GRP osmosis repairs

[Chris Partridge]

I say chaps....
A very decayed grp rowing boat has come onto eBay for not much money, but the seller describes the condition thus:
The hull moulding has some dings and scratches but also suffers from advanced osmosis, or lots of tiny little holes or indentations in the outer surface of the fibreglass. It's an unsightly cosmetic defect but the boat still floats; if the wooden parts were replaced, and a couple of rowlocks fitted, it would be useable.

Can the osmosis be fixed reasonably cheaply?
I think it could be the PRRB with a bit of modification....

[alopenboat]

On 9 Nov 2013 at 14:52, Chris Partridge [via UK HBBR  wrote:

>
>
> I say chaps....
> A very decayed grp rowing boat has come onto eBay for not much money,
> but the seller describes the condition thus: The hull moulding has
> some dings and scratches but also suffers from advanced osmosis, or
> lots of tiny little holes or indentations in the outer surface of the
> fibreglass. It's an unsightly cosmetic defect but the boat still
> floats; if the wooden parts were replaced, and a couple of rowlocks
> fitted, it would be useable.
>
> Can the osmosis be fixed reasonably cheaply?
> I think it could be the PRRB with a bit of modification....

Unless the boat has been kept in the water I would very much doubt
that it is osmosis. If it is osmosis it would be expensive to fix
properly.

--
Hoping for calm nights

Alastair Law,      
Yeovil, England.
<http://www.little.jim.freeuk.com>          

[Timmo]

Agree with Al that it's not likely to be full fledged osmosis. Probbaly doesn't need to be expensive. On a big yacht there can be an inch or so thickness of glassfibre to soak up water and delaminate, normally in inaccessible places down in the bilges. Cost is in hauling the boat out, getting at the problem, grinding out areas and then drying the rest before rebuilding.

On a polyester glass lay up only the gel coat layer is waterproof, the lay up resin is water permeable. This row boat may have been left with water in it, that can lead to water entering the glass layers and trying to escape through the gel coat. 

If the hull is still firm and solid to the touch itt may only need the gel coat sanding off the affected areas, leaving under cover for some time for the glass to thoroughly dry out and then the top coat replacing. If the glass has delaminated and gone mushy it will be more work but that doesn't sound the case.

A good sand down and a couple of coats of two pot will probably make the boat look like new.

Tim.

[BrianP]

It does look a bit unpleasant. Quite large holes. As hire boats I guess they were left in the water all season. It could have dried out though by now. If so then it's just a question of belt sanding the gel coat away and they epoxy coating the surface to seal it, then paint, or perhaps just paint since it will not be spending long periods of time afloat.

I think if you actually saw the hull you would be able to tell if it's gone soft and horrible. Take a small blade or something to prick the surface to see if water lies below the gelcoat.

If solid and just need re-finishing then it could be just the ticket. It is a nice looking shape.

Brian

[Jeremy]

In all probability it's not true osmosis, just a rubbish layup, most probably just a poor gelcoat and initial layup.  When boats are laid up in a hurry by hand I've seen builders lay the first layer of CSM on to the still tacky gel coat quickly, smooth it down and then just whack a layer of resin on.  Often this first layer fails to wet out properly, as it's just too easy in a slack production place to "paint" the first layer of resin on and not properly consolidate and wet it out with a roller.

There are some understandable reasons for this with production small boats,  If the guys are in a rush they may be putting the first layer of mat on before the gel coat has hardened enough to make it robust, so may be cautious when rolling it out, for fear of damaging the partially cured gel coat.

The result is voids right behind the gel coat, which is the worst possible place for them.  Water then gets pulled in to these, absorbs salts from the resin and expands, forming the blisters.  More often than not on a small boat these will only extend through the gel and maybe the first layer of glass.

Sanding the gel off, grinding out the bigger pits and then leaving the hull to dry out in a warm place for a while should fix the underlying problem.

If the hull is then refinished by filling the holes then laying a thin layer of glass cloth over it (as if covering a ply or strip hull), using epoxy, finishing off with a PU paint, the hull should last for years and years.

[Paul H (admin)]

From what I have read Jeremy is spot on. Magazines for the yachties say that manufacturing defects cause the blistering in boats from the 70s and 80s.
The solution is cutting away the damage and thorough drying with dry heat, followed by an epoxy repair. Adequate drying can take some time apparently as you don't want to trap water underneath the epoxy.

cheers
Paul

[BrianP]

Now the yellow hull eBay listing has finished, they have listed another, described as "filthy old fiberglass rowboat"

 http://www.ebay.co.uk/itm/Filthy-Old-Fibreglass-Rowing-Boat-or-Skiff-Hull-/251378354180?pt=LH_DefaultDomain_3&hash=item3a87514804