acid etch

[robert401]

Does a new concrete floor need acid etching before epoxy is applied, and if you dont etch it will paint still stick?

 

[Ray-CA]

I would say yes. The etching give the epoxy something to grab onto.

But, I'm not an expert, nor did I stay at a Holiday Inn Express.

Ray

 

[AlphaGarage]

And if that Holiday Inn had any epoxy coated floors hopefully they listened to you and etched them before applying the epoxy. Because even if it was fresh concrete it should be "profiled" before applying most coatings.

The profiling can be done with acids or by grinding or shot blasting.

The etch/grind will give the concrete the correct physical "profile" providing millions of tiny footholds for the coating to mechanically, and with some coatings chemically, anchor to.

And wait 28 days after the pour before taking any of these steps.

 

[robert401]

Thanks for the reply. I did stay at the Holliday Inn ,and I will definately be etching the floor!

 

[tcianci]

Just don't try to etch the floor at the Holiday Inn

 

[rburke65]

You put a light broom finish on the concrete, then you turn around and grind it off before you acid etch??? Or am I confused? Thannks.

 

[gatchel]

You put a light broom finish on the concrete, then you turn around and grind it off before you acid etch??? Or am I confused? Thannks.

+1

Confused too...

 

[LegacyIndustrial]

Floors needs a profile similar to 80-100 grit sandpaper.
A broom finished floor can be really aggressive, or can be similar to sandpaper.
IF it's too aggressive your coating will not cover it over leaving a "rough" epoxy surface, probably not what you are looking for.

If it's too aggressive you will need to grind it.

Your surface texture tends to telegraph through the coating.

 

[Bad Idea]

You wouldn't grind and etch, you would do one or the other. As stated above, the goal is to get a profile on the concrete for the epoxy (or urethane, or acrylic...) to grab onto.

 

[lateapex911]

I understand that if the surface is "soft", (easily marred by a screwdriver) it should be ground. What's the proper procedure for grinding? Rent a grinder? Which one? What abrasive?
Or is etching an alternative?

 

[Boz86]

The profiling can be done with acids or by grinding or shot blasting.

Is etching just as good as grinding? Going to be doing this soon and in my case the acid looks a lot easier.

 

[rugerlady]

The acid does a sufficient job, but diamond grinding is the preferred method of profiling. You can rent a walk behind machine from most any tool rental company or some Home Depots.

 

[Boz86]

I'll do it the preferred way, then. Hate to do it wrong and waste money and time.

 

[Edger]

Acid etching is vital. New concrete will never allow a coating to stick even with a broom finish. The trouble is the shiny surface left when the water evaporates, this shiny surface is even on broom finished concrete and will not allow the coating to soak in properly. So acid etch, shotblast or grind the floor first. A good way to acid etch quickly and get an even finish is to use a long nap roller with a long handle and a plastic paint tray. As you get to the end of the roll path move a bit faster to flick the acid out from the centre of the roller cover so the end of the path is similar to the beginning. Don't be a smarty pants and flick it everywhere cause it burns holes in clothing and stains metal. Mix it strong too, about 3 or 5 parts of water to one of acid and if possible blast it off thoroughly with high pressure water - that means very close with 2,000 to 3,000 psi pressure. Grinding is better, but acid etch is dirt cheap. Hope that helps a bit.

 

[Edger]

If it is soft you have a problem. Better harden it after a very light diamond grind. If it does not have any shiny bits maybe you could harden it without diamond grinding and then paint. Concrete hardeners are cheap and effective, but if you do not then the concrete will wear away under the coating and the coating will look like it is bubbling and peeling. Soft concrete turns to powder when it is subjected to heavy loads and this can happen under the coating, seen it many times.

 

[pauls340]

When you trowel finish concrete and your finisher "milks" the surface, that laitance surface will prevent most coatings from sticking for any permanent amount of time. You should either mechanically remove the surface by grinding or you can etch it. I had a sales call today to a large floor specialty coating company in Pt. Huron Michigan and they grind all their floors ever since the EPA reduced the VOC levels in adhesives.(1999)

 

[VersatileBuildingProducts]

Take a look at this blog article. Acid etching is not a great way to go about it. You are far better off mechanically grinding.

Acid Etching Concrete Pre-Epoxy - Why It's a Bad Idea

 

[Edger]

Take a look at this blog article. Acid etching is not a great way to go about it. You are far better off mechanically grinding.

Acid Etching Concrete Pre-Epoxy - Why It's a Bad Idea

Interesting article, but they seem to mainly have a problem with the surface not being water blasted properly after etching rather than anything else.

I was an epoxy contractor and I did a few acid etch preparations although it was not my preferred way to prepare. I tried to get all the information I could on etching and found most of it confusing and much of it conflicting to each other. Some advocated a special type of neutralizer, some not, but I never had an adhesion problem although I always water blasted the surface thoroughly and I never neutralised.

My work was mainly factory floors where the treatment was rough, and if I was coating my garage I would acid etch because the loading and treatment is not as strong as a factory where they occasionally do forklift donuts.

You can find more information at http://www.situp.com.au/Concrete garage floor coating.html

 

[Cruzin90]

I tried to get all the information I could on etching and found most of it confusing and much of it conflicting to each other. Some advocated a special type of neutralizer, some not, but I never had an adhesion problem although I always water blasted the surface thoroughly and I never neutralised.

Concrete is alkyline (base) and acid...is an acid. What do you get when you mix a base with an acid? Answer: A salt and salt is corrosive. You should neutralize the acid somehow, you can use sodium bicarbonate (baking soda). At the very LEAST, wash the concrete thoroughly.

 

[Jaguar Fan]

Concrete is alkyline (base) and acid...is an acid. What do you get when you mix a base with an acid? Answer: A salt and salt is corrosive. You should neutralize the acid somehow, you can use sodium bicarbonate (baking soda). At the very LEAST, wash the concrete thoroughly.

The concrete neutralizes the acid.

but you do need to thoroughly powerwash afterward to remove the salt. I needed to powerwash two or three times, IIRC, with the wand tip ~10 inches off the flor to get rid of loose powder. It will be obvious during the powerwashing.

 

[Edger]

Concrete is alkyline (base) and acid...is an acid. What do you get when you mix a base with an acid? Answer: A salt and salt is corrosive. You should neutralize the acid somehow, you can use sodium bicarbonate (baking soda). At the very LEAST, wash the concrete thoroughly.

Why does the acid not completely neutralise when in contact with concrete because there is a lot more alkaline concrete than acid on top of it? And does the baking soda or other neutralizer make the salt non corrosive or is it to mop up leftover aicidity? I could never understand these things so any information would be great.

 

[AlphaGarage]

Muriatic acid reacts with the calcium in the concrete, that reaction does neutralize the acid, but there's no guarantee that there's enough calcium to fully neutralizer all the acid. Likewise exposure to air also neutralizes the acid, as does the water used to dilute the acid, but even then the acid may still be a bit "hot". That's why you should use baking soda in addition to flooding the floor a couple of times.

Pretty much all the pro contractors will grind or shotblast to prep, but even they will use acid on occasion, like in a situation where it's critical that no dust be generated, like a micro-chip facility.

I'd say that probably 80% of our DIY jobs acid etch, and we haven't had any problems with our BondTite primer lifting from the concrete yet.

 

[Edger]

Muriatic acid reacts with the calcium in the concrete, that reaction does neutralize the acid, but there's no guarantee that there's enough calcium to fully neutralizer all the acid. Likewise exposure to air also neutralizes the acid, as does the water used to dilute the acid, but even then the acid may still be a bit "hot". That's why you should use baking soda in addition to flooding the floor a couple of times.

Pretty much all the pro contractors will grind or shotblast to prep, but even they will use acid on occasion, like in a situation where it's critical that no dust be generated, like a micro-chip facility.

I'd say that probably 80% of our DIY jobs acid etch, and we haven't had any problems with our BondTite primer lifting from the concrete yet.

Fair enough, thanks Fred.

 

[YourGreatGarage]

Just me 2 cents - I do this everyday and never use acid. Rent a Diamond grinder or don't do it.

Tony
www.YourGreatGarage.com

 

[LegacyIndustrial]

Tony:

Nice web-site. Are you guys busy in Tampa?

 

[NewShockerGuy]

I finally got muriactic acid shipped to me. And since it's been so nice I am getting ready to do the garage FINALLY..lol

What are the steps that everyone recommends doing the floor.

Degrease? (what product to use)
Powerwash
Acid Etch
Power Wash
Let dry completely?
Acid etch again
Power Wash
Let dry...

Then start epoxy?

Thanks,
-Nigel

 

[srode]

I would just etch it once and power wash a couple times if you use 50% solution and heavy. That's what it took on my last section of 3 to get a good texture and get it clean of the residue. Make sure you wear safety glasses and a pump sprayer that has an all plastic wand - except the tip - my first one had an aluminum which looked like a sprinkler after 2 rounds with it.

I also found a product called OSR (Oil Stain Remover) from lowes ended up working the best on my deep oil stains where it had soaked into the slab. 3 Applications letting it dry up for about 12 hours and sweeping had it gone. Acetone and a scrub brush worked well on most spots, just not this one deep stain.

 

[NewShockerGuy]

How long do you leave the acid on the actual concrete? Until it dries?

I just did a little test on a brick in the back porch that needed cleaned and it was fizzing like hell..lol Like movie type stuff.... then after about 35 seconds no longer fizzed so i just rinsed it off... Should you agitate the acid INTO the concrete/brick that you are trying to clean/etc or do you wait until the acid has dried?

Also should you get the surface damp first OR should the surface be dry when applying acid?

Thanks,
-Nigel

 

[srode]

Lightly wet the fllor then apply and scrub while it's fizzing and after it's done fizzing too. Do a section about 2 or 3 feet by 2 or 3 feet at a time is what I did. I didn't let mine dry, just started pressure washing when it was complete, no reason to let it dry but don't know if it would hurt anything either as long as you rinse it off reasonably soon afterwards and pressure wash.

 

[rugerlady]

You should NOT let the acid/water mixture dry on the concrete before rinsing it off. This could act as a contaminat later.

 

[AlphaGarage]

As mentioned earlier the acid leaches the calcium, removing it from the concrete, but it doesn't vaporize that residue. The freed calcium remains in suspension in the acid/water mix. If the mix is allowed to evaporate the calcium residue/dust is deposited back onto the concrete, and it doesn't just rest on top of the concrete - it adheres to it. It sticks well enough to be difficult to scrub off, but not that well that it won't ever release at some later date.

If you coat over the floor without removing the calcium dust the epoxy will stick to the calcium dust instead of the underlying concrete, over time the calcium dust will probably lift off of the concrete, and at that time it will take the coating off with it.

To avoid that failure you want to make sure that the water/acid doesn't dry but rather is rinsed off, rinsing off the calcium dust at the same time.

So only etch an area small enough that you can apply the solution and let it sit for about 15 minutes without it drying off. That means that on a hot day you may want to etch several smaller areas instead of the entire floor.

 

[ggcdad]

Is there anyway to make sure the acid has been completely removed from the concrete?

 

[Edger]

I used to let the acid dry every time without coating problems because the floors were usually around 10,000+ sq.ft which were too big to keep wet and I experimented with water blasting to remove the residue. I found that 3,000 psi up close (one inch) was the minimum pressure required to remove it. The only effective way to do that was to use a high powered "spin jet" which looked like a lawnmower and had jets of water blasting down at the slab while the arms that held the jets rotated quickly. I think Karcher have these.

I hated to take chances with prep and I was surprised on a recoating job to find that the original coat was prepped with acid etch and not fully water blasted, I could see the white residue in some areas around the edges. It was a real pain to remove from those edges because it had adhered very well!

 

[ggcdad]

I ground mine using an Edco 11" grinder. The third bay which is just storage is nice and rough, but the two bays where the cars park are not that rough. I did go over those two bays an extra time with the grinder, and am wondering if it might have made it smoother rather then rougher. And I'm wondering if I should acid etch those two sections, or maybe going over it with the power washer will rough it up.
Any thoughts?

 

[ggcdad]

One of my Epoxy-coat clear coat kits came exploded. When I opened the 5 gal bucket, I found that the interior bucket(s) had opened up inside - sticky mess.
The replacement one came today, and I just opened it and found the same thing - a sticky mess. Either UPS is really "drop" shipping these or they are not getting sealed properly at Epoxy-Coat.

Christine - I'm hoping you can help get another replacement out to me by Sat. I don't want to put this off another weekend. I'll call in the morning.

 

[Edger]

If the diamond grinding left a polished surface the diamond segment bond was too strong. Wrong segments for the hardness of your floor. Try the water test, if it soaks in readily you should be OK. Also there should not be a shine. If there is you may have to acid etch.

For more info see http://www.situp.com.au/Grinding Hard Concrete.html

 

[ggcdad]

Water soaks in easily and there is no shine. Hopefully I'm OK.
Thanks Edger.

 

[charger891]

I just did acid etching last weekend on my driveway curbing, the firts thing in the instructions stated no not acid etch , it will effect the lime in the concrete and you wont get the full effect of the acid stain, my concrete was 30 days old and stained corectly. i`m no expert but it worked.

 

[AlphaGarage]

I just did acid etching last weekend on my driveway curbing, the firts thing in the instructions stated no not acid etch , it will effect the lime in the concrete and you wont get the full effect of the acid stain, my concrete was 30 days old and stained corectly. i`m no expert but it worked.

Instructions were correct - if your going to acid stain the concrete then it's best not to acid etch it first. Different colors and stains use chemicals that react with material in the concrete to achieve the desired color change. Acid etching may remove one of those elements (most likely calcium) which means there's none left to change color.

Sounds like that wasn't an issue in your case, glad it worked out.

 

[ggcdad]

Well, I decided to acid etch those two car bays again.
I picked up Muratic acid and did almost a 1:1 ratio. And then I power washed it.
It still didn't seem to rough it up too much though, but it's a little better and as good as it's going to get.

And Christine is was able to get another replacement clear coat out which should arrive Friday - yeaaaaaaaa. Much appreciated Christine!!!!