Poly or epoxy, not sure what to go with?

[jeffrey.bean]

I’m redoing a 1990 Chawk 18, stringers transom and obviously the sole.
I’m in the process of removing all the old core material and plan on using ACX plywood.
This is my first restoration and have no real experience with either, beside small repairs.
I’ve heard not to use poly if it’s below 65°, can epoxy be used at lower temps? I’m in MD and doing the work in my garage. I’ll be using space heaters to bring the temp up, but not sure if I’ll be able to hit 65 in Jan/Feb.
What is the procedure if I do a layup, on say a stringer one day and can’t get back to do the bulkheads that tie into it for a few days, how do I tie in the next lay up? If using epoxy, do I just wipe the blush off, or do I need to sand as well, what about poly?
Thanks

 

[racerone]

I use West System epoxy.---More $$ but does not have that awful smell.

 

[Scott Danforth]

Epoxy if you have a long time to cure (epoxy cure times go up exponentially if the temps are low)

poly if you want to save money, are going to be gel coating, and you want to layup and go

 

[tpenfield]

I built my custom fiberglass swim platform in my garage during the dead of winter. Temperatures in the garage were typically 60˚F (ish).

First, I would use poly since it is easier on the wallet. If you have an 'attached' garage, you could vent fumes from the garage and bring warm air from the house. Not sure if epoxy will buy you anything as far as working temperature.

2% MEKP and you may have to tent the work area and force warm air from a space heater or even a hair dryer. Make sure to have your 'fire prevention safety hat' on in setting up anything to add heat to the work area. Don't go over 3% MEKP

The nice thing about the using poly in lower temperatures is that it will slow the curing down, so your working time is increased. Then you can tent the work and add some heat to cure.

A quick sanding or even a wipe with acetone will prep bonding surfaces for the next day or 2.

 

[jeffrey.bean]

Thanks for the info, leaning towards poly due to cost, heck, the boat was built with it 33 years ago, and this is the first rebuild.
I have a couple electric heaters I can put under the hull to warm things up

 

[88 Capri (2022 SOTY)]

Jeffery, I used poly

Thanks for the info, leaning towards poly due to cost, heck, the boat was built with it 33 years ago, and this is the first rebuild.
I have a couple electric heaters I can put under the hull to warm things up

Ventilation it extremely important! The fumes from using poly are very nasty!

 

[stresspoint]

plenty of things to consider before making a decision on what resins to use.

as you are new to this epoxy is the most forgiving , poly takes some skills that come with practice , it can also be messy around the garage if you are not careful.

epoxy will give you better overall strength , poly will also give strength and a good bond "however" prep is important.

those are the main points you should ne spending the extra on epoxy , yes it is expensive , but a hell of a lot more forgiving .

one point when using epoxy is always ware gloves , that goop is poisonous.

 

[racerone]

Wise man said.-----" some folks do not have the money or time to do it right the first time.---But they always find more time to do it over "

 

[todhunter]

I found that the hype about poly being difficult and not forgiving to be false. Both poly and epoxy stink - yes, poly has a more potent smell, though. Neither will want to cure in cold temperatures. Both are messy. Both are plenty strong for your boat. Here are some benefits of using poly:

+ Cheaper than epoxy
+ Probably what your boat was built with, so no worries about bonding to your boat, or doing future repairs
+ You can gelcoat over it
+ You can do several layups in a day if you're trying to cram work in on weekends
+ No sanding required between layups, as long as you are using non-waxed resin
+ You can adjust the cure speed based on amount of catalyst added
+ Works with CSM

If working with a reasonably sized batch of poly resin (~24 oz or less), I never had an issue with it kicking before I was ready during my restoration project. To me this seems to be the #1 concern for people questioning poly vs. epoxy (with strength being a close 2nd). Mix it with less catalyst if you're working in hotter temps / direct sunlight or if you feel you need more time on the layup. You can go down to 0.75%. Mix it with more catalyst if you are working in cold temps or if you want to move onto the next layup quickly. You can go up to about 2.5%.

Full disclosure - I did my restoration in my insulated garage with heat and AC. In the summer I tried keeping it below 78F and in the winter I tried keeping it above 62F. In the summer at it's hottest, the fastest kick I probably got was about 25-30 minutes...still plenty of time for a reasonably sized layup.

 

[jeffrey.bean]

Thanks for taking the time to write that, much appreciated.
I have been leaning towards poly, mainly due to cost, heck that’s what the boat was built with 33 years ago.
Thanks again

 

[stresspoint]

i pick my fights what jobs to use polyester or epoxy on.

for the sake of safety ,IMHO stringer and transom replacement by someone not competent in FRP repair should always be done with epoxy.

 

[Scott Danforth]

i pick my fights what jobs to use polyester or epoxy on.

for the sake of safety ,IMHO stringer and transom replacement by someone not competent in FRP repair should always be done with epoxy.

why?

 

[88 Capri (2022 SOTY)]

Thanks for taking the time to write that, much appreciated.
I have been leaning towards poly, mainly due to cost, heck that’s what the boat was built with 33 years ago.
Thanks again

Someone gave me the same example to a similar question I asked but they also added that this time it will be done correctly, meaning it will last much longer than the initial build.

 

[Scott Danforth]

The key to either poly or epoxy is the prep

When you think you are done grinding.............you have much more grinding to do

 

[jeffrey.bean]

The key to either poly or epoxy is the prep

When you think you are done grinding.............you have much more grinding to do

Lol, time to break out the tyvek suit and respirator

 

[88 Capri (2022 SOTY)]

On the subject of grinding, when you see the "pink" glass you know you're done in that spot anyway lol.
You can see the examples in this picture.
When using acetone to clean and prep for glass you can never use too much.

 

[Scott Danforth]

When you see daylight you ground too far.....LOL..... We all have been there

 

[Baylinerchuck]

When you see daylight you ground too far.....LOL..... We all have been there

Man ain’t that the truth!!

For me it’s poly all the way. For all the reasons @todhunter said.

 

[froggy1150]

Poly fumes are volatile. Must wear vapor cartridge on resperator. Exposure effects are temporary. Epoxy is opposite.fumes just smell some but... Contact exposure is cumulative and never goes away. Once you have epoxy toxicity you have it for life
Fyi

 

[Scott Danforth]

with the composite experts at my fingertips at Marine Concepts and various carbon manufacturers within the marine and aerospace fields.... im good. same prep work needed for both epoxy and poly with regards to surface prep.