Sandblasting epoxy between layers

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

  1. upchurchmr
    Joined: Feb 2011
    Posts: 3,094
    Likes: 163, Points: 63, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    Anyone have actual information?
    What is the difference in adhesion between abraded/ sanded and not abraded?

    I bet that data does not exist and you can't show that it matters.

    Old wives tales abound online.
     
  2. DogCavalry
    Joined: Sep 2019
    Posts: 981
    Likes: 477, Points: 63
    Location: Vancouver bc

    DogCavalry I aim to misbehave.

    It is certainly true that boatbuilding is a very conservative field. Testing should be fairly easy. I'll do a set of controlled tests.
     
  3. upchurchmr
    Joined: Feb 2011
    Posts: 3,094
    Likes: 163, Points: 63, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    That would be great.
    Please be prepared to show your laminating method and testing setup and method.
    I'm not sure how I would set up such a test without expensive equipment.
     
  4. fallguy
    Joined: Dec 2016
    Posts: 3,997
    Likes: 627, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    The only way to test would be coupon testing where you create two substrates and epoxy bond to them and pull. It has already been done.

    too tired to look now, but there are some papers on the subject

    My experience is that thin fairing compounds do suffer adhesion issues if key is lacking. But dust could be a factor in that experience as well.

    Dropa glob of epoxy on the dirty concrete floor and wait a week. On removal; it takes up the concrete.
     
  5. upchurchmr
    Joined: Feb 2011
    Posts: 3,094
    Likes: 163, Points: 63, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    Did you sand the concrete? Perhaps it would be better to use materials somewhat close to what we use. Epoxy on concrete certainly works well.
    It would be good if you found the coupon testing for us.
     
  6. fallguy
    Joined: Dec 2016
    Posts: 3,997
    Likes: 627, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    I can't find the article on a quick search.

    But ASTM D-882 is the bond strength testing standard.

    The study I read I can summarize.

    It said wire brushing was the best bond, followed by low grit sandpapers. Dusts and dirt were always an impediment or worked against bond strengths.

    In my reading; I have also seen where sanding beats peelply, but peelply is not bad.

    rxcomposite may have the best source information as he has in the past had access to more data

    The bottom line is his surface is curing a bit too raggedy for sanding easy. And he needs to consider peelply or live with some bond risk or try to finish within the Silvertip chem bond window of 72 hours.

    My experience with concrete is presented for anecdote only. A glob of epoxy falling on a dirty floor still bonds well enough to essentially pass a bonding test which is fail if it shears with no concrete and pass if it shears with concrete. Most of the epoxy drips on my floor are now getting sanded for that reason.
     
    DogCavalry likes this.
  7. DogCavalry
    Joined: Sep 2019
    Posts: 981
    Likes: 477, Points: 63
    Location: Vancouver bc

    DogCavalry I aim to misbehave.

    West system manufacturers at epoxyworks.com have done very extensive tests. Their findings are online and readily available.
     
    BlueBell likes this.
  8. Chris Rogers
    Joined: Apr 2020
    Posts: 25
    Likes: 10, Points: 3
    Location: Boston, MA

    Chris Rogers Junior Member

    Peel ply is the best - ideally the plain nylon (often with red-stripes) kind wet out on top of the glass tight with a squeegee and rolled with a bubble popper. Too much resin and it gets wavy and floats causing trouble.

    Next best is to de-blush with water and sand. 80 grit (really anything from 40-180 will do) sandpaper for any high spots followed by red Scotchbrite to remove any shiny areas. Good vacuum and wipe with acetone - or a dry cloth until there's no dust. Working within the "green window" of the epoxy while the material is B-staged but not fully cured can be good but the risk of dealing with uncured epoxy dust is a real issue.

    If you can lay up clean without a blushy resin (humidity is a big factor with blush) it is reasonable to go for the next ply as soon as the first is tacked up - and maybe cut off any sharp bits with a carbide scraper before laying up the next ply. This is in the "art" zone and it is helpful to have some experience with your resin system...

    Plenty of debate about how to do this and lots of good data - and also lots of rules of thumb based on questionable stuff. Good luck!
     
    fallguy and DogCavalry like this.
  9. DogCavalry
    Joined: Sep 2019
    Posts: 981
    Likes: 477, Points: 63
    Location: Vancouver bc

    DogCavalry I aim to misbehave.

    Thanks Chris. I think, in hindsight I'd have had an easier time of it with peelply. Or even just regular poly to make the whole thing uniformly shine. The heavy glass I'm using has massive texture when cured, so regular sanding just isnt possible. At least not with any expectation of scuffing everything, or even most of it. Getting to 50% surface area cost me some glass, and a lot of time.

    It is, as you say, an art.
     
  10. DogCavalry
    Joined: Sep 2019
    Posts: 981
    Likes: 477, Points: 63
    Location: Vancouver bc

    DogCavalry I aim to misbehave.

  11. Chris Rogers
    Joined: Apr 2020
    Posts: 25
    Likes: 10, Points: 3
    Location: Boston, MA

    Chris Rogers Junior Member

    That's not that bad! I'm not sure how much area you have to cover but Scotchbrite is great for this kind of thing - it works best if you sand first like you've done to remove the sharp stuff. Sanding with hand-held paper on the same angle as the top set of glass tows can be ok sometimes.

    You really do need to make most of the shiny bits go away or adhesion could be an issue. Practically this depends on what you're building and how it is loaded and what it goes through over time: stress, moisture and heat-wise. If its mostly there for abrasion resistance then it may not matter how perfect your prep is.

    What weight is the glass? Are you sheathing over wood?
     
  12. DogCavalry
    Joined: Sep 2019
    Posts: 981
    Likes: 477, Points: 63
    Location: Vancouver bc

    DogCavalry I aim to misbehave.

    It's 18oz biax over strip plank.
     
    BlueBell likes this.
  13. SamSam
    Joined: Feb 2005
    Posts: 3,900
    Likes: 197, Points: 63, Legacy Rep: 971
    Location: Coastal Georgia

    SamSam Senior Member

    That heavy of a fabric will take more resin to fill in the valleys, so watch for air bubbles there.

    This is kind of long and a repeat of things I've posted before, but something might be of use to you.

    I never used epoxy, but I've read the uncured dust (cure takes a week or so I hear?) can be just as bad as the liquid for skin reactions and such and even worse for the lungs as you inhale actual particles of uncured epoxy instead of only vapors.

    You mentioned sanding for 16 hours and being covered in glass, I always disliked that so I would cheat every way I could. I would use the heaviest grit possible (16-24-36) and bear down on grinders so they rotated slowly and didn't throw glass all over. It was surprising how much smoke the motors could put out and still work. I would have a shop vac hose right there to catch the stuff in real time, and have the exhaust out of the boat and aimed downwind. I would have a window fan right close aimed away downwind and if there wasn't a wind blowing I would have another fan further away upwind to create a general breeze so there was a downwind. Instead of vacuuming or blowing the dust away, if I could, I would wash it away with the water hose. If I was able to let stuff dry for awhile or overnite, I could do that most of the time. If I was able to do that, I would have a light spray directed to where I was working so there was no dust created. Even with that, there were several months a year that long pants and sleeves were not an option off the job.

    Everyone has a plan for cleaning up, mine was to wet the arms and hands with water and then use an air hose at an acute angle to blow the water off, the theory being the water and air would pull the fibers out of your skin somewhat. Who knows. Everybody there said that helped so that was what we did. I never bothered with cold water showers or anything, but what I would do was first get wet and wipe off with a washrag, continuing the pull the fibers out of the skin approach. After that my routine was to soap up and thoroughly scratch with my fingernails everywhere there was glass, my arms, legs, hands etc. This going on the premise that instead of having all these millions of fibers sticking out of my skin and getting constantly irritated by clothes and furniture and sheets, it was better to just break them off at the skins surface and be done with it. I truly believe that helps a lot.

    One of the handiest things I used was a sharp paint scraper like this...
    [​IMG]
    It has 1 replaceable blade with 4 edges you can sharpen with a file (round the corners) in less than a minute and it creates no air born dust. You get a good grip with the knob so you can go at stuff like a gorilla and loosening the knob allows a new edge to be rotated into place. Much cheaper than discs and you can go at stuff in the early, green stage when discs become plugged up with soft resin. That thing, combined with good bubble buster rollers or squeegees, being neat and orderly, and doing as much as you can while the glass is wet, to eliminate areas that will need to be ground when cured, can make a large difference on the itch factor and the overall speed of the project. It's much easier and quicker to get things right with a roller or squeegee than with a grinder.
     
    DogCavalry likes this.
  14. fallguy
    Joined: Dec 2016
    Posts: 3,997
    Likes: 627, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Those dusts are 'hot' indeed.

    masks and long sleeves and gloves at a minumum
     

  15. AndrewK
    Joined: Mar 2007
    Posts: 475
    Likes: 33, Points: 28, Legacy Rep: 344
    Location: Australia

    AndrewK Senior Member

    Use a grit impregnated composite fiber bristle wheel and a drill. They look the same as wire wheels.
     
    DogCavalry likes this.
Loading...
Similar Threads
  1. simon
    Replies:
    17
    Views:
    7,321
  2. Cedric Oberman
    Replies:
    2
    Views:
    193
  3. Mark C. Schreiter
    Replies:
    18
    Views:
    503
  4. tbelliot
    Replies:
    7
    Views:
    392
  5. DogCavalry
    Replies:
    16
    Views:
    653
  6. Heynow999
    Replies:
    8
    Views:
    503
  7. Gasdok
    Replies:
    10
    Views:
    494
  8. ahender
    Replies:
    5
    Views:
    471
  9. mudflap
    Replies:
    23
    Views:
    778
  10. S17665
    Replies:
    4
    Views:
    531
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.