Oil contaminated GRP

PuffTheMagicDragon

PuffTheMagicDragon

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Sand-blasting the underwater parts of the hull prior to renewal of the epoxy coating has revealed a slight leak at the joint between the lead ballast and the keel moulding. This appears to be from a weep around the keel bolt that sits in the deepest,most inaccessible part of the bilge sump. It is not the weep that worries me.

Some oil that must have been floating above an inch or so of water has now seeped out and has left a mark on the exposed fibreglass. My question is: what steps should I take before I start to apply the new epoxy? I am repeatedly spraying with strong kitchen degreaser (Chante Clair) and can see an improvement. Some people have suggested bathing the area liberally with acetone and applying the epoxy as soon as the acetone evaporates.

Any other ideas / suggestions please?

oilseepage.jpg
 
I'm less concerned about the epoxy application than the fact your boat has a leak? The proper way to sort is dropping the keel, but a compromise could be grinding out the area of the leak with a angle grinder and thin cutting disc and sealing with sikaflex or similar. Once that is done clean the area again for the epoxy and off you go. A less destructive method could be cleaning the bilge thoroughly, then attempting to clean the leak path with a solvent(possibly meths) then inject a low viscosity sealant; the solvent and sealant would need to be sucked through using a vacuum pump, probably sucking from the outside.
 
penfold said:
I'm less concerned about the epoxy application than the fact your boat has a leak?
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The leak isn't really an issue because it only became apparent when the previous epoxy coating was blasted away. Once the outside is re-coated with epoxy no water will come in through there. In fact, the only water in the bilges comes from the stern gland and the occasional spillage.

The proper way to sort is dropping the keel, but a compromise could be grinding out the area of the leak with a angle grinder and thin cutting disc and sealing with sikaflex or similar. Once that is done clean the area again for the epoxy and off you go. A less destructive method could be cleaning the bilge thoroughly, then attempting to clean the leak path with a solvent(possibly meths) then inject a low viscosity sealant; the solvent and sealant would need to be sucked through using a vacuum pump, probably sucking from the outside.
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If only it were that simple! The suspect keelbolt nut sits in the bilge sump. Unfortunately this is some 90cms below the floorboards and is a little pit of around 4 inches square. There is no way that an angle grinder can get down there to do some useful work. If the leak was serious I would consider removing the nut using a socket on a very long extension and somehow placing a grommet around the bolt before replacing washer and nut.

My only worry at this stage remains adhesion of the epoxy. The meths idea is intriguing. I am pretty sure that it would easily seep through the same path that was followed by the oil; would it destroy or kill any oil remaining along the leak path?
 
Neither meths nor acetone is a good solvent for oil. You need a light hydrocarbon for best effectiveness. By far the most readily available is petrol, although this contains some additives that just might interfere with something. The fuel sold by Coleman for their lanterns would be excellent, it is a pure hydrocarbon, heptene I think. Lighter fuel would work but it is very light and could well evaporate before it has done its work. Otherwise paraffin is OK but can be difficult to fully remove afterwards.
 
Vyv Cox, if I am understanding correctly, you are suggesting the use of a light hydrocarbon to, effectively, thin down a heavier hydrocarbon (engine oil). Perhaps I am not using the correct terminology.

Would this eliminate the adhesion problem that I am anticipating or am I simply worrying unnecessarily? Since the epoxy coating is a considerable expense, both in terms of cash and in effort, I would like to do a good job and avoid having a weak spot in the system.
 
The grease that kitchen degreaser removes is fat, so it's not the best thing for what you want to do.

Vyv has the right idea. Acetone is no good for oil, I know I tried to clean an engine with it and it was useless.

Petrol and paraffin are both good but are either not that volatile or leave some residue.

iso-Propanol (IPA) is what we use in cases where we need something miscible with water and things like petrol/oil, it evaporates well too.

Meths would be a reasonable substitute to IPA, but probably best to just use it to remove the petrol or paraffin that you used to remove the oil.
 
PuffTheMagicDragon said:
If only it were that simple! The suspect keelbolt nut sits in the bilge sump. Unfortunately this is some 90cms below the floorboards and is a little pit of around 4 inches square. There is no way that an angle grinder can get down there to do some useful work. If the leak was serious I would consider removing the nut using a socket on a very long extension and somehow placing a grommet around the bolt before replacing washer and nut.
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What I meant was to grind along the seam from the outside of the hull as you showed in the photo. Using that method you can probably ignore the bilge beyond cleaning it. The grinding will remove a little GRP, but that will give you a groove to squirt sealant into.
 
penfold said:
What I meant was to grind along the seam from the outside of the hull as you showed in the photo. Using that method you can probably ignore the bilge beyond cleaning it. The grinding will remove a little GRP, but that will give you a groove to squirt sealant into.
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OK. That's clearer now. I think that I could even fill the groove with a mixture of resin and micro-fibres / chopped strands as necessary. This would ensure bonding of the subsequent epoxy coating thus providing a total seal against the ingress of water through the lead / keel joint.
 
I suspect a simple coating will crack as soon as you crane the boat back in.
I would suggest cutting a 3mm square section slot all around the top of the lead and filling it with polyurethane sealant, e.g. sikaflex.
But really, it might be time to have the keel off.
 
When she was lifted there was absolutely no sign of movement and the previous epoxy coating (Aquastop by Veneziani) of the total wetted area was intact around the joint between the lead and the rest of the fibreglass keel.
 
PuffTheMagicDragon said:
Vyv Cox, if I am understanding correctly, you are suggesting the use of a light hydrocarbon to, effectively, thin down a heavier hydrocarbon (engine oil). Perhaps I am not using the correct terminology.

Would this eliminate the adhesion problem that I am anticipating or am I simply worrying unnecessarily? Since the epoxy coating is a considerable expense, both in terms of cash and in effort, I would like to do a good job and avoid having a weak spot in the system.
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If you are trying to remove the oil stain shown in your photo prior to epoxying then yes, use a light hydrocarbon solvent first. I'm not sure about the IPA, it's the basis of screen de-icer and not a lot different from meths chemically. After the hydrocarbon solvent I would be using a good detergent.

Overall, I'm not too convinced by the theory of oil leaking out of your bilges but no water leaking in. If going to the expense of an epoxy coating I would prefer to know that the keel bolts are all sound before starting.
 
PuffTheMagicDragon said:
When she was lifted there was absolutely no sign of movement and the previous epoxy coating (Aquastop by Veneziani) of the total wetted area was intact around the joint between the lead and the rest of the fibreglass keel.
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Well it looks to be leaking now, so there is a crack of some sort.
If I were buying the boat, I'd want the keel off.
What are the keel studs made of?
 
vyv_cox said:
Overall, I'm not too convinced by the theory of oil leaking out of your bilges but no water leaking in. If going to the expense of an epoxy coating I would prefer to know that the keel bolts are all sound before starting.
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I came to that conclusion because it was when the previous epoxy treatment was sand-blasted, thereby exposing the lead / keel interface, that salt water started to seep slowly out of the joint. This later became a seepage of oil, which led me to the conclusion that the water was from the bilges rather than water trapped in the interface. Engine oil floating on bilge water would be able to seep out around the keelbolt only after the water on which it was floating was gone. The entire underwater area had a coating of epoxy (Veneziani Aquastop) that was around 1mm thick. Had there been a direct connection with the outside (i.e., before the sandblasting) I would have expected to have a bilgeful of water, which was not the case, even though most of the hollow GRP keel is taken up by a flexible fresh water tank of some 110 litre capacity.

Having said that, I shall certainly try to find a way of redoing the nut on the suspect keelbolt and then sealing it off on the inside - possibly even encasing it - as a second line of defence after the exterior treatment.

Does that make sense?
 
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