acid etching

[Kapt]

My floor is 5 months old and has never been parked on, so it's fairly clean and oil free.

I'm getting ready to epoxy my floor with Epoxy-Coat and thought I could just acid etch without the need for renting a grinder.

I followed the instructions and diluted the muriatic acid 4/1 and applied it to a small section of the floor. I was expecting it to foam for about 20 seconds, but all it did was foam on the initial contact for less than 5 seconds. I scrubbed with an acid brush, then rinsed. It didn't seem to do much so I repeated the process, but this time it barely foamed at all. I experimented on a very small area with no dilution of the acid and it seemed to do the job. The concrete started to look like fine sandpaper.

Is there any downside to using a stronger solution?

 

[mhoffm911]

Yes, it could eat away your concrete and cause it to pop. All of the stuff I have read is that you are going for a sandpaper finish (which it sounds like you have reached). If I did anything, I might do it 1 more time and then do the epoxy after the floor has been dry for a couple of days.

 

[ni[x]it]

I used a 50/50 and applied it from a bucket by slinging the water, out of the bucket, across the floor.

Also, you MUST get a power washer to wash the concrete after applying the acid and letting it work. There will be a white residue after the etching that must be removed. Rent one for $100 and consider it a cheap investment in a quality project.

 

[snorvet]

The acid that comes with Epoxy-Coat does seem weak when you dilute it per the instructions. But mine turned out ok. Just rinse very well, maybe with some baking soda, and let dry completely.

 

[novas]

I used "phosphoric acid" from Sherman Williams this morning and found it was not effective. Then used muriatic acid on the previous and the rest of job and it worked great. I agree it doesn't foam for long so I kept it on each section for 20-30 minutes and just pushed the brush back and forth to distribute and keep wet with acid. Towards the end it was a little pasty, I then rinsed and when dry it had the "tooth" that is needed. Mixed the acid at 4 water to 1 acid. I agree with Ni[xi]t the power washer is a must. Good luck!

 

[novas]

Correction, I used 6/1 instead of 4/1 Sorry about that it was getting late and too many fumes...

 

[boiler7904]

I used a 4:1 solution of muriatic acid when I did my floor last fall. It was about 3-4 months old and had a fairly heavy coating of the builder's standard clear sealer. Two rounds of acid washing was enough to get a good tooth to the surface to apply epoxy to.

 

[hatchy]

I used 4:1 with mixed results; It worked on most of the floor, but some areas, the floor was still smooth, but there areas are small--less than 1 sq ft per area. How perfect does the etching need to be? I know it's desirable to get the entire floor to be 80-120 grit like, but are these pockets really going to hurt, or are we all just paranoid?

(A little tired about a weekend of prep work)

 

[boiler7904]

I used 4:1 with mixed results; It worked on most of the floor, but some areas, the floor was still smooth, but there areas are small--less than 1 sq ft per area. How perfect does the etching need to be? I know it's desirable to get the entire floor to be 80-120 grit like, but are these pockets really going to hurt, or are we all just paranoid?

(A little tired about a weekend of prep work)

I had a few spots like that. Did as much etching as I could, let it dry for a week before putting down the epoxy and no problems to date after a year.

 

[hatchy]

Thanks! Then I wont worry about getting the spots then

 

[Hammerdown]

The downside to using a strong dilution would be that acid actually eats the surface of the concrete. This provides an "etch", which is creating a mechanical profile in the substrate but deteriorating the surface to do this. If too much is used, the surface can become soft and/or powdery, which is counter-productive to the adhesion of the coating. Trying to coat a soft/powdery surface would be like painting sand, you will not get a long lasting/durable coating. I would only use the recommended method from the manufacturer to ensure the best results. If you wanted to create a strong mechanical profile I would suggest grinding the floor to do so.

 

[hatchy]

Thanks Hammerdown, that's excellent info!

 

[z28toz06]

Also keep in mind that the acid (muriatic) will react with the alkaline in the concrete which is a base, thereby neutralizing it somewhat after a few minutes. They recommend that you scrub the area for 4 or 5 minutes and then sprinkle the baking soda and power washing it off. I rinsed twice with the power washer.

 

[Hammerdown]

Also keep in mind that the acid (muriatic) will react with the alkaline in the concrete which is a base, thereby neutralizing it somewhat after a few minutes. They recommend that you scrub the area for 4 or 5 minutes and then sprinkle the baking soda and power washing it off. I rinsed twice with the power washer.

For sure! Concrete is alkaline, acid is, well... acidic. When the two meet it causes a chemical reaction. If done properly, they cancel each other out and the concrete becomes neutral, or a 7 on the PH scale. This will allow a coating to get the best adhesion, when the concrete is neutral. The baking soda will ensure the acid is neutralized when it is rinsed out.

 

[Kapt]

Thanks for all the advice. Here's what I finally did.

I wound up etching 3 times. Home Depot sells muriatic acid in two gallon packages. I mixed it with water 4:1 and applied it with a plastic garden watering can. After the foaming stopped (about 10 seconds max) I scrubbed with an acid brush, followed by a powerwash. I did about a 12'x12' section at a time. After I was done with the acid and powerwash, I saturated the area with a solution of baking soda and water, followed by a really good last rinse with a hose.

I wound up with about 2/3 of the floor with the proper consistency of 80-100 grit sandpaper, and the other 1/3 fine sandpaper. I'm not doing anymore.

I almost think it would have been less time and effort to rent a grinder.

I going to wait a few more days for the floor to dry, then I'll post some pics after its done.

By the way, the one quart container of muriatic acid the I got with my kit from Epoxy Coat is supposed to etch 500 sq ft. Not even close, unless I totally screwed it up. I wound up using a total of a little more than 2 gallons of acid (diluted 4:1).

 

[Hammerdown]

It sounds like they might have called for a dilution rate of 8:1 if they only gave you a quart. Let us know how it turns out.