Caulking cotton and sealant?

[moresparks]

Is this a dumb idea?
I have a large gap to fill underneath the rubbing strake. It is not structural but cosmetic.
GRP Boat by the way.
The gap was previously filled with some sort of putty that over the ages deteriorated cracked and fell out in places. I have removed all the old putty but now faced with a large gap.
Have tried sealant in a small section but will need quite a number of tubes to fill the gap.
So,... just thinking... would putting caulking cotton mixed with the sealant “bulk” the gap successfully or just dig deeper into my pocket and pay for around 15 tubes of sealant?
Any other alternatives would help, bearing in mind it needs to be flexible.
I even thought of using builders’ weatherproof caulk before finishing off with sealant!!
The challenge is to have a smooth final finish.

 

[prv]

If the gap is that big, maybe some pieces of hardwood to fill out the bulk of it? If they’re bedded in sikaflex or whatever (sort of like mortar between bricks) then the fit doesn’t need to be boatbuilder-precise.

Pete

 

[moresparks]

Hi – many thanks for your response – the gap is on average 25mm x 15mm. And it does need to be at least a little flexible.

 

[moresparks]

Apologies .. I failed to mention that the rubbing strake is a stainless steel extrusion with a rubber insert.

 

[Hacker]

Why does it need to be flexible? GRP isn’t particularly flexible. The correct procedure would be to grind back and fill with epoxy and cloth. Deep voids could have a balsa or foam core adding.

 

[prv]

Apologies .. I failed to mention that the rubbing strake is a stainless steel extrusion with a rubber insert.

Ah, ok. I was imagining a teak one. Not wood to fill this gap, then.

Pete

 

[Catalina36]

Unless you're a fish you probably can't see it so why bother about filling it?

 

[Rappey]

Is this a dumb idea?

Not a dumb idea at all. That is essentially the way sealant should be used to bridge a gap.
Take a upvc window when fitted. There is a gap between the window edge and the wall.
The fitter then ploughs tubes of silicon in the gap until it's visibly full.
The silicon is now stuck to multiple planes and will therfore peel off one side eventually.
The correct way is to put a non stick foam strip in the gap, set back about 5mm then the sealant is applied over the foam so it contacts the wall and window frame so it can move with expansion and contraction without peeling away on one side.
Same theory with sealing teak decking.