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Discussion Starter · #1 ·
Hi,

I have some non-structural glass work that I'll soon be involved in where I'll be able to save alot of time by using 2-part epoxy over plywood..

The issue is though I've never had great luck painting the stuff with standard one part paints and this particular project is going to need a hard gelcoat type finish...

What I'd like to do is just finish it by applying cheap white poly gel coat right out of the can, however I don't know how well it will stick directly to 2-part epoxy.. it seems like it would but epoxy is hard to coat and I'm not sure what the result will be.

Another idea is a tie coat.. not sure what the correct tie coat might be though..

Another idea is 2-part epoxy gelocat as that may not need a tie coat..

Another idea is awlgrip, but I've got no experience with that and I know less about how it is applied to 2-part epoxy and/or if I'll have any practical way to apply it..

I'd like something that will go off in humid ~50 degree temps without issue (my garage). Epoxy is best as temps do not matter but I've never had a problem with poly as I just add a little extra hardener.

Does anyone know what works?

Thanks,

Jon
 

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You could use a laminating resin, which never gets to a hard cure, but stays a little sticky so the next coat will stick. Best bet is to check with the west system guys, they really know what they are talking about.


This post edited by MakoMike 04:09 PM 02/06/2008
 

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Discussion Starter · #5 ·
System Three

For tie coats I found they reccomend the following in their FAQ's:

System Three wrote:
Can I put polyester gelcoat over cured epoxy?
In general, polyester resins won't cure properly or bond well to epoxy resin products without a "tie-coat" barrier resin in between. System Three SB-112 resin system can be used as a tie coat in between epoxy laminating or coating resins, and polyester laminating or gelcoat resins. Using this resin allows you to gelcoat an epoxy-built or epoxy-repaired boat.

Jon
 

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leakyrivot wrote:

For tie coats I found they reccomend the following in their FAQ's:

System Three wrote:
Can I put polyester gelcoat over cured epoxy?
In general, polyester resins won't cure properly or bond well to epoxy resin products without a "tie-coat" barrier resin in between. System Three SB-112 resin system can be used as a tie coat in between epoxy laminating or coating resins, and polyester laminating or gelcoat resins. Using this resin allows you to gelcoat an epoxy-built or epoxy-repaired boat.

Jon

Good find.
Here's ashot of my new dash board...
 

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Normally the only obstacle to a proper Gelcoat over epoxy cure is the amine blush issue. Amine blush is the residue that follows a cureing of epoxy and inhibits the sticking of anything to the epoxy coat finish. As such, you need to remove the amine blush, which can be done with a scotchbrite pad and some elbow grease. Once the amine blush is removed you can lightly sand the surface, wipe with solvent and gelcoat not problem.

One caveat is to make sure the epoxy is FULLY cured. Epoxy, especially in cooler weather takes a while to cure, so make sure you wait a while and allow ALL of the amine blush to come out. Actually you may be better off letting it cure, cleaning, letting it sit some more, cleaning and then gelcoating. But, the bottom line is that you can gel over epoxy. Once cure its like any other fiberglass.

BTW I noticed you mention something about temp not being a problem for Epoxy. Thats not true, you need at least 50 degree farenheit for epoxy to cure properly..and the warmer the better.

Poly can cure down into the 40's with a touch of extra hardener (but not too much)

This post edited by GradySailfish 02:58 PM 02/08/2008
 

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GradySailfish wrote:

Normally the only obstacle to a proper Gelcoat over epoxy cure is the amine blush issue. Amine blush is the residue that follows a cureing of epoxy and inhibits the sticking of anything to the epoxy coat finish. As such, you need to remove the amine blush, which can be done with a scotchbrite pad and some elbow grease. Once the amine blush is removed you can lightly sand the surface, wipe with solvent and gelcoat not problem.

One caveat is to make sure the epoxy is FULLY cured. Epoxy, especially in cooler weather takes a while to cure, so make sure you wait a while and allow ALL of the amine blush to come out. Actually you may be better off letting it cure, cleaning, letting it sit some more, cleaning and then gelcoating. But, the bottom line is that you can gel over epoxy. Once cure its like any other fiberglass.

BTW I noticed you mention something about temp not being a problem for Epoxy. Thats not true, you need at least 50 degree farenheit for epoxy to cure properly..and the warmer the better.

Poly can cure down into the 40's with a touch of extra hardener (but not too much)
Would a good sanding be ok? I've taken off a good top layer of the epoxy/fiberglass.
 

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Would a good sanding be ok? I've taken off a good top layer of the epoxy/fiberglass. wrote:


Yes but make sure you use water and a little dish soap. The Amine Blush as Gradysailfish mentioned is water soluble only!! Solvents won't touch it. If you follow the above advice and wet sand it out a few times after a good cure, you should have no problem sticking gelcoat to it. After that wipe it down with MEK or Acetone.
 

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Dorymate, never knew you visit CSC. Cool !

Yes, make sure you scrub the glass first, becasue if you sand without scrubbing you are basically pushing the amine blush into the underlying laminate. Plus you will gunk up your sandpaper. You can as dorymate said use dishwashing soap, or you can use a scotchbrite pad. Your choice.
 

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Although the above recommendations may produce a satisfactory result, they are far from what one might beleive he is acheiving.

Certain cured epoxies do become coated w/ an amine blush in humid conditions, or some even just when exposed to air during the curing process. You can easily wash the amine blush off w/ soap and water, which will prepare it for conventional coatings. However, most epoxies use an amine based hardener (which causes the amine blush),and this type of product will always have free radical amines on the surface of the coating. The amines will inhibit the curing process of a polyester resin, basically preventing complete cure of the polyester immediately at the surface of the epoxy. The Gel coat will appear to cure fine, but unknown to the owner, there is not a complete cure at the interface, and the only thing tying the two producs together is either the deep groves from sanding, which the cured portions of polyester may bite into, and the overall cohesion of the gel coat, which will maintain integral coaitng until a chip or crack develops.

Onward, remember that the greatest appeal of gel coat is that it will chemically and mechanically bond w/ the structural components of the polyester/fiberglass construction. When applied to epoxy, the best one could hope for, even disregarding amine inhibition, is a mechanical bond. Gel coat is brittle, and thick by application, so w/o the chemical reinforcement of the resin/fabric behind it, it is more liable to fail.

As mentioned before, epoxy is more temperature sensative than polyester. Even though there are epoxy formulations developed to work in temperatures below forty degrees, they are quite viscous in the lower temps, and difficult to work w/. They are also susceptable to high humidity, and the cure time will double w/ every ten degree temperature drop. Polyester can be treated to work in virtually any temperature.

If you can get epoxy to cure at a given temperature, you will have no problem overcoating it w/ Awl Grip, or any other premium two-part package. It will maintain it's color and shine longer, is easier to recoat, and will look a thousand times better than a gel coat that wasn't applied into a mold.

Paul
 

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Gradysailfish wrote:
You can as dorymate said use dishwashing soap, or you can use a scotchbrite pad. Your choice.

Or both.:)

Capt Paul wrote:
If you can get epoxy to cure at a given temperature, you will have no problem overcoating it w/ Awl Grip, or any other premium two-part package. It will maintain it's color and shine longer, is easier to recoat, and will look a thousand times better than a gel coat that wasn't applied into a mold.

Thats what I would do unless you are **** bent on using Gelcoat. Try Interlux Perfection with roll and tip method.

This post edited by Dorymate2530 09:23 PM 02/09/2008
 

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Well, I was **** bent on using gel coat...and boy what a pain. I got it 99% to stick and cure, but I had a few spots that just would not cure. :(
I used the scotchpad and water method and the only spots that didn't cure properly were a few thin lines where my work met the original gel coat. I patched those areas and got most of it nice and hard, by using PVA mold release to cover the patches.
I just put a final layer on tonight. I hope it all cures. :) I want to sand it and wax it and be done with it.
 

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blush problems...

Why not just just MAS products, low viscosity resin and slow hardener? No blush. No curing problems. Will take primer/paint, varnish, readily. Good stuff to work with.

Been using it out in the garage all winter. I keep it above 50 degrees whenever feasible when putting down a lot of it, starting the bigger jobs early on Saturday to make the most heat all weekend long. Sometimes the overnight chronic temp drop cannot be helped but this has not created any problems for me. Not being in a hurry for a big winter project, not a big deal to wait and extra day here and there to ensure proper curing.

I hear they have come out with a faster hardener that is also non-blushing.

It is probably not likely the best product, I don't know much about glassing, so the MAS products are great for beginners to use (when building a 16 foot long glass over wood kayak [a mistake would be very costly]), being it is generally not a problematic product and compatible with a multitude of top coatings.

One other thing of note is we only wipe this stuff down with laquer thinner and let it evaporate for at least 45 minutes. Acetone and mineral spirits have too many impurities to use for the wipe down.



This post edited by Fishbust 06:58 AM 04/05/2008
 

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