Polyurethane Paint on Epoxy

[thinwater]

Shoalcove nailed it; wash it with a 3M scrubber and TSP. Then sand. The blush just clogs finish sand paper anyway.

Everyone who has done much with epoxy has done this once. If they did it twice (raise your hands!) thinking this time the project was very small and they had sanded enough, they felt pretty stupid the 2nd time.

And skip the paint on the inside. I have used pigmented epoxy for this and been pleased 15 years later.

[MichaelC]

I am building a 32' hard chined double ended gaff cutter. [3rd big boat, maybe #20 overall]. Half the time that I come on this site I learn something. This thread is such a thread. Thanks for the posts everybody. You are the greatest!

[svpresent]

Well, I followed West Systems' advice and removed the wet paint. I used brushing thinner on a cloth. The removing process was surprisingly easy. If I had known that up front I'd have done that earlier.

Now the Easypoxy is removed and looking at Mark's post I've decided to use epoxy as a final finish instead of paint. This sure will be up to the wet conditions inside the fridge, thanks for the advice.

West Systems said there have been numerous occasions where the 105/206 mixture was used for the final finish in coolers with great succes. To get the white color they advised me to use their 501 pigment.

After cleaning and sanding the existing epoxy, I will first put on a layer without the pigment cause the pigment makes it harder to "connect" to the dry surface. West Systems say start with pigment in the second layer cause wet on wet is much easier and the pigment won't cause any trouble then.

Well, I've learned something here.
Thanks to all.

[PAR]

Unless you can insure the epoxy coated (pigmented) area will not receive UV rays (direct or reflected), then you have to overcoat the epoxy with something (varnish, polyurethane or paint). Other wise UV will eventually break down and depolymerize the epoxy.

Easyepoxy does take a long time to cure, particularly in humid conditions. I also don't like how quickly it "chalks" up, but some folks like it and it does "flow" nice. With the advent of all the new paints and coatings now, it's foolish not to use a primer, especially the recommended topcoat manufacture primer, if you're a novice painter. If you don't have a "handle" on what they've done to many of these paint formulations in the last decade, you can be in for a big surprise.

How do you know if you're a novice to these new paints? If you are using their "brushing agent", or their brand "tropical reducer" or their brand "wetting agent", or don't own a can of xylene, nor know why you would want to own one, etc. then you're best off using the recommend stuff.

Primer serves other functions as well as offer a tooth and bonding agent between substrate and topcoat. If using Easypoxy, use their "Undercoater" I think it's called or a good quality single part enamel primer, like Pre-Coat. Primer can solve a lot of issues and if used well, can make a topcoat look better then it should.

All epoxies blush, even the ones that say non-blushing on the label. Some are much more tolerant to blush then others, but they all will blush under the right conditions folks, so don't be fooled. There's several reasons for it, but most boil down to; a slight variance in the hardener/resin ratio, which leaves an unreacted glycidol oxygen or amine hydrogen molecule bloom on the surface of the cured matrix (depending on which is in excess, hardener or resin) or a conditions induced amine congregation at the surface of the matrix, where it interacted with the moisture in the environment (read high humidity makes it much worse). As a result, if you are working the field or in rough, non-environmentally controlled conditions, the wise fabricator assumes there will be some level of blush on any freshly cured epoxy surface and removes it prior to any additional efforts.

[muskoka]

We painted West system epoxy as follows:

1. Light sand to remove amine blush;
2. Clean with spirit wipes;
3. Prime with a 2-pack primer;
4. Apply 2 coats of 2-pack polyurethane paint.

I don't think polyurethane paint works that well without a primer. And the 2-pack will give a much more durable finish. Fridges take a beating.

[PAR]

Sanding amine blush is a recipe for disaster. You're effectively mashing the uncured amines into the surface as much as removing them, which can contaminate subsequent coatings, layers, etc.

Amine will wash off with water, though a little white vinegar mixed in helps cut it. If you must use a solvent use isopropyl alcohol, xylene or denatured alcohol. Use diluted at least 50%.

Some single part, modified polyurethanes/alkyds and some LPU's react (badly) with some brands of epoxy. It's the nature of the beast and primer is the ticket. If you're doing a "real" paint job, then primer is blocked down, possibly several times before the topcoat goes down. If you're looking for a smooth finish, primer is a must. If you take a short cut and it doesn't work out, then . . .

[muskoka]

PAR,

I'm working with a Kiwi shipwright who's been doing this for 25 years. Sanding does not 'mash' the blush into the epoxy. Have you ever sanded an oil stain out of wood decking? Well, wood is a lot more porous! Once sanded it's air blasted, spirit wiped then fingers off.

Anyway, We used a high build primer before painting. Make sure the primer coat is the finish you want because even a high-build paint is unforgiving of surface imperfections.

[GordMay]

Originally Posted by muskoka

... Sanding does not 'mash' the blush into the epoxy...
... Once sanded it's air blasted, spirit wiped then fingers off...

Zinc stearate is applied to some types of sandpaper to keep it from loading quickly. Stearate, a chemical similar to animal fat, has the potential to create a contaminated surface just by sanding. We suggest you use aluminum oxide or waterproof wet/dry sandpaper that has not been treated with stearate.

Every last particle of sanding dust does not need to be removed to get good adhesion. Get the bulk of it off and consider the remaining dust as an epoxy filler. Good methods for removing sanding dust are to vacuum it off, sweep it off with a non-contaminated bench brush, or wash it off with water.

It is a common practice to use compressed air to remove sanding dust. However, aside from the mess created by blowing dust, it is possible that blowing compressed air on the surface will contaminate the surface with compressor
oil or water.

Amine blush may be formed when epoxy cures. Amine blush is water soluble. Many organic solvents are completely ineffective for removing it. That is why we suggest washing
an epoxy surface with water (water clean enough to drink) using a Scotch Brite™ pad (or wet sanding with waterproof wet/dry sandpaper) and drying it with paper towels before continuing with another operation. Soapy water, or water with ammonia or bleach, is not necessary and may leave a residue— another possible surface contamination.

Above excerpted from ➥ http://westsystem.com/ss/assets/Uplo...tamination.pdf





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[thinwater]

Originally Posted by GordMay

Zinc stearate is applied to some types of sandpaper to keep it from loading quickly. Stearate, a chemical similar to animal fat, has the potential to create a contaminated surface just by sanding. We suggest you use aluminum oxide or waterproof wet/dry sandpaper that has not been treated with stearate.

Every last particle of sanding dust does not need to be removed to get good adhesion. Get the bulk of it off and consider the remaining dust as an epoxy filler. Good methods for removing sanding dust are to vacuum it off, sweep it off with a non-contaminated bench brush, or wash it off with water.

It is a common practice to use compressed air to remove sanding dust. However, aside from the mess created by blowing dust, it is possible that blowing compressed air on the surface will contaminate the surface with compressor
oil or water.

Amine blush may be formed when epoxy cures. Amine blush is water soluble. Many organic solvents are completely ineffective for removing it. That is why we suggest washing
an epoxy surface with water (water clean enough to drink) using a Scotch Brite™ pad (or wet sanding with waterproof wet/dry sandpaper) and drying it with paper towels before continuing with another operation. Soapy water, or water with ammonia or bleach, is not necessary and may leave a residue— another possible surface contamination.

Above excerpted from ➥ http://westsystem.com/ss/assets/Uplo...tamination.pdf





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Funny.

IF sanding would remove amine blush, we wouldn't have this thread....

Different products, different rules. Some products do not have a water soluable blush, so sanding+solvent would work.

[GordMay]

Originally Posted by thinwater

Funny.
IF sanding would remove amine blush, we wouldn't have this thread...

I wasn't trying to be funny; just trying to cite an expert opinion (WEST Systems).

The OP:
"... sanded it and put 3 layers of west system epoxy (105/206) on it, 3 layers wet in wet. Turned into a beautiful flat and shiny surface. Then cleaned it with solvent, sanded it to a frosty appearance with 150 grid and cleaned it again..."

[PAR]

I've run across both issues Gord, both anti-clog agents and amine impacted into the surface from sanding. I think most shops know about using compressed air on a freshly prepped surface too. You have to work clean.

There are a few popular brands of sand paper that I just can't risk using. I'm also very aware of the chemistry I'm working with, much more so then the average craftsman. You'll note the solvents I listed all are water soluble and have high molecular pressure, which makes them well suited as cleaners. In fact I have a combination of chemicals I use as a pre-mixed "tack-rag" prep. My friend, the local fire marshal just shudders when he sees the "chemical" corner of my shop. It scares the hell out of him and he tells me so. But he also knows that I'm organized, keep everything in one location and work neat. He's told me the local fire house has a "fire plan" for my place. He explained that hardware stores, gas stations, etc. require special fire fighting tactics. My local fire station (about a mile away) will fight a fire at my place from a 100 yards away with a canon. Apparently, they are as scared as the Mike the fire marshal.

[thinwater]

Originally Posted by GordMay

I wasn't trying to be funny; just trying to cite an expert opinion (WEST Systems).

The OP:
"... sanded it and put 3 layers of west system epoxy (105/206) on it, 3 layers wet in wet. Turned into a beautiful flat and shiny surface. Then cleaned it with solvent, sanded it to a frosty appearance with 150 grid and cleaned it again..."

Sorry for my lack of clarity; I agree with you completely. What I thought was funny were those suggesting that sanding was effective on West Systems products. Clearly, the OP was having a problem and clearly both West and the other posters know the sollution for this problem; soap and water scrub. Posts like that always remine me of the many calls I have made to factory reps and been told "you can't be having that problem", when clearly I am.

[muskoka]

Originally Posted by GordMay

Above excerpted from ➥ http://westsystem.com/ss/assets/Uplo...tamination.pdf

From West Systems:

"Despite the dust, a freshly sanded surface is about as clean as a surface can get..."

"Before applying finishes other than epoxy (paints, bottom paints, varnishes, gelcoats, etc.), allow epoxy surfaces to cure fully, then wash and sand."

Read the excerpt provided by Gord: West Systems suggests sanding for surface preparation on West Systems products.

[GordMay]

Originally Posted by muskoka

... Read the excerpt provided by Gord: West Systems suggests sanding for surface preparation on West Systems products.

Further quoting WEST Systems:

“... Good methods for removing sanding dust are to vacuum it off, sweep it off with a non-contaminated bench brush, or wash it off with water...

... Amine blush may be formed when epoxy cures ... That is why we suggest washing an epoxy surface with water (water clean enough to drink) using a Scotch Brite™ pad (or wet sanding with waterproof wet/dry sandpaper) and drying it with paper towels before continuing with another operation...”

[PAR]

Amine blush can be expected to form on any epoxy. Once you understand the chemistry, it becomes obvious. Unless you have highly controlled laminating or coating conditions, then you would be best advised to assume you have a blush and wash it off.

This simply means unless you are bagging, infusing or working in a controlled environment (temperature, humidity, etc.), then you will have a blush to some degree, regardless of resin brand or type. You can take your chances or wash it off, your choice.

This isn't supposition or speculation, it's fact and easily verified by calling tech support over at West System or other epoxy reformulator.