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Rust on the inside


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Due to the helpful nature of CW members I would like to ask another question of anyone with experience of the following

 

Our NB is 10 years old and today we removed a washing machine which revealed a 4" hole through the paneling where the waste water tube was centred. The area around it was exposed down to the steel hull and we saw the steel was very rusty made up of rust flakes with a collection of rust dust and flakes collected in a pile at the bottom of the hole sat on the insulation?

 

Is this something to worry about or just a normal issue. We're concerned as there may be worse affected areas that we can't see behind the paneling and insulation elsewhere on the boat.

 

Is there anything that can be done?

 

Thank you

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one possibility is that there has been a condensation problem associated with the lack of insulation in that particular area, if that is so it would be a local problem. To confirm that though you would have to check in other areas.

For treatment Vactan seems to be preferred by posters here

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Without seeing the installation it is difficult to give a diagnosis, but on a positive note, a great heap of rust flakes actually represents very little thickness of steel being lost. I cannot remember the proportions but seem to think that 5mm of rust flake represents less tha 0.5 steel. Someone else will be along soon to confirm or rubbish my estimate.

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Thanks for the replies so far. Seems that it's the exposed steel around a hot water outlet that's affected by condensation (also going by replies on other sites) according to most

 

Advice I've been given is scrape rust off, treat it with rust remover chemical, prime it and fill hole with expanding foam

 

Cheers

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My findings on my previous boat were similar to David's. A lot of rust flaking for very little steel loss. Treat it with some anti-rust stuff, prime paint and insulate if appropriate. A thickness test is the only real way if you are concerned.

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My findings on my previous boat were similar to David's. A lot of rust flaking for very little steel loss. Treat it with some anti-rust stuff, prime paint and insulate if appropriate. A thickness test is the only real way if you are concerned.

Will get a thickness test done when I haul it out to get the hull blackened. Thanks for your opinion.

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Be careful about filling w foam if you may ever want to get the fittings off. I stuffed those holes w rockwool instead as easier to remove if needed.

Sprayfoam can easily be dug out of small areas with a chisel if necessary. Water vapor can pass through rockwool unless there is also a vapor barrier. Compressing the rockwool to prevent this will just reduce its insulation properties. If the area has already suffered from corrosion, then after treating I would use sprayfoam every time.

Edited by blackrose
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Volume of rust = 6×volume of steel I was taught. You'd be very unlucky for condensation alone to have caused structural corrosion damage in this sort of situation.

If you use spray foam keep it off the threads of any fittings you may ever need to undo.

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Good advice re-threads; sprayfoam can stick like the proverbial. A few roof slates are stuck on my house with that stuff and have been like that for many years, even vertical ones on the dormer.

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