Adding some weight and thickness to reproduced fg part

Discussion in 'Materials' started by swade, Jun 13, 2010.

  1. swade
    Joined: Jun 2010
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    Location: apollo beach,fl

    swade Senior Member

    Hi All!, New here!, I have a small project I need some advice on. I have a small project boat and had to reproduce a part that is no longer available. It's just a bulbish looking hatch that covers a porta potty area. it's probably around 24x24 hinged on one side with a gas strut that holds it open then a windscreen mounts on top.

    Anyways I somehow miraculously muddled through after a few mistakes making a form and glassing it and it fits really good. It's resin with 3 layers of 1.5 oz mat at this point from my first layup.

    The 3 layers is pretty solid right now but you could still flex some if you wanted to which I would guess could crack the qcell fairing or gelcoat once I get it on. So I was just going to add a few more layers on the backside (which can be unfinished) but I'm wondering if I should do something with some cabosil to add some heft or maybe use resin, chopped strand and cabosil in a mix and just get it on in a thick layer.

    This is an original one:

    http://www.flickr.com/photos/32698314@N05/4695342152/

    What would be a good easy way to add some heft and thickness on this unfinished side to the 3 layers i have now

    Thanks for any help!

    shannon
     
  2. Herman
    Joined: Oct 2004
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    Herman Senior Member

    For weight: Just keep on rolling with glass. Cabosil will not help you with that.

    For thickness: use some bulker mat (Coremat) and put another layer or 2 of glass over that.

    The latter will make a lighter and stiffer product, generally.
     
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  3. swade
    Joined: Jun 2010
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    swade Senior Member

    Hi, Thanks for the info! ok i'll just add a few more layers of glass that sounds like that will work without driving a ways to find some coremat.

    Can I use regular primer as a guide coat when i go to fair out the topside or will it interfere with gelcoat?
     
  4. apex1

    apex1 Guest

    Coremat is easy to have everywhere they sell glassfibre, but to build up beef another layer of mat or fabric does it.

    Did you apply gelcoat already? It is absolutely not necessary.
    Primer, filler, sand and paint (the last two positions probably more than once), thats it.
    In case you have a gelcoat, NO it will not interfere, gelcoat is basically just poly resin and pigment.

    Regards
    Richard
     
  5. swade
    Joined: Jun 2010
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    swade Senior Member

    Hi Richard,

    No it's not gelcoatted or painted yet, the top is just the fiberglass from laying up over the form. I did add an initial filler layer today to the top (resin, qcell & a bit of cabosil). So next on that side is to do another filler layer to fill in low spots,etc and get everything smoothed out, so I was wondering if a special primer was needed to act as a guide coat so i could see any dips,etc from the sanding board (though most of it would get sanded off) or if any ol primer from home depot,etc would work.

    After that's smooth i'll work out the details of gelcoat or paint, just happy to have made it this far =)
     
  6. swade
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    swade Senior Member

    Hi Richard, Not sure what advice I'm not following?, the first question was about filling the back side with some thickness & weight, coremat sounds fine but the glass supply is an hour away, the advice to keep adding glass layers sounded as an acceptable alternative for this parts purpose. I followed that advice and am adding additional glass layers to the back.

    Perhaps i shouldn't have asked two questions in one topic..I think that is where the confusion lies. I understood hermans response that for strengthening the back the cabosil added nothing, I was hoping to get away with a just mixing some kind of thick stuff up and slathering it back there since it can look unfinished, but see I should add more glass layers.

    But the cabosil you seem to be responding too was mentioned in the context of finishing/filling/fairing the outside. The advice from the fiberglass supply was to add some cabosil into the resin mix to create fairing filler, i couldn't really sand that at all with all of these curves..it was like sanding concrete.

    Through googling I switched to some generic qcell obtained from a boat supply house. The qcell sands like i need but I had read a few docs which advised adding some cabsil (but the majority qcell) so the resin wouldn't run on vertical surfaces. qcell alone seems to thicken it up enough for my needs though incidentally.

    So that 2nd question was about fairing/filling the outside unfinished surface and if i needed to use a special primer to act as a guide coat to spot dips when sanding.

    I understand my project is simple for this sites main topic =) before posting i did a search for simpler topics like mine and saw there was discussion so figured it was ok, but perhaps it's not?
     
  7. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    Apex quote..... "I am, to remain humble, the one who produces more boats per annum than all the rest of the forum members accumulated."

    ...interesting indeed....
     
  8. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    Statistics can be interesting & as "one" may be diluting the achievements & contributions of others. All the best in your endeavours from Jeff.
     
  9. apex1

    apex1 Guest


    Sorry when my comment was too sharp. It was not my intention to insult.

    I understand that you have made the hatch in a female mould, is that right? Then you have a relatively smooth surface already, right? In that case a spray on filler would be sufficient and that would be easy to sand.

    Or did I misunderstand?

    Regards
    Richard
     
  10. Frosty

    Frosty Previous Member

    No its probably true and paid his cheap labour in Turkey less than one of the other builders.


    Oh sorry my words are harsh but I wont delete, I will just apologize a little bit.


    Please get it with a grain of salt.
     
  11. swade
    Joined: Jun 2010
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    swade Senior Member

    no it is from a form i had to make as original wasn't available nor did i have a suitable one for a mold. From some additional googling seems graphite power works fine (or rattle can if it's light dusting and sanded off) so I'll go that route.
     
  12. apex1

    apex1 Guest

    Graphite powder makes a relatively hard surface (and it becomes el. conductive). Paint (or primer) will not stick so good on it. Therefore I would not recommend that.

    But why not just primer, filler, paint? Is the surface too rough or uneven?

    Regards
    Richard
     
  13. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    Swade, a rattle can is often used, a guide coat really helps you from getting "snowblind" whilst fairing, even a crosshatch of pencil will do for a small area. When you apply gelcoat to a part as a coating you will need to add some wax in styrene solution to it so it can cure non tacky, then it is generally known as flow coat- it can be bought as such too. All the best from Jeff.
     
  14. swade
    Joined: Jun 2010
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    swade Senior Member

    Thanks all for the tips! helps greatly.
     

  15. Herman
    Joined: Oct 2004
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    Herman Senior Member

    Havent read this thread for a while:

    For the backside: You wanted extra strength / stiffness, and extra weight. As glass is heavier then resin, using a glass resin mixture is better then a glass/aerosil mixture (cabosil=aerosil=silica). Of course you get extra strength as a bonus.
    If you wanted to greatly improve stiffness, you should go for extra thickness, and a piece of coremat helps in that. Just do cover it with another layer or 2 of glass and resin, as to form a sandwich construction.

    On the exterior you do want a nice and smooth finish, and I understood you have not decided which route to follow:

    -1. Primer and paint

    -2. Gelcoat (topcoat) and buffing

    Option 1 has the advantage that it is quite easy to do, does not need an awful lot of sanding, and the last coat, if done well, gives good gloss.
    As a guide coat you could use about anything, like carbon powder (3M has nice sets for that), pencil hatchings (works nicely on wood as well) or a mist coat of acrylic paint from a spraycan.
    A filler can be made from resin and Q-Cell, indeed with a touch of Aerosil, if needed. Make sure you use a good course sandpaper when fairing up. With too fine sandpaper you will have a hard time getting things nice and fair.
    Using 100% Aerosil is a pig to sand. WAY too hard. Everyone seems to make that mistake only once. (I did...)
    When everything is nice and fair, just follow the route that your paint supplier describes, usually primer, filler (perhaps 2 coats) and paint (usually 2 coats).

    Option 2:
    When everyting is fair, spray or brush the part with parafinated gelcoat (topcoat). Do this as nice and smoothly as possible. After cure, wet sand until fair, buff and polish. Sounds easy, but is a hell of a job. You risk sanding though the layer of gelcoat, in which case that areas needs to be recoated, and overall it is quite some work. Some people rely on this, however.

    Have fun!

    About a 1 hour drive: No polyester shop in your area? Perhaps a small repair shop, a car tuner, pond manufacturer, etc.
     
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