Chart for poly resin cure times vs. temp vs. MEKP?

[larboc]

Im working with bondo poly resin and I just had a 6oz mix with 55 drops go solid in about 60 seconds. Warm outside which i think is to blame, is it safe to keep going leaner with the mekp? What would happen if I added 5 drops per ounce instead of the recommended 12? just takes longer or does it never really harden like it should?

Is there a chart someplace that would give me a better idea as to how to mix for temperatures?

This is really frustrating, I've got to redo some stuff now because it hardened before I had my clamps on.

 

[Yacht Dr.]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

Hello larboc..

welp..the thing is, with poly resins being so different in manufacturing and grades, there really is no " chart " that would cover all of them. Only for "grades" of resin. Shelf life can play a factor in cure times as well..

Ill bet your going along..everything fine..then BAM ! It kicks off so fast that you dont even have time to put your brush in a soak ..

Try mixing a couple oz's with fewer drops and see what the pot life is. If that still gives you problems then find some low VOC resin. It will give you much more pot life.

YD.

 

[larboc]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

More like I'm pouring resin on both pieces I'm laminating, then all the resin in the mixing cup falls out in one piece and everything goes hard. It seemed like the stuff in the can got hard faster than what I had already poured.

I put the bondo can in the freezer to lower it's temp down and I'm going to give that a try.

At what temp does it kick without a catalyst? I had some dribble on the outside of an empty can setting in the sun kick and go hard. No chance it had hardener.

 

[Yacht Dr.]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

It wont "cure" .. it will get hard. DO NOT use just resin without MEKP.

Maybe you should go back to were you got it from and tell them the shelf life must be too old and want a replacement can.

However.. In my experience some brands .. cough.. are not worth the trouble for lams. only for filler mixes ( fast cure time ).

YD.

 

[larboc]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

It works ok if its early morning when its still under 70 degrees, but in the daytime when it's in the 90's it kicks too fast with the same amount of hardener. Thats why I was wondering if drastically reducing the amount of mekp would be ok to do if it still hardened in 10 mins or so.

 

[Yacht Dr.]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

Test whatever you change in the ratio mix before you put it to use on your boat m8..

Yes you can add less MEKP without a problem as long as it cures.

Touchy subject.. use your best judgement

YD.

 

[Mark42]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

Last month I did the recessed deck on the Hard Top project using Bondo resin because I had it on hand. Even on a 80+ degree day, I had 4-5 minute working time. I worked the larger areas with a spreader to get a quick coat down, then set the glass, then had another 6 oz ready to mix . Then mixed it and dumped it on top and worked it in. No problems.

I was working in the garage, just inside the door. I did reduce the hardener two drops per oz, to get a little more time. My guess is the resin is on the old side.

It does kick fast, but its meant for small body repairs, not large areas. So its a fast set to keep the body work going.

 

[jonesg]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

I mixed up 1/2 gal poly resin for a deck job, mixed it for about 30 seconds max and poured the whole lot out of the bucket onto the deck.

Mixing for longer than that or leaving it in the bucket spells doom.
I also scaled the catalyst way back .

Good resin such as evercoat or the stuff glassite sells includes a schedule on the can, as temp (and batch size)goes up the catalyst ratio adjusts down.
I recall the amount for a qt could be reduced from 15cc down to 11cc when temps ranged from 59F to 90F. Thats almost 30% swing in catalyst ratio.

Resin sold retail doesn't have a large batch schedule because the assumption is you're doing small job, look at the mixing tray they include, it probably holds a pint on a good day.

So if its 80f outside and you assume quarter gal of resin means add a quarter of the catalyst?, you're WAY over and if you mix thoroughly for a minute or two.... it'll pop off too fast. Mixing is friction. I look for the color change and thats it....20 seconds maybe of thorough mixing.

its simple physics...
Volume increases by the cube (x3) but surface area only increases by the square (x2) so resin mixed in a bucket is retaining and increasing in heat by a factor of 3 compared to a laminate at twice. If the direction say to mix thoroughly for 2 minutes, forget it, you ain't gonna get a big batch out of that bucket. Those directions are for half a cup.


UV resin was available before MEkp came along, it was the mekp which made poly useable at room temps, even with UV lights there were problems.

I think uncatylized resin which goes hard on the outside of the can might be lacking in cobalt which is added as a preservative and reactor, ask ondarvr.

 

[ondarvr]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

I'm somewhat confused as to why some retail resin suppliers use resins with such short gel times, it seems to be the main complaint from most users. I should find out who supplies them (Bondo brand) and ask why they spec a resin like this. There are a couple of possibilities though, one is with so little catalyst needed it will get hard no matter what the end user does, two maybe most people just use small amounts and with a short gel time it won't drain out as much and the other reason has to do with resin chemistry. The inhibitors used in resin tend to work better over time and some of the promoters will lose their strength during that same time period, so as the resin ages the gel times will become longer, it will still develop chunks in the container, but the reaction when catalyzed is slower. They may start with a fast gel time so even when the can has been sitting on the shelf for a year or more it will still get hard.

Most laminating resins in production shops have gel times of around 20 minutes, they can be had with gel times from 3 to 60 minutes though, then add in the different types of catalyst and you can get just about any gel time you want.

The best way to catalyze is to measure and use from 1 to 2%. get some small calibrated containers for resin and then even smaller ones, or a marked eye dropper for catalyst. If they're marked in grams or CC's it even easier... 100 cc of resin will use 1 to 2 cc of catalyst. Resin gel times are set at 77F, for every 15 degrees above 77 it will cut the gel time in half, for every 15 below 77 it will double the gel time. This isn't exact, but close enough to give you a good idea.

 

[jonesg]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

as the resin ages the gel times will become longer, it will still develop chunks in the container, but the reaction when catalyzed is slower. .

I've got gal of resin like that , got it cheap. The top of the can is rusty so its been round a while. It took almost an hr to start to gel, by that time I went to ace and got a qt of resin and put a hot coat on top, the whole thing went off together. I drill a hole to test and it set up ok.

 

[Mark42]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

When did benzoyl peroxide stop being the catalyst for resin? I remember in the 70's mixing in hardener that was labeled benzoyl peroxide and laughing because the popular acne medicine was 5 percent benzoyl peroxide. Now it seems all you see is MEKP.

 

[ondarvr]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

When did benzoyl peroxide stop being the catalyst for resin? I remember in the 70's mixing in hardener that was labeled benzoyl peroxide and laughing because the popular acne medicine was 5 percent benzoyl peroxide. Now it seems all you see is MEKP.

BPO is still used, mostly in body filler, but there are still BPO resin systems. It just isn't as user friendly as MEKP, so unless needed for a special purpose MEKP is the catalyst of choice. You can get other types of catalyst that can be blended with MEKP, or used alone to speed up or slow down the cure.

 

[rngale]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

Isnt the world or resin's grand! Are you guys that are having problems doing any work in the sun with the mixed resin? IF so that is part of the problem.
There is a possibility that the resin you are using is promoted for colder climate areas of the country. When i was building boats up here in the north east we had what we called summer resin's and winter resin's all it amounted to was how much it was promoted, but we had to be careful as to which resin we were using at certian times of the year.

If we wanted to use uo the remainder of our winter resin in early summer we would throttle back the cat. to about 1% sometimes a little less depending on the layup. some of the layups were 3 layers of 3205, which allowed for lower cat settings due to the shear thickness of the laminate.

 

[jonesg]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

I just re-cored my deck, the original coring looks like some sort of cardboard honeycomb, it got wet and flattened out.

I removed that and mixed up some chopped glass ( old glass boats left over from seacast material) , cabosil and mixed about 40% less mekp , I spread it out 3/4inch thick , pushed some matt into it and a flash coat of finish resin just as it got warm.
And it still got too hot to touch.
Deck's solid though.

Store it in a cool place, mix it in the shade and apply it quickly in the sun.
Works a treat for me.

 

[legoman67]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

When we did our transom we mixed resin by the liter, usually with 5-10 ML of catalyst. We had about 2 hour working time. If we needed a quick batch we would mix with 15-20 and would have about 30 min work time. Ours was done between 15-25*C. We based all our mixing from the chart on the side of the can

 

[escapade]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

I was wondering the same thing as well,

when i was mixing my bondo brand resin, I used less them normal amounts of hardender so I could get it all set up the way I wanted, and its nice and smooth and hard.

 

[getusummm]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

I have worked with the bondo brand resin for years. I finally bought some real resin to work on my boat. No more scrambling and running to make sure I get the resin on before it kicks. I recommend ordering some real resin or even going to West Marine and getting their boat yard resin. The difference is night and day.

 

[jonesg]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

I was gonna try west marine resin, but the price!
It was $26 a qt.

fiberglasssite sells good resin, the wax is bottled seperately so you can mix it with or without. Its guranteed fresh and a lot cheaper than west marine.

 

[getusummm]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

A gallon of poly is $40 at west marine. Granted it is higher than ordering, it beats wasting numerous batches due to quick kick times.

I have been buying my supplies from Advanced Plastics. I am using Vinyl Ester for my project. Their prices are hard to beat, but shipping might be the deciding factor depending on where you live. I usually find a reason to go to New Orleans for the day and avoid the hazmat charges. I also have a little marina/boat yard that is local and sells poly for $23 a gallon if I was ever in a bind.

 

[larboc]

Re: Chart for poly resin cure times vs. temp vs. MEKP?

I've been doing 5 drops per oz now and its working great. I make extra sure to mix well.