BONDO: Any Way To Lengthen Set-Up Time ?

Hello:
Have been playing for the first time with with BONDO to fill in some siding cracks.
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 ?
Thanks, Bob
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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 ;-).
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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.

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I have seen the same thing with mortar and grout, or was it my imagination?

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not the water is pressed out. It is not really setting just loosing the water.
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 tip.
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wrote:

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 done.
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.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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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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Hello:
Justg a quick thanks for all the help.
Bob --------------------

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