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Thread: Bondo, but which kind?

  1. #1
    Senior Member John Y.'s Avatar
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    Bondo, but which kind?

    I want to refinish a cabinet that I will paint, so the filler I use does not have to match color. I have heard that Bondo is what I need, but there are many varieties, from the grey stuff you see on cars to the home filler material that I saw in a hardware store.

    What is best for filling in nicked corners and small areas of the plywood missing veneer adjacent to the edges? Need to have the Bondo able to form a corner, again in small areas.

    Appreciate your help. Thanks.

    John Y.

  2. #2
    Senior Member Steve's Avatar
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    Aloha John

    What you need is the bondo that has fiberglass fibers in it. It is usually a dark blue color. There are 2 types.... short and long fibers. Use the short fibers bondo. A gallon can at an auto store will run around $25US. There are quart cans available also. Some hardware stores have bondo in the paint dept. Home Depot over here has qts. of the fiberglass bondo.

    Some helpful hints.
    When mixed properly, the work time is around 3-5 minutes. It is exothermic, so the bondo will get warm when setting.

    For edges, I use 2 pieces of wood to make a form for the bondo to make it easier. Have the jig ready if using one. Add another piece of wood for a corner. I sometimes make a corner form to place over the damaged corner to set the bondo.

    Wrap the wood in wax paper, bondo doesn't stick to it. I sometimes will apply the bondo, then put on wax paper and thensmooth the surface of the bondo.

    If the hole is big, screw in some small screws in it to increase the adhesion of the bondo.
    Wood needs to be clean. No dust, dirt, oils, paint etc.

    Mix small amounts to start with. So one doesn't rush to apply the rest before it starts to harden.

    Applying just a little bit more than is needed is best.

    Use a " cheese grater" rasp or to cut down the exess bondo just before it hardens fully, but not before it starts to set. Otherwise it will be a mess and the bondo will pull out of the hole.
    If you do use the cheese grater, apply duct tape on areas next to the holes so as not to scratch.

    If you are careful and apply neatly and such....
    Sanding after hardening will be sufficient.

    Use a piece of glass to mix the bonco on. Easier clean up. Acetone works to clean tools, hands etc. MIX the bondo COMPLETELY with the hardner.

    I use a metal spatula, 3" to mix and apply. Just before it sets up, I use a razor blade to clean my spatula.... comes off easier. Another 10 min. and it cleaning will be with a wire brush or sander.

    The bondo will take around 5 to 30 min. to harden depending on hardener used and temp. of room etc.

    After hard, sanding can be done. It will be a lot harder than most woods, so be careful as too grit of paper, pressure and such.

    After sanding, exam and reapply if necessary.
    Prime before finish coat is a must.
    There are several different grades of Bondo.
    I like this one as it is tougher.
    I use it alot on remodles, ie... replacing door know on front door with one that doesn't cover hole... Fill hole with bondo and then re-drill etc.
    Termite damage etc.

    Of course use a dust mask when sanding and ventilation when mixing.

    Yes it is very durable....and when set it is part of the wood.

    If they are real small dents or holes, using the other bondo is fine and it is a little less hard. I haven't used the lightweight bondo on wood.

    PM me is you need more info.

    It is very easy.

    Steve

  3. #3
    Administrator Mr. Widget's Avatar
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    I would add to Steve's thorough and helpful guidance, that when using the "cheese grater" you need to do it as soon as the bondo is solid but before it is fully hard. It will still have a sheen to it. It gets more matte as it cures. This stage requires experience, bondo is cheap so experiment on a scrap of wood. If you attempt to carve it too soon the bondo will release from the wood, if you wait too long it becomes very hard and you will be sanding for a long time. I would recommend that you get some very coarse sand paper to start with and use progressively finer grits. I start with 60 or 80 and finish with 320- 600 depending on the finish desired.

    I am not fan of the fiberglass reinforced bondo as it doesn't finish quite as nicely as regular bondo and they both seem to be equally robust. Regular generic bondo from an auto body supply shop is about $12 a gallon.

    In addition if you need a finer finish do not use spot putty. All of the spot putties that are in tubes and are air dry will shrink with time. I use a catalyzed glazing putty from Evercoat. It is essentially a finer grade of bondo. It isn't as good for large gap filling but it is harder and will hold an edge better than standard auto body filler (Bondo is a brand name for auto body filler).

    A dust mask is good if you are outdoors, if you are inside a carbon filtered respirator would be best.

    Widget

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    RIP 2011 Zilch's Avatar
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    See also:

    Abatron WoodEpox

    Not as cheap, 2-year shelf life, but easier to finish.

    60-minute pot life after mixing....
    Last edited by Zilch; 07-24-2004 at 05:36 PM.

  5. #5
    Senior Member John Y.'s Avatar
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    My thanks to all for the quick and erudite replies. I am overwhelmed with the info. Upon consideration, and a further look at the damaged cabinet, I believe that effective repairs can be made by re-veneering the small patch strips on the edges and corners and filling in the small crevases with, maybe, the lighter Bondo product. I am sure that I may have overstated the severity of the defects. I need ounces, not gallons of filler.

    Mr. Widget, I understand that you are in the model building business. Do you remember a product that was called Durotite Surfacing Putty? I remember it being used on wind tunnel test models in the '50s. It dried quite hard and did not shrink. The same company produced a "Wood Dough" which, while great for household use, was soft and shrank. This may be the current DAP product. What happened to Durotite, and what do they use to fill gaps and screw holes in the wind tunnel these days?

    I shall file away the very helpful hints on Bondo for future need. Thanks.

    John Y.

  6. #6
    Administrator Mr. Widget's Avatar
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    Originally posted by John Y.


    Mr. Widget, I understand that you are in the model building business. Do you remember a product that was called Durotite Surfacing Putty? I remember it being used on wind tunnel test models in the '50s. It dried quite hard and did not shrink. The same company produced a "Wood Dough" which, while great for household use, was soft and shrank. This may be the current DAP product. What happened to Durotite, and what do they use to fill gaps and screw holes in the wind tunnel these days?

    Durotite sounds familiar, but I can't place it. Maybe you are thinking about Durham's Water Putty? It is a powder that you mix with water and it makes a putty that is fairly nice to work with, tenacious as hell, sands and finishes well, is very hard when cured, and shrinks very little. I usually use bondo as I don't want to wait for drying. I can work the bondo in 15 min.

    Any of the air dry fillers will shrink as the water or solvent evaporates. Another nice feature of Durham's Water Putty is that it doesn't have the toxic fumes that most of the products I use have.

    Widget

  7. #7
    Senior Member John Y.'s Avatar
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    Mr. Widget,
    I am sure the product I have in mind was Durotite. It was really good. Applied like you would use spackle or "mud", it could be smoothed with a putty knife, shrank an undetectible amount, and dried to a hard , sandable surface. It was ready mixed in a small can, which was good, because, once opened, it did not last very long without hardening. Guess it's no longer available. Can't find anything on Google.

    I will keep my mind open on the Durham's putty, although I think I will go with the Bondo product, especially if I can get it in a small quantity. Thanks.

    John Y.

  8. #8
    Your Memory Lives On RIP Tom Loizeaux's Avatar
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    For the cabinet restoration on my JBL studio monitors I used a 2-part epoxy wood putty. It comes in a plastic tube where you simply pull of as much as you need, remove the seperator, mash it together well and push it into the damaged areas. What's especially nice about this stuff is that you can smooth it with a wet putty knife and give the area a very smooth, glass-like surface. Once it gets warm and starts to set-up, it can no longer be molded. It can be sanded and painted with great results. This stuff can be found at better, pro wood supply shops.
    This may be similar to Bondo, but this stuff is made for wood cabinet repair.
    I'd give the exact name, except I'm posting this from out of town so I can't go and look it up until tomorrow.

    Tom

  9. #9
    Senior Member John Y.'s Avatar
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    Tom,

    Sounds good. I would like to have the name when you get the chance to find out. Thanks.

    John Y.

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