filling large voids

Discussion in 'Fiberglass and Composite Boat Building' started by robwilk37, Dec 26, 2012.

  1. robwilk37
    Joined: Nov 2010
    Posts: 120
    Likes: 3, Points: 18, Legacy Rep: 24
    Location: san diego

    robwilk37 Senior Member

    im changing the porthole/light configuration in my new cabin top. the PO had also changed the original lights and used an extensive amount of bondo as filler, so what ive got after grinding and laying new glass is a rather uneven cabin side. eventually ill wrap the entire new cabin top with a couple of layers of biax/epoxy, but for now i want to get close to fair and a primer coat. is there any problem having some (< 1/4") filler between layers of glass? this filler will be an epoxy/cabosil/fibers blend, wet on wet, no need for sanding. better to wait for all the layers then fill and fair with balloons, keeping the filler as the outside surface of can i use structural filler between glass laminations?

    TIA
     
  2. tunnels

    tunnels Previous Member

    Fillers are not structual !!!

    Any filling should only be the surface no more then a 1/16 " at the most !! the rest should be glass materials /epoxy if thats what you using !! . The more filler you use the more likely to get cracks shrinkage and for it to fall out if it get banged dinged or the hull moves in any way . filler is just for the surface filling thats it dosent mater if it has micro fibres or what ever . keep it to a thin as possible coating !!
     
  3. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 479, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    That's simply ridiculous Tunnels. You can use a thick filler base and it's done all the time. A fillet is a thick filler base, often with fabric over it, seen commonly without issue. Cosmetic filling would be nice, if it could be constrained to 1/16" thick areas, but only in a perfect world does this exist. In reality quite thick globs of fairing compound are employed, usually with few ill affects, other then weight and strength issues.

    This said, biax isn't particularly easy to fair, so I'd apply this reinforcement first, then fair the cabin walls after. To make fairing over the biax easier, use Mylar or stiff plastic sheeting material. Just place it on the wet fairing compound, then very lightly roll it in, so you have continuous contact. Wait for it to cure and peel the Mylar or plastic sheet off the work. The result is mirror smooth and saves a lot of sanding time.
     
  4. tunnels

    tunnels Previous Member

    You can do what you like !!
    If it was a porthole it needs to be structual so glassed properly . if you glass the ouside and fit a core or what ever and glass the inside then thats fine the outside would only need a skim of filled to san:Dd and fair and when painted again look like it was never there !!
    Right ??
     
  5. robwilk37
    Joined: Nov 2010
    Posts: 120
    Likes: 3, Points: 18, Legacy Rep: 24
    Location: san diego

    robwilk37 Senior Member

    thanks par. yeah it didnt make a lot of sense to me lamming up endless half-dollar sized pieces of cloth to fill in the low spots, the other option of course is to keep grinding away at the highs but seems wasteful. im assuming the more fibers i can get in the bog the better? i like the mylar idea. curious as to why biax is more difficult to fair... maybe because it drapes easier and therefore telegraphs the lows more?
     

  6. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 479, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Yep, that would be my approach, a heavy milled fiber mixture, with enough silica (cabosil) to get the viscosity you need, for vertical work. This mix has excellent compressive strength, which is good under the port flanges. Biax has to have it's stitching ground off, which tends to make a mess of the surface and because it does conform so well, you have lots of "hidden" lows that you still need to fix. If it was me I'd do a multi stage affair. The first would be to bulk in the areas you've removed bog and the lows with the high density filler, trying to get it reasonably fair. Then the biax to return some integrity to the panel, grind the stitching off, more fairing, then a finish cloth (6 ounce or less), topped with Mylar, to help with a smooth surface.
     
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