repairing bilge and replacing ballast

[simonebb]

I have recently acquired a 40ft, cruiser stern, Norseman, Hancock and Lane. It has become a major project, (never the intention!) having discovered a large amount of water under the cabin floor. The windows, hatches and around the chimney flue were all leaking significantly. the ballast, 2 ft square concrete slabs, were wet and orange with rust. Having identified the leaks I am now in the process of beginning to put her back together, I am going to clean back the metal on the inside and re prime with Bonda rust primer. So a few questions:

Can i re-use the existing ballast, I was going to lay the ballast on roofing felt and cable housing to raise it a little but I have read that roofing felt can trap moisture, would i be better painting a bitumous paint on the primer instead?

This is just the beginning there will be many more questions!!!

Thanks

Simone

 

[BEngo]

Re-using the existing slab ballast is OK. You might want to give it a good pressure wash and to ensure it is dry before it goes back in the bilge.

 

Any continuous sheet will trap moisture ( condensation or leaks) between itself and the base. Bitumen with cable housing will be fine. No need to put primer under it as it sticks better to steel.

 

The most important thing is to cut an access hatch at the back and to check the bilge is staying dry regularly- say monthly. That way you can tackle any problems as soon as they arise and before they become major.

 

As you rebuild its a good idea to ensure there is a water vapour barrier between the cabin and the insulation. That will prevent condensation on the cabin sides behind the insulation. Sprayfoam has a built-in vapour barrier but kingspan, rockwool and polystyrene all should have a separate barrier- builders thick polythene sheet and duct tape is good for polystyrene and rockwool or for aluminium faced kingspan the aluminium tape is good.

 

N

[simonebb]

Re-using the existing slab ballast is OK. You might want to give it a good pressure wash and to ensure it is dry before it goes back in the bilge.

 

Any continuous sheet will trap moisture ( condensation or leaks) between itself and the base. Bitumen with cable housing will be fine. No need to put primer under it as it sticks better to steel.

 

The most important thing is to cut an access hatch at the back and to check the bilge is staying dry regularly- say monthly. That way you can tackle any problems as soon as they arise and before they become major.

 

As you rebuild its a good idea to ensure there is a water vapour barrier between the cabin and the insulation. That will prevent condensation on the cabin sides behind the insulation. Sprayfoam has a built-in vapour barrier but kingspan, rockwool and polystyrene all should have a separate barrier- builders thick polythene sheet and duct tape is good for polystyrene and rockwool or for aluminium faced kingspan the aluminium tape is good.

 

N

Thanks N, Nice to know I can re-use the ballast and thanks for all the tips re having an inspection hatch etc, dont think I can stretch to sprayfoam and was planning to use kingspan or similar product, if I understand correctly you are saying that all the joints of the kingspan should be filled and taped over with the aluminium tape? Someone has also mentioned a newish product called superquilt, is this something you have come across?

Simone

[Grace and Favour]

Thanks N, Nice to know I can re-use the ballast and thanks for all the tips re having an inspection hatch etc, dont think I can stretch to sprayfoam and was planning to use kingspan or similar product, if I understand correctly you are saying that all the joints of the kingspan should be filled and taped over with the aluminium tape? Someone has also mentioned a newish product called superquilt, is this something you have come across?

Simone

Simone,

 

When insulating your boat, it's important to get the insulation material (e.g. Kingspan/Celotex) to adhere to the steel everywhere, you need to avoid any airgaps, because any airgaps will create condensation - and condensation will eventually rust.

 

Superquilt will work, and it's kight and easy to use, (I've used in our demountable wheelhouse roof). However, because it's so extremely flexible, you may have a problem getting it to adhere to your steelwork, and you may also need more than one layer* *(I'm being cautious here, because I do not know haw effective it is compared to Kingspan)

[BEngo]

Sorry I can't help on superquilt- never seen it. Your interpretation of what to do with kingspan foam sheets is good. thre is some risk of cold bridges where any frames are, but thin foam or polystyrene between the tape and the lining will sort this.

 

 

N

[simonebb]

Simone,

 

When insulating your boat, it's important to get the insulation material (e.g. Kingspan/Celotex) to adhere to the steel everywhere, you need to avoid any airgaps, because any airgaps will create condensation - and condensation will eventually rust.

 

Superquilt will work, and it's kight and easy to use, (I've used in our demountable wheelhouse roof). However, because it's so extremely flexible, you may have a problem getting it to adhere to your steelwork, and you may also need more than one layer* *(I'm being cautious here, because I do not know haw effective it is compared to Kingspan)

 

I was wondering how you get the superquilt to adhere to the steel, I know with kigspan/celotex you use adhesive, is it the same with superquilt as all the examples i have seen it has been nailed in place? I have been told ithat superquilt has the same thermal values as the others.

Simone

Sorry I can't help on superquilt- never seen it. Your interpretation of what to do with kingspan foam sheets is good. thre is some risk of cold bridges where any frames are, but thin foam or polystyrene between the tape and the lining will sort this.

 

 

N

Thanks again N, the clarification helps as I am a total novice!!!

Simone

[dmr]

Bonda primer is my favourite primer but is not very tough, I suggest a couple of coats of bilge paint on top of it (I like the Rylards light greenyblue one). You could then maybe put waxoyl or similar on top of that but not sure about this.

Bonda primer is best on clean steel, if you cant achieve this (which is likely) then the red version of Owatrol would be better.

 

.............Dave

[trackman]

Sticking insulation perfectly to the steel isn't absolutely essential ad long as there is a complete vapour barrier on the inside (warm) face of the insulation.

Sprayed foam is vapour proof itself and having no joints if applied correctly, needs no separate barrier.

Many foam boards are also vapour proof (those with aluminium foil backing definitely will be), but being cut and jointed to fit, they have gaps that let vapour through. Seal these and there will be no condensation behind the insulation. Leave any gaps and there surely will be!

Ideally joints would be filled with sprayed foam then taped over with aluminium tape.