LVP Install on Uneven Slab

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DanLn

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Hello,

I’m planning on installing Rigid Core LVP in my basement in the coming weeks. The flooring was previously carpeting and the concrete subfloor has a number of areas that are between 1/8 to 1/4 inch out of level. I was wondering if it’s be possible to fix these spots without pouring self leveling cement across the whole basement? Can I pour SLC in only certain spots? I’ve included photos of some the two types of issues that in dealing with. The first is a valley in the floor (about 1/4 inch out of level) and the rest are raised portions of the floor (I can’t really tell what is going on with the concrete in these spots) I have about 4-5 instances of each of these issues across my 1000sqft basement. I would appreciate any guidance you all might have on rectifying these issues before I install. Thanks!
 

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Mark Brown

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You have a bit of work ahead of you my friend.
Depressions and high's are the death of floating floors. You are correct in assuming they need to be addressed. As for the use of self leveler, it is not warranted in most of the instances that it is used and we can all blame the internet and HGTV for that nonsense. Get yourself a 14" trowel and some floor patching compound, preferably from Ardex or the like and fill those in. You can map them out with your straight edge and a pencil and then go to town.
Looking at that concrete, there seems to be a lot of trowel ridges and the like, you are going to want to grind those off as well and make sure that where all your footings are that you get those nice and level/smoothed out as well. Concrete can be a bear sometimes and most of it was never finished with the thought of hard surface flooring in mind so it does take a bit of work but it is done all the time and you can do it too.
 

MikeAntonetti

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I’d say work with exterior rated patch and a screed.

here’s a takeover I did from homeowner attempt.
 

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DanLn

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Wow guys! Thanks so much for taking the time to reply. I will go ahead and start grinding down the high spots and filling the lows as advised. I really appreciate it!
 

highup

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I’d say work with exterior rated patch and a screed.

here’s a takeover I did from homeowner attempt.
That's quite a setup you have Mike. Very impressive.
I'm guessing you charge this guy about 75 bucks to flatten this floor.
😁
What Mark mentioned about trowels, might be better suited for a final coat.
If you have a two or three foot span that has a low spot, I think it's better to take a screed of some sort to fill the low spots. Being that you're doing this yourself, time is not money, or not in the same sense as paying someone.
Do like Mark said with the level or a flat piece of angle iron or aluminum. .....whatever you have available.
I have a 2 ft 3 ft 4 ft 5 ft and 6 ft section of 3/16" by 2 inch lengths of angle aluminum that I use for screeding filler. It's a lot cheaper to purchase these kind of things at a industrial steel supply shop rather than at a hardware store.
Map out the floor in two directions. Take your screed or level or whatever, and move across the floor in each direction in a pattern similar to a tic-tac-toe game. Find and outline the very location that a floor begins to fall into a depression or become a high spot. Find and outline the exact perimeter where the floor begins to deviate. You might want to go across it a second time and mark an estimated deepest depth and draw a ring around that area too.
You will now have a circle at the highest point in the slab where it begins to change, and a second circle or oval showing the deepest part of the depression.
Once you have all your circles and arrows and 27 8x10 colored and glossy pictures with circles and arrows and a paragraph........
..... Wait a minute I'm getting too deep into this 😁
Just saying that once you have the floor mapped out really well you can begin filling the low spots. If it doesn't turn out perfect on first pass, no big deal. It's better off to underfill, and then make a second or finish coat to blend everything together.
Between the two coats, you will probably be well off to check the floor for flatness a second time to see if you now have any raised or high spots because of excess leveling compound or blobs that you didn't notice as you were spreading it.
After the leveling compound has set up a little bit but is not totally dry, this would be the time to use a handheld razor scraper and scrape off any spots that are obviously too high.
If you wait until the filler is totally dry to do the scraping, the process might be a lot more difficult because the filler has hardened up considerably.
Just remember, you don't have to do all the filling in one flawless step. It might be easier to fill the deepest spots and then mix a thinner coat to screen over everything to do your final smoothing.
 
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C.J.

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One thing you can do to see how well of a job you’ve done prepping your slab is to click together multiple planks over an area that you want to check and walk on them. You will know if there is a hump or a dip or some other kind of BS that won’t play nicely underneath your floor when you do get around to installing it. Ridgid core is marketed as not needing as much subfloor prep but the reality is that it actually needs a flatter, more pristine surface to install over because the planks themselves are less forgiving. I would even do this test in areas that you didn’t prep to see how well suited they are for your new floor. Concrete turds and trowel chatter may be bad enough to negatively effect your installation even though one might think the slab looks just fine.
 

MikeAntonetti

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My gig above I tried hard to convince the homeowner to go gluedown.

before I forget. Floating plank all lock together and try to stay on an even plane, ceramic tile can somewhat ride the surface(lippage), I read manufacturers gluedown hardwood instructions saying 1/8” in 10 ft flatness(future failure I may have to rip out) the adhesive is stating tacky, so the unflat floor drops onto slab when walked on, then pops up to the plane of adjacent hardwood making noise.
 

Csason

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I would use about a bag of Mapai (sp) on that... mix it according to directions and pour away. If you can get the new Mapei (sp) HCL which is supposed to be more fool proof (thinner and seeks its own level ) even better. ALL the clic floors LOVE a nice flat floor and they hate undulations, in fact just about everyone I read says "must be no undulations over 1/8" over 8 (or ten) feet. Also nothing more than bla bla bla" Amazingly that stuff works like a champ just like in that picture up there . I have had jobs where I poured 28 bags in a badly pitted wood floor removal involving chalky crap concrete in a 1500 sq ft job so its easier with a drill and a stir stick from Home depot and a five gallon bucket.
 

Csason

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My gig above I tried hard to convince the homeowner to go gluedown.

before I forget. Floating plank all lock together and try to stay on an even plane, ceramic tile can somewhat ride the surface(lippage), I read manufacturers gluedown hardwood instructions saying 1/8” in 10 ft flatness(future failure I may have to rip out) the adhesive is stating tacky, so the unflat floor drops onto slab when walked on, then pops up to the plane of adjacent hardwood making noise.
Hey Mike I just did a job up there in INverness, I ran into ol Gene Odom while I was up there I stopped at that old Jeep next to
that flooring shop on the southside. Gene was Ronnie Van Zants best friend and was on the plane with them when it crashed (Lynyrd Skynyrd) He actually does ceramic with a guy from Jax but lives there in Inverness. We stayed at the iNverness Hotel across from the Cedar River restaurant
 

MikeAntonetti

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This town strains not to grow, boating, airboats, huntin, old people not wanting traffic, a good area to retire, I just got here way too soon. Haven’t been to that restaurant, there’s 3? In other areas, why here? So many went out of business, Zaxbys, another pizza chain, just a weird area for normal business. Certain buildings are notorious for issues, that was Citrus Hills condos, shoddy work. I’m across from Bowling Alley neighborhood.
 
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