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goodkarma 07-09-2008 11:47 AM

Epoxy Paint on Previously Painted Concrete Floor
 
Will epoxy paint with the chips and clear sealer work over an already painted concrete basement floor? The paint has stayed on well except in a few spots where we get a small bit of water during heavy rains. We want the total area to look nice and have no spots where the paint has "blistered" and come off and are wondering if this is a solution for us.

Please advise! Thanks.

Pro Painter 07-09-2008 01:18 PM

A chain is only as strong as its weakest link, so if the old paint has a tendency to come up, the overcoat is not likely to cure that.

Epoxy paints stick well to some kinds of paints and not others. Without knowing everything about the chemisty of the paints, it's impossible to say with certainty what does and does not work.

Sometimes primers can help things to stick to other things. There was a good post about the different kinds of primers on another forum, at http://www.city-data.com/forum/house...-tutorial.html .

Names of things cannot always be trusted. A few years ago Home Depot was selling, under the Morwear brand name, an "Enamel" and an "Epoxy Enamel". Both were latex paints, clearly stated on the side panels to be water-cleanup. Merchants nowadays all-too-often tell the consumer what they think will impress the consumer, regardless of truth or actual meanings of words.

Epoxy paints *should* be two-component products. Some may be solvent-borne [In my opinion, those are best] and may also be waterborne, wherein the Part A and Part B are both water-emulsions. The waterborne epoxy paints are not high-build paints, in that they are only about thirty percent solids. The solvent-borne paints are more of a high-build epoxy paint, being about sixty percent solids. You get what you pay for...

Some solvents can cause swelling and wrinkling of some other paints. Test what you have there before you use a high-quality two-component epoxy paint. Soak a paper towel with a bit of lacquer thinner and scrub the old paint. See if it dissolves, wrinkles or softens much.

If it seems to have some integrity, clean it with an alkaline detergent such as automatic dishwasher detergent in water, rinse, dry, and apply a test patch of your new paint. Let it cure, then try to scrape it off. If it really sticks, then you are reasonably safe in going ahead.

Good luck

slickshift 07-09-2008 07:03 PM

You'll want to check with the specific epoxy manufacturer
I know of some that will work fine on that surface, and some, not so much
Check the specific TDS (technical data sheet) for the product you are going to use

The absolute best way will always be grinding off the old coating

Nestor_Kelebay 07-09-2008 08:57 PM

ProPainter:

You said: "Names of things cannot always be trusted. A few years ago Home Depot was selling, under the Morwear brand name, an "Enamel" and an "Epoxy Enamel". Both were latex paints, clearly stated on the side panels to be water-cleanup."

That word "enamel" is a perfect example. The meaning of the word has become well settled to mean a paint that dries to a harder, smoother film than you'd normally expect.

In fact, the very first "enamels" were almost certainly made by tinting varnish in a paint tinting machine, just as thought it was a deep tint base. Years ago, varnish only came in semi-gloss and gloss. Also, varnish typically contained more "copals" than the oil based paints of the time, so it dried to a harder film than the linseed oil based paints. As a result, "enamels" were paints that dried to a harder smoother film than people expected from the linseed oil based paints they were used to.

In 1956, the Bayer Company (the Aspirin people) patented the very first alkyd based "polyurethane". And, since then, polyurethane has come to replace varnish as the clear coat of choice over wood. So, an "enamel" nowadays would simply be a polyurethane based paint, like a polyurethane floor paint. Alternatively, if you wanted to make an enamel nowadays, you would tint a can of polyurethane "varnish" or polyurethane hardwood floor finish in a paint tinting machine. You'd end up with a "paint" that dried to a harder and smoother finish than one would typically expect from oil based paints.

But, the truth is that continuing improvements in paint binders and additives means that EVERY paint dries to a harder, smoother film than the same paint did only 5 or 10 years ago, so EVERY paint could theoretically be called an "enamel". And, some paint companies have come to calling everything they make, except for their dead flat latex paints, "enamels". In that context, the meaning of the word changes to "buy me".

So, I agree with you on the use of the word "enamel". It really has no more effect on a paint's performance if a manufacturer chooses to slap that name on the can than a racing stripe has on a car's performance.

However, I think you're using that word "latex" incorrectly when you say:

"A few years ago Home Depot was selling, under the Morwear brand name, an "Enamel" and an "Epoxy Enamel". Both were latex paints, clearly stated on the side panels to be water-cleanup."

There are lots of waterborne paints, and all of them clean up with water, but they are not all "latex" paints. There are waterborne alkyds (where they add polar groups to alkyd resins to make them soluble in water), there are waterborne polyurethanes and waterborne epoxies. All of them would be "water clean-up", but none of them could correctly be called a "latex" paint.

The phrase "water clean-up" simply means that the wet product can be cleaned off with water, but that's NOT the same thing as saying it's a "latex" paint.

In my humble opinion, before you can call something a "latex" paint, it has to have other more important similarities to latex paints as well, not just being water clean-up. It would have to be made of the same kinds of plastics as latex paints are, and I believe it would need to form a film by coalescence like latex paints do.

Otherwise, we could call the finger paints children use in kintergarden "latex" paints too, couldn't we? These paints dry the same way that muck turns into mud, by simple evaporation of water. So, they're definitely water clean-up. But it would be more than a stretch to say they're "latex" paints.

Pro Painter 07-09-2008 09:27 PM

Hello, Nestor. Nice to meet someone as knowlegeable as you out here in forum-land. I was just on my way out and saw this, so a brief reply: I am calling them latex because they were latices; that is to say, a water-borne emulsion of little sticky droplets of resins, suspended in a vehicle that is water. I did not think highly of either of them because they had poor adhesion when cured, and the fellow who bought them and showed me the results was highly upset, because he thought those names meant high-performance, high-quality paints.

It is true that waterborne paints might have water-soluble resin systems in them. These didn't. To my knowlege no one is making a two-component epoxy paint that uses water-soluble resins; I don't even know that it is possible. The only ones I am aware of are the emulsion-type systems, and seem to be about thirty percent solids. A decent oil-base enamel used to be fifty to sixty percent solids....ah, those were the good old days....

...speaking of which, I seem to recall that latex originally meant the sap of the rubber tree, which had the physical characteristics of an emulsion. Eventually water-suspensions of acrylic resins were developed to make waterborne paints that had the potential to compete with the solventborne more durable enamel paints...I think that was about sixty years ago. The needed a name to differentiate it from oil-base paints that were called Enamel, and used the technical term that describes water-emulsions particularly back then...and Latex it was.

At least I think that's how it happened. Time to go. 'night, all.

Nestor_Kelebay 07-09-2008 10:55 PM

Quote:

Originally Posted by goodkarma (Post 137464)
Will epoxy paint with the chips and clear sealer work over an already painted concrete basement floor? The paint has stayed on well except in a few spots where we get a small bit of water during heavy rains. We want the total area to look nice and have no spots where the paint has "blistered" and come off and are wondering if this is a solution for us.

Please advise! Thanks.

GoodKarma:
If I were you, I would look in my yellow pages phone directory to see if there are any companies listed under "Industrial Coatings" in your area that you happen to know also sell paints. If there are, then these companies won't be doing powder coating work, they'll be selling epoxy and isocyanate based polyurethane coatings.
Phone them up, and ask to speak to their industrial coatins sales rep. Explain your situation to the fella, and see if you can get a small sample of their epoxy floor paint to use only on the WET and blistered areas of your garage floor.
My concern is that the old paint on your garage floor may very well have been an epoxy garage floor paint, and it may have blistered, cracked and peeled because of water migration through the concrete in those spots. And, if that epoxy paints stays stuck down well, then you can always paint over the trial epoxy with another coat when doing the whole floor.
But, the epoxy you put on those wet areas will determine what would have happened there had you painted the whole floor, and that is the key here.

I agree with a previous post that suggested removing the old paint on the concrete. However, about the only way I know of to effectively remove a fully cured alkyd, polyurethane or epoxy paint from concrete is by sandblasting. Or, perhaps, getting on some rubber boots and some scuba tanks and scrubbing that floor with paint stripper.

I do think that if I wuz in your boots, I'd test an epoxy floor paint on the areas that have proven to be where other paints have failed. That's a much better option than to paint the whole floor with epoxy and have it fail in those same spots, isn't it?

Pro Painter 07-10-2008 01:04 PM

That's good advice, goodkarma. Let us know how it all works out.

Incidentally, there is one paint stripper I know of that takes off acrylic-latex, oil-base enamel and some of the less-robust epoxy or polyurethane paints and doesn't require a gas mask and scuba tanks to use, and that's Peel-Away #1. They make other number-versions, but I am only recommending the #1 for any porous surface. If your concrete is damp where you need to do blister-repair, there is only one product I know of that will glue down a paint to damp concrete, and that's Damp Concrete Primer. You can find both of those with an Internet search.


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