Slab prep for tile or LVP

[djarchow]

I originally started this discussion over on the old thefloorpro forum but the forum shut down. Hopefully I can resurrect it here. Thanks in advance for any help. I am finishing my basement and have about 550 feet of area I want to use tile or maybe LVP, both of which would be professionally installed. The area includes a hallway, and an open bar/eating area.

I am aware of the subfloor flatness requirements for both tile and LVP and my slab doesn't meet them. I have talked to multiple installers (including one that already laid 200 feet of tile for me in another part of the basement) and flooring stores in town and none of them are concerned about installing over my slab with no prep despite my telling/showing them the condition. I measured the slab with a laser in a 1 foot grid and am attaching an image of the floor and the measure heights. I had a guy who mostly does commercial floor prep agree to do about 5 hours of hand grinding as he couldn't get his 3 head grinder or scarifier down our stairs. He made things better than they were but still nowhere near what the tile council or the LVP mfg. require with some spots still about 1/2" higher than the rest of the slab, The highest spots are mostly around 3 lally columns. I have also used a 9' straight edge to find the worst spots and despite the elevation changes, was better than I expected (closer to flat but not level) but the red areas and to a lesser extent the brown areas in the attached image are still a problem.

I am considering renting an Edco (non-turbo) 10" single head walk behind grinder and Edco Vortex 200 vacuum this weekend and trying to even thing out, especially in the high red and brown spots. I don't expect to completely fix the problem; but if I do need to put down SLC, I would rather do a 1/4" lift rather than 5/8", especially over 500+ square feet. My slab is hard and would require soft bond tooling so I would get red Dyma Dot tooling which come in 30/40 grit. The red and brown areas are about 115 sq feet with an average height of 5/16". Edco says the grinder will remove 1/32" an hour over 200 sq. feet; so in theory over the whole weekend I should be able to get this better than it is now. I have never ground concrete before so there is always the chance I will screw things up worse, but gouges. etc. could always be filled in with patch or SLC.

Does this seem like a reasonable plan? Will one set of tooling be enough or given my concrete hardness, will I burn through more than one set? Any other suggestions or gotchas?

Thanks for any help.

Regards, Dennis

 

[Mark Brown]

You are already 1000% ahead of most installers out there as you have proved from your experiences with them and their "no problem".

Your plan is solid and I remember you from thefloorpro.com I like you, you are SMRT

 

[MikeAntonetti]

Uh, if it’s the 115 volt machine it’s slow, the soft bond means it releases(wears away the metal) exposing more Diamond material in the matrix. It’s hard to know what to throw at your slab machinery/equipment wise without starting the job, I then see feedback from what I think I should use to what is working fastest and most efficient. I’d probably start with a medium bond, what’s the aggregate? In florida it’s lime”stone” nice and soft.

I have parted the sea to get the ride on scraper into the trailer.

who could forget that graph?

 

[djarchow]

Uh, if it’s the 115 volt machine it’s slow, the soft bond means it releases(wears away the metal) exposing more Diamond material in the matrix. It’s hard to know what to throw at your slab machinery/equipment wise without starting the job, I then see feedback from what I think I should use to what is working fastest and most efficient. I’d probably start with a medium bond, what’s the aggregate? In florida it’s lime”stone” nice and soft.

I have parted the sea to get the ride on scraper into the trailer.

who could forget that graph?

Mike,

The graph is better than before after the grinding I had done already

Yes it will be the 110v Edco non-turbo grinder. I will have it for the whole weekend so I do have time. I asked the guy who did some hand grinding already and and he said the concrete was very hard. He started with a medium bond diamond wheel and it was really slow and switched to a soft bond to make more progress. Our aggregate is mostly river rock. He said the concrete guys had power troweled the heck out of it which made the surface harder. I don't have a mohs tester but my high carbon steel Benchmade knife didn't even make a mark. I had to use a carbide router bit to scratch it.

Thanks for your help! Dennis

 

[MikeAntonetti]

You have a dedicated 20 amp outlet? Like a washing machine, that will help because it’s gonna want amps. I would definitely get two sets of diamonds, either return them or here’s some I bought on eBay used.

 

[MikeAntonetti]

Ok so sometimes I need dwell time. Ain’t no way in hell( that’s my rebellious side speaking) I’m going to not have a scarifier to take down 1/2”, Edco CPM-8 would be my choice. The grinder would fine tune.

segment contact and downward pressure determine aggressiveness. Less segments means more downward pressure.

 

[djarchow]

Mike,
Thanks for the replies. I do have dedicated 20 amp circuits near the concrete. I know the scarifier will be quicker but no one in town rents one one that is electric. They just carry the gas ones. Not great for indoors.

Thing is, I don't have to take down much area that is 1/2" The entire 115 sq feet I am planning to grind is an average of 5/16" above the rest. I have maybe 40-50 sq feet that is between 3/8 and 1/2" high. I would like to drop the highest spots down to a 1/4" above the rest of the floor and then if I have more time and energy (and tooling left) work on the whole 115 sq feet to see if I can bring the whole thing down another 1/8th or so and call it quits. So in the end, I would only be taking off an average of about about 3/16" over 115 sq. feet. Hopefully doable over the weekend.

Again. thanks!

 

[MikeAntonetti]

Sounds reasonable.

 

[djarchow]

Well the grinding is going much slower than expected. Edco says their non turbo 10" grinder should be able to grind 1/32" off 200 sq feet in an hour. They don't specify if that is with hard or soft concrete. I have been grinding on 16 square feet for 3 hours and maybe took it down a 1/16" Maybe a couple cups of dust in the Edco dust extractor. I am using 30/40 grit soft bond (red) Virginia Abrasives Dyma-dots. With the proper bond tooling for the concrete, is there much difference in speed grinding hard vs. soft concrete? I am attaching a pic as I think the tooling may be glazing over. Thanks for any suggestions.

 

[MikeAntonetti]

They don’t look glazed, there’s tiny Diamond pieces and then trail of metal behind them. It would be smooth flat if glazed. Hard bonds glaze cause the metal is too hard.

part of reason is too much contact area of diamond segment for the machine. If there were 1 diamond segment per piece it would create more downward pressure.

that is why removing depth from slab I prefer beating the concrete downward like the scarifier does, then I smooth with grinding discs. And also why I have many grinders and end up using 7” hand grinder as their faster than stand up machines. But again finding the right blade with few segments may be a challenge, I see turbo type blades with full amounts of segments, that tends to ride on surface versus dig down.

 

[djarchow]

Mike, thanks for the reply. The reason I thought they might be glazing is that when I first started, you check the grinder for level by letting it run in a spot for a few seconds to see if it grinds a complete circle. That removed all the top surface and left a groove I could easily feel. Now if I do that on a fresh spot of concrete, it just mostly just leaves some circular scratches but nothing like when I first started. I added an extra 25 lbs of weight on the front of the grinder but it didn't seem to make much difference

Looking online I see recommendations for grinding hard concrete to wet it first or to throw down some sand. Do you think this might speed things up. Is there any chance my tooling is the wrong bond? Like I mentioned previously, a knife with good steel didn't even scratch it.

Thanks again for all your help.

 

[MikeAntonetti]

Soft bond is almost the weakest metal matrix to expose the diamonds. There’s SS and SSSS that I’ve seen. You shouldn’t need those. It’s physics first, you’re moving a disc parallel to a surface. Planers/scarifiers or even scabblers hit at a perpendicular angle pounding downward. They use carbide and don’t work on the diamond theory.

The creme of Portland cement on surface can be a bit difficult to break through, I remove Thinset a lot, and I use the slab surface to ride the diamond blades on, I’m trying to grind sideways.


I don’t know many alternative ways to accomplish your desire. Chipping hammer chisel bits, hard to control depth continuous, Bush. Bits 4sq inches minimal gain versus effort.

You’re in a boat I was years ago at my rental facility with the equipment available, no diamonds and no dust control though,

 

[MikeAntonetti]

Edco- equipment “development” company, for the “stone ages” I have 5 of their grinders sitting in my garage. 2 scarifiers, 2 scabblers.

for a different type job I brought 3 grinders, enee, meene, miny, but Edco Mo stayed home.

to get some more work out of the grinders you could put it out of level and it would apply more pressure on one side(front or back of machine) to dig in better, see how it acts, then move the machine at a speed and direction that’s consistent.

 

[highup]

You are already 1000% ahead of most installers out there as you have proved from your experiences with them and their "no problem".

Your plan is solid and I remember you from thefloorpro.com I like you, you are SMRT

CJ can't spell. He said you're smart.
It's amazing that you know the tolerance of the floor and none of the installers or the flooring companies do. When they say 3/16 in 10 ft that's a rule that can sometimes be easily broken. You need to adhere to that rule as close as you can. The most emphasis goes to areas that will not be covered with furniture. You can get away with more in the last two feet next to a wall will have a couch over it. With tiles, if it flows out of whack, you may have one tile tipping up and one tile tipping down and changing one tile creates a problem with the next tiles and the next tiles.
Hi however do not do tile but I'm sure if a tile installer knows a small area that's a little bit out of tolerance can flatten that tile down a tiny bit farther to make the floor flat. That of course is only possible to ceramic tile and a very skilled tile installer that has actually checked the floor for flatness and knows how to correct a minor problem as a progresses.

 

[highup]

No

Well the grinding is going much slower than expected. Edco says their non turbo 10" grinder should be able to grind 1/32" off 200 sq feet in an hour. They don't specify if that is with hard or soft concrete. I have been grinding on 16 square feet for 3 hours and maybe took it down a 1/16" Maybe a couple cups of dust in the Edco dust extractor. I am using 30/40 grit soft bond (red) Virginia Abrasives Dyma-dots. With the proper bond tooling for the concrete, is there much difference in speed grinding hard vs. soft concrete? I am attaching a pic as I think the tooling may be glazing over. Thanks for any suggestions.

View attachment 12450

In that area where you took off 1/16 of an inch, how far do you think you actually needed to go?

 

[djarchow]

Thanks for all the replies. I went to the rental place and swapped the 30/40 grit dyma-dot for an 18 grit dyma-seg. It started cutting great but just like the other one, after 10 minutes it was just polishing the concrete. I took Mikes advice to tilt the grinder and it started digging in better but was a bear to wrangle. I also started throwing down sand every 10 minutes or so to help wear away the bond since the concrete is so hard it wasn't even wearing down soft bond tooling.

After maybe 7 hours of grinding today and 3 hours last night I got most of the red areas in the chart above ground down maybe 1/8" from where I started. I was hoping for at least 1/4" off all the red and brown areas above. I got nowhere close to that. I will go at it again tomorrow but with as much as the grinder is digging in now and wanting to spin in circles, I am really sore tonight so I may not be as motivated tomorrow. I may try upping the added weight tomorrow and see if I can reduce the angle of the grinder a bit so it doesn't throw itself around so much.

 

[MikeAntonetti]

Some grinders have variable speed and direction control. That would’ve helped with control of unit and changing direction of rotation from clockwise to counter clockwise helps with diamond exposure as they wear.

The unflat floor adds to the instability of the grinder.

 

[djarchow]

Thanks to everyone for all your support. I spent almost 17 hours this weekend grinding on about 120 square feet. As I mentioned, the concrete was extremely hard, at least on the top where the concrete guys power troweled it within an inch of its life. Even the soft bond tooling just stopped cutting after a few minutes. Thanks to Mike for his recommendation to change the angle of the grinder to get the tooling to dig in more. I also threw down sand to help cut into the bond more quickly. The further I got into the aggregate the faster things were going but I simply ran out of time and energy. A scarifier would have made easier work of this but the only ones I could get were gas powered and not a great choice for in the house.

After all the grinding I got all of the red (worst) areas in the above chart down closer to the rest of the high spots as well as blended in the whole area better than it was which should reduce the amount of SLC or patch we need to use.

For your viewing pleasure, here is the updated measurements for the floor. Thanks again for all the help and encouragement.

Dennis

 

[MikeAntonetti]

That is one hell of a graph. I kinda like it,

 

[highup]

That is one hell of a graph. I kinda like it,

It would be nice if they had an app like that you can put on your phone.
You know, stick your phone on the ceiling, test yourself timer, and it would do the rest.