I have to fill some rotted areas in the exterior frame of some windows. I
already have some latex exterior putty which I can build up in layers. The
areas in question are about as wide as a pencil and maybe twice that deep.
I've heard that some people use Bondo for these situations. Is there a good
reason to prefer that product?
I've used Bondo several times before, for exactly the purpose you're
proposing, and it's worked well. I always used an oil-based primer on it. No
idea if a latex primer would work or not, but it sure oughta be primed with
Bondo is talc (and other minerals) added to *polyester resin*, not putty.
It cures when a catalyst is added. When cured it is reasonably hard but not
as hard as plain polyester resin or polyester resin with cab-o-sil. Talc in
rock form is about as impervious as you can get, shouldn't be much different
in powder form; polyester resin isn't affected by water.
I'm not sure the definition of "putty" as used here, but the Bondo I am
familar with is a 2-part epoxy product. I never getting long enough setting
time but I've used it to repair dry rot after digging out the infected area
and treating with a borax solution.
I disagree....Bondo is a polyester resin NOT an epoxy.
Epoxy is a better material & more expensive than Bondo.
For interior repairs, Bondo is fine, for exterior Bondo is "ok" except
If you want an exterior repait to last use an epxoy ........like
WoodEpox or LiquidWood from www. abatron.com
". . .(although, I am not a chemst). . ."
I am. Bondo is an unsaturated polyester resin which "sets" through
the action of a peroxide hardener.
Misc stuff: -Reduce the peroxide level to slow the cure down and
give more working time. Test your ratio, too little peroxide may
not produce a complete cure.
-Good epoxy beats good polyester when exposed to
weather. However, in this application, the wood will go first.
You must measure the two parts correctly. Proportioning errors can
produce degraded epoxy.
-Good epoxy costs more and can cause allergic
-I used painted Bondo ifor a rotted wood repair
at my daughter's house in Tampa. Looks good after 4 years.
It works great on interior apps, exterior as well but NOT good on
I've had Bondo fail miserably on redwood window sills.
The Bondo repairs are were primed & painted with very good oil based
The repair failed in less than a year.
I called Bondo tech rep & got the comment "we don't recommend it for
use on redwood".
After that I switched to epoxy (www.abatron.com) for all exterior wood
here's the best comparison I could find
You don't need layers with either polyester or epoxy "putties". Best to
overfill slightly and cut off most of excess with a chisel after it has set
but still not really hard. Sand smooth when fully cured. OR - just over
fill and sand flush.
The nice thing about Bondo (polyester putty) is that you can control the set
time to a degree. Even setting slowly it is *much* faster (minutes) than
epoxies (overnight); additionally, it doesn't blush amines like epoxy nor
does it degrade under UV like epoxy.
With either, you need to *thoroughly* mix the resin with the catalyst. With
Bondo, the colored "cream" hardners are easier to use than liquid as the
color tells you visually how well they are mixed.
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