Polyester resin shrinkage. Is this a real concern?

[44'cruisingcat]

Originally Posted by Wind River

This is my concern, bad bonding. I don't really trust the old laminate to not to be contaminated to some degree from moisture, seeing that it is a 36 year old polyester boat with blisters (below the water line).
If the old laminate was nice, clean, top quality laminate, I would not be as concerned with bonding, but my gut is saying it is not.

If you're concerned about bonding, I'd use epoxy. Especially bonding to old polyester.

In all likelihood poly or vinyl would be fine for this job. But you're probably going to worry anyway.

[Redreuben]

Vinyl Ester can last for ages if you periodically stir it up by bubbling dry air through it.
Most poly resins only go off from styrene evaporation.
Your biggest issue no matter what you use is surface prep, 125mm angle grinder 40 grit discs, get rid of as much gel oat as you can and get down to the resin with glass fibre in it. Wash clean with lots of acetone. Done.
Catalyse polyester no less than 1% vinyl Ester at 1.5% or it won’t cure hard enough follow manufacturers advice.
If you stick with poly/vinyl you can use poly/vinyl gelcoats to finish.
Go epoxy and your committed to 2 pack all the way. $$$$$
The problems with epoxy are; money, time in that it is a much slower cure and holds up work, that may work for you.
Once you use epoxy that’s it epoxy or 2 pack all the way, fairing, topcoats, any further mods or repairs has to be epoxy and 2 pack.

Poly is not suitable for osmosis repair it’s the cause. Vinyl Ester is good, manufactures of quality boats skin with vinyl Ester before using poly for economy. Epoxy is Rolls Royce.
There is no question epoxy is better, if you can’t get other resins considerably cheaper keep looking something isn’t right.
Cheers RR

[jimbunyard]

As others have noted, polyester resin should be substantially less expensive than epoxy; either you've not found the right suppliers or, less likely, the lower epoxy price is a reflection of its' quality.

I would never buy either resin based on it's shelf life; buy enough to do the job at hand. Regardless of what it says on the label, you just can't have enough control of the supply chain to know what the actual shelf life will be. I've had epoxy resins solidify in less than a year and have used good iso after having it in the drum for a year and a half.

The 'bonding issue' is more an effect of preparation; properly prepared, you won't have one with either epoxy or polyester.

As for cheaper being the only reason for 'pros' using polyester, that just isn't the case. It is used because it's properties best fit the application, from both a structural viewpoint and a cost/benefit analysis, in both repair and new construction.

As noted several times, use of poly will speed your project up probably by half, at least until you develop efficient laminating experience (which will probably be right about the time you finish the job), and once you've gone to epoxy, there's no going back. Though the new wisdom is, with proper preparation, you can use polyester gelcoat over epoxy, if you're worried about bonding new polyester to old polyester, gelcoat over epoxy should give you an order of magnitude more worries…

Don't think the epoxy sensitivity issue has been brought up, if you're the allergic type make damn sure you use adequate protection to avoid becoming sensitized...

Perhaps a more esoteric reasoning needs also to be introduced. You've already used Corebond to secure the Coosa panels to the inner skin. Corebond is polyester resin mixed with, as far as I can determine given the weight per gallon, glass beads. Since the real strength of the deck is determined by the separation of the inner and outer skins and their bond to the separating core, it seems a little odd to be questioning bond strength of poly at this point, given that (very roughly) at least half of your deck's strength already relies on just that bond. To venture even further into esoterica (and doubt), does the differing strengths of the two resins contribute to or detract from the overall structure's strength?

I realize I may seem to be plugging for polyester but really I'm not. Use whatever you feel most comfortable with and makes most economic sense.
My point is only that with proper preparation, either is perfectly adequate.

And I can't resist two more pictures.

They're both of my own boat, a 1969 Morgan revived after a bout with Katrina and apparently the end of a piling. After the storm, in which it appears to have dropped onto a piling (circled in red) it was left ashore, abandoned for 18 months. The condominium owners finally got tired of it, had it pushed back in the water with a backhoe, and gave it to the backhoe operator, from whom I purchased it several months later, leaks and all. Towed it to the yard, repaired the hole with good iso polyester resin, roving and mat, put a new used diesel in, built a new rudder, put a new bottom job on it, motored it home (about 6 months after beginning).

The pictures are from 4 years later, the next bottom job. Notice the lack of bonding problems. The areas circled in yellow were gouges and did not penetrate the hull, but no bonding issues there either.

The second picture is just for orientation and reference.

[Benz]

The deck and house of my boat are polyester that I laid up myself. There have been no issues in 10+ years. You can get beyond the air-cure problem easily by returning the day after your last layer of laminate (or the next week or whenever), and skimming a coat of fairing compound over it all. That keeps the air out so the resin cures, and of course, sands easily. If you use poly or vinyl, you can use the cheapest and best fairing compound, Polyfair. Comes in way cheaper than any epoxy fairing goo, and sets up quick enough to do multiple skim/sand cycles in a day. I buy it in 5-gal pails. Later on you can pin-hole with Bondo, since they're compatible. As you proceed down the path of fairing and paint prep, you can also use Duratek primers, which are way cheaper than epoxy primers. Finally you can use gelcoat, though for the final bit, I prefer investing in 545 primer and Awlgrip.
As for adhesion, dear me, look at all the surface area you're bonding to! Think of all the molecules holding hands along that long, long stretch of surface. It's plenty.

[Cadence]

If you decide on poly, you may want to consider iso as apposed to just a laminating resin. Regular resin will leach MEK. This over a period may have an adverse effect on the bonding of whatever you choose as a surface coat.
Maybe someone in the business can comment on if it is or isn't a concern.

[TeddyDiver]

Originally Posted by jimbunyard

As others have noted, polyester resin should be substantially less expensive than epoxy; either you've not found the right suppliers or, less likely, the lower epoxy price is a reflection of its' quality.

I would never buy either resin based on it's shelf life; buy enough to do the job at hand. Regardless of what it says on the label, you just can't have enough control of the supply chain to know what the actual shelf life will be. I've had epoxy resins solidify in less than a year and have used good iso after having it in the drum for a year and a half.

The 'bonding issue' is more an effect of preparation; properly prepared, you won't have one with either epoxy or polyester.

As for cheaper being the only reason for 'pros' using polyester, that just isn't the case. It is used because it's properties best fit the application, from both a structural viewpoint and a cost/benefit analysis, in both repair and new construction.

As noted several times, use of poly will speed your project up probably by half, at least until you develop efficient laminating experience (which will probably be right about the time you finish the job), and once you've gone to epoxy, there's no going back. Though the new wisdom is, with proper preparation, you can use polyester gelcoat over epoxy, if you're worried about bonding new polyester to old polyester, gelcoat over epoxy should give you an order of magnitude more worries…

Don't think the epoxy sensitivity issue has been brought up, if you're the allergic type make damn sure you use adequate protection to avoid becoming sensitized...

Perhaps a more esoteric reasoning needs also to be introduced. You've already used Corebond to secure the Coosa panels to the inner skin. Corebond is polyester resin mixed with, as far as I can determine given the weight per gallon, glass beads. Since the real strength of the deck is determined by the separation of the inner and outer skins and their bond to the separating core, it seems a little odd to be questioning bond strength of poly at this point, given that (very roughly) at least half of your deck's strength already relies on just that bond. To venture even further into esoterica (and doubt), does the differing strengths of the two resins contribute to or detract from the overall structure's strength?

I realize I may seem to be plugging for polyester but really I'm not. Use whatever you feel most comfortable with and makes most economic sense.
My point is only that with proper preparation, either is perfectly adequate.

..snip

Just a couple of remarks:

If you had studied a bit of epoxy you'd known that warming up epoxy resin restores the liquid state.

Time saving? Not true in this scale as you can laminate first layer as much as you want, then start the next layer later when the first is not tacky but still a bit soft. With fast kicking poly you must do smaller area once and preferably have more labour force on the job as the time window is much shorter.

Right, but with epoxy generally just nitrile gloves, for sanding dust respirator. With poly should use respirator for gases also laminating.

The last one I agree

Teddy

[Benz]

Originally Posted by Cadence

If you decide on poly, you may want to consider iso as apposed to just a laminating resin. Regular resin will leach MEK. This over a period may have an adverse effect on the bonding of whatever you choose as a surface coat.
Maybe someone in the business can comment on if it is or isn't a concern.

This is absolutely not a concern.

[TeddyDiver]

Originally Posted by Benz

This is absolutely not a concern.

Just a concern for your helth.

[Cadence]

Originally Posted by Benz

This is absolutely not a concern.

Thanks! As I said I didn't know but the ability to leach that nasty stuff came to mind.

[44'cruisingcat]

Originally Posted by jimbunyard

As for cheaper being the only reason for 'pros' using polyester, that just isn't the case. It is used because it's properties best fit the application, from both a structural viewpoint and a cost/benefit analysis, in both repair and new construction

Sorry, but this is clearly not true. Vinylester offers the control of cure times and the ability to bond with gelcoat that polyester does but also has superior secondary bond strength and is resistant to osmosis.

Yet some pro's still use polyester.

There really is only one reason for this.

Cheapness.

[Cadence]

Originally Posted by 44'cruisingcat

Sorry, but this is clearly not true. Vinylester offers the control of cure times and the ability to bond with gelcoat that polyester does but also has superior secondary bond strength and is resistant to osmosis.

Yet some pro's still use polyester.

There really is only one reason for this.

Cheapness.

Cure time on polyester is controllable, depending on temp. primarily. I feel sure manufacturers are working in a controlled environment such that the catalyst rate is pretty much constant. I would also bet those using poly are using a significate barrier coat. The manufacturing processes have changed since the time of boats with blisters.

[44'cruisingcat]

Cure time with vinylester is similarly controllable.

In use, vinylester is very similar to polyester. It's properties are superior though. And it costs more. Although not a lot more.

And yes, poly boats will be given a barrier coat. Because they need one.

There's a guy in Australia who used to build production boats, then later moved on to building custom boats with their owners.

He told me that for a 46' monohull, the difference in cost between vinyl and poly was a few thousand dollars. He said that in production he would use poly, because that few thousand was profit. In the custom boat, the owner chose the resin. None opted to save the few thousand.

[Benz]

Originally Posted by TeddyDiver

Just a concern for your helth.

While poly and vinyl-ester smell to high heaven, and yes, you should not drink the MEK, those resin systems are far less unhealthy than epoxy. Boatbuilders around here have been laminating with MEK-catalized resins from when they dropped out of high school to retirement with no "MEK sensititvity." There are also dozens, young and old, who have become epoxy sensitized from incautious use, and one at least I know was hospitalized and cannot now even be around grinding dust.

Point is, unless you squirt the MEK into your eye, there's not a lot of risk. Getting catalized poly/vinyl resin on your skin doesn't hurt you, and the only reason people wear respirators is to shut out the smell. Most don't. OSHA does not require respirators for use with MEK-cat resins, but they do for use with epoxies. Hmmm.

[Benz]

As far as osmosis which was just mentioned: the project in question is a deck. It does not sit 24-7 in water. Vinylester is way better for a hull that's gonna sit in the water, but given the price diff it may not be better enough to justify for a deck.
If budget was no issue, I'd always choose vinylester over poly for a big project. But if budget was no issue, I'd also always pay someone else to do it. Poverty or penury can make you look long and hard at other suitable options. In this case, polyester resin is a perfectly reasonable one.

[clockwork orange]

Ben, you make a very good point about osmosis not being an issue with the OPs project. These poly vs epoxy debates often go off track with folks pushing their favorite goo. Back in post # 12 i mentioned that pros typically use what is appropriate for the job at hand and as you point out the job at hand, in the OPs case does not require protection from osmosis. We live in a one size fits all world and epoxy is a clear choice for the amateur to have a small kit around to do small repairs but when faced with a larger project where you need order in a larger quantity you get the opportunity to actually use what is appropriate for the job at hand where.


Steve.