Sandblasting epoxy between layers

Discussion in 'Fiberglass and Composite Boat Building' started by DogCavalry, Aug 9, 2020.

  1. DogCavalry
    Joined: Sep 2019
    Posts: 1,136
    Likes: 636, Points: 113
    Location: Vancouver bc

    DogCavalry I aim to misbehave.

    Hi all. I'm using the heaviest biax glass I could find on my boat, and when it cures, it has massive texture. Like a pair of corduroy trousers. So to apply the next layer I need to scuff the surface to get a good bond, but as soon as I try for more than a tiny area scuffed, I'm sanding off glass. Wire brushes have a hard time getting into the texture. I read in some industry paper that sandblasting is used. Does anyone have direct experience with this?
    20200808_183425.jpg 20200808_182444.jpg 20200808_182428.jpg
     

    Attached Files:

    fallguy and BlueBell like this.
  2. gonzo
    Joined: Aug 2002
    Posts: 15,126
    Likes: 899, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    I have used a sandblaster or repairs for many years. For new laminates, the easiest way is to keep on adding before it completely cures. If you only want to remove the blush/amine layer, a scrubby pad and detergent will do it.
     
  3. BlueBell
    Joined: May 2017
    Posts: 1,564
    Likes: 393, Points: 83
    Location: Victoria BC Canada

    BlueBell "Whatever..."

    I have only used baking soda blasting on polyester for an epoxy barrier coat application.
    It was to remove the bottom paint and gelcoat on an unfaired matt/roving/matt on ply.
    It worked great but took a long time.
     
  4. fallguy
    Joined: Dec 2016
    Posts: 4,161
    Likes: 697, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    All you need to do between coats is take off the stitching; knock down some shine. Leave no steps or address any steps with a quick coat of thixo before glassing on another layer...

    verify no blush or greasy surface as well; those must be washed with soapy watm water

    I run 40-60 grit over it. It takes a wee bit of glass. Based on my review of your pictures; you are going a bit too far down, but fine.

    Make sure to use a bubble buster for consolidation. A squeegee never gets things as flat for me. The glass needs to look good n flat after consolidating.

    Best also if you can operate within the Silvertip chem bond window of 72 hours. I realize it isn't always possible.

    The only time I have seen delamination within my project is ultra thin coats of fairing on areas that didn't get enough key (sanding).

    Blasting is unneeded.

    Also. You can try peelply. That is more proactive. But, be warned. Do not apply peelply near gelation. It will grab the glass and lift it while you adjust the peelply. And you will be very sad the next day.
     
  5. fallguy
    Joined: Dec 2016
    Posts: 4,161
    Likes: 697, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Watch the video. 29 minutes to 31 for application and 40 minutes for removal...

    guy is painfully slow...

     
  6. fallguy
    Joined: Dec 2016
    Posts: 4,161
    Likes: 697, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Here is a shorter, better one.

     
  7. upchurchmr
    Joined: Feb 2011
    Posts: 3,122
    Likes: 171, Points: 63, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    I wouldn't do anything that cuts glass.
    A waste of your money and time.

    Better to use thinner glass and do two layers.
    Or peel ply and vacumn.
     
    SamSam and fallguy like this.
  8. DogCavalry
    Joined: Sep 2019
    Posts: 1,136
    Likes: 636, Points: 113
    Location: Vancouver bc

    DogCavalry I aim to misbehave.

    Thanks all. I'm much heartened by your help and advice, as always.
     
    fallguy and BlueBell like this.
  9. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,600
    Likes: 817, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    It certainly is not wise to be sanding through the glass, to any extent, I'd be more inclined to screed the surface with lightweight epoxy bog, and sand that.
     
    fallguy likes this.
  10. fallguy
    Joined: Dec 2016
    Posts: 4,161
    Likes: 697, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    a quick light low grit sanding and your advise combine well
     
  11. DogCavalry
    Joined: Sep 2019
    Posts: 1,136
    Likes: 636, Points: 113
    Location: Vancouver bc

    DogCavalry I aim to misbehave.

    Thanks again. The confusion comes from lack of clarity in instructional materials. Even the Gougeon Brothers book isn't clear on this. Sand between cured coats? What percentage of surface area? To get to 100%, literally half my glass would be gone. That seems bad. In hindsight, what I should have done is use poly film on the wet epoxy. That would have left a very smooth regular surface. Could have roughened that in a fraction of the time, and lost no glass.
     
    BlueBell likes this.
  12. fallguy
    Joined: Dec 2016
    Posts: 4,161
    Likes: 697, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    I am not a fan of the poly film. It leaves a shiny surface whereas the peelply leaves a matte surface suitable for bonding, although I prefer sanding it a tad. You could try both to determine a personal preference.

    Much of boat building is closey held knowledge. Sort of strange thet way. I think builders just work so hard; they don't take the time to educate/video tape.
     
  13. DogCavalry
    Joined: Sep 2019
    Posts: 1,136
    Likes: 636, Points: 113
    Location: Vancouver bc

    DogCavalry I aim to misbehave.

    As far as poly goes, I'm resigned to some sanding anyway. Just getting a flat surface to sand where I'm not cutting glass with every movement of the sander would be nice. I spent 16 hours sanding it to the state in my pics. And I obviously lost some glass. It's in my skin now.
     
  14. BlueBell
    Joined: May 2017
    Posts: 1,564
    Likes: 393, Points: 83
    Location: Victoria BC Canada

    BlueBell "Whatever..."

    Don't forget the objective here.
    To clean and abraid the surface.
    Shouldn't washing, rinsing, and wire-brushing (with the fiber striations) be more than adequate?
    Oh, and chemical wash/rinse at the end.
     

  15. fallguy
    Joined: Dec 2016
    Posts: 4,161
    Likes: 697, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Yes. But John is just learning, so he is worried about shiny areas below the sander.

    Epoxy is very strong; some shiny spots here n there are not horrid. I use a dime for reference. If I have anything bigger than a dime; I hand sand the spot with 40-60 grit early. Later after fairing moving up in grits to 120.

    I never wire brush, but that can get low spots a key and perhaps a bit better than my sandpaper method.
     
    DogCavalry likes this.
Loading...
Similar Threads
  1. simon
    Replies:
    17
    Views:
    7,390
  2. Cedric Oberman
    Replies:
    2
    Views:
    282
  3. Mark C. Schreiter
    Replies:
    18
    Views:
    705
  4. tbelliot
    Replies:
    7
    Views:
    460
  5. DogCavalry
    Replies:
    16
    Views:
    749
  6. Heynow999
    Replies:
    8
    Views:
    592
  7. Gasdok
    Replies:
    10
    Views:
    588
  8. ahender
    Replies:
    5
    Views:
    567
  9. mudflap
    Replies:
    23
    Views:
    856
  10. S17665
    Replies:
    4
    Views:
    602
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.