Slowing Poly Cure Time

[Mark42]

I want to slow the poly cure time to get another 5 or 10 minutes working time. Did some searching in this forum and found this thread that addressed slowing cure time:

http://forums.iboats.com/showthread.php?t=219539

My question is how much to adjust the hardener for about 30% increase in cure time?

Using Bondo (3M) brand resin with a working time of about 12 minutes. The mix ratio is 0.37 oz hardener to 29 oz resin. That makes a ratio of 1.2% (0.37 / 29 = 0.012). To get another 10 minutes cure time at "room temperature" should the ratio be changed to about 1%?

I see where ondarvr said not to go below 1.2% due to strength loss, but in this application, strength is not a big issue, and neither is water proofing. I'm working on the windshield frames, which are above the water line, and will be painted. Any extra strength added to the plywood is a plus.

I usually speed up cure time, not slow it down.

Any advice is appreciated!

Mark

 

[ondarvr]

Re: Slowing Poly Cure Time

You can drop it to 1.0 or .9 and if you mix it very well you'll be fine, but it may not give you an extra 10 minutes.

You're at the mercy of the exact resin supplied for this purchase when buying retail. Retail resin outlets and companies may change the resin supplier without notice and what you get may be different than the last time it was purchased, so the resin may have significantly different characteristics. Plus it can be difficult to make a big swing in gel time only using catalyst ratio changes. If you can keep it cool, the times will be extended a great deal, for every 15 degrees below 77F it will almost double the gel time and when you increase the temp it will cut in half the gel time for every 15*F.

 

[Mark42]

Re: Slowing Poly Cure Time

Yeah, thats what I get for not ordering exactly what I want from a online supplier. But I wanted to get to glassing those windshield frames today, and didn't want to order a gallon or so of resin, pay shipping, etc when I had a some resin left from making emblems. So I picked up another 29oz of the same bondo stuff figuring it would work fine. Then this morning, I realize I don't even know if this resin has wax in it or not! It doesn't say on the can, but I remember it always curing a little tacky, so I think not.

See what happens when I rush? I forget the details! LOL!

 

[lowkee]

Re: Slowing Poly Cure Time

Would putting it in the fridge for a ~20 minutes give you the extra time you need without messing with more/less hardener?

 

[drewmitch44]

Re: Slowing Poly Cure Time

I have done the refrigerator trick and it worked out pretty good. I would keep the resin in my mixing container in frige until i was just ready to wet out the glass and rush it out of the house and apply. In the middle of the summer it seems like that is the only way to do anything when its 100+ degrees outside. Keep the resin cold and mix the hardner cold with it and you get a lot more working time. I had a little college dorm frige that i kept in my shed last summer for just this purpose. I kept the resin at 36 degrees so that way is was pretty cold.

 

[Mark42]

Re: Slowing Poly Cure Time

That may be the better idea! Think I'll give it a try. I have to wait for the glue to fully cure before glassing over it, so there is some time to let the resin cool in the fridge.