how long does it take for PE & VE resins to come full cure? Questions on shop heating/temperature

Hi,

I've been finishing a 32 foot downeast, working on it fairly steady since the spring. I'm in NH, temps are now way out of range where you can run PE & VE resins/gelcoats without heating involved.

The boat is in a fairly well closed off tent, not airtight but generally so, not insulated at all though. In about any temp outside (ie 20F) I can run my kero heater for about 2 hours (on the ground) and the temperature of the hull gets up to 85F no matter where I shoot it with a temp gun on the inside, basically the air in the tent is up at 85 degrees and sooner or later the hull follows suit. But I do not trust those things for more than a day of monitored work, sooner or later I gotta shut it down..

My strategy so far has been, mix resins at max (the actual manufacturers max not over catalyzed) hardener ratio, get the work down and within an hour it's "cured" initially. Next I setup a small/safe electric heater, tent the small area I'm working in or put some foam insulation panels around the work, and I shutdown the kero heater - the electric heater, depending how well I close things off, can hold an area at a > 50F degree ballpark safely for an extended period of time to allow for further curing..

I guess #1 is this a reasonable strategy? #2 My concern is then how long do I need to hold the temperature to assure a complete/good cure and what temperature should I be sure to hold to?

One thing that comes to mind in this is I'm aware that although resin may seem cured, it may not ever get to full strength potential if you are working out of temp ranges, and since these resins cure for awhile beyond when they harden, I don't want to be cutting off the heat too soon.

Thanks in advance!

Jon

 

That's a tough question because every resin, and type of resin can be different. A typical general purpose ORTHO-DCPD blend will cure rather quickly compared to a normal VE.

They all recommend to use them at a minimum of 60F, 24 hours would be a safe timeframe, but for a full cure even some polyesters and VE are post cured to speed any residual cure (cross linking). Many times you can increase the thickness of the laminate so it will generate the required heat on it's own, but if the part doesn't need to be that thick it's not really an option. Faster gel time resins can help, so can adding more cobalt and/or DMA.

One other thing when using some kerosene heaters, they can leave deposits on the surface of the parts, the more enclosed the tent is the more likely it will leave deposits

 

To test if your strategy is working, invest (or borrow) a Barcoll hardness tester instrument. It is expensive but if you want to be confident about your method, use it as it is a must for every shop that is not environmentally controlled.

The rule from LR is >
3.8.3 Removal from the mould is not to be attempted until
a minimum Barcol reading recommended by the resin
manufacturer or a value of 20 has been attained. Subsequently,
the moulding is not to be moved outside of the controlled
environment until a minimum Barcol reading recommended by
the resin manufacturer of 35 (or equivalent) has been recorded.<

Full cure would be at 40 to 45 but that would be after the part has been sitting in the warm shop for several days. Could have been fully assembled by then.

 

When you say "but for a full cure even some polyesters and VE are post cured to speed any residual cure" - by that you mean basically heating the surface up to 100F or something after it's cured, with a hair dryer or something like that?

My basic layup strategy has been if I'm tabbing with a schedule of a layer of 3/4 mat, layer of 1708, followed by a layer of 3/4 ounce mat for instance, I run the first layer of 3/4 mat wider than the other two and use VE, then switch over to PE for the next two layers. The PE is a winter blend interplastics ortho however the VE just doesn't come that way.. Now the VE cure is very rapid though, at 2% and 85 degrees you got about 10 minutes from adding catalyst before a batch can no longer be used to wet anything out, and after 15 to 20 minutes there's no possibility of working anything you put down - working time is better at 1.25% when it's 85F but I'm trying to make sure it does go off well so sacrificing working time - also what I'm doing now is all small stuff anyway, largest thing is 8 inch tabbing, I really don't need the working time anyway..

That VE actually took some getting used to - when I was working a yard or so of 1708 at a time on my stringers it was very hard to get the working time needed. It's got a much stronger kick than PE if you are in it's temp range, however out of it's temp range the stuff might not cure - very finicky stuff but generally it cures faster is what I've found.

I get how that could happen on the kerosene heaters, always split on the use of these things. Another strategy might be a series of smaller propane heaters but it would take at least a few (in the size that can run on 20 lb tanks) to make the 200K BTU the kerosene heater produces very practically... Do you figure the deposits are more than a superficial issue cleaned away with acetone or does it do some other damage? Is it like a diesel soot or actual oil residue you are thinking of?

I'm being very careful on my prep, but I think with a well operating heater sitting on the ground pointed toward the bow, there is probably not much of anything wafting way up in the cabin where I'm working. Of course later when I move into the open part of the hull again I'll need to clean things again but I gotta do that anyway - even if it's unwaxed resin only 1 week old, and even if it's just gelcoat going on there, I'm in the paranoid habit of a sanding and cleaning it w/ acetone anyway. I figure a good mechanical bond trumps a questionable chemical bond every time.

Put a couple pics below, the heater isn't shown in these but is placed up in front of the bow and directed under the hull sorta pointed a the staircase in the picture but from 20 feet away (so it's not roasting anything on my hull).

Jon

 

This is basically what you should be looking for VE resin (attached).

Basically, you mix at maximum allowable for a fast cure. Thin laminates tends to disperse heat easily due to proportionally large surface area while thick laminates allows the exotherm to build up. A temp gun is more accurate way of doing it but in its absence, touching it with a hand can be something like uncomfortably hot.

Post curing raises the final cured mechanical properties of VE laminate and works best with low resin content and high fiber ratio. Barcoll reading of 50-55 is possible. 20 deg C must be maintained at least 24 hours. 50 deg C @ 24 hours seems to work best.

Perhaps Ondarvr has more available data since he is in the resin business.

 

Since you aren't doing large areas you can use one of the low cost halogen shop lights, they produce a great deal of heat and can warm the surface to any temp you would like. Just make sure you keep it a good distance away, you can easily overheat the laminate.

 

The differences you see between the two resins is why there's no blanket answer to cure times, while each resin type has it's own tendencies, they can be altered by how the resin is formulated. If the VE is promoted when you get it then it's most likely Interplastc 8117, it's been around for a very long time and is fairly easy to work with. There are resins formulated for 4"+ thick laminates and 1/16" laminates, using one for the wrong application can create cure issues.

A laminate of two 3/4oz mat and one 1708 is a thin laminate, normally you would lay down twice that at one time, so the peak exotherm would be higher.

 

OK cool - I see 68F 24 hours on the VE is getting you to what they seem to feel is a maximized property - I can about hit that without much trouble.

ondarvr, we had talked about this a little before with another question I had - it's vipel F010-TBN-23, you helped me identify as a straight VE.

Funny I forgot about it but I did pick up one of the heat lights as I started brainstorming on winter work, may need to see out a stronger fixture though. I've got the standard heat lamp fixtures they sell for livestock stuff, sometimes they slip or fall off with the weight of the big bulb. That's actually the same thing I light the boat with, however I use LED bulbs that do not get hot for safety.

I did checkout the barcol meter - found one on Ebay for $350/offers, in my hands though in this environment not sure it's going to be the right thing. Resin gets cold it gets harder, warm it up gets softer, inexperienced hands, I think I'm better off putting the effort into giving the resin the environment for curing.

Yes all this stuff is fairly thin laminate, taking corecell panels laminated with 1708, maybe one layer of mat over that as a veil, and tabbing them to the hull. The most structural thing involved was a bunk, all non structural interior parts.

Thanks!

Jon