Minimum working temps for polyester resin

Working with orthothalic laminating resin from LBI. Will be bonding to 25 yr. old poly resin and want a reasonably strong bond. Often in Maine we get a "January thaw." Ours is later this week. Tempted to do a bit now instead of all in April/May. Forecast is there may be a 46F day with a 34F night, 40 the next day. One layup. Too cold??

Thanks

 

I've been working the last couple weeks in temps ranging from the 30s at night to 50 in the daytime but I'm using a heater to warm my shop up to 60 but that doesn't last long as soon as I air the place out. It takes longer to cure using standard catalyst mix but it does cure. Not sure if I would consider working outside this time of year. I honestly don't know what the temp of the resin is after sitting in the unit overnight.

 

This will probably start another big debate, but here goes.

60F is the recommended low temperature for working with polyesters, it will get hard at lower temps, but may not fully cure, and even at 60F you may get some post cure as the weather warms up. On some parts the actual strength and cosmetics aren't that important, so it's not as much of a concern.

It's all about how warm the laminate gets when it cures, a thicker laminate with a fast resin will generate more heat, so while it's below 60F, enough energy may be created to get a good cure. A thin laminate with a summer blend resin may not.

For small layups it's easy to warm the area up a little, halogen shop lights work well for this, but you just want to warm the area, not cook the resin, so if using a light keep it well back from the surface.

When doing large areas you should tent the project to retain heat and control the temps.

 

Its doable at 40F tempo but you will likely be outside of mgs recommendations. Also remember mfgs are ultra conservative and each has different min and max values for hardener and temps. Mfgs are in total CYA in this regard and the limits can be successfully pushed beyond print. It also depends on regular poly or vinylester for values.

If you have no baseline data to compare with do a test panel to find out cure time. Poly cures like other coatings. It gets hard quickly but doesn't fully cure for days to weeks. To get max hardness it needs to get the initial hardness within the mfgs timeline, which is normally in minutes, not hours or days. The cure curve starts very fast (minutes), then tapers out (days-weeks). Get a cure graph from the mfg. Some have both the cure time and hardness shown for comparison. Of course this is all calculated and subject to variations.

If doing a sample, record temp, humidity, amount of resin, amount of hardener, time of mixing in pot, pot life and time of application. Lastly, the time it takes for the surface to get hard to touch. You now have a baseline measurement and can adjust hardener for future work.

LBI says 60cc (2oz) max hardener per gal is good for 52-60F. This is less than the generic industry standard max of 2.6 oz (2%) per gal and 60F min. You can also warm the resin and part before mixing and use external heat on the laminate as already suggested.

Good luck.

 

Humidity and sunlight are factors too obviously.

 

Just remember everyone here is giving a "you'll probably be ok" type answer. There is nothing wrong with that, but the chances that you don't end up ok may be more hassle than the time savings is worth.

I don't want to do it twice, especially when doing it twice means I have to clean up my mess from the first try before I can fix it.

 

If you want a strong bond use epoxy. Epoxy will bond to old polyester resin. It is not recommenced to use polyester resin to bond to old polyester resin.

Mind the temperature requirements for resins and hardeners. It is critical you stay within specified temperature range!

 

I would definitely agree. Polyester isn't a good choice of resin for patching. On top of that I would say that yesyou can get less expensive epoxides as well, but i'd opt for a brand with excellent reputation in the marine industry.

 

It's interesting that when someone asks for advice on polyester resin that people will tell them to use epoxy and that polyester basically doesn't work to scare them or make them doubtful. I've been using polyester resin for 31 years and I've used epoxy too. The reality is that both work provided you know what you're doing. Yes, epoxy is stronger and bonds better but that in no way means that polyester resin won't bond to polyester resin adequately. People have been doing it with success for longer than I've been alive. More boats have been built and repaired with polyester resin than epoxy. Everyone harps about all the problems you can have with polyester but those occur when you don't know what you're doing. If you want the best, use epoxy and spend 4x more - if you want to repair or build something on a budget then by all means use Polyester. I will gladly give you the number of my composites dealer here in VA - they sell it all and are experts in using it all and been in the boat building business since 1926 and will tell you exactly what I have.

 

^^^
+1
I'm glad I didn't have to type that, thank you, very accurate info.

 

Hi Brett and Ondarvr,
I agree with you, but why make life harder on yourself?

Polyester is known to not bond well to itself once it's cured.

Most of the 2nd hand boat market is polyester resin...we know that, but that doesn't mean it's not easier to work with epoxy and as an amateur, you have have more consistently successful results with epoxy.

Again, why add the risk for a relatively speaking small savings percentage?

 

Hello Scot.

I have the option to use poly v. epoxy and I don't consider polyester resin harder by any stretch of the imagination, in some areas it's much easier. I'm an amateur with lots of experience, I guess but I'm just trying to help.

As far as why should anyone use polyester - here's a few reasons:

1. 4x more costly is not a small percent in anyone's book.
2. Polyester resin sands 100x better than epoxy and sanding is brutal labor
3. Polyester resin is easier to mix with various fillers do to the hardner ratio
4. Poly has a wider range of working temps because you can vary hardner amounts more easily across any batch size.
5. Poly to poly is easier to blend when sanding too (a factor of #2)
6. It's the smell of surfboards (works for me)

As for the bonding thing, I'll state it again. Poly does bond to cured poly, not as strong as epoxy but it works just fine for most applications. I just ripped a boat apart that was built in 1983 and modified a few years later. The poly they used was still securely bonded to the degree I had to grind it down. This is because the people that modified the boat prepped the surface correctly. Anyone can learn to use polyester if they put effort to it and I'm happy to help them. I'm not trying to cause a scene or anything but I don't think you are painting an accurate image of polyester resin and it's practical applications.

Once again - yes, epoxy is stronger and bonds better but polyester resin will do the job to most people's satisfaction if used "correctly".

 

You can get epoxy everywhere from 10:1 ratio to 1:1 ratio. It depend on what's used for the hardener and to what density. 1:1 epoxy mix you can feel free to mix it for a whole hour if you want, and it will have a softer structure than the 5:1 or 10:1 mixes, and softer than your polyester, yet still have the tensile strength of an epoxide.

This affects all of your other points about useability and ease of working with sandpaper, blending, etc etc.

If the cost of your resin is preventing you from building a boat, then you shouldn't continue....The cost of resin is a tiny percentage of the cost of the total boat, and therefore I say again...the cost difference is negligible.

 

1:1 and 10:1 epoxy are special order items that no amateur will ever encounter. 3:1 and 4:1 epoxies are the common industry ratios. Polyester uses drop per ounce - I can fully mix my filler BEFORE adding hardner which has no impact on my cure.

Boat building and boat repair are not things limited to rich people.

And that gets to the core issue. A normal amateur isn't going to have multiple ratio mixes of resin around for his projects or need special order items to do something. It's a luxury that may be nice but it's not practical.

Polyester resin is it - you add various things to alter it's state and it's cheap. I can add wax to make it sand, fillers to thicken, acetone/styrene to thin, fibers to strengthen, tint to color and I can vary my hardner which is nothing by volume to kick it fast as hell or slow as a snail. I don't need different products to do it.

You don't like polyester resin, then don't ever use it. Don't look at it, don't talk about it but don't butt into a conversation about it and tell us we can't use it.

 

I posted this year's ago on another boating forum, but it fits in here.


I deal with many different markets in the composites industry, not just the marine end of it and for the most part I agree with XstreamVking.

Since I don't see bond failure as an issue in anything I've built or repaired with polyester or VE over the last 40+ years and it isn't really an issue for my customers, which have built many thousands of boats themselves, it seems the bond issue is more a case of poor workmanship or bad design. The prep needed for either type of resin is the same, epoxy may let you do a poor job with a little better chance of success though.

When I see bond failures it’s typically when a rookie decides to do a F/G repair on his boat (you can insert any item in place of a boat) and heads down the hardware store. They buy whatever resin it is that has been sitting on the shelf for a couple of years and some cloth (no mat), no sand paper, acetone, or any other needed items. They pull the boat out from under a tree in the side yard, use a damp cloth to move some of the leaves away and then make a feeble attempt to wipe off the green and brown slime that has accumulated on the surface for the last 10 years.

At this point they remember they should sand the surface, so they go back in the garage and find an old piece of fairly fine grit sand paper that's been used many times before on other projects. Now they make a couple of half hearted passes over the surface with the sand paper, which instantly clogs up with the damp green gunk still on the surface. It gets one more wipe with an old rag that was last used to check the oil on his truck and he now feels he’s ready to catalyze some resin.

Now, how much catalyst to add…..was that 2%, 20%, 50%...and how do you know what 2% is…or did they say 2 drops per quart…oh well, it’s not that important, I’ll just pour a little in…oops…too much (I think). Now where is that old paint brush I used to do the trim on the windows a couple of years ago…..there it is…wow, maybe I should have cleaned it better…sort of stiff. OK, now I just pour some resin on the surface and lay this 1’x1’ piece of cloth on it, I only “prepped” a 6”x6” square, but it should be fine…maybe even stronger. Let’s see, what do I do with all this extra resin…it sure took a lot less to wet out that piece of cloth than I thought. I think I’ll just pour the rest of it around on some of the other cracks to strengthen other areas too…don’t want to waste it. Looks like rain…good thing I’m done…now I’ll go in and have a beer.

A week later he heads to the lake puts the boat in the water and it doesn’t leak, it was a successful repair. Two weeks later he runs over a big wake while pulling a tuber and the repair starts to leak, he reaches down and grabs a corner of the cloth that is sticking up, the part he couldn’t get to lay down, must have been because it was folded over. He pulls and the cloth comes right off with little effort and he's shocked. That night he goes on line and asks on a boat forum why it failed, he tells them he did everything according the directions but it still failed. He is told that polyester resin is very weak, won’t stick to anything and that he needs to use epoxy, so he orders some online the next day. While waiting for the epoxy to arrive he starts to clean off the “failed” polyester resin and finds it is sticking in some areas and won’t chip off. About this time the neighbor sees what he is doing and offers him the use of a small grinder, this speeds things up dramatically and removes all of the old resin and green slime that was still on the surface. A couple of days later the epoxy is delivered and so is some biax, he also ordered the roller and squeegee the guys online said he would need, plus he picked up some new brushes.

This time he remembers its a 1 to 1 mix (and with a little work he can figure how much of each that is), stirs it well and from his experience before, plus the advice from the forum he uses the correct amount of resin to wet out the several layers of glass to build the surface back up and works all the bubbles out.

This time the repair holds up, now he goes back online to the forum, and he’s one of the experts on the forum now because he’s done a repair before, and tells everyone how bad polyester is and that they should never use it and epoxy is the only thing that works. Sound familiar.


Back to the other stuff.

If properly designed an epoxy hull will be no stronger than a polyester or VE hull designed for the same use, only lighter, this is where the DIYer comes up short. They tend to use about the same laminate schedule as they would with polyester or VE, so they have the same weight with a much higher cost and an over built part, or repair, this results in no advantage or benefits from using epoxy. I hear people frequently say that you will save weight by doing an epoxy repair, well it would need to be a very large repair to make a meaningful difference in the weight savings. You may save the weight of a six pack on a large repair...and well….that may be very important to some people…more beer.

As for strength, most epoxies list their physical properties after being post cured, if you don't post cure it don't expect to get close to them. Also any medium to slow cure epoxy really needs to be post cured, they fall well short of the listed properties without this step.

The other issue with strength is when using low viscosity epoxy infusion resins is they tend to be much weaker than higher viscosity resins. This has to do with how they reduce the viscosity. What can happen is the physical properties can drop to a level equal to, or below those of a VE resin.

Even the many thousands of low quality ski boats built to very a low price point with the cheapest polyester resin available rarely have an actual resin/glass failure, the wood rots and they tend to hold up OK until the wood it nothing more than pulp. And even then the owner has no clue there is an issue until his foot falls through the deck.

As for high end custom or semi custom boats, why not use epoxy, it’s a great product and will allow you to build a much lighter craft. These tend to be purchased in relatively small numbers by people that can afford this type of toy, not the every day guy.

As for the type of boats repaired or modified on this site, epoxy may be a good choice for them, that is if your plan is to put the largest outboard on it you can and then push it to the limit. Although a VE is easily up to the job. For the many more that just want their ski or fishing boat back on the water, I can’t see a good reason for using epoxy.