Polyester/Epoxy Compatibility

[Del]

Past threads have eluded to incompatibility between epoxy and polyester resin. I've been unable to find the root issue by searching the forum.

Can an epoxy repair be bonded to existing polyester resin substrate if proper preparation is performed, or is the incompatibility a chemical one where the bond will eventually fail no matter how it's done?

 

[El Mar]

Epoxy will go over poly, poly should not go over epoxy.

It has to do with the amine blush the epoxy excretes while it is drying. Different brands are worse than others.

 

[cobia23]

X2, epoxy can be used over poly for repairs. The thing you have to watch out for when doing this, is if you plan to use gelcoat, the gelcoat is poly based and may not bond with the epoxy repair.
I know people who have gelcoated over epoxy with good results, but they were pro fiberglass guys. I wouldn't feel confident doing it myself, I would stick with a paint, like awlgrip or alexseal.

 

[WC1966]

In reading the instructions carefully for the West Systems Epoxy I read that rinsing w/fresh water and using a Scotch Brite pad followed with a final rinse would remove the blush. I followed the directions and did not have a problem applying a rolled on gelcote finish. And I am not a pro in any stretch of the imagination.
Worked for me,

 

[Eastporter]

I used the West System Epoxy and didn't rinse or buff. I did use Interlux Epoxy Primer and it encapsulates all epoxy repairs with ease (this is recommended by manufacturer prior to paint with Perfection or Brightsides).

 

[WhaleTail]

just filled one through hull and three old overboard discharges. we used west system thickened with 406 silica to fill original holes. Once they were set washed the blush off with red scotch bright and warm water. Sanded the epoxy with p36 then went over with layers of 1.5 oz matt and poly. Will finish with gelcoat over the matt.

Had no problems with the poly bonding with the epoxy.

I have also heard if you use a vinylester based marine filler such as 3M premium filler you can use that to fair the epoxy repair and then gelcoat over the epoxy.

 

[petrel]

I was told that polyester does not make a good bond over epoxy because of the difference in the size of the molecules. The molecules in the polyester are bigger. So when you put epoxy onto polyester those little molecules fill in and and make a good secondary bond. But when you go over epoxy with polyester, the bigger molecules can't really take root in the the smaller molecular structure of the epoxy and that is the reason not to do it.

 

[Del]

Thanks all for the guidance. I am rehabbing areas that have had prior repair work by a previous owner and am apparently heading in the right direction with epoxy over poly.

One final question though. Can I assume that sanding an epoxy filled area would remove the amine blush prior to application of a primer, or is the water flush a necessity for some reason?

 

[El Mar]

Sanding will not remove it totally, it just spreads the "wax" around. Also, thinners and solvents don't touch it. Only water.

 

[Del]

Sanding will not remove it totally, it just spreads the "wax" around. Also, thinners and solvents don't touch it. Only water.

"Only water" is especially counter intuitive to me. Thanks loads!

 

[Eastporter]

I never had any blush on my epoxy repairs and I used gallons and gallons of the stuff. Who is having blush with West System?

 

[El Mar]

I never had any blush on my epoxy repairs and I used gallons and gallons of the stuff. Who is having blush with West System?

West is one of the worst ones. That is what I use on my skiff projects with the kids.

 

[WC1966]

I never had any blush on my epoxy repairs and I used gallons and gallons of the stuff. Who is having blush with West System?

Here is the Surface Preparation recommendations from WS. Key wood seems to be "may'! I chose to follow their recommendations for the simple reason that I did not want to create my own problems by choosing to ignore a manufactures guidelines. I do not build/repair boats and learn as I go, did I spend way too much time? Of course,:shock:

Cured epoxy-
Unless you're using WEST SYSTEM's blush-free 207 Special Clear Hardener, amine blush may appear as a wax-like film on cured epoxy surfaces. It is a by-product of the curing process and may be more noticeable in cool, moist conditions. Amine blush can clog sandpaper and inhibit subsequent bonding, but this inert substance can easily be removed.

Surface Preparation[/PHP]​

 

[Eastporter]

Epoxy Blush

http://www.westsystem.com/ss/assets/Uploads/Ew20Contamination.pdf

http://www.jamestowndistributors.co...ne=adwords!6456&keyword=interlux_epoxy_primer

Here's a good article on surface prep. Blush is likely- but honestly didn't notice this on my project. I did notice it yellowed after curing but I believe this is due to the pigment of the epoxy with hardener added. The epoxy primer I used bonded to the epoxy so I did not need to wash and buff as directed in this article. Does anyone have a photo of blush on a project that you can post? I just reread the directions and it does say to use a surface prep cleaner or clean cured epoxy. Too late now... I believe I wiped everything down with watered down rag before I put primer down - I can't remember.

 

[WC1966]

Eastporter,

"I can't remember" LOL and that is why I read the directions, frequently..

 

[cobia23]

http://www.westsystem.com/ss/assets/Uploads/Ew20Contamination.pdf

Interlux Epoxy Primekote

Here's a good article on surface prep. Blush is likely- but honestly didn't notice this on my project. I did notice it yellowed after curing but I believe this is due to the pigment of the epoxy with hardener added. The epoxy primer I used bonded to the epoxy so I did not need to wash and buff as directed in this article. Does anyone have a photo of blush on a project that you can post? I just reread the directions and it does say to use a surface prep cleaner or clean cured epoxy. Too late now... I believe I wiped everything down with watered down rag before I put primer down - I can't remember.

You probably won't be able to see it in a picture. I first noticed it with my project when I went to sand, it gummed up the paper almost immedaitely.
You can definately feel it though, It feels as if there is a layer of wax on the surface. Thankfully it is easy to get rid of with just water, and maybe a little dish soap in it.

 

[jawz]

blush - gotta be removed...

true story here:

a guy i know "mad mike" - a nice enough guy,he plays way above his skill level - he borrowed some stuff from me,west system epoxy,and some chop strand putty - he was constructing "gutters" for his shamrock...a few days later he snapped - "that stuff i got from you wouldn't set up" - i asked him how he mixed it - then,asked him about amine blush - he never removed it...

 

[petrel]

All we ever did prior to panting or recoating was a thorough sanding and then a wipe down w/ laquer thinner. Never had a problem w/ that.

 

[Eastporter]

I know it got rained on one night before I did any fairing and I had to wipe it down the next day. I'm good!