How much foaming from acid etch?

[Twizzstyle]

I just bought a house (my first) and I am prepping my floor for epoxy (Epoxy Coat).

Over the weekend I cleaned the garage like crazy (was already just about spotless), and today I did the acid etch (used the prep stuff that came with my epoxy coat kit, which is just muriatic acid I think).

I was expecting major foaming, but didn't get that. I'm just curious what I should expect. I wouldn't say there was no foaming... It was definitely fizzing everywhere, just not visually foaming like crazy. There were a few spots that foamed up a little. The video on the Epoxy Coat website where they spray it on doesn't really foam at all, but some other videos I've seen there is almost instant foaming, and a lot of it.

I'm just worried there might be sealer on the concrete and I'll have to rent a grinder. Was really hoping to do the epoxy this weekend, might not happen if I have to find a grinder.

For what its worth, when washing the floor, the water never beaded up, so I'm hoping that might be a good sign.

 

[AlphaGarage]

A good fizzle is perfect. Foaming usually indicates that the acid concentration is too high.

If water soaks in evenly, odds are there's no sealer present.

 

[Ruddy]

My first time, I had the floor too wet before I sprayed the etcher down, so it didn't fiz where there were little pools of water. Also, I think I read that if it "smokes" it too concentrated!

 

[Twizzstyle]

Great, that makes me feel a lot better. The floor was pretty wet when I sprayed the etcher down (not standing water, I had just pressure washed it, but gave it a good squeegee before doing the acid... but it was still wet).

After scrubbing and letting it sit for a few minutes, it turned a slightly yellow hue. Good sign, bad sign?

Thanks guys!

 

[Twizzstyle]

Would there be any harm in sanding the floor, and then re-etching? Just for peace of mind? I might get more acid, and make it a little more concentrated and try again tonight, putting it on with the floor not quite as wet. I'd just hate to go through all this work and have the floor peel up!

 

[nate379]

It can't really be "too" concentrated. I did 100% acid baths 3 or 4 times before my slab was rough enough.

I wore a gas mask though, don't think a person would last long otherwise.

 

[Twizzstyle]

Oh yeah definitely wearing a respirator, no worries there

Guess I'm back to the scrubbing tonight My arms are sore.

 

[AlphaGarage]

Another point to consider... You want to use enough acid to do the job, but not more. You want to avoid a situation where still "hot" acid gets into the concrete and lies there. What can happen is you think there's not more acid, then it soaks into the concrete, the epoxy coats the acid and encapsulates it, so it stays "hot" beneath the epoxy, after a rain hydrostatic pressure causes the acid to rise to the surface and reactivate, it doesn't react with the epoxy but it can react with the calcium in the concrete, it dissolves the calcium, and the epoxy bond is weakened because it's no longer adhering to a solid substrate but to calcium dust released from the concrete.

Doesn't happen too often, but is definitely a cause of some coating failures.

So, don't go overboard with the acid, either in quantity or concentration. Do not allow the etching solution to dry on the concrete. Neutralize the acid wash, baking soda in water will do the trick, ammonia (being liquid) is even better, but that will produce harmful fumes so you must use an appropriate breathing filter (one designed for organic vapors). Rinse well, a lot of water with a broom action will work, pressure washing will also work but if the pressure is too high it will force the acid wash into the concrete.

Muriatic acid is toxic and caustic stuff, these suggestions and tips aren't complete so don't rely entirely on them, be sure to carefully read and follow all precautions and safety warnings. Usually the package will have have complete directions, if not find them from another source.

You can also over profile the concrete. Not a big deal but it can cause you to use more material then you need to, or end up with a rough finish. We suggest a profile texture comparable to 80 - 120 grit sandpaper. Why do more work or buy more material than necessary?

 

[Twizzstyle]

Great feedback and info, thanks Fred!!!!

 

[Twizzstyle]

Ok I did another round of etching last night, the concrete etcher they had at home depot was phosphoric acid, not muriatic. Should do the same trick. I didn't dilute it as much as I did before, and I got a lot more foaming this time. I wouldn't say it was crazy, but it was visibly different.

Yet even still, after rinsing and squeegee'ing, I wouldn't say its totally rough. There are blotchy areas where its a rough sand texture, but the majority of the garage is still quite smooth. Water doesn't bead up on it, but I wouldn't say it soaks in really really fast.

Here are some before/after pictures.

BEFORE

AFTER

The lighter areas are where its rough (I need to pressure wash it tonight, I think the cloudiness is from baking soda that I didn't rinse out well enough). The darker areas are still pretty smooth, maybe a LITTLE bit rougher than before. I guess I was expecting the acid to eat through the whole top layer of concrete revealing just the substrate sandy surface - but maybe I was wrong?

 

[rugerlady]

Great, that makes me feel a lot better. The floor was pretty wet when I sprayed the etcher down (not standing water, I had just pressure washed it, but gave it a good squeegee before doing the acid... but it was still wet).

After scrubbing and letting it sit for a few minutes, it turned a slightly yellow hue. Good sign, bad sign?

Thanks guys!

The yellow is a good sign that the acid is working. Like I said in the PM, if you are not getting a profile of 100-120 grit sandpaper, you may want to consider grinding.

 

[Twizzstyle]

Ok, thanks Christine! Appreciate the help!

 

[TheBanker]

Be sure and triple rinse.

 

[Jaguar Fan]

Be sure and triple rinse.

^^^ +1 ^^^.

On my project, I used an electric costco-quality pressure washer to rinse. Once it dried, I could see the "brush marks" of the pressure washer spray. That indicated to me that I had not been aggressive enough in washing. So, I went after it again, keeping the tip of the pressure washer wand about 6 to 10 inches from the concrete and carefully went over every square inch.

After it dried, the "brush marks" were gone.

Note: check with the manufacturer of your product. I think you might need to let it set a week or so to thoroughly dry out so it passes a "plastic tarp" wetness test once again.

 

[Twizzstyle]

Well, I decided to go ahead and rent a big grinder and grind the floor. Boy am I glad I did. Turns out there WAS indeed sealer on it. Couldn't really tell before grinding, but as soon as I started, the sealer was coming off in hard little clumps, with a foul plasticy-chemical smell. once through the sealer, it was nice billowing concrete dust!

I will get some more pictures up soon and maybe a more detailed thread, once I get the epoxy down end of the week. The floor is probably ready for the epoxy now, but I am going to do one more acid etch tonight, just to put my mind at ease. Then let it dry all week, and do the epoxy this weekend.