Layering Epoxy molds, timing.
02-24-2018, 04:47 PM
#1
Thread Starter
Layering Epoxy molds, timing.
How long can I wait between layers when laying up a new mold using thin epoxy? Can there be 24 hours between layers, or do I have to get the next layer on while still tacky? Trying to decide if I want to build the mold over several days next week, or wait until the weekend to do the one side in one day like I have been. It is a two part mold which means it will take 2 weekends to make, one day to wait, then a day or two to cure. Going to be using a 5:1 thin epoxy similar to West Systems, non waxed.
02-24-2018, 05:13 PM
#2
I build a commercial project that has a total of 24 layers of 8oz. per sq. yard cloth. I use West epoxy, and layup 4 layers a day for 6 days, until it's done. 24 hours is adequate time between layers.
02-24-2018, 05:25 PM
#3
Thread Starter
Cool, I was hoping there wouldn't be an issue. I know that some systems that once cured requires sanding and scuffing for a good mechanical bond, and that would not be good for a mold.
02-25-2018, 09:06 AM
#5
Thread Starter
I will when it arrives. Trying a new system from Total Boat. Half the price of West Systems. Couldn't beat the price, 1 quart with hardener, pumps, mixing cups, stir sticks, gloves, everything needed to mix and apply for $49 shipped. I was going to get some from US Composites, but when I added it all up for 1 quart kit, and just the pumps, with shipping it was the same price without the mixing cups, gloves, etc.
02-25-2018, 10:58 AM
#6
Some epoxy's don't bond well ,if they have cured too far,and others need to give off more exothermic heat,before laminating on top of a layer.(it can cook the previous coating and the surface of the mold)
02-25-2018, 05:10 PM
#7
Thread Starter
I have had that happen the first time I tried making a mold out of polyester resin, the stuff used for automotive repairs. Wont use that ever again for mold making. Might work OK for a part, but not for a mold, makes too much heat and cooked the wax off the part, wound up tossing the whole thing in the trash. The way I made my last few molds is I start early in the morning with the gel and layer of fine cloth, let that setup until it is firm and tacky, then apply the next layer of heavy glass mat, then let that set up , and follow up with another layer or two until I am satisfied with the thickness. I then do the other half the next day after releasing the plug from the fresh mold, clean up the flange, reset the plug in, wax the flange, and apply PVA to the entire thing and make the second half. I put dimples in the flange while I'm at it for aligning the mold.
I was thinking of doing a layer one night, another layer the next night, and another one the next, then let it cure until the weekend, then hit the other half and have it ready on Sunday to make parts.
I was thinking of doing a layer one night, another layer the next night, and another one the next, then let it cure until the weekend, then hit the other half and have it ready on Sunday to make parts.
02-25-2018, 05:53 PM
#8
Usually,too much resin,regardless of type,creates exothermic heat.If you had bondo filler,it hates heat,and reacts with the wax,the pva,the gelcoat,and anything else.My personal experience says...use in thin layers,and gradually build.while one layer is going off,the next layer won't start to heat up,until the previous one is well on it's way to curing.It depends on the Individual mix,and when it sets.
Last edited by alex5; 02-25-2018 at 05:56 PM.
02-25-2018, 06:32 PM
#9
sometimes,you can make,an epoxy filler using cabosil,and 5 minute epoxy(even 30 min)..make sure you have lots of cabosil,by percentage.Be prepared to remove the excess,while it is soft
02-25-2018, 07:51 PM
#10
I have had that happen the first time I tried making a mold out of polyester resin, the stuff used for automotive repairs. Wont use that ever again for mold making. Might work OK for a part, but not for a mold, makes too much heat and cooked the wax off the part, wound up tossing the whole thing in the trash. The way I made my last few molds is I start early in the morning with the gel and layer of fine cloth, let that setup until it is firm and tacky, then apply the next layer of heavy glass mat, then let that set up , and follow up with another layer or two until I am satisfied with the thickness. I then do the other half the next day after releasing the plug from the fresh mold, clean up the flange, reset the plug in, wax the flange, and apply PVA to the entire thing and make the second half. I put dimples in the flange while I'm at it for aligning the mold.
I was thinking of doing a layer one night, another layer the next night, and another one the next, then let it cure until the weekend, then hit the other half and have it ready on Sunday to make parts.
I was thinking of doing a layer one night, another layer the next night, and another one the next, then let it cure until the weekend, then hit the other half and have it ready on Sunday to make parts.
Next, I would cure the mold for at least a couple of weeks before you try to pull a part from it. If that resin will tolerate an elevated temperature post cure you might be able to shorten that time to a week. On a new mold I would use at least 6 to 8 coats of wax and PVA.
Good Luck with your project.
Scott
02-26-2018, 07:40 AM
#11
Thread Starter
Here are two molds I have done with WS and mat, and they came out great. The first one I just didn't have enough graphite, so didn't get it completely covered in black, and did get a couple small bubbles, but the second one came out perfect.
