Multihull Specific Fairing Question

Discussion in 'Boatbuilding' started by CatBuilder, Apr 15, 2012.

  1. CatBuilder

    CatBuilder Previous Member

    Fairing my hulls, I am ending up with a 1-3mm or 1/16-1/8 inch layer of bog over most of the glass on a finished, faired hull. This is prior to any primer or paint system. Just brown microballoon fairing bog, which, I understand also needs another coat of neat epoxy to keep it watertight.

    Is this amount of fairing bog reasonable?

    Will it add too much weight?

    Any thoughts on how much it will add?

    Am I doing this right and is this the lightest way to do it?
  2. mastcolin
    Joined: Jun 2005
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    mastcolin Senior Member

    You don't need to coat filler mix with resin mix. Use paint. Dunno what scheme you are going with and how you are thinking of painting. Normal scheme is to use epoxy primer onto sanded filler. If you use Awlgrip Highbuild you then need to use Awlgrip 545 before topcoat. International scheme is Interprime 820 then their undercoat etc. You can apply 545 direct onto filler but I don't like this. The solvents from the 545 can swell the balloons and you have to apply lots of 545 to fill the porosity of the filler which can trap all the solvent in the filler. I'd recommend speaking with your resin supplier for their experiences - different suppliers have differing opinions. Listen to their experience(if they have any:))
    Last edited: Apr 15, 2012
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  3. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    1-3 mm or 0-2mm finished is great(I have seen to 12 mm & heard of up to 75mm- but this was to get a boat to measure for a class rule!)

    Once fair it's reasonable to scrape a higher density filler over the surface to fill pin hole/small bubbles- it's only a "crust" but will save filling these with paint & possible solvents to give problems later. Jeff.
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  4. CatBuilder

    CatBuilder Previous Member

    Whew! Thank you!

    I figured the 5 to 10 gallons (20-40 liters) of extra epoxy used to fair the hull would be a lot of added weight. Now that I hear there are much thicker fairing coats added to boats, I am quite relieved. I thought the 3mm max was going to be enough to ride her down on the waterline. Shows how little I know about this step. :)

    The way I was able to get close to fair before infusion was that I faired the foam hull before the dry glass went on for the infusion process. So, the glass was infused onto a nearly fair core to begin with. There are only a few little bumps and wobbles here and there that you need a batten to detect. I put basically a 1mm coat on everything just as a sealer, with another 2mm or so in places it's out of whack. Of course, there are the inevitable spots (such as the bow) where you just pile the bog on to get the right shape, but mostly, it's a 1mm skim coat with a couple mm's of extra for some dips.

    The bog piled on the bow is all under the infused glass though, as a core.

    Thanks for easing my mind here. I was worried I was weighing the boat down too much with the fairing coat.
  5. hoytedow
    Joined: Sep 2009
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    hoytedow Carbon Based Life Form

    How about some new photos? :D
  6. CatBuilder

    CatBuilder Previous Member

    Hoyt, it's still a bunch of parts, so there is nothing interesting to put up yet.

    I'll get some new photos as she starts the assembly from part into a boat.
  7. tunnels

    tunnels Previous Member

    Any high build 2 pot and add Q cells to the mix and some thinner so it can come out of a spray gun !!. If you play with the amount you mix in a pot of paint you can build up to 2 mm or 3 mm without to much problem !Q cells makes it easy to sand and fair with a long board . used to do the first coat an any job a bright colour and sand to but not through .
    Can build same with Dura tech as well but have to get the sanding done as soon as possible because it hardens off and makes sanding heavy going , Finish with a 2 pot primer that will give you a good base for the top coat . Always use a tinter in the undercoats /high builds etc so you can see where the highs and lows are and dont sand through the very first coat you put on !!.
    Happy long boarding !!!:D

  8. hoytedow
    Joined: Sep 2009
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    hoytedow Carbon Based Life Form

    It would be nice to see the parts as they are before the assembly to get an idea how they will fit together.
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