Repairing and Re-gelcoating Fiberglass canoe

Discussion in 'Fiberglass and Composite Boat Building' started by trailrunner, Sep 18, 2013.

  1. michael pierzga
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    michael pierzga Senior Member

    Colour matching is a skill.

    I watch the local gel coat guy and he goes thru much effort to match colour

    Most boats are white...difficult. To determine what white he first cleans the gel coat then bleaches out any organic stains with acid, machine polishes a section to cut off the oxidixed layer and then lays out two or three test patches to get the best match. Even then his guess may be off and back to the drawing board.
     
  2. SamSam
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    SamSam Senior Member

    Matching colors is one thing, if the two different gels are the same color a year later is another thing.
     
  3. SukiSolo
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    SukiSolo Senior Member

    Thanks Michael. That's not far from what I do which is cut back with G3 Farecla or 800 grit then try and 'see' the colour in good daylight, preferably not direct sunlight. Cleaning with Acetone is a must as well. Sometimes putting a colour near it say printed paper or a plastic 'thing' will tell you which direction you need to go in.

    'Whites' can be pure or any colour added or combination. Because the shifts are so small I mix some pure white with say a hint of pure yellow to get it diluted massively. You need this 'first distillation' just to get a weak enough tint to put in the pure white added to the gelcoat. Mint green, pale salmon, pale sky - just some of the diluted colours needed to get the correct white. Usually I can get it inside 2 goes now. Weird one recently was a French Blue, foxed me for a while until I realised you need red in it. British Racing Green - simple, blue, yellow and black.


    Lots of of dinghies are grey and the combination of Super White and Light Aircraft Grey will give you a lot of the range including Laser grey. Some of the manufacturer supplied matching gel colours are so far out it is a disgrace.
     
  4. SamSam
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    SamSam Senior Member

    I worked with a guy sandblasting and painting bulk oil tanks and to make a five gal pail of white paint 'whiter', he would add a few ounces of black. It seemed to make it a 'sharper' white.
     
  5. PAR
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    PAR Yacht Designer/Builder

    Color matching is just knowing you materials and the color wheel. There are lots of whites. Learning which is which just requires experience. Whites can tint all around the color wheel, just like any other color. Generally most colors tend to skew towards the warm or cool side of the spectrum and having the understanding of what causes this and what colors to use in the adjustment process again is just having a clue about what you're doing. This is one reason gelcoat jobs in the driveway just don't work out well. Most folks haven't a faint idea about color, especially the very subtle manipulation of the whites.
     
  6. TANSL
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    TANSL Senior Member

    Excuse me, sir, whites manipulation is more difficult than that of the Green, and why?.
     
  7. PAR
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    PAR Yacht Designer/Builder

    Whites can be much more subtle then the secondaries (like greens), mostly because the secondaries become something else pretty quickly once you start adding to them. Whites and blacks can take a great deal of manipulation, before they become something else, such as an ivory, pink or a purple. Primaries are less sensitive to manipulation than the secondaries, but they too tend to become something else pretty quickly compared to whites and black. Why - well this is just the way your eye works when perceiving colors. Your brain permits subtle changes in whites and blacks, while accepting them as remaining a white or black, more so then colors. If you add a touch of blue to a green, you eye sees teal, but add the same amount of blue to a white and you eye still sees a white, just a "cooler" version. Simply put with whites and blacks you mind's eye accepts a much larger color gradient, before it calls the new color something other then a white or black. It's just the way it is and a pro may not understand why this occurs, but does recognize what is necessary to make it occur, which is what a client pays for.
     
  8. TANSL
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    TANSL Senior Member

    I see that is a very subjective question that can not be explained properly because the same procedures, as that, not worth for two different subjects.
    Anyway, speaking of "secondary" colors, the white color is the most "secondary" of all.
     
  9. michael pierzga
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    michael pierzga Senior Member

    How does the colour sensing machine work ?

    The gelcoat guy brings a portable machine to the boat and with a sensor records the colour so that the mixing machine can compile the correct colour shade
     
  10. TANSL
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    TANSL Senior Member

    Exactly, that is the solution. A little expensive but it is perfect, at least more reliable than what my eye, untrained in the science of colors, can appreciate.
     
  11. PAR
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    PAR Yacht Designer/Builder

    The eye is more sensitive than a machine, which is called a called photometer (spectrophotometer) BTW and in this regard and the eye is the ultimate decision maker too. I don't know of a single gelcoater or painter that uses equipment like this. Even if you do use a color scanner, most of the time you still have to fine tune the color by eye.

    White is not a secondary color, nor is black. Orange, green and purple are secondary colors. Red, yellow and blue are the primaries. There's nothing subjective about color or mixing color, unless trying to define what a real ivory might be, which could be subjective, but is also only a name. Mixing to match is just an eyeball thing and you either know how to do it, or you learn or pay someone that already does. It's not especially difficult, though as you learn, you'll make a lot of bad batches.
     
  12. TANSL
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    TANSL Senior Member

    Since I do not know anything about colors and how they are measured, I searched Wikipedia information about it and, from what I understand, the "spectrophotometer" is not used, or anything, for what you say. I may misunderstand and therefore I'm wrong.
    Identifying the color has a lot to do with the RAL code colors, which is what the professionals use to identify a color. Do you know what that is?.
    The primary colors, I think, are those who have no mixture of any other color. Colors "secondary" are obtained by mixing in varying proportions of the primaries. According to this, White is the most secondary of all colors.
    Cheers
     
  13. michael pierzga
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    michael pierzga Senior Member

    Nothing wrong with eyeballing. But custom mixed gelcoat is one Kg minimum purchase.

    A Bad guess is expensive.
    And since you cant bring a 25 meter boat up to the shop for examination field guess work is used.

    How this colour machine works is a mystery to me. i will ask the gelcoat guy whats up
     
  14. SukiSolo
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    SukiSolo Senior Member

    A lot of my repairs are very small, maybe the ding off a screw on a jetty, sometimes a T bone on the water. Hardly worth getting a photometer!.
    Fortunately the local chandler/repairer and myself are pretty good at getting the colours by eye. 1.5 gm of gelcoat isn't going to whet any manufacturers appetites. Add up the repairs on a boat , say 4-10 areas and its worth doing.

    In fact I'm mixing him a batch of Laser grey as strangely Laser can't supply it here in the UK, courtesy of some 'Torch' thing.....:D

    However occassionally I do get largish areas and usually mix a small test batch first to check the clour. Hardest thing is getting the match absolutely exact because the gloss off the new gel is slightly different from the gloss of the surface to be repaired. Just an effect from the liquidity of the fresh gel, also different gelcaot manufacturers seem to have different tint 'clear' gels!.

    Fun one recently was a 2.4 meter which leaked. Could not find leak but it went down to Poole got hoisted and godawful 'patch' ws found under centre of keel. Find that, when it is on its trolley!.
     

  15. PAR
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    PAR Yacht Designer/Builder

    That's the ticket, you do a test patch and zero it in. Blending in large areas is tough, but there are tricks to knock down the gloss or bring up the old areas to a similar shine. If I'm asked to do a large area, I'll usually insist on doing the whole side, from rail to chine crease or across a full transom, etc.
     
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