Smooth finish on fiberglass - Projectboat

Discussion in 'Boatbuilding' started by Robero, Mar 13, 2023.

  1. Robero
    Joined: Jan 2023
    Posts: 2
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    Location: Finland

    Robero New Member

    I have just made my first fiberglass laminating work for my project boat. The boat had a big hole / part missing att the rear by the transom.
    I covered the hole with filling it underneath with plywood covered in wax. I then started to thicken the area with fiberglass on the plywood until i got up on the edges were the deck part matched somewhat ok with the rest of the boat.

    I understand that doing this by hand manually trying to match thickness and smoothnes is hard without moldparts, so it does not need to be perfect. You can allways sand, fill, sand for good end resultats.

    My question is how to get somewhat smooth finnish for fiberglass before paint?
    Iv read about applying only resin afterwards and sanding it.
    You can also fill with body filler and sand alot.
    Maybe thick layer of topcoat and sanding it ”flush”?

    Pictures attached, bear in mind this is one of my first times reparing bigger parts.

    Attached Files:

  2. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    I really wouldn't recommend body filler as it usually contains a filler powder that absorbs water.It can work for a boat that is normally kept in covered storage and only gets taken out for short trips before being returned to dry storage.Otherwise it is better to use a sacrificial layer of glass that can be sanded back to a near approximation of a good surface and to apply a mix of resin and microballons for the next step.It is possible to spray gelcoat over the repaired area but it will tend to make everything else in the workshop sticky and is best done in a plastic temporary tent.The alternative is high build primer and then paint after flattening the primer.Which may still leave a problem with blending the edges and the original surface.
    fallguy likes this.
  3. Robero
    Joined: Jan 2023
    Posts: 2
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    Location: Finland

    Robero New Member

    Thanks for reply.
    What do you think about topcoat without thining it out? I was thinking about topcoat with roller and then sanding it and re-apply. After this Epoxy primer, or just topcoat thinned with styrene.
    Final product is not meant to be as the rest of deck is, just masked straight and painted with normal white.

  4. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Fairing compound, not body filler which is hygroscopic unless sealed with layers of sealants.
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