Have been playing for the first time with with BONDO to fill in some siding
Boy, the stuff sure sets-up quickly; a matter of a few minutes.
Is there any way to lengthen the set-up time, without degrading any of
its other properties ?
The set-up time of bondo is controlled by two things - first, the amount of
hardner you use, and second, temperature. You can use VERY little hardner
in bondo and the product will still set-up fine. The hardner really isn't a
hardner at all. It is a catalyist which speeds the curing process. Less
catalyst = slower curing, not "won't cure". In fact, if you let bondo sit on
the shelf long enough, it'll cure without the hardner, and will have the
same properties as bondo mixed with hardner.
So, to answer your question, use far less than the recommended amount of
hardner and you'll slow the reaction. Also, the cure slows down if you mix
smaller batches, because the larger the batch is, the more it heats up. As
it heats up, it cures faster and creates a continuous cycle of getting
hotter and curing faster. It is an exothermic reaction, and can get out of
control to the point of catching fire. Spreading flaming bondo is best left
for the pro's ;-).
I found another way to speed it up -- pressure! In addition to the amount of
hardener, and the ambient temperature, put it under pressure.
I wanted to fill some holes in concrete and anchor some eye bolts into the
holes. So I mixed up some Bondo with a little hardener to extend its working
life, then packed it into a large 3/4" diameter syringe with a large tube on
the end to get it down into the hole drilled in the concrete. All went fine
untill I pressed onto the plunger to get the Bondo to inject into the hole.
The moment that I applied pressure to the plunger the Bondo instantly set up
into a solid lump. I got nothing out the tube. I was able to push a nail up
the outlet tube and remove the Bondo in one solid piece.
not the water is pressed out. It is not really setting just loosing the
FYI they make caulk tubes for setting anchor bolts. The tube has 2 section.
The nozzles have a spiral center. When you squeeze the trigger the two parts
mix together by swirling in the nozzle and totaling mixed as it leaves the
Sure -- mix in the correct amount of hardener. If it sets in a few minutes,
you're using too much.
Set time also varies with temperature -- the hotter it is, the faster it sets.
If you're storing the stuff in your garage, try storing it inside the house.
Then take it out to the garage to mix it, and bring it back inside when you're
Main problem, though, is that you're mixing in too much hardener. The easiest
way to avoid that is to buy a few of the plastic spreaders that they make for
it (you should be able to find them at the same place you bought the Bondo).
Mix in just enough hardener -- and NO MORE -- to make the mixture the same
color as the spreader. That's why they make them that color.
Doug Miller (alphageek at milmac dot com)
Just use less hardener. I like to make a round circle of bondo and then
make a smiley face on it with the hardener. That seems to be about
right for me. It does harden to a non-workable state pretty fast, no
matter what you do, so you have to be ready to go with it.
If you are using Bondo on siding, make sure to paint the heck of it.
Bondo will absorb water if left uncoated. I'm not sure what the result
is on the side of a house but on a car it causes a mess.
There is fiberglass filler that you can get that is waterproof. It's
harder to sand and work with but you don't have to worry about failure
due to water.
In your case, this news is probably too late but something to keep in
mind next time.
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