathed boats.

CW

[Paul H (admin)]

Chaps,

The original foredeck that dates back to 2006 is in great condition; I used the same Jotun paint on both sections of the foredeck.

I can only think the new ply was not sealed well enough with epoxy, prior to the undercoat. Or the top coat did not have enough coats - in fact I can see a few lines in the grain that are dark. An extra 2 coats with a roller might have sealed better.

There is a void in the ply perpendicular to the gunnels that may have transmitted water. Who knows.

The entire area is sealed now and I cut a rough shape of ply to fill 80% of the area. Lots of filling and sanding will bridge the gaps.

The foredeck gets covered in mud, sand and seaweed so I'm not looking for a showroom finish. 😀

Paul

[Chris Waite]

The thing is Paulie

The surface of unassisted ply tends to open, represented by those "lines in the grain", even if epoxy and polyurethane coated (and this is aggravated by bending the ply, even ever so slightly).  Something as simple as a polycotton bed-sheet epoxied over the top, prevents that becoming a problem.

Mere smear-on plastic gloop just does not have the same tensile strength as plasticised woven material.

 

Well bother

CW

 

[Paul H (admin)]

Chris

Ah, that explains what happened. The new ply stressed and opened up.

But why did the 2006 ply survive?
It was a better quality. The old offcuts feel heavier and stronger and have a thicker veneer.

Modern ply from Buildbase is called "film veneer", obviously meaning the veneer is very thin and hence suffered from bending stresses.

I'll try a different supplier the next time I buy plywood.

Paul

[Chris Waite]

Or you could sheathe and breathe

More easily ever after

CW

[Paul H (admin)]

I have added a 5.5mm ply insert and filled gaps where the surface was uneven, using thickened epoxy.

I added a thin epoxy layer last night by LED streetlight, using a finger drawing circles to hopefully ensure a consistent thickness. Great results this morning as the epoxy did not run:



If it hardens in the sun later, it should sand smooth and I'll experiment with a patch of poly-cotton sheet. We have an old sheet that is thin enough to blend in with the surrounding paint layer.

Cheers
Paul

PS: Photo Compress is a free app that quickly resizes a high-res picture to under Nabbles 1MB limit. 👍

[Paul H (admin)]

It's ready for undercoat. A good thickness of epoxy protects the grain.
I used the sunlight to show the finish.



The Jotun Penguard HB primer gives a thick coating to hide small marks. It's epoxy based so bonds well to the epoxy on the wood.

I don't normally use this much epoxy. I'll see how it performs during the season.

Paul

[Chris Waite]

Ply with the outer veneer running at right angles to any curve is going to tend to want to open up, making sheathing a worthwhile proposition, but it looks as if you've run the ply patch across the hull, meaning any camber on the deck runs with the grain, so the patch may still be sailing into the future when all of us and Millibee are just history.

Looks as if you've painted your cabin with a delicate blue-grey floor paint Paulie

Is that so?

CW

[Paul H (admin)]

Chris,

The blue tinge is a camera artifact, due to the very strong contrast in the picture.
The cabin and foredeck are identical colour to the naked eye.

It's a strong fix - I certainly hope the grandchildren keep her as an airloom!

Paul