Electric floor scrubber for acid etching?

[s10xtremist]

I'm not going to scrub 1200 sq. ft. of concrete with a plastic brush on a broom handle. So, I was thinking it would be a good idea to rent a 14" scrubber for the weekend and make it easy. This is the type of machine I'm looking at:

I'll use the long-handled brush for the corners. Would this method be okay to scrub with a 1:3-1:4 muriatic acid/water solution? I'm a bit concerned that the spinning action of the scrubber would just polish off the surface that the acid removes, leaving me where I started but with slightly thinner concrete. If it matters, the concrete was poured at the end of March, and was power-troweled to a finish that I'd guess feels similar to 500-grit sandpaper.

 

[Shea]

When you acid etch you only want to lightly scrub the solution into the concrete. The reason for this is to encourage a more consistent etch. The scrubbing machine will be flinging acid around (dangerous) and is overkill for what you need to accomplish. It will also help embed the solution deeper into the concrete which will make it harder to neutralize when rinsing.

It's going to take more effort working a floor buffer like that around 1200 sf. of floor as well vs. lightly running a push broom over it.

 

[chiplee]

In the application instructions for the Profiling acid from Surface Geltek, it says you can work the acid into the concrete with an electric floor scrubber "if necessary". It will be a PITA cleanup on the rented scrubber when you're done. Personally, I didn't think the acid stayed active long enough to really get much use out of a scrubber. It may come in handy for removing whatever acid you use and the calcium carbonate that is left behind by the reaction, but a pressure washer did the trick for me. It's so arid where I am you really can't prevent the acid from drying on the concrete in some places, so a pressure washer is a must. I etched 5 times with various products before I got the floor where I wanted it for a coating.

 

[s10xtremist]

When you acid etch you only want to lightly scrub the solution into the concrete. The reason for this is to encourage a more consistent etch. The scrubbing machine will be flinging acid around (dangerous) and is overkill for what you need to accomplish. It will also help embed the solution deeper into the concrete which will make it harder to neutralize when rinsing.

It's going to take more effort working a floor buffer like that around 1200 sf. of floor as well vs. lightly running a push broom over it.

Didn't think about the flinging part of it. Also, I didn't know that all I had to do was "lightly run a push broom over it". I thought it was something that needed lots of vigorous scrubbing with a lot of pressure on a broom.

In the application instructions for the Profiling acid from Surface Geltek, it says you can work the acid into the concrete with an electric floor scrubber "if necessary". It will be a PITA cleanup on the rented scrubber when you're done. Personally, I didn't think the acid stayed active long enough to really get much use out of a scrubber. It may come in handy for removing whatever acid you use and the calcium carbonate that is left behind by the reaction, but a pressure washer did the trick for me. It's so arid where I am you really can't prevent the acid from drying on the concrete in some places, so a pressure washer is a must. I etched 5 times with various products before I got the floor where I wanted it for a coating.

Very insightful input. I have a pressure washer, which I was actually about to go out and use on the floor now just to clean away the loose stuff.

So, all I really need to do is:

1) Wet the slab

2) Spread the acid/water solution with a garden waterer over an area that I can work before it dries

3) Make a few passes with a plastic-bristled push broom

4) Repeat for the entire slab

5) Clean the concrete with a pressure washer


Where can I get a pH test kit for concrete?

 

[chiplee]

Didn't think about the flinging part of it. Also, I didn't know that all I had to do was "lightly run a push broom over it". I thought it was something that needed lots of vigorous scrubbing with a lot of pressure on a broom.



Very insightful input. I have a pressure washer, which I was actually about to go out and use on the floor now just to clean away the loose stuff.

So, all I really need to do is:

1) Wet the slab

2) Spread the acid/water solution with a garden waterer over an area that I can work before it dries

3) Make a few passes with a plastic-bristled push broom

4) Repeat for the entire slab

5) Clean the concrete with a pressure washer


Where can I get a pH test kit for concrete?

They don't have to be "for concrete". You're testing the rinse water, so any test strip will do. They sell them at Walmart. If you rinse three times with high pressure water it's going to be so diluted you'll find the pH is between 6 and 9. Worth checking though. My final cleaning before starting the clock on drying time was with TSP. Trisodium phosphate (TSP) is Na3PO4, which when dissolved in water turns basic. That should be sufficient to neutralize any remaining HCl after the 3 rinses.

 

[shaun oriold1]

IF you're willing to rent this machine, why not rent a grinder. It wont take much more effort to grind the floor?

 

[s10xtremist]

They don't have to be "for concrete". You're testing the rinse water, so any test strip will do. They sell them at Walmart. If you rinse three times with high pressure water it's going to be so diluted you'll find the pH is between 6 and 9. Worth checking though. My final cleaning before starting the clock on drying time was with TSP. Trisodium phosphate (TSP) is Na3PO4, which when dissolved in water turns basic. That should be sufficient to neutralize any remaining HCl after the 3 rinses.

That makes sense about the pH test. I'll probably do the TSP just to make sure.

IF you're willing to rent this machine, why not rent a grinder. It wont take much more effort to grind the floor?

Wouldn't a grinder be way too harsh? My concrete is only 5 months old and has a nice and smooth finish. I just need it to have a little more tooth to it, not chew it down to the aggregate.

 

[shaun oriold1]

Wouldn't a grinder be way too harsh? My concrete is only 5 months old and has a nice and smooth finish. I just need it to have a little more tooth to it, not chew it down to the aggregate.

On the contrary, the grinding will do a better job at preparing the floor than the acid will. Also epoxy doesnt like moisture, so you dont need to pressure wash the floor, and allow drying time. You can grind, and coat the same day.

 

[jaye944]

hey sx10,

ok here's my 2c's and maybe I'm reiterating..

1> Acid etch, 5:1 is better... Mist water on floor, spray using a watering can, leave for a few minutes, then BRUSH WITH A BROOM, nothing more., Neutralize, with 1lb box of baking soda in 5 gallons of water.

2> Grinding floor, use a proper floor grinder, homedepot did both, the grinder was $180 and the other one about half that, but SERIOUSLY the grinder was fcuking excellant

Good advise from Shaun and Shea, so also listen to what they have to say

 

[s10xtremist]

On the contrary, the grinding will do a better job at preparing the floor than the acid will. Also epoxy doesnt like moisture, so you dont need to pressure wash the floor, and allow drying time. You can grind, and coat the same day.

Can you elaborate on how the grinder will do a better job at preparing the floor than the acid will? The description on the equipment rental's site says:

"The gasoline powered surface grinder features 6 grinding stones that are typically used for light concrete grinding applications. Normal applications include removing a broom finish or smoothing high spots. Can remove up to 1/4" of concrete from the surface- effectiveness can depend how much aggregate is present in your concrete."

I don't have any broom strokes or high spots, and I really don't see why I would need to remove anywhere close to 1/4" of the surface. Maybe I need a different type of grind stone? Their site just lists one type.

hey sx10,

ok here's my 2c's and maybe I'm reiterating..

1> Acid etch, 5:1 is better... Mist water on floor, spray using a watering can, leave for a few minutes, then BRUSH WITH A BROOM, nothing more., Neutralize, with 1lb box of baking soda in 5 gallons of water.

2> Grinding floor, use a proper floor grinder, homedepot did both, the grinder was $180 and the other one about half that, but SERIOUSLY the grinder was fcuking excellant

Good advise from Shaun and Shea, so also listen to what they have to say

So, I'm back to teeter-tottering on acid vs. grinding. When you say "homedepot did both, the grinder was $180 and the other one about half that, but SERIOUSLY the grinder was fcuking excellant", what do you mean by "homedepot did both"- they had two types of grinders and one was about half the cost? What condition was your concrete in before starting any of the prep and coating?

I'm kinda leaning towards just acid etching since I really feel that all my concrete needs is to be etched. But, before I open a $50 case of acid and can't return it, I just need to make sure.

 

[Notgrownup]

If you do rent a scrubber rent a auto scrubber, its way lower rpm's and ***** up all the water in one pass...you can use a scrubbing pad like a Black stripping or Blue scrubbing pad? Then to rinse use clean water with baking soda... (premix a batch of baking soda with cold water) add this to the scrub water... it will also help neutralize the etching stuff in the machine...make several passes...

 

[shaun oriold1]

Can you elaborate on how the grinder will do a better job at preparing the floor than the acid will? The description on the equipment rental's site says:

"The gasoline powered surface grinder features 6 grinding stones that are typically used for light concrete grinding applications. Normal applications include removing a broom finish or smoothing high spots. Can remove up to 1/4" of concrete from the surface- effectiveness can depend how much aggregate is present in your concrete."

I don't have any broom strokes or high spots, and I really don't see why I would need to remove anywhere close to 1/4" of the surface. Maybe I need a different type of grind stone? Their site just lists one type.

So grinding is a preferred method as its able to be controlled. You can grind off more if you need to in certain areas. Acid doesn't really give you that option. Also Grinding isnt toxic on the environment, or dangerous to you.
Grinding will also clean any oils, sealers, or dirt on the surface of the floor. Acid might sit on top of them, not reacting with the floor in those areas.

IF you do any patch filling, you'll need to grind afterwards for that too anyways ( though this can be done with a hand grinder)

Most grinders will not remove a 1/4" without a lot of time and effort. Usually its a 1/16-1/8" or so at max. Think of a grinder like sandpaper. Sure you could remove 1/4" with an orbital sander, but you'll be there for a while doing it!

There are probably also some high spots which are not super noticeable. When concrete guys float the floor, they usually do it from the driveway, causing ever so slight waves when they're pulling the floats across, and they re-possession their hands..

 

[Falcon67]

Weenie - I did 960 sq/ft three times with a mop, push broom and squeegie.

 

[s10xtremist]

So grinding is a preferred method as its able to be controlled. You can grind off more if you need to in certain areas. Acid doesn't really give you that option. Also Grinding isnt toxic on the environment, or dangerous to you.
Grinding will also clean any oils, sealers, or dirt on the surface of the floor. Acid might sit on top of them, not reacting with the floor in those areas.

IF you do any patch filling, you'll need to grind afterwards for that too anyways ( though this can be done with a hand grinder)

Most grinders will not remove a 1/4" without a lot of time and effort. Usually its a 1/16-1/8" or so at max. Think of a grinder like sandpaper. Sure you could remove 1/4" with an orbital sander, but you'll be there for a while doing it!

There are probably also some high spots which are not super noticeable. When concrete guys float the floor, they usually do it from the driveway, causing ever so slight waves when they're pulling the floats across, and they re-possession their hands..

So, grinding will leave a grainy surface sufficient for the epoxy to stick to, comparable to acid etching, but more even? Maybe I'm just not envisioning this correctly, but I'm looking at grinding as leaving a very rough, chewed up, and irregular surface. My concrete has no float marks as it was power troweled, and it's very flat as felt by gliding over it on a "Power Wing". (My neighbor's 8-year-old was checking out the slab one day and let me ride his Power Wing. My first observation was how consistently flat it was.) I'm sure I can keep the grinding machine moving so as to not remove more material in spots. I just don't want to risk creating uneven areas if I were to pass over/overlap areas one too many times. I take it all I need to do is to keep the machine moving and maintain an organized pattern throughout the entire floor? Forgive me if I'm overthinking this. I'm well over the project's budget and I'm operating on a week-to-week spare cash budget, so I can't afford to screw up anything. Having NO experience in this sort of thing has me feeling sickly cautious.

Weenie - I did 960 sq/ft three times with a mop, push broom and squeegie.

I am. I was born with a fcuked-up spine, I have to be careful when it comes to manual labor that involves long-term repetitive movements. This is why I'm trying to learn every detail of what's involved in either method.

 

[shaun oriold1]

So, grinding will leave a grainy surface sufficient for the epoxy to stick to, comparable to acid etching, but more even? Maybe I'm just not envisioning this correctly, but I'm looking at grinding as leaving a very rough, chewed up, and irregular surface. My concrete has no float marks as it was power troweled, and it's very flat as felt by gliding over it on a "Power Wing". (My neighbor's 8-year-old was checking out the slab one day and let me ride his Power Wing. My first observation was how consistently flat it was.) I'm sure I can keep the grinding machine moving so as to not remove more material in spots. I just don't want to risk creating uneven areas if I were to pass over/overlap areas one too many times. I take it all I need to do is to keep the machine moving and maintain an organized pattern throughout the entire floor? Forgive me if I'm overthinking this. I'm well over the project's budget and I'm operating on a week-to-week spare cash budget, so I can't afford to screw up anything. Having NO experience in this sort of thing has me feeling sickly cautious.

Grinding will leave the surface perfect for epoxy. It will be smooth to the touch, but rough enough for epoxy to bite into the concrete. I tell my customers that its like pouring wax onto sandpaper vs. glass. Glass will peel right up. Sandpaper is going to be tough as heck to pull the wax from.

If your floor was power troweled you're going to have a super smooth floor. Smooth isnt good though. Its also going to be very hard which makes grinding slightly tougher. Totally doable though.

With a grinder, the key is to keep it moving. Which is literally a side to side motion. I usually go over the floor left to right, then front to back. The side to side in my case is about a 8" swing. 4" off center each way.
Nothing too drastic. Depending on the grinder you use will determine how its going to act. My Werkmaster will keep grinding in one spot if I leave it be. My Husquvarna will keep moving my itself. Even if I were to hold it still, it spins at such a low RPM it wont damage the floor. Dont be intimidated by it at all. In my mind, acid is more screw-up-able then grinding.

If you're at the end of your budget. I would say grind the floor. Its a guarantee its done properly. Half the floors I do are ones where customers have done something themselves, and I'm there to replace it properly. I hate to take their money sometimes, but I hate a crappy floor more!

 

[Shea]

Grinding will leave the surface perfect for epoxy. It will be smooth to the touch, but rough enough for epoxy to bite into the concrete. I tell my customers that its like pouring wax onto sandpaper vs. glass. Glass will peel right up. Sandpaper is going to be tough as heck to pull the wax from.

If your floor was power troweled you're going to have a super smooth floor. Smooth isnt good though. Its also going to be very hard which makes grinding slightly tougher. Totally doable though.

Excellent explanations about grinding

For people still on the fence about grinding vs acid etching, you can read more about it here.

 

[rafa04]

just try it , so you know the fact about it

 

[Notgrownup]

I guess you could rent that machine and buy a sanding screen to go on it....that would be an option...don't know what the cost difference would be

 

[LegacyIndustrial]

Simply put:
Acid Etching presents greater risk....
Here is how we look at prep methods:

Floor Preparation



Acid Etch:

Pro: Least expensive, easily accomplished.

Con: Acid is dangerous, does not address laitance in substrate surface, not consistent, PH issues possible.

Diamabrush head mounted on a floor buffer(Legacy favorite):

Pro: Light weight, easy to operate, low cost rental or purchase.

Con: Not as consistent as a shot-blaster, not able to accept down-pressure, dust containment.

Diamond Grinder:

Pro: Aggressive, able to add down-pressure, low cost rental and available.

Con: Not as easy to operate, dust containment, tooling is expensive.

Shot-Blaster:

Pro: Best method for consistent prep, Adjustable profile, excellent dust containment, easy to operate.

Con: Not able to rent, very expensive to buy, typically have to hire a prep company to accomplish.

 

[s10xtremist]

Grinding will leave the surface perfect for epoxy. It will be smooth to the touch, but rough enough for epoxy to bite into the concrete. I tell my customers that its like pouring wax onto sandpaper vs. glass. Glass will peel right up. Sandpaper is going to be tough as heck to pull the wax from.

If your floor was power troweled you're going to have a super smooth floor. Smooth isnt good though. Its also going to be very hard which makes grinding slightly tougher. Totally doable though.

With a grinder, the key is to keep it moving. Which is literally a side to side motion. I usually go over the floor left to right, then front to back. The side to side in my case is about a 8" swing. 4" off center each way.
Nothing too drastic. Depending on the grinder you use will determine how its going to act. My Werkmaster will keep grinding in one spot if I leave it be. My Husquvarna will keep moving my itself. Even if I were to hold it still, it spins at such a low RPM it wont damage the floor. Dont be intimidated by it at all. In my mind, acid is more screw-up-able then grinding.

If you're at the end of your budget. I would say grind the floor. Its a guarantee its done properly. Half the floors I do are ones where customers have done something themselves, and I'm there to replace it properly. I hate to take their money sometimes, but I hate a crappy floor more!

Excellent explanations about grinding

For people still on the fence about grinding vs acid etching, you can read more about it here.

Simply put:
Acid Etching presents greater risk....
Here is how we look at prep methods:

Floor Preparation



Acid Etch:

Pro: Least expensive, easily accomplished.

Con: Acid is dangerous, does not address laitance in substrate surface, not consistent, PH issues possible.

Diamabrush head mounted on a floor buffer(Legacy favorite):

Pro: Light weight, easy to operate, low cost rental or purchase.

Con: Not as consistent as a shot-blaster, not able to accept down-pressure, dust containment.

Diamond Grinder:

Pro: Aggressive, able to add down-pressure, low cost rental and available.

Con: Not as easy to operate, dust containment, tooling is expensive.

Shot-Blaster:

Pro: Best method for consistent prep, Adjustable profile, excellent dust containment, easy to operate.

Con: Not able to rent, very expensive to buy, typically have to hire a prep company to accomplish.

This is the detailed input I needed. I now feel that I have a solid understanding of what I'm in for. Thanks for y'all's patience and explanations!