Wood Bondo?

Several years ago, a repair guy took care of a small area of rotted wood on an exterior window sill by gouging out the rotted area and filling with some sort of bondo-like wood filler. It seems to have held up pretty well. Any idea what the stuff is called and where it is available?
Thanks in advance . . .
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It may have been.
Several package it marketed for wood w/ tan/brown catalyst instead of the typical blue/green for automotive -- Minwax brand is one usually readily available. (It doesn't indicate what it is on the label, but when I last checked it shared MSDS data w/ the Bondo-products which is pretty much a clue... :) ).
If you do use an automotive filler (much cheaper, generally), choose one w/o the fiberglass as it may tend to "fluff" more and leave a raised grain effect that's more effort to eliminate.
--
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Bondo. Same as used on cars.
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Most box stores have the MinWax kits. They consist of a penetrating 'hardener' which is simply a high solids lacquer, and ordinary Bondo. For small jobs, it is pricey but effective and in my experience, pretty durable. You could probably the get same results with an oil base polyurethane varnish allowed to soak well into the wood and allowed to cure, then built up with standard Bondo. Use whatever filler hardener seems appropriate, red, white, or clear. Best selection will be found at auto body supply stores, Farm and Fleet, and similar outlets. Study up a bit on autobody filler tools and techniques if you have any large fussy detailed areas to repair.
Joe
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I've used regular Bondo on wood many times. As long as your are going to paint it the color shouldn't matter too much.
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As everyone has mentioned......Bondo can be used successfully for wood repair.
BUT I used a Bondo on exterior redwood sills ~20 years ago and it FAILED in less than a year! I used Bondo instead of an epxoy based wood filler (Bondo was about 1/3 or 1/4 the price of the epoxy product"
I called Bondo tech support & asked them about this.......the tech rep said "we do not recommend Bondo for the repair of redwood in exterior situtations".
To which I replied "I guess I missed that warning on the label".
I switched to www.Abatron.com products; Liquid Wood & Wood Epox. Expensive stuff but bullet proof. Needs to be painted to protect from UV but I have some 20year+ WoodEpox that I shoved into holes in a sttuco'd wall that get morning sun for about 2 hours. The stuff has been unpainted & has held up very well.
The Abatron products that I have used have excellent performance......I used then 20 years ago & again 2 years ago (to do some addtional work, not re-work).
I wood use Bondo for interior work without a second thought BUT I would never use it again on exterior work. YMMV.
The stuff is a lot more $'s than Bondo.
cheers Bob
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Bondo works just fine on cars, even those that are used outdoors >G<

Epoxy resins are simply more $$ than polyester resins. The characteristic odor of uncured Bondo is from styrene, a reactive diluent which makes the product even less $$. So buy whichever system does what you really need.
Joe
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Yes, Joe...Bondo works fine on cars......even those used outdoors, just not cars made of redwood (what other woods?)
According the Bondo tech support, Bondo (at least the formulation sold 20 years ago) is not for use on redwood in exterior apps..... I wonder if there are other species of wood for which Bondo is also "not recommended".
The take away message from Bondo tech support was "Bondo is not good for exterior use with redwood".
I extrapolated it to.....I don't risk using Bondo for exterior wood repair.
Having experienced an exterior repair (of redwood) that failed, I decided to not take that chance again......
So the only different between epoxy resin and polyester resin is cost?
cheers Bob
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No. The characteristics of the two systems are quite different. Speaking in generalities, epoxies are very low cure shrinkage, very good adhesiveness. Cure can be effected by numerous types of coreactants and catalysts. Response to fillers varies all over the place, typically 50% for a mineral filler to 90+% for zinc powder. This gives competent formulators like West and Abatron a huge palate of materials to achieve the desired properties. Consider this: the new Boeing Dreamliner is said to be all carbon fiber/epoxy. Polyesters cure by a free radical mechanism initiated usually by organic peroxides. Cure rates are often much faster than epoxies. From a resin standpoint, many of the same fillers will work with either system. The poyester resins are often better at UV resistance than epoxies, but the latter can do quite well if hardeners are chosen carefully. Rubber compounds cure by the same mechanisms as polyesters (as do vinyl resins) but have few inter chain cross links which makes them elastomeric. Bottom line here may be Bondo is good outdoors on any substrate properly prepared. Likely the world renowned Forest Products Laboratory mavens in Madison, WI would know why your redwood to Bondo interface failed. Cheers,
Joe
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Thanks for the details, I was a little worried that you were going to say that polyesters could completely replace epxoies...........
My recollection as to the Bondo tech support explanation for the Bondo / redwood failure.....the naturally occurring chemicals in the redwood prevented good adhesion and proper curing. Painted over with oil base primer & paint the Bondo cracked and failed. Hence my reluctance to use it again outdoors. Probably unjustified superstition but I never wanted to have to re-do an exterior wood restoration where Bondo failed again.
I've had great results with epoxies & I know the epoxy products will easily last decades.
Actually I had my chance to ask the FPL guys about it at a wood conference in New Orleans ~94 but I was too busy quizing them about water repellents / wood preservation and completely forgot about the Bondo disaster.
cheers Bob
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wrote:

Bondo does not last long on cars if used to repair rust holes. No matter how well the rust is removed to bare metal, bondo HOLDS MOISTURE. While the surface is painted, the rear of the bondo in the hole is exposed, and absorbs water. Thus, it rusts away the metal around it. I'd suspect that used on wood, it must be well sealed from moisture or it will cause rot.
I used some JB Weld on a rotting spot in my wooden garage door. I dug out the rot, and poured the JB weld in the hole. I applied another coat later to form the surface. It's been a permanent and durable patch, and I know it does not absorb water.
Jim
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That i sexactly what happens. The bondo lasts maybe a year or two and then falls out. You need an epoxy filler not a polyester filler like bondo.
One such product that comes to mind is www.rotdoctor.com. Usually you scrap out the rot and then use a watery "stabilizing" epoxy to penetrate deeply and solidify any rotted wood fibers. Then you use the putty like epoxy to fill the cavity.
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