DIY fairing boards

Discussion in 'Fiberglass and Composite Boat Building' started by Scuff, Jul 30, 2020.

  1. brendan gardam
    Joined: Feb 2020
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    Location: east gippsland australia

    brendan gardam Senior Member

    whats your preferred fairing compound for glass jeff.
     
  2. waikikin
    Joined: Jan 2006
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    Location: Australia

    waikikin Senior Member

    Depends on the substrate & job. If I was finishing some mdf plug with a seal of glass to build tooling it would generally be Q cells with a dash of colloidal silica and similar for any polyester job with the paste pre mixed in buckets(power stirred with the mixer through a hole in a board to keep the dust in) and catalyzed later . Sub waterline generally better to go epoxy and same required over any epoxy substrate would use Qcells, or the purple brown phenolic micro balloons again with a little colloidal silica added- this helps the filler come off the broad knife a bit smoother and neater. On epoxy we'd sometimes use a final screed of West microlight mix as it goes on sweet and smooth but use the cheaper extenders for bulking out. Often now I'll just get the pre blended International 833 or the equivalent Jotun or other brand- often called "frog bog" as it's green:)
    Edge tools such as planes work very well on extended resin, they do need a touch up on the oilstone now & then but a lot more satisfying than grinding away on the torture board all day- where they really come into great use is where you might need to "top up" some small areas to height- the action of the plane actually just cuts the high spots off whereas sanding can give a halo effect around the top up. Some jobs with heaps of energetic(young & cheap) labour can be achieved with a bulk overfill then apply the boards and labour wholesale... I'm a bit older and slower so like to sneak up on the surface fairness, usually three careful screeds will get there. The use of a fairing/torture board will always be required for the best result but I use a combination of board, plane, 8" planetary action rupes sander, 6" rupes random orbital, 7" festo rotary sander. Guide coat always handy as without easy to get snowblind as to what & where the surface is at. Another trick on flattish surfaces which are actually harder than curvy ones is to use bog battens to define edges and mid panel fair lines, I think in auto trades now they call them "splines" but basically smooth battens that get loaded with filler, applied to surface then taken off after setting- (they need release agent). I use 25mm 12mm x 3mm aluminium channel as cheap and sits pretty fair.
    So choice dependent on substrate and on budget also, I'm getting to old to enjoy the dust in both mixing and sanding so dont plan on doing to much in future but who knows as work and business very variable currently..
    Jeff.
     
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  3. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    The guide coat to spray on...how do you not interfere with epoxy bonds of follow on layers of epoxy compounds?
     
  4. brendan gardam
    Joined: Feb 2020
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    Location: east gippsland australia

    brendan gardam Senior Member

    excellent. thanks.
     
  5. brendan gardam
    Joined: Feb 2020
    Posts: 319
    Likes: 32, Points: 28
    Location: east gippsland australia

    brendan gardam Senior Member

    great post
     
  6. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    Agree Brendan, seems Sailhand uses a very similar process, I've evolved mine to minimise the effort and material use. One of the best tools for small areas is a planetary action sander, I've had the Rupes model for I think about 27 years, if its a panel say 600 x 900 it will be sorted in no time if you float the machine right. I've personally never used the machine style that Sailhand also posted though I can see that they'd be pretty handy if on an open panel with no chance of an inside corner, I saw a hydraulic model used years ago but the guy just hired it and had little idea despite good advice. Be very careful of vibrating machinery as they will do damage to your hands and fingers. One issue I have is after 40 years my "trigger/rude" finger to right hand has a tendon pain... lots of spraying, jockying screw guns and MIG welder triggers has taken toll with vibrating machines not helpful either.
    Jeff.
     
    Last edited: Aug 6, 2020
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  7. sailhand
    Joined: Jan 2017
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    Location: australia

    sailhand Senior Member

    I typically mark around any depressions/holes/scratches that appear after sanding with guide coat with a pencil. Once marked everywhere I scuff out the guidecoat with sandpaper by hand for small areas and a random orbital for larger areas being careful not to remove my pencil marks. Just basically remove the guidecoat if using a spray paint misted on. If using the powdered type guide coat a quick wipe with acetone and then a light key sand only if the bog is older than a few hours. It also depends on size of the hole. If its a tiny scratch glazing putty is quick and easy if its a large area then a good keysand for secondary bonding is essential. The guide coat should only be the lightest of mists and therefore easily removed. You will be surprised how much it stands out against snow white bog, really easy to see.
     
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