Foam insulation and aluminium.

Discussion in 'Metal Boat Building' started by Robbo, Aug 5, 2010.

  1. Robbo
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    Robbo Junior Member

    Hi all, new on here so go easy on me please!
    Ive done a site search but havent come up with anything on the subject of spray foam (in its various brand names) and using it on aluminium hulls.

    Can anyone tell me whether it can be sprayed straight onto bare ally plate, or some prep or coating is needed?

    Which brands are more suitable?
    I havent found any of the manufacturers websites which mention its suitability or otherwise for a direct application.

    cheers guys!
     
    Last edited: Aug 5, 2010
  2. marshmat
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    marshmat Senior Member

  3. KnottyBuoyz
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  4. Robbo
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    Robbo Junior Member

    thanks guys, I probably should elaborate a bit more.
    The application is for a plate alloy runabout, between the stringers and for the purpose of sound deadening and bouyancy.

    Normally block foam is placed under the deck, but Im not sure why you couldnt spray foam onto the plating. Perhaps the boat manufacturers do, Im not sure.

    But it would seem to me to be ideal on all counts-noise, bouyancy etc.

    More block foam could be added if required for the correct bouyancy margin.

    As its sealed under the deck, fume/fire isnt an issue.

    The only thing Im not sure of is its compatibility (chemically/corrosive before it reacts) with aluminium.

    Also perhaps there is a good reason why not that I havent thought of.

    Hell if you banged a small hole in the bottom it would even prevent water coming thru to a certain point.

    Any input??
     
  5. Robbo
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    Robbo Junior Member

    thanks anyway guys, I'll approach some manufacturers instead.
    Id thought it would be a "common knowledge" subject on here:)
     
  6. KnottyBuoyz
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  7. Robbo
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    Robbo Junior Member

    thanks for that Knotty, the Armaflex probably isnt enough on a highspeed vessel for sound deadening, plus it doesnt have bouyancy.
    Mainly after a sprayfoam product that is compatible with aluminium, if thats possible/available.
     
  8. KnottyBuoyz
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    KnottyBuoyz Provocateur & Raconteur

    I remember reading a few years ago about a couple in Ontario who were building an all aluminum Diesel Duck. I tried to find the reference but couldn't. If my memory serves me correctly they spray foamed the entire hull inside to the waterline with a closed cell fireproof foam.

    Update: Found it. http://web.archive.org/web/20040811192301/www.msdieselduck.com/updatesjan2004.htm It's really slow to load. Patience required.
     
  9. apex1

    apex1 Guest

    That is not the whole story!

    Of course Armaflex is sound deadening (and there is a special product in the line), and as sure it provides buoyancy (but is too expensive to be used in m³ blocks).

    And the spray on foam still is a poor choice on Al as on steel!

    Regards
    Richard
     
  10. alidesigner
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    alidesigner Senior Member

    We use thermatec sheets for a few reasons.
    1. Its approved by the marine dept.
    2. Fumes. You dont want to risk an explosion when you are welding the deck in.
    3. Future repairs/mods will be easier as it wont be stuck to the area being repaired.
    4. Corrosion over the life of the boat would be an unknown with spray in - ali needs oxygen to form its protective coating.
    5. Its easy. Just cut it with a knife or jig saw and drop it in. No plate prep required.
    6. Its easy to calculate the correct volume needed.

    In commercial boats we have sprayed on panel damping compounds such as deci damp but it doesnt provide buoyancy, only noise reduction. The plate had to be prep'd first.

    The sheet foam will do a great job reducing the noise.
     
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  11. Robbo
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    Robbo Junior Member

    thanks for that Steve. regarding corrosion Id have thought that so long as the foam compound wasnt attacking the alloy, itd be no different to paint which also excludes oxygen to the plate surface and the sound deadening would be far better with something bonded to the plate than just laying in there?
     
  12. alidesigner
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    alidesigner Senior Member

    No worries Robbo. Let me preface this by saying the following is what I think and is not based on any research.

    Paint systems are a combination of etch, primer, and top coats and are designed to replace the natural oxidation layer of ali and hence minimise corrosion. Primers are porous and need a top coat to keep moisture out (aka the rusty cars you see driving around in primer). A spray in foam may not be designed that way so who knows what long term protection it will have, if any at all. It could even be corrosive if applied direct. If applied over primer it still might let moisture through.

    Even paint isnt perfect. If you have ever seen paint bubbling near a stainless fitting you will see that the ali under it is powdery and white.

    The approved foam we used is closed cell, so moisture cant get through it. The way we install it allows the hull to drain. The risk with spray in is that it may effectively be open cell so moisture could work its way through it over time. (ali hulls sweat) So even if the foam itself doesnt attack the ali, if it lets moisture through it could eventually cause problems. Depends on the product I guess.

    So for me its safer to just use an approved product and not risk any problems later on. Plus the explosion risk. I have seen photos of a boat (not ours) that expolded due to fumes from a coating they were putting in. It was a write off. Luckily the welder wasnt seriously injured. Also the approved foam is self extinguishing so weld spatter just smoulders and goes out.

    Noise is transmitted in 2 ways, air borne and structure borne (vibration). Sound deadeners bonded to the plate such as decidamp add mass which damps the vibrations and reduces structure born noise. Foam absorbs air borne noise but does not reduce vibrations. A spray in foam that is bonded to the ali will be relatively light so will not have much effect on structure born noise and will act the same as loose foam in absorbing air born noise. A thorough noise treatment system will have both. You can buy sound deadeners in stick on panels and only need to cover around 70% of the panel.

    Hope that helps with the decision making.
     
  13. Robbo
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    Robbo Junior Member

    Thanks steve, yes that is what Im looking for, an approved closed cell foam, used as it is commonly on steel vessels, sprayed onto the plating.
    It was mentioned in a vessel review in "Fisherman and Boatowner" magazine.
    When you say aluminium "sweats" I presume you mean condensation (which most sorts of bonded insulation should stop), rather than permeating thru?
     
  14. alidesigner
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    alidesigner Senior Member

    I was assuming that you would coat the bottom and fit the deck later so condensation would form on the under side of the deck and drop onto the foam. Might not be such a big deal though.

    Maybe the answer can be found at www.sprayfoam.com
     

  15. apex1

    apex1 Guest

    "Approved" and "sprayed on" does not perfectly go together as the industry after some 20 years notices now.

    Insulating with closed cell rubber foam (Neoprene) or Armacell (synth. rubber) against condensate is the proven and safe alternative.
    The stuff for extra flotation can and should be a completely different animal, and can be cheap PS for example.

    Regards
    Richard
     
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