any advice on caulking a wide seam

[lapwing]

I've removed the old antifoul and paint from the bottom of my 85 year old half decker. In so doing so I've uncovered a few areas where the caulking needs to be redone which I'm proposing to do with cotton and black pudding -a mixture of some kind of bitumen tar and cement. A couple of seams are of irregular width - varying from about 2-3mm to 8-10mm. The wide bit is only about 900mm long and it looks as if it has been like that for many years. The seam was filled with some kind of set mastic which was starting to break down. I've cleared the seam of mastic but am now left with a length of seam with a clear 8mm gap between the planks.

The planks are about 15mm mahogany fixed to oak ribs at about 8" centres and bronze floors. Access to the inside of the hull is very limited in the area of the wide seams and any replanking etc. would require the deck to come off first.

What is the best way to make the seam watertight? I can see two options

Option 1 - router out a clean edge to one of the planks and epoxy in a tapered spline to bring back the seam to a manageable 2 mm and then caulk the seam with cotton and black pudding.

Option 2 - temporarily tape up the inside of the seam in order to provide something to pack against and then refill the seam with some sort of sikaflex mastic, removing the tape after the mastic has set.

Option 2 looks like being the easier solution but I don't like the idea of relying on a plug of mastic to keep me afloat.

I'm also not sure that mastic and old wooden boats go together particulary well - as part of the work I've also been removing various plugs of mastic that have been used to cover over countersunk nail and and screw fixings. In nearly every case the wood around the holes looks as if it is starting to soften. Wheras where the fixings have been filled with red lead putty or normal putty the wood is perfect - I'm assuming that it is something to do with the linseed oil is leeching out of the putty and helping to preserve the wood.

Any advice or suggestions would be appreciated.

 

[ccscott49]

I've removed the old antifoul and paint from the bottom of my 85 year old half decker. In so doing so I've uncovered a few areas where the caulking needs to be redone which I'm proposing to do with cotton and black pudding -a mixture of some kind of bitumen tar and cement. A couple of seams are of irregular width - varying from about 2-3mm to 8-10mm. The wide bit is only about 900mm long and it looks as if it has been like that for many years. The seam was filled with some kind of set mastic which was starting to break down. I've cleared the seam of mastic but am now left with a length of seam with a clear 8mm gap between the planks.

The planks are about 15mm mahogany fixed to oak ribs at about 8" centres and bronze floors. Access to the inside of the hull is very limited in the area of the wide seams and any replanking etc. would require the deck to come off first.

What is the best way to make the seam watertight? I can see two options

Option 1 - router out a clean edge to one of the planks and epoxy in a tapered spline to bring back the seam to a manageable 2 mm and then caulk the seam with cotton and black pudding.

Option 2 - temporarily tape up the inside of the seam in order to provide something to pack against and then refill the seam with some sort of sikaflex mastic, removing the tape after the mastic has set.

Option 2 looks like being the easier solution but I don't like the idea of relying on a plug of mastic to keep me afloat.

I'm also not sure that mastic and old wooden boats go together particulary well - as part of the work I've also been removing various plugs of mastic that have been used to cover over countersunk nail and and screw fixings. In nearly every case the wood around the holes looks as if it is starting to soften. Wheras where the fixings have been filled with red lead putty or normal putty the wood is perfect - I'm assuming that it is something to do with the linseed oil is leeching out of the putty and helping to preserve the wood.

Any advice or suggestions would be appreciated.

I know it wont be easy, but option one is by far the better solution.

 

[tillergirl]

I'd think I'd go for Option 1 everytime. Don't like being kept afloat by a bead of mastic. My only fear would be the accuracy of my routering but that's one thing I'm not brilliant at. Personally I would be using red lead putty but that's a personal choice. It's always worked for me.

 

[rich]

When I routed the deck on Hermees, I pinned a batten along the seam,after a lot of measuring, it was worth it in the end.

 

[Kukri]

Option One, no two ways about it.

 

[stephenh]

Option 1

However: I once (under supervision of an old hand) caulked a very wide seam by screwing (screws only - no glue) a well painted strip of 1/4" marine ply, on the inside and to ONE plank only; this gave a 'base' to this area of the seam which was then loaded with paint, cotton and red lead putty in the usual manner.

It worked very well and was still there 10 years later !

Good luck.....

 

[oldfrank]

Or you could replace one of the planks - and in doing so, you'll discover what is really wrong. My strong personal preference is only to spline above the waterline. OF