polyester 'bondo' filler and west epoxy...

Discussion in 'Fiberglass and Composite Boat Building' started by firepiper, Sep 4, 2007.

  1. firepiper
    Joined: Aug 2006
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    firepiper Junior Member

    can I use polyester filler to fair between coats of west epoxy? I was kinda sloppy while doing a transom repair and now have some pretty good fairing work to do. The filler is just easier and quicker than thickening the epoxy. thanks
     
  2. Capt. Chris
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    Capt. Chris Junior Member

    I would not use a polyester over epoxy. You will have bonding issues for sure. Mix west 410 fairing compound with their epoxy then coat (roll) the repair with clear epoxy. It's always best to stick with epoxy on top of polyesters, never poly over epoxy. I know the drying times are much longer with epoxy but that's the only downside besides the expense. Don't forget to scrub down the cured epoxy to remove the amine blush. This blush if not removed will also give you bonding problems. Good luck. Chris
     
  3. alan white
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    alan white Senior Member

    I agree with Chris. 410 microlight uses so little resin anyway that cost isn't a big issue using epoxy. You'd be amazed how much fairing compound a small amount of epoxy can make. The cost is in the fairing compound, which you have to use anyway, no matter which resin.
    Fast-cure hardeners will speed up the cure time, but one must be careful using those hardeners with microlight, as the mix is so light for its volume, it heats up prematurely in the pot just because the catylizing heat can't escape fast enough. Experiment.

    Alan
     
  4. PAR
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    PAR Yacht Designer/Builder

    I'll ditto the micro balloons instead of bondo (which doesn't stick well to epoxy, absorbs moisture and will shake out from vibration). Add a touch of silica or micro fibers to the mixture AFTER you have mixed in the balloons, which will stiffen the mixture enough to keep it from sagging on vertical and overhead surfaces. An easy way to keep the heat down to a minimum is to do your finial mixing on a large smooth, flat, surface, like a piece of glass, plastic Tupperware lid, etc. This keeps the "mass" of the thickened epoxy to a minimum in any location, which staves off the heat build up. I mean really spread it out, like over a 2' square area of the mixing board. This works very well and permits you to skim off just what you need in neat, controllable amounts. If you don't have a stiffening agent (silica, micro fibers, etc.) then you can substitute regular old flour. Yep, the stuff your mom used to make bread and pies. Sift it real good and use sparingly, AFTER the balloons have been well mixed in. This mixture will sand nearly as easily as Bondo, holds a better edge and sticks to the work.
     
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  5. Jimbo1490
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    Jimbo1490 Senior Member

    Let me provide a bit of counterpoint. There are good marine duty fillers on the market which are based on polyester resin that are promoted for benzoyl peroxide cream hardener. When you say 'bondo', I hope that is what you mean and not auto body filler, which has no proper use on a boat hull. You could use one of these marine duty 'bondo' type products and they do work over cured epoxy substrates provided that you provide sufficient 'key' for adhesion either by thoroughly sanding with 36-80 grit sandpaper sandpaper OR by applying a woven release fabric over the uncured epoxy layup. This latter method is the best way since it may prove difficult to sand down into every little low spot before applying the filler. If you did not uses a woven release when you layed up the epoxy, then you are stuck with sanding. Remember that it's the low spots where the filler will live; these are the places that really must have good key for adhesion. Polyester resin has very poor adhesion without mechanical key. Epoxy, OTOH will still stick. It would probably stick much better with key, but the adhesion will probably be quite adequate even without carefully abrading every square inch. For this reason, epoxy is probably the best way to go.

    If you will be doing a LOT of fairing, the thickened epoxy may actually be faster to apply as well since you can mix a much larger batch and hit all the low spots at once. One thing nobody mentioned is to mix in some talcum powder with the thickeners. This will make the filler spread nice like bondo and sand easier once cured. You don't have to buy 'industrial' talc, just get plain old baby powder. Check the ingredients and make sure you get one that's just talc and fragrance, no corn starch, aloe vera, etc. The fragrance will make it smell nice when you sand it, too :D
     
  6. lewisboats
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    lewisboats Obsessed Member

    Talc is a rock...it doesn't sand that easy (from experience).

    Steve
     
  7. Jimbo1490
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    Jimbo1490 Senior Member

    Yes, talc is a mineral (magnesium silicate) but so is glass (silicon dioxide) which is often used as microballoons. The hardness of either mineral is dependent more on the form of the the mineral that is being considered. Talc is composed of little flakes that tend to line up together and lay flat when spread with a paddle or squeegee. Every commercial filler out there is formulated with talc because it improves both spreading and sandability. Can all those formulators be wrong?

    Jimbo
     
  8. mydauphin
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    mydauphin Senior Member

    I mix many thing with epoxy to generate different consistencies and control costs. My favorite is dust from my sander either polyster or epoxy with a liquid mix. I also add a little color talc to make it easier to work with. Just remember to mix A and B first then what ever powrder you want to add strength, or easy of sanding or abrasion, etc...
     
  9. Jimbo1490
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    Jimbo1490 Senior Member

    A quick look at the MSD sheet for Awl-Fair shows that it is "10-25%" talc by weight. Here's an idea: Why don't you write in to Akzo-Nobel and tell them how wrong they are to put that much talc in Awl-Fair since it is, by your experience, ruining its sandability :D :D :D :D

    Jimbo
     
  10. fiberglass jack
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    fiberglass jack Senior Member

    did you use the smooth or rough side of the sandpaper, :D :D :D
     
  11. Pericles
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    Pericles Senior Member

    Spread on the fairing coat and then lay on a sheet of polyester film and roll it flat. Allow resin to dry and peel off the polyester film, to reveal a beautifully smooth surface. This, of course, proves that polyester will not stick to epoxy, which I believe was your question.

    http://duckworksmagazine.com/03/r/articles/glass/bottom.htm

    Polyester Film
    A clear plastic release film supplied on a roll 92cm wide. Suitable for covering flat surfaces. Resin will not react with this surface, unlike polythene, which will wrinkle.

    http://www.cfsnet.co.uk/acatalog/CFS_Catalogue__Polyester_Film_87.html

    Fairing? You'd have to be crazy to want to do fairing. :D :D :D :D


    Pericles
     
  12. northerncat
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    northerncat Senior Member

    ill second the talc is a rock quote and reiterate dont go there,(unless you can sand it all 4 hrs after putting it on while its nice and soft) this is also from experience also the glass spheres are hollow so whereas the talc is still a rock
    sean
     
  13. PAR
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    PAR Yacht Designer/Builder

    To settle this debate, Jimbo is correct in that most all fillers use talc, but usually not a very high percentage. If used with a high percentage, it becomes progressively more difficult to sand (based on percentage) and this can be attributed to its density, which is why it's effective in filler mixtures in small percentages. This is why I always mix the light weight materials in first (balloons, etc.) to get the "bulking agent" mixed to the amount I want, then I add a "thickening agent" (talc and other materials) to control the sagging or running tendency. There are lots of things you can use to bulk or thicken up goo. Filler mixtures can be engineered as heavily as laminates or you can use the general rules of thumb, as most do. For the average repair or build, the general guides work very well, usually offering much more strength or sandability then usually necessary (once the user is experienced). For light weight and/or highly stressed elements, careful selection and application of fillers can save substantial weight, which in some boats may mean the difference between being middle of the pack or front of the fleet. Cost is also an issue on larger projects. If you can reduce the filler needs and maintain the strength/weight requirements of the build, then considerable savings can be included both in labor and materials.
     
  14. Jimbo1490
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    Jimbo1490 Senior Member

    Yes but it just happens to be the softest rock yet classified, which is soapstone, AKA welder's chalk. I usually add about 10% after adding my other fillers. It does make a big difference in the spreadability; it spreads more like bondo or peanut butter and reduces sagging more than other fillers. With microballons only, the filler tends to 'brreak up' when tapered out during spreading, especially with a very dry mixture. Talc reduces this tendency a lot, so you can make very dry mixtures and still successfully apply them.

    Jimbo
     

  15. lewisboats
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    lewisboats Obsessed Member

    See now... there was my problem. I was at NG summer camp and brought my boat to do some finishing. I forgot my fillers...or they blew out the back of the p/u...and needed something to fill. I used pure talc baby powder as the sole thickener. As stated before...it was tough to sand.

    Steve
     
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