Gelcoat cure time

Discussion in 'Materials' started by Mark Hodges, Feb 13, 2021.

  1. Mark Hodges
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    Mark Hodges Junior Member

    So I have a 1990 wellcraft 20 fish that when I pulled the outboard off to do repairs it also pulled the gelcoat off due to the sealant that was used to seal the bolts. I sanded the area and brushed on a thick coat of unwaxed gelcoat then sprayed PVA over the repair. I waited about 24 hours then sanded the repair and realized I still had some low spots so I wiped the area with acetone to add more gel and when I run the acetone over it the gel got tacky and I noticed that it was wiping the gel off.
    Did I not wait long enough before attempting to sand and recoat ? The gel seamed to be really hard and sanded good...

    Thanks in advance

    Mark
     
  2. ondarvr
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    ondarvr Senior Member

    Gel coat can be affected by acetone if it's not fully cured.

    How much catalyst did you add.

    And what's the ambient temperature.
     
  3. Mark Hodges
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    Mark Hodges Junior Member

    I only mixed up 1oz of gel and I used 14 drops of catalyst the temp was around 68 the gel started to kick in about 10 minutes so I hit it with pva
     
  4. ondarvr
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    ondarvr Senior Member

    It is very difficult to accurately measure catalyst ratios when mixing such small amounts of gel coat, and the drop method is poor at best. So sometimes you get it right, and sometimes you don't.

    Using a small scale that can be found on Amazon or eBay for under $15 will yield far more consistent results.

    And in the lab 100cc of gel coat is the normal amount mixed because it will give repeatable results.

    After saying that, leave it sit longer before sanding, another thing to try is buffing before sanding. Buffing it first will heat the gel coat instantly and help it cure more thoroughly.
     
  5. Mark Hodges
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    Mark Hodges Junior Member

    Ok thanks I will pick a scale up for the future.. also when the direction's are instructing to 12 drops to 1oz are they talking 1oz in weight because I was mixing it by volume.?
     
  6. ondarvr
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    ondarvr Senior Member

    It's close enough either way, the QC lab will go by weight. All the equipment that pumps and sprays resin or gel coat mix by volume.
     
  7. kapnD
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    kapnD Senior Member

    Best practice would have been to fair the repair area before applying the finish.
    I use a heat lamp to insure cure before sanding.
     
  8. Mark Hodges
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    Mark Hodges Junior Member

    Ok what exactly does it mean to fair ? I see it mentioned a lot. If you are talking about feathering out the area for repair by means of removing gel and making the place larger i did that as part of the prep work... also I did put a heat light on it after I finished applying it....
     
  9. gonzo
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    gonzo Senior Member

    Wax is really cheap and gets the best results. Otherwise, use a sheet of mylar or other similar material over the repair.
     
  10. Mark Hodges
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    Mark Hodges Junior Member

    Where is a good place to get it because every where I see it's about $16 an ounce
     
  11. ondarvr
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    ondarvr Senior Member

    PVA works fine, you won't get better results with wax.
     
  12. gonzo
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    gonzo Senior Member

    You already spend more than $16, not counting your time.
     
  13. Mark Hodges
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    Mark Hodges Junior Member

    Oh I agree with that i just thought that when you said it's cheap that you knew of a place it was cheaper
     
  14. gonzo
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    gonzo Senior Member


  15. Mark Hodges
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    Mark Hodges Junior Member

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