How to see imperfections in a workpiece

Discussion in 'Fiberglass and Composite Boat Building' started by aaronhl, May 13, 2020.

  1. fallguy
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    fallguy Senior Member

    3M guide powder goes on dry powder with a little pad like a wax pad... I don't really like the mist coats because it gets all over everything.. I do also like the dykem idea from Cy. I get tired of the black powder residue of the guide coat getting all over stuff. CAUTION though! Acetone leaves a residue and it will attack paint. It is not fully inert after flashing. I would probably use something a little friendlier as the mix; like denatured alcohol perhaps.
     
  2. aaronhl
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    aaronhl Senior Member

    Have a few more questions..

    I haven't started spraying yet, so can you roll grey duratec primer on a mix of existing epoxy/epoxy fiberglass/poly gelcoat?

    How do I then put a colored top coat on, like a red colored top coat, does duratec also have colored options for top coat?

    Or do you mix the high gloss duratec additive to gel coat for a colored top coat?
     
  3. ondarvr
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    ondarvr Senior Member

    You can roll it, but spraying will yield a much better surface that requires less sanding. There are some techniques that can help though.

    You can get Duratec top coats in a few different standard colors.

    Again, spraying the top coat will yield a much better surface that requires far less work to get it right.

    Get some Duratec GelX, it will make spraying in warm weather much easier by extending the gel time.
     
  4. aaronhl
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    aaronhl Senior Member

    Most recent project is a flat splashwell I am working on. You can see the piece I epoxied in is wood covered with fiberglass. I want to fill and fair with some epoxy, then put a layer of 1700 biax glass over it to strengthen the whole splashwell, even putting some of the fiberglass over the red parts. Would it be okay to use the Duratec 707-007 surface primer to coat over thing as I sand the whole area smooth? I am hopeing a few coats of the duratec 707-007 surface primer will fill the fiberglass texture and blend the fiberglass hull into the wood part...See pics attached
     

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  5. ondarvr
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    ondarvr Senior Member

    Yes, but the surface needs to be fully cured, clean off the blush, then abraid the surface.
     
  6. SamSam
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    SamSam Senior Member

    It's probably too late for now, but next time, aside from the guide coats and Dykem type markers, lighting works well. Like it was said, low angle viewing to cast shadows (in a darkened room with a handheld light or flashlight) and especially, when the surface gets to having a bit of reflection, a bunch of long florescent lights. They will show up any waviness in the reflections off of the project. The reflections will be curved, but waviness in the curves is not good. They are hard to eliminate, but the less waviness, the better.
     
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  7. aaronhl
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    aaronhl Senior Member

    Thank you, never too late because this wont be my last project...
     
  8. aaronhl
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    aaronhl Senior Member

    Would I be able to put duratec primer down and then if needed after sanding apply epoxy if I need to fill or fair an area? I will try to get it as perfect as I can before putting the duratec down, I feel it might be a little hard seeing the blemishes without a consistent color coating.

    I have having trouble selecting the right duratec primer because there are many options as far as primers... What version or model number should I be looking at?

    As far as the info about the guide coating, that seems like a great idea and will be ordering some of it soon.
     
  9. Blueknarr
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    Blueknarr Senior Member

    Remember,
    Guide coats don't necessarily show imperfections. They only show areas which haven't been sanded. They need to be used with good longboard fairing techniques to be effective.
    I have seen people with bad sanding techniques use guide coats to de-fair a surface.
     
  10. ondarvr
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    ondarvr Senior Member

    Why would you want to apply epoxy over the Duratec?

    Use the 707-007, or 707-061 for slightly easier sanding.
     
  11. ondarvr
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    ondarvr Senior Member

    It's best to not mix and match resin types when working on something like this. Stick to one and use it throughout the build process.
     
  12. aaronhl
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    aaronhl Senior Member

    Thanks for the help so far. I bought some duratec sanding primer and found out how great the stuff is. I rolled it on because I don't know how to spray yet. I put 3 layers on the piece and it came out very rough so I have to sand it starting with 80 grit to break down the rough orange peel. It is very easy to sand just like drywall compound. So this is a project to hopefully one day be able to take a mold off it.

    It is tough to make perfectly smooth because of all the pin holes in the workpiece now, but I am able to see them because the black duratec sanding primer changes color to gray as I sand it. I feel the only way to make it perfect is to spray it. I see myself using a lot of this stuff especially once it starts getting warmer and I can work on the boat outside. The duratec sanding primer will help tremendously for the project I started the thread for.

    I would like to try to match a red color as the duratec only comes in neutrals. Am I able to dye a white duratec sanding primer just like I would gelcoat?

    Do you think I would have a smoother finish that the sanding primer if I roll the duratec high gloss for a final plug layer? Or rolling anything tend to have the same rough finish?

    And actually after I took those pictures, I sanded more to remove a lot of the pitting, there is still some so that's why I feel spraying the high gloss would be the only way to make it smooth?
     

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  13. ondarvr
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    ondarvr Senior Member

    Rolling leaves a rough surface, and the more you roll, the rougher it will get.

    To help eliminate excessive sanding, use a squeegee or yellow bond spreader to spread more primer over the part.

    Let the rolled on primer harden for an hour or two, then pour some primer on the surface. Use the squeegee to spread it around, it will only fill the low spots, it won't add anything to the high spots.

    This results in a significant reduction in sanding.
     
  14. aaronhl
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    aaronhl Senior Member

    Good advice I will try it on the next application. I dont think I will get the sanding primer as glossy as needed to pull a mold off of it however.
     

  15. wet feet
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    wet feet Senior Member

    If you really want to know how to find the imperfections,I know some experts at spotting them-they often help me by pointing them out.I would love to do the same for them-but they never seem to produce anything.......
     
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