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Coal Sacks on the Roof


Flibbertigibbet

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1 minute ago, Dr Bob said:

The only one I am missing is the crested one but the only live in the frozen north so I'm not going up there.

Surely you don't mean........ Scotland! 

 

Anyway Dr plastic, back to the OP. Does summit in the coal bag react with the paint? 

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1 minute ago, Dr Bob said:

We had our bote repainted last winter as the coal bags on the roof had wrinkled the paint. An air gap is the best thing.

 

Well obviously this is why the coal tit was invented, to suspend the bags above the roof. 

 

How many tits per bag do I need? 

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54 minutes ago, rusty69 said:

Was he related to Karl S Berg?.... Probably, no, I am far from certain. 

I thought that they came in sixes - so if not 100% then the next best would be 83.3% (approx). But where's the proof?

Edited by Mike Todd
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Many thanks for all the responses. I am aware of the problems caused by damp, but this appears to be something much more vicious, as the bags have only been up there a matter of days, and it does look like spots of paint stripper have been dripped on the roof.

 

I took a picture, I hope it appears here. The top coat was wrinkled and softened, it just rubbed off when touched. It's dried flaky now. Bit annoying as I touched up all the rough bits of the roof last year.

 

Lucky I still have some paint left!

 

 

IMG_20190928_160529.jpg

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The plastic sack is relatively inert compared to the coal inside the bags. When I was helping to restore a couple of 1890s steam boats on the Thames we had to pull out the coal bunkers to de-rust and epoxy the bilges underneath. The corrosive action of the coal that had fallen down the sides of the bunkers and ended up in the bilges was very clear to see compared to other parts of the bilges. Coal sacks are only thin and contrary to popular belief thin plastics aren't waterproof and do allow water to slowly permeate through. So in addition to direct exposure to water running in and out of those small holes you get in the sacks which has picked up coal dust, I suspect that there's some permeation through the bags of whatever the acidic and corrosive chemical solution that's created inside them when the coal gets wet. This is all in addition to the trapped moisture effect on the paint as described in other posts.

 

I use these rubber mats with dimples underneath, which at least reduces the contact surface area and allows the water to run underneath rather than sitting there trapped.

Image result for homebase large rubber scraper mat

Edited by blackrose
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2 hours ago, Flibbertigibbet said:

Thanks for the idea of the rubber mats. Do you have a link for them?

Edit, don't worry, found it! https://www.homebase.co.uk/rubber-interlocking-mat-black_p377115

 

They're the ones. You can get the same stuff in doormat sizes for about £6 or £7 on ebay and cable tie them together but I doubt it works out any cheaper.

 

Wilko also do a thinner doormat version for about £4 but the quality isn't as good.

Edited by blackrose
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My boat had these types of mat on the cruiser stern when I bought it. Despite looking like the will avoid water collecting, they didnt work and, once removed, we found a pretty rusty old deck underneath. So I wouldn't rely on them on the roof with coal sacks, unless I was disciplined enough to remove it all every few weeks and give it a good wash and rinse.

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9 minutes ago, Richard10002 said:

My boat had these types of mat on the cruiser stern when I bought it. Despite looking like the will avoid water collecting, they didnt work and, once removed, we found a pretty rusty old deck underneath. So I wouldn't rely on them on the roof with coal sacks, unless I was disciplined enough to remove it all every few weeks and give it a good wash and rinse.

Have the same problem in my lockers. Put rubber mats in thinking it would let water flow out from under kit stored and am now having rust problems. Do not know what the answer is.

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