Welding and insulation

[Morris]

When getting small welding jobs done (filling rust pits for example) is it normal or advisable to remove all the internals behind the area to be welded? Would fibreglass insulation be a problem if left in situ?

[pete.i]

When I looked at a boat a couple or three years ago that had had some overplating done we found burnt wood on fixed furniture items inside the boat where the welding had taken place on the outside. Needless to say we didn't investigate further nor did we buy the boat. So, personally I would remove everything in the area where any welding is going to take place.

[john.k]

If the metal being welded is paper thin,then it will certainly heat white hot from a weld on the other side .......on the other hand ,if its 1/4 thick ,then a small weld wont set the boat afire...........some plastics dont light but just char ......however in a fire they will burn.,.

[Arthur Marshall]

I think fibreglass is fireproof? When I had my boat replated a few years ago I left everything in place - I'd insulated with that highly compressed foil backed stuff from Pilkingtons. No problems at all.

Time before it was all polystyrene sheets, which caught fire nicely and it all had to be stripped out - I had to refit the boat completely afterwards.

[john.k]

The actual pure fibre is not flammable .....its either glass or slag fibres .......however if there is a any plastic resin mixed in ,then it will burn .........the worst can happen with fibres is they may melt and stick to the steel..........any internal paint or rust proofing will be burnt away .

Edited May 9, 2023 by john.k

[beerbeerbeerbeerbeer]

Fibre glass/Rokwool is ok. 
I left everything in place when I had a lot of welding done. 

I did remove one panel to begin with as a tester to see what happened. 
I’d suggest you do similar, watch from the inside and see how it goes. 

[Morris]

Thanks for the replies. Arthur, Goliath - did you notice any smell from welding with everything still in place? (not the time with the polystyrene sheets - that sounds like it was an ordeal) When we were looking round boats to buy one had an acrid plastic/ rubber burning smell and I wondered if it was from welding. 

[beerbeerbeerbeerbeer]

The internal of my hull is coated in bitumen, so yes there were bad fumes and some smoke.

The Rockwool absorbed most of the smoke. 
I’ll post some photos later as examples.

 

But my best advice is to remove a panel if possible and observe what’s happening.

You ought to have someone on board, preferably you, fire watching.

oh, and there’s no bad smells now, not from the welding anyway 

[Alan de Enfield]

35 minutes ago, Arthur Marshall said:

I think fibreglass is fireproof? When I had my boat replated a few years ago I left everything in place - I'd insulated with that highly compressed foil backed stuff from Pilkingtons. No problems at all.

Time before it was all polystyrene sheets, which caught fire nicely and it all had to be stripped out - I had to refit the boat completely afterwards.

 

I once saw a Reliant Robin catch fire, by the time I had overtaken it, it was a heap of ashes.

It literally burnt away in seconds.

Its the resin rather than the glass fibres that burn - which is why fire blankets are often made from fibreglass strands (instead of the once used asbestos)

[beerbeerbeerbeerbeer]

Poor quality photo from a video, but gives you the idea.

The hull had some over plating done. What you see in this photo of the interior is the top edge of a sheet of steel being welded into place on the other side. 6mm steel onto iron over 1/4” thick.   Deep penetrative welding.  
I completely exposed the hull in one place to see what was going on regards the metals. And I left some with rockwool  in place to see what happened to that.

The rockwool had a silver backing facing the metal.

The smoke you see is from off the bitumen. And you can see how it bubbled and crawled away.

If anything was to catch fire I thought it’d be the bitumen.

 

 

 

 

I ain’t no expert, just telling you my experience.

I reckon you’ll be ok, but do get professional advice from the yard.

Pull a bit of insulation out and put your fag lighter to it, see if it burns or shrivels/crawls away.

 

Stripping out the whole interior has to be the very very last resort.

 

Edited May 9, 2023 by Goliath

[David Mack]

This is what happened when I had some welding done on a sprayfoamed hull.

 

 

[blackrose]

It depends on the job. If it's just a small job it's unlikely to set the insulation on fire. Does anyone seriously rip out the lining and insulation when they're having new anodes welded on for example - assuming there's insulation behind that area? Certainly have someone inside the boat just to make sure, but to be honest unless you've taken the lining out then there's not a lot you're going to be able to do about it if it does catch fire!

[Jen-in-Wellies]

1 hour ago, blackrose said:

It depends on the job. If it's just a small job it's unlikely to set the insulation on fire. Does anyone seriously rip out the lining and insulation when they're having new anodes welded on for example - assuming there's insulation behind that area? Certainly have someone inside the boat just to make sure, but to be honest unless you've taken the lining out then there's not a lot you're going to be able to do about it if it does catch fire!

The usual places anodes go, on the bow and stern swims, are away from the cabin, so unlikely to have insulation behind. If there are mid hull anodes, then yes.

[ditchcrawler]

58 minutes ago, Jen-in-Wellies said:

The usual places anodes go, on the bow and stern swims, are away from the cabin, so unlikely to have insulation behind. If there are mid hull anodes, then yes.

My bow and swims are both insulated as the side of the hull down to about 3" above the base plate. I had a flange welded onto the removable engine room roof hatch, that was insulated with spray foam and it didn't actually catch fire, smoked a lot but catch

[blackrose]

1 hour ago, Jen-in-Wellies said:

The usual places anodes go, on the bow and stern swims, are away from the cabin, so unlikely to have insulation behind. If there are mid hull anodes, then yes.

 

My bows are insulated because without insulation I found the whole area was prone to pretty bad condensation. So I spray foamed the area myself. Any area connected to the cabin is likely to sweat. Even if it's separated by a wooden door the cabin heat will get through and cause condensation. 

 

I also have mid hull anodes. I sometimes wonder why others don't. 

Edited May 9, 2023 by blackrose

[ditchcrawler]

1 hour ago, blackrose said:

 

 

I also have mid hull anodes. I sometimes wonder why others don't. 

I use to twat them on things