Pinholes in gel coat

Discussion in 'Fiberglass and Composite Boat Building' started by jellycoat, Oct 3, 2020.

  1. jellycoat
    Joined: Oct 2020
    Posts: 3
    Likes: 0, Points: 1
    Location: CHARLESTON

    jellycoat New Member

    After repairing some gel coat gouges w 3m marine filler (which came out fine w no pinholes) I mixed some gel coat (2oz) which contained wax with few drops of styrene and then mekp catalyst (10-15%) and sprayed using Preval aerosol spray.

    Let it cure for 24, came out looking as it should w slight orange peel. Felt hard and not tacky so began wet sanding at 400, 800 and then 1200.

    Two things: first the paint began grabbing sand paper (sticky) and forming little globs of paint that were difficult to remove. Any ideas?

    Second, tiny pinholes were observed in groups at many different locations. I was able to target them and wet sand them out but curious what caused it to prevent future pinholes.

    Thank you in advance for help
     
  2. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,277
    Likes: 694, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Surely you didn't add 10-15% of catalyst ? What is the "paint" you are referring to ?
     
  3. jellycoat
    Joined: Oct 2020
    Posts: 3
    Likes: 0, Points: 1
    Location: CHARLESTON

    jellycoat New Member

    No thats an overstatement, but had to thin it enough to spray properly without spitting thick gel coat. And the paint referring to is the repaired spot w new gel coat. Thanks
     
  4. ondarvr
    Joined: Dec 2005
    Posts: 2,468
    Likes: 292, Points: 83, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

    Lots of things you mentioned can cause pinholes.

    10-15% catalyst, should be 2%

    Preval sprayers can introduce propellant into the gel coat if not used correctly.

    Fillers like that tend to leave tiny defects in the surface that gel coat which has been thinned enough to spray through a Preval won't hide completely.

    Gel coat clumping on the sand paper is from it not being thoroughly cured. Possibly from being over catalyzed.
     
  5. jellycoat
    Joined: Oct 2020
    Posts: 3
    Likes: 0, Points: 1
    Location: CHARLESTON

    jellycoat New Member

    Great information thank you. Few follow up questions:

    how do I properly measure 2%

    Using the preval, easy to use on side of hull (holding vertical), however works poorly underneath boat on keel (when tilted) any tips to use properly?

    Would a system like 3m accuspray accuspray be worth the 300 investment? Or something similar?

    What is a solid thinning agent to use instead of me over catalyzing that will have a good impact?

    What filler do you recommend, thought 3m was pretty reputable?

    Thanks again
     
  6. ondarvr
    Joined: Dec 2005
    Posts: 2,468
    Likes: 292, Points: 83, Legacy Rep: 506
    Location: Monroe WA

    ondarvr Senior Member

  7. kapnD
    Joined: Jan 2003
    Posts: 740
    Likes: 99, Points: 28, Legacy Rep: 40
    Location: hawaii, usa

    kapnD Senior Member

    Your catalyst ratio is off the charts, no wonder your repair has problems.
    Cut it down to 2%, and be sure to mix it well.
    Is your catalyst fresh?
     

  8. IanH
    Joined: Mar 2019
    Posts: 10
    Likes: 0, Points: 1
    Location: UK

    IanH Junior Member

    Duratec make a high gloss gel coat additive which makes it easier to spray and avoids the need for wax.
     
Loading...
Similar Threads
  1. Seb790
    Replies:
    5
    Views:
    4,768
  2. EXITcomposites
    Replies:
    15
    Views:
    6,640
  3. convincor
    Replies:
    7
    Views:
    90
  4. Scuff
    Replies:
    12
    Views:
    307
  5. Mark C. Schreiter
    Replies:
    18
    Views:
    384
  6. doogymon
    Replies:
    12
    Views:
    367
  7. wesley Sherman
    Replies:
    14
    Views:
    492
  8. ahender
    Replies:
    5
    Views:
    411
  9. E350
    Replies:
    17
    Views:
    1,144
  10. bedfordd
    Replies:
    9
    Views:
    1,036
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.