getting that mould perfect

Discussion in 'Fiberglass and Composite Boat Building' started by gages, May 11, 2010.

  1. gages
    Joined: Jun 2008
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    gages Junior Member

    I have manufactured a kayak mould and found getting those last sanding swirl marks out very hard and frustrating.
    Does any one have any tricks that might like to share in getting that mould perfect?

    Thanks
     
  2. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    You have to buff them out with a product made for buffing out "those last sanding swirl marks" in fiberglass molds. I haven't been involved with molds for awhile and don't know the latest bestest stuff, but someone will come along who does. It is not hard to do and within an hour your mold will be perfectly shiny.
     
  3. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

  4. Boston

    Boston Previous Member

    I've done my share of fiber glass repair and what I used to fill swirl marks is called glazing compound

    its almost like wood filler

    I would use a heavy squeegee and just press it into the area and squeegee it over
    if done right no sanding is needed
    works like a charm and Im sure it would fill those swirls no problem
     
  5. gages
    Joined: Jun 2008
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    gages Junior Member

    Awesome thanks

    The mould has come up perfectly sanding down to 2000 wet and dry and then cut polish followed by a finish polish and since you know it so personally after making it, in the right light or shade I can see these little swirls here and there and want a 100% job

    Thanks
     
  6. Boston

    Boston Previous Member

    ya well if you dont get those out of the mold you will probably have them show up in your finish product

    so cool
    stuff is most easily obtained from the folks who make Bondo for cars
    they use it to fill little bubbles in the bondo
     
  7. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    Glazing compound is not for tooling surfaces, it won't hold up.
     
  8. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    All the work should be done on the plug so that if anything needs to be done on the mold it is only a finish polishing. If you still actually have noticeable swirl marks after finish polishing, somewhere along the way you didn't properly finish the step you were at. Hopefully your 2000 wet and dry step took out all the previous marks from whatever step was before such as 1200 w&d. You might go back to a thorough cut polish and a thorough finish polish.

    A white or light colored product shows up flaws the least.
     
  9. hoytedow
    Joined: Sep 2009
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    hoytedow Carbon Based Life Form

    Have you tried buffing with toothpaste?
     
  10. Wynand N
    Joined: Oct 2004
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    Wynand N Retired Steelboatbuilder

    The way we do molds.

    1. Build plug and smooth - apply tow coats of silicon free ram wax. Then cover over with PVA mold release.
    2. Laminate the mold in/over plug, reinforce, cure and the remove from plug. Wash PVA of mold.
    3. Now the fun starts. The complete mold get sanded down with wet/dry sandpaper in the following sequence; #400, #800, #1200, #2000 grit paper. When at the #2000 stage, the mold should be glass smooth with all imperfections such as "orange peel" marks scratches etc that may be on the mold removed.
    4. Now start with silicon free release ram wax. I usually apply about 7 coats with each coat polished to a shine. After seven coats the mold will be mirror like and the moldings popping out later will not stick and have a high gloss and smooth.
    Usually, after a molding is popped from the mold, we give the mold a light single layer of polish before starting the next molding.

    From experience I found the best way to apply the ram wax is to wet the applicator cloth before applying the wax. This will make buffing easier and not get sticky. Let it dry, buff and repeat as many times necessary.
    BTW, at my shop we only polish and buff molds by hand. The polisher is only used on moldings that may need a bit of shine.

    Hope this helps.
     
  11. hoytedow
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    hoytedow Carbon Based Life Form

    Thanks, Wynand. :)
     
  12. SamSam
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    SamSam Senior Member

    I've read a number of times where people do the majority of the finish work on the mold instead of the plug. It's never made sense to me because it is so much easier to work on the positive convex plug (outside of a ball) than the negative concave mold (inside of a ball). Working on the plug allows one to use long sanding boards and powered sanders etc. Working on the mold usually means small sanders or actual hand sanding which introduces/enlarges the irregularities which give unfair, rippled surfaces. Although a mold may be perfectly smooth and shiny, if it doesn't have a fairness over the whole surface that leaves solid straight edged reflections, it lacks the ability to produce a quality product as far as appearance goes.

    There is also a tendency for whoever builds something to see problems that no one else ever does.

    As far as getting rid of them, I guess it depends on from what stage of finishing the swirls were left. I had a brand new buffing pad leave a series of swirls all over a new mold once because there was a tiny lump of excess glue in the lambswool (from the glue that glued the lambswool to the pad). You might check that.
     
  13. Wynand N
    Joined: Oct 2004
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    Wynand N Retired Steelboatbuilder

    As a matter of fact, we take great care preparing the plugs for the mold as perfect as possible since it is easier as you described. However, when a mold is pulled from a plug, it is never perfect and even if a mold comes off the plug looking smart, it still get the treatment as describe in my post above. The resulting glossy glass like sheen is worth the effort.
    By making a living as a professional GRP boat builder / fiberglass product manufacturer, I learned the hard way what works best for me.

    Exactly why all my molds only get polished by hand...being there, got a T shirt and a badge;)
     
  14. gages
    Joined: Jun 2008
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    gages Junior Member

    Awesome replies --I'll take heed of some of this advice and some of the links were helpful as well
     

  15. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    One of the best products I have found to remove swirl marks is 3M polyurethane polish, and use a waffle sponge pad.....it is designed to remove swirl marks from two pack after repairs, very , very fine polish.
     
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