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‘Elastic’ metal filler for roof plates


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I have a double welded roof seam joining two roof plates. To level the roof out and ‘disappear’ the seam the builder has used a body filler to conceal it. This has failed and cracked after a few years. I presume it is due to expansion and contraction of the roof due to the direct sun and weather, along with vibration and movement in all boats. The scar To be filled is approx 1200/150/7mm

 

I am looking potentially at Devcon fillers and a two pac elasticised paint unless anyone has a better suggestion.  

 

Thank you

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The plates dip toward the join along the full length of the roof curve. It has been double welded and the weld sits proud by 5mm ish. When built it has been filled to give the impression of no seam. The roof plates rise by approx 8mm from the seam to the roof level.  The bad filler has been removed to leave a 150mm scar. We don’t know how far further the filler goes but the rest of the roof is stable. 

Last time it was repaired with isopon and that has lasted 3 years before cracking. Just looking for a better alternative.

 

This is an older shell and very sound, we have no plans to chop the roof just return it to its previous build standard

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8 hours ago, Proteus said:

The plates dip toward the join along the full length of the roof curve. It has been double welded and the weld sits proud by 5mm ish. When built it has been filled to give the impression of no seam. The roof plates rise by approx 8mm from the seam to the roof level.  The bad filler has been removed to leave a 150mm scar. We don’t know how far further the filler goes but the rest of the roof is stable. 

Last time it was repaired with isopon and that has lasted 3 years before cracking. Just looking for a better alternative.

 

This is an older shell and very sound, we have no plans to chop the roof just return it to its previous build standard

I can't get a mental image of what this looks like from your description. Any chance of a picture of the roof? Might spark some ideas from people.

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The boat builder's filler of choice is P38. You will need to get the roof back to bare metal, and fairly rough to help it stick.  Attack it with a 40 grit disc in  an angel grinder, or a similarly coarse belt sander

 

Apply the filler when the roof is cool, so the liquid in the filler has time to get into the  scratches before it sets.  The roof .must be well above dew point though.

 

N

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If the new filler is well adhered, then something that may increase its life is to paint the roof a light colour, rather than dark. Sunshine can get a dark roof up to a much higher temperature and differential thermal expansion between the filler and steel will increase the risk of disbonding over time.

  • Greenie 1
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7 minutes ago, Sir Nibble said:

How about a paintable mastic?

Whatever is used will only be temporary.

The roof gets very hot in the sun,and very cold at night.With the expansion and contraction,the filler will sooner or later unstick.

The paintable mastic sounds the best idea,in that it will be easy to remove and replace when it deteriorates.

Mastic tape as used for fitting windows would be easier to get a smooth finish,rather than the stuff from a tube.

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51 minutes ago, Sir Nibble said:

How about a paintable mastic?

 

Yes I'd just use Stixall. You'll need to abrade both sides of the seam and clean off the dust with a cloth dampened with white spirit. Available in clear, black or white and is overpaintable.

 

https://www.toolstation.com/stixall-adhesive-sealant-290ml/p77137

 

https://www.everbuild.co.uk/wp-content/uploads/2012/05/STIXALL-V1.1.pdf

 

P38 filler might be the boat builder's filler of choice but I don't think they'd use it to fill an open seam as it's not flexible enough and will just crack - as will any other rigid car body filler..

9 minutes ago, Tracy D'arth said:

Spray on Automobile Underbody Stone Chip Preventer, its plastic, will never fall off.

TD'

 

Can it bridge a 7mm gap? It doesn't really sound like it was designed for this job.

Edited by blackrose
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6 minutes ago, blackrose said:

 

Yes I'd just use Stixall. You'll need to abrade both sides of the seam and clean off the dust with a cloth dampened with white spirit. Available in clear, black or white and is overpaintable.

 

https://www.toolstation.com/stixall-adhesive-sealant-290ml/p77137

 

P38 filler might be the boat builder's filler of choice but I don't think they'd use it to fill an open seam as it's not flexible enough and will just crack - as will any other rigid car body filler..

 

Can it bridge a 7mm gap?

As I read the OP there is no gap, 1200 long by 150mm wide, 7mm thickness?

TD'

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If you can afford it there are epoxy fillers (west sytems beind the best known) which are elastic/flexible, but as with most epoxy systems it comes at a price, and it sounds as though you would need a lot.  Well keyed they should last.

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45 minutes ago, ditchcrawler said:

I think the plats are just buckled as they come to the welded joint so the seam dips and he is trying to get it flat. In my opinion he is on to a loser.

This is something that should be asked on a yachty forum they are quite keen on hiding bumps and dents with filler, those of us with real boats live with the weld and dips created as the metal shrinks as do commercial boats trains and others "the hungry horse look"

Welding shrinkage actions (Faulkner, 1977) | Download Scientific ...

 

 

Working narrowboat near Norton Junction... © Roger Kidd ...

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3 hours ago, blackrose said:

 

 

 

P38 filler might be the boat builder's filler of choice but I don't think they'd use it to fill an open seam as it's not flexible enough and will just crack - as will any other rigid car body filler..

 

 

Car body fillers like Isopon etc are polyester resin based - as in GRP. The polyester is not flexible - actually quite brittle so not a good idea for this job. A flexible epoxy would be far better but not sure even that would keep up with the constant thermal cycling in the summer. It would be more flexible, adhere better and have less shrinkage on cure than a polyester but still might not be good enough.

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You can buy aluminium filler very dense and heavy also very good, its waterproof unlike normal fillers and I would think have a stretch shrink similar to the boat itself. U pol D is its name but others are available

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17 hours ago, Proteus said:

I have a double welded roof seam joining two roof plates. To level the roof out and ‘disappear’ the seam the builder has used a body filler to conceal it. This has failed and cracked after a few years.

 

Like this.

 

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