Garage flooring grinding questions

[SPaikmos]

Hi all!

I just erected a 1440sf shop and am planning to do polyurea flooring. I bought a ton of product from Scotty at Legacy Industrial, and am doing the flooring prep now. My plan is as follows:

1) Aquadike moisture barrier (my contractor did NOT put a vapor barrier - long story)
2) Epoxy primer coat (off white)
3) Polyurea color coat (white)
4) Polyurea top coat (clear)

I have a concrete slab, it was poured in two phases. The perimeter + footings were done in one pour, and the interior slab portion was done as a separate pour.

I started grinding last night using a 10" grinder rented from Home Depot. This works ok, but there was a TON of dust and it made it impossible to see how the grinding is going. At first, I was thinking "I'll just scuff up a bit, it'll be a couple hours and all good". Going back this morning, I can see some areas exposed the aggregate, and some did not. I'd say I got about 50% good grind vs barely ground.

Now, I plan to rent a dual head EDCO grinder from an industrial rental place. My questions:

1) This time, I plan to use a vacuum. I went to HD and they have a 16 gal Rigid shop vac and offer a HEPA filter w/ bags. Is this a good setup for fine silica dust?

2) The other option is to rent a purpose made vac for concrete dust. Will this be better than the Rigid?

3) Now that I've blown fine silica dust everywhere, what's the best way to clean it out? My shop is 36 x 40 x 18. I used a leaf blower to blow dust around, and opened the garage doors and windows to air it out.

4) Do you recommend using a solvent to mop up dust when I'm done with the grinder? I was thinking to spray it down with water, but it seems some folks here are averse to using water. Ideally I could grind the floor on Friday and start applying coating on Saturday, but not sure how to mitigate the dust.

TIA!

 

[SolarColumbia]

The concrete surface profile you achieve will depend on the bond of the diamonds. I rented the 22" Edco. They had only medium bond diamonds. I ground it forever and it wouldn't get any rougher. Apparently I needed softer (or harder) bond diamonds, but that's one of the perils of rental equipment.

The Edco collection vac I rented with it didn't collect hardly any of dust while grinding and fortunately I wore a dual cartridge mask or I'd have grey lungs. I was able to use it to vacuum most of the dust in between and after grinding and kept my mask on for that. I then cleaned up further using my 18 gal Shop Vac with a fine dust collection bag. I next hosed it off repeatedly and kept brooming the water out until the dust was nearly all gone.

I allowed the floor to dry for about 8-9 days before coating.

 

[SPaikmos]

I hear you about the grinding pads. I looked online to see if I can buy some magnatrac pads, but wasn't able to find them easily or for a good price. I found some sets that were several hundred dollars, but I didn't need that many pads (came as a variety pack).

I'm still not sure if I really need to grind the surface; when my slab was poured, I told the guys not to put any sealer or protectant on it, since I plan to do the polyurea. The surface was very smooth, so maybe CSP0?

Looking at many threads on here, it looks like many folks take it down a good 1/8" or so and hit the aggregate. That's what got me thinking about grinding more thoroughly.

8-9 days is a long time to wait... I was hoping to shorten that to 1 or 2 days. It sounded like some folks use a solvent to remove dust, any idea what's recommended?

 

[p00p]

hose it down & out of dust & use a few dehumidifiers with a few fans running non stop from the time you stop the water runoff up until you are ready to epoxy the next day.

It should be ok to coat in 12 hours after doing the above.

 

[SPaikmos]

Unfortunately I don't have the equipment to do that. It's already sketchy enough using 150' x 2 extension cords to run the grinder AND shop vac...

Is there a way to empirically test when the concrete is ready to apply a coating? I assume people wait 7-10 days (as above) as a rule of thumb, but it'd be nice if there's a way to know when it's safe to proceed.

 

[SolarColumbia]

There's the 24" square of plastic garbage bag taped down on all edges. See if dampness appears after 24 hours. Crude, but it's something. You can buy a calcium chloride test. Not very expensive. I don't think you need to wait over a week but I had time so figured why not?

You could vacuum/sweep and do the denatured alcohol mopping.

Also, you don't need to grind to aggregate unless that's the only way to reach CSP. I probably was closer to CSP 1 than 2 after my disappointing grind but I rationalized that many people just etch to CSP 1, and I was applying 63% solids primer.

 

[SPaikmos]

Also, you don't need to grind to aggregate unless that's the only way to reach CSP. I probably was closer to CSP 1 than 2 after my disappointing grind but I rationalized that many people just etch to CSP 1, and I was applying 63% solids primer.

That's what I was thinking too. My grind was adequate in some sports, and swirl marks in others (i.e. 'swirls' were deep, but the area not swirled was virgin concrete).

Since the concrete is brand new and unfinished, I'm thinking it's probably ok, but better safe than sorry, right? I don't want to be *that guy* who didn't take the time to do proper prep and is now learning the hard way why people stress on prep.

Regarding the vacuum, does anyone know if the Rigid 16 gal + HEPA filters are ok? Now that I can post links, I linked them here.

 

[SPaikmos]

fwiw - here's what the floor currently looks like. You can see some of it is ground ok, but not really to the aggregate.

 

[SolarColumbia]

My understanding is that the Hepa is what you want for silica dust. The one I rented which was specifically for concrete dust had Hepa filters.

At this point you could try more grinding. For edges and corners the diamond cups you buy on line for angle grinders are more aggressive but I doubt you'd want to do that size area with one. If you do, get some good knee pads and a 3M mask.

There are some good etching options, too. I've not tried Eco Etch or the Tech Gel but they SAY they give a good profile and are easier to use. I had some Rustoleum etch left over I put down after but it's pretty mild citric acid based. You'll spend probably a couple hundred on either of those so not really cheaper than grinding. Hopefully some of the more experienced people will weigh in here.

 

[SPaikmos]

I went over the garage floors this weekend. Spent about 30 hours total with the grinder, my hands are raw now.

The garage floor looks more uniform, but still not great. The dual head grinder was more like a single head because they had me purchase new magna trap blades and those didn't properly "bed in" until I was almost done.

The Legacy Industrial Aquadike says CSP3, but I'm thinking I'm at a CSP1 or CSP2. Definitely not rough by any imagination. I sent some pics to Scotty, and he recommends acid etching. I was thinking to try and rent an air scabber this weekend. Has anyone used one, and know how well it works?

Everytime I ask about CSP3 with contractors and machine rental folks, nobody knows what I'm talking about. WWYD? Rent another machine for another weekend to try and get it right, or just go ahead as-is? I'm guessing this is what people talk about when they say to take the time to prep it correctly...

Has anyone used Aquadike before?

 

[SolarColumbia]

I think you could do an etch and since your initial coat is to be a lower solids primer you'll be okay.

 

[rjacobs]

When I did my garage floor prior to Nohr-S, the grinder sucked and probably looked like your floor in post 8. I did what I could with what I had. I wasnt sure I "opened the pores" so to speak, but when we went to wipe down with denatured alcohol, it absorbed pretty easily.

So we went ahead and laid the primer coat down...

NOW with you doing a moisture barrier coating BEFORE the primer coat, I dont know. I thought the primer coat they sell in the kit is supposed to bond to bare concrete, but obviously if Scotty is advising to use it, it will work with their product.

Mine is in my garage so will likely hold up to parking cars on it for many many years, but who knows.

 

[SPaikmos]

I poured the Aquadike yesterday and did the primer today. Polyurea goes down tomorrow.

I wasn't happy with the grind job, Scotty wasn't either so I rented a shot blaster and did it all over again. I've did 2 passes with the single head grinder, 4 passes with the dual head, and now 4 more passes with the shot blaster (east <--> west, then north <--> south covering the same spot 4x).

I've probably spent 60+ hours on prep for 2500sf, and I ran out of xtreme set 100 to fill cracks. I've taken a bunch of pics and will post some more when i'm all done...

 

[SolarColumbia]

That ought to do it.

 

[SPaikmos]

You would think so, but I'm not convinced I hit CSP-3. I used theS-280 shot which is really fine (specified at 250,000 pellets per pound!). The surface was smooth.

I am not a concrete expert, but I'm thinking I should have used a bigger size, like S-390 which is 93k pellet per pound. That would probably leave a more abrasive surface, but I had no idea what I was using. Just went on the recommendation from the fellow at Kleen Blast, who said that's what most people use.

I just did my color coat of polyurea, and will be finishing up with the gloss coat in a couple hours. I used 5 gallons on 1400sf and ran just a smidgen short, I could have used another quart.

Just about everything imaginable that could go wrong has gone wrong. The only good thing is I like the Legacy Industrial products, and Scotty has been a great resource in advising me. If i could only push past my own limitations, I'd have an awesome floor! Ah well, I'll have to be happy with a nice one, at least.

 

[LegacyIndustrial]

You would think so, but I'm not convinced I hit CSP-3. I used theS-280 shot which is really fine (specified at 250,000 pellets per pound!). The surface was smooth.

I am not a concrete expert, but I'm thinking I should have used a bigger size, like S-390 which is 93k pellet per pound. That would probably leave a more abrasive surface, but I had no idea what I was using. Just went on the recommendation from the fellow at Kleen Blast, who said that's what most people use.

I just did my color coat of polyurea, and will be finishing up with the gloss coat in a couple hours. I used 5 gallons on 1400sf and ran just a smidgen short, I could have used another quart.

Just about everything imaginable that could go wrong has gone wrong. The only good thing is I like the Legacy Industrial products, and Scotty has been a great resource in advising me. If i could only push past my own limitations, I'd have an awesome floor! Ah well, I'll have to be happy with a nice one, at least.

Mr. S, you are doing great! Thanks for the kind words!