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Welding to a Sprayfoamed Hull


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There has been some speculation on the forum about what happens when you try to weld to a hull that has been insulated with sprayfoam.

Last week we had Belfast on dock for a survey, which showed up a need for some patches to the hull. When Belfast was last refitted in 1996 the main cabin roof, sides and hull side were sprayfoamed. Belfast was built in 1936 with 1/4 inch thick mild steel side plates, riveted to rolled iron knees.

There was no way I could remove all the fitted furniture and cabin lining to allow removal of the sprayfoam in the areas to be welded, but I did (eventually) manage to remove one lining panel and expose the foam.

I stood inside the boat, on firewatch, while the welder did the first patch. This is what happened!   

First, as he began welding, there was a bit of a sizzling sound, like water boiling, then yellow smoke starting appearing - not from any obvious gap, but just generally from the foam. There was a slight hot plasticcy smell, but nothing acrid. A few traces of brownish liquid appeared on the surface of the foam, and I nearly called a halt to the operation, but the smoke didn't seem to be getting any worse, and so we carried on and the patch was completed. When the welding stopped the smoke ceased, and the yellow haze hanging in the air began to disperse. Apart from the brownish liquid stain, there was no obvious damage to the foam.

And so onto the second patch, shown below. The hatched green area on the left is where there is a knee under the foam, and in this area there was no discernible effect, presumably due to the thicker metal conducting the heat away. The red line indicates the approximate position of the weld, and on this patch there are some areas where the foam has 'erupted', with the yellow smoke coming mostly from these eruptions. But otherwise no damage to the foam.  In the fullness of time I may cut out the erupted areas and replace with sprayfoam from a can, but for now I have just put he panel back. 

Welding3.png.bb6d679daa10b2548ef5c3c0c654d987.png 

So for the rest of the patches I just let the welder get on with it, observing from inside the boat in case of fire, but seeing nothing. Not even any yellow smoke and virtually no smell, all of which seem to have been contained behind the lining.  

So was I just lucky? Or has the whole issue been blown out of proportion?

  • Greenie 1
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Take care to not breathe in the fumes from the burning/charring spray foam as they probably contain isocyanates and cyanide gas as well as CO.  After welding, if you do add more foam from a can I would use the fire retardant grades as the 'normal' stuff could catch fire and burn during welding.

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11 hours ago, David Mack said:

There has been some speculation on the forum about what happens when you try to weld to a hull that has been insulated with sprayfoam.

 

So for the rest of the patches I just let the welder get on with it, observing from inside the boat in case of fire, but seeing nothing. Not even any yellow smoke and virtually no smell, all of which seem to have been contained behind the lining.  

So was I just lucky? Or has the whole issue been blown out of proportion?

That matches my own observations.  I have welded several things, including quite a large piece round the chimney to our sprayfoamed 4 mm roof and seen more or less the same things.  It helps not to make long continuous weld runs and, where the foam goes all soft  I pushed it back into contact with the metal as it cooled.

 

N

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3 hours ago, Phoenix_V said:

We have had welding done over sprayfoam, no problems. I would be more concerned about wooden battens, hidden wiring etc!

I used to work on Belfast, is she in private ownership now?

Yes. Dacorum  Narrowboat Project have closed down and we bought Belfast earlier this year.

I wasn't worried about battens as they are all visible on the inside face of the sprayfoam and there isn't much (any?) wiring in the hull as the main cabin has virtually nothing electrical beyond lighting in the ceiling.

Edited by David Mack
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When we had some welding done the smoke coming off the, professionally applied spray foam in 2000, was horrendous. Thick, yellow and acrid.

i rigged up a long length of hose pipe, which I gaffa taped to our vacuum cleaner. I put the vacuum cleaner on the back deck and used the setup to follow the line of the welding with the hose sucking the smoke away to the outside.

it would have been impossible to stay inside the boat to fire watch otherwise. Maybe the chemicals used in the spray foam in 2000 have changed but I would recommend setting up a similar extraction system, in advance, if you're having any welding done.

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On 21/08/2017 at 07:14, Robbo said:

Here’s a few insulation material’s and how they react to a heat source.   

 

Well there we go. Cringe worth from a scientific angle, but it terms of crude real world testing interesting none the less.

Small scale testing where we have replaced anodes appears to show our EPS boards blacken and shrink away, but do not support fire. Which is obviously good!

 

Daniel

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I have had my 50x10 barge over plated around the entire water line. She is spray foamed and I observed much the same as the OP. 

As I had a lot of charred foam, I decided to scrape back and fix with stuff in a can. Here's where it gets interesting: in some places the foam had blistered up, and left a void behind. Some of these voids had cracks or small pin holes, and these collected condensation, so when I came to open them up rusty water came gushing out. It was only a few months between the welding and me getting around to fixing the insulation.

So, if you have had welding done, I would absolutely encourage you to scrape back that singed foam, just in case!

 

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