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Unread 06-09-2021, 07:30 PM   #1
SDQS
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The snowball effect

Hello Gentlemen,

I've been lurking for years and finally registered as I continue along in my project and have come upon a question that I would like to see what you guys say about it. It has to do with concrete floor slab flattening.

Background: House built in 1960, no vapor barrier below slab. We intended on doing kitchen cabinets only until the cast iron stack literally collapsed and crumbled in the wall after removing the sink and wiggling trap arm sticking out of the wall. That led to demoing 80% of the house (floor, drywall, both bathrooms, etc.) and saw cutting and re-piping all the DWV lines in ABS.

I have every inch of the concrete exposed in the house. I don't live in this house so I can take my time and do everything as best as possible. I've been a car guy for over 25 years so working with tools and my hands is no issue. I am aiming for getting the floors flat enough for LFT (1/8th in 10' and no more that 1/16th in 2') even though we're not planning on tiling the house immediately, I want it to be ready for that for if/when we decide to rip up the laminate and lay long, narrow wood plank look tiles or real hand scraped wood floor in the future.

I've removed all the previous floor material and am now working on starting figuring out what to do with this slab. We have a number of issues:

It's not flat nor level
there are cracks
efflorescence in two rooms coming up through the slab
tons of thin set that needs to be ground off
quite a bit of mastic that needs to be ground away (dining area, bathrooms)
old attempt at waterproofing membrane in office that needs to be ground off

Now, I've taken measurements of the kitchen and used a laser level as a reference line (53.5" off the ground, approximately and depending on where you measure from) and I put those measurements into Excel to try to create a heat map so I could visualize where the highs and lows were. Here's the issues: I have only found one person who said what to use as a reference when comparing your numbers, and they said "find the center of the room and use that measurement as your starting point". What if the center is in a depression or on a hump?

I chose a different method, but I don't know if it's what you guys would do or is right. I measured from my laser line down to the concrete as close into each corner of the space as I could and recorded those measurements. I then took the average of those numbers (53 & 13/16") and subtracted it from all my measurements taken in every, single square foot, so I could see the subtle variations in the floor surface elevation. I partially did this because I could spend hours on the floor with a 6' level (longest I own) trying to figure out where the bumps and valleys are and never really get a good idea.

This is just the first area of the house that I'm focusing on to try to work out what I'm going to do with this floor. I need to rent the 10" walk behind grinder from HD to get the mastic and thin set off. The new flooring will go throughout the entire house except the two bathrooms, which those'll be tile.

Am I going about this right? This is going to be an extremely long project (have you seen the pictures?) and I really appreciate all the input and advice to come. Thank you for helping me.

How do I rotate the images and enlarge them? CX?
First picture: dining area in foreground just through door, kitchen in background. Saw cut trenches visible
Second picture: dining area (mastic) visible at bottom and living room with thin set and front door to house
Third picture: kitchen on left (mastic), bar and living room corner and you can see down the hallway (thinset)
Fouth picture: my heat map for the kitchen floor. The bottom is south and south in the kitchen is to the left, in both pictures
Attached Images
    
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Last edited by SDQS; 06-09-2021 at 07:59 PM. Reason: pic descriptions
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Unread 06-10-2021, 09:26 AM   #2
cx
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Welcome, Mike.

Fun project!

As to the photos, you need to ask someone who might have some idea about that. CX ain't the right guy. You take the photos with a telephone?

First thing I'd recommend is that you purchase a 10-foot aluminum or magnesium straight edge. Probably add $150 to your remodeling budget.

Second thing would be to put a geographic location into your User Profile.

You have done at least a rudimentary test for moisture vapor emissions on that slab? With no vapor barrier material under the SOG it would be a good idea to know what you're dealing with there.

While "heat-maps" can be informative, the real method you want to employ for real-world results is the ten-foot straight edge and you want to measure flatness from the high point in the area to be tiled. For concrete that is seriously out of flat, you'll likely want a combination of grinding high spots and filling low spots. Doesn't hafta be pretty, just hasta be flat.

Are we seeing repair ditches and patches in your photos, or are those light areas something else?

My opinion; worth price charged.
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Unread 06-10-2021, 01:09 PM   #3
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Hi Cx, good to hear from you.

I'm in San Diego and I did change my profile to reflect that. I'll work on getting a 10' straight edge. Any tips on where to pick one up? Amazon wants crazy money to ship one they sell.

Those pictures were with my phone, the initial picture wasn't turned counterclockwise until here. Looks fine on my end. I used to have to load pics into photobucket then add the link to the post to get nice, large clear pictures to show up in threads on another forum, is that how people do it here?

And onto the problems with the house. There is thinset in the living rooms, down the hallway and the master bedroom. The kitchen and bathrooms and other two bedrooms have mastic. So, my thought for trying to get some measurements up front was the grinder rental is like $180 a day. So if I could get an idea of where the highs were I could try to get the thinset off and mastic off and then work the high spots, since time will be ticking away that day and I wasn't trying to do my figuring while on the clock, so to speak. The house is about 1100 square feet and I will have to go over every inch of the house with that machine to time will be in short supply that day. But, it sounds like I need to go rent the machine, get rid of the thinset and mastic and then start taking serious measurements. I wouldn't be able to get any meaningful measurements with a straight edge now in the kitchen, hallway or master because of the thinset that's still there.

I haven't done the water vapor test because the skin of the concrete is flaking really bad and there's that white salty crusty stuff when it rains in the front corner bedroom where someone already tried to put down a paint on water barrier. It failed becuase of their lack of prep I think. The master has some slight flaking along on on exterior wall and so becuase of that, I wanted to just paint the entire floor with like dry-lok or Redguard or something.

The other issues is the water table is only about 15 feet down here and the dirt doesn't drain very well, which is odd for San Diego county but I think it's because this used to be an old citrus grove. My neighbor has a well and I've seen the water. It was pretty shocking to see it so close to the surface.

EDIT - Forgot to add, I think the ditches that you're seeing that are lighter colored concrete are my areas where we saw cut to remove the old, nearly rusted shut cast iron DWV lines and replaced it all with ABS. What a job that was.

Sorry for the length of these posts. I just have a lot to illustrate and it's hard to clearly do that via text in a short manner sometimes.
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Last edited by SDQS; 06-10-2021 at 01:23 PM.
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Unread 06-10-2021, 02:29 PM   #4
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Mike, For any tools in San Diego I would suggest going to Marshall's Industrial Hardware on Production Ave in Miramar. Make sure you allow yourself enough time to brows as you will be in actual tool heaven. Also the best place in town for any fastener needs.
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Unread 06-10-2021, 03:06 PM   #5
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Mike..in some cases and when pushed to the limit, you can always try to find some LONG 2x4's that are reasonably flat. Those can be used for determining the flatness of a floor.....
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Unread 06-10-2021, 04:04 PM   #6
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I get my long straight edges from a local (San Antonio) drywall, plaster and stucco supply house called Lynwood, Mike. Might look for something like that in your area.

Don't think I've ever met a ten-foot 2x4 that was straight enough to flatten your floor to the necessary specification. Even after I ran it through my jointer I don't think I'd trust it. Nothing quite like a hollow magnesium 1x4 for the task.
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Unread 06-10-2021, 04:26 PM   #7
SDQS
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Thanks guys for the tips. I had an "oh yeah, duh!" moment and checked White Cap, they had a 1.5"x3.5"x10' aluminum screed that will work. I just went and picked it up. $90 out the door. Got it home and placed my 6' level on it and couldn't see any light between them, so I think it's pretty flat.

John, good tip, I hadn't thought about Marshalls. I work near there and have been going there for the specialty stuff that you just can't find anywhere else for years. Definitely have to limit myself there; that place can be dangerous. You must be in SD too? What part?

So now the fun will start and I guess I'll go around the house here in a bit and start doing some investigation. So, when you guys do this, do you go from one corner of the house and just work across to the other? Or just try to lay that thing every which way and just see if the same high spot keeps showing up the more you move around? I have a can of markout paint, but it's messy indoors and maybe just a sharpie mark would be better denoting the high spots?

I just feel like there's a right and a wrong way to go about this and I haven't quite found the right way, yet.
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Unread 06-10-2021, 04:55 PM   #8
jadnashua
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I'd try to find both the high and low points. You can grind the high points, and fill the low ones. If you can afford it, you could pay someone to pump in SLC, but that gets expensive, and doesn't necessarily make things flat or level unless you're good at it. To get SLC truly flat, you need some special tools and the realization that just like pancake batter doesn't fill the pan in one level, neither does SLC without some help. Knowing the differences between the high an low points will help you decide how much to grind off, and where to fill. What they used for aggregate in the concrete pour can make that effort harder if it's larger, harder stones.

Using a floor grinder/scarcifier can get rid of the high points, but takes some skill, too, and gouging out a section can happen just like when using a belt sander with a coarse grit on wood. Makes a dusty mess, too!
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Unread 06-10-2021, 05:51 PM   #9
SDQS
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Jim,

Agreed on all points. I haven't gotten to the point of seeing what the cost would be to pay someone to do SLC on the whole place, but, I know when to cry Uncle and let the real pros who do it day in and day out with the knowledge and tricks that only time can teach come in and do their thing. I need to spend some time in there with the 10 footer and make marks on the areas that just have mastic since I can't really tell what is going on under the remining thinset in the other parts of the house. I know there are some low spots that they filled, because I can see an initial float layer of thinset. I know, that's not what it's recommended for but people do it all the time and I have thought about it too to be honest haha.

So, I think the best thing I can do is work the mastic areas with the level and try to get a game plan for them. Then go rent the machine for 8 hours and get rid of all the thinset and mastic and utilize whatever remaining machine time I might have after that on flattening.

Then I can see a uniform (not flat) concrete surface that we can address the waterproofing and cracks in. How does that sound to everyone? Am I missing something? Let me know, I'm all ears.
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Unread 06-10-2021, 07:35 PM   #10
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Photo Orientation

Mike, welcome........... as far as your photos being oriented correctly, just take the pictures with your phone turned sideways. Then just upload them directly using the manage attachments button below. I found the sideways instructions in a post somewhere or maybe it was in the Liberry.

Lately, I have been able to upload photos that were taken with my phone in the upright position and they loaded with the correct orientation. Not sure why it works sometimes? Works every time when pics taken with sideways phone.

You might have already figured this out as I only see one of your pics with incorrect orientation.
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Unread 06-10-2021, 09:25 PM   #11
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There are a few Cementous patching compounds that are easier to use on smaller depressions...you might look into Henry's Liquid Backerboard...it also doesn't require a primer.

I don't know the best way to try to solve your slab moisture issue. Many of the materials list maximum water pressure that they'll work with, so you need to know what your situation is. That can affect many finished materials you might choose for your floor. SO, many topical waterproofing materials just won't stay bonded, depending on the level of the pressure. That can change, maybe radically, depending on whether you're in the dry or wet season, if CA has a wet season reliably any more.
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Unread 06-10-2021, 11:21 PM   #12
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On the picture question, some phones, like iPhones, will save the picture with metadata that says it's rotated wrong, and the phone will automatically rotate it when viewing it on there. But when you upload to sites like this, it will be wrong. You can get third party image apps on your phone that will show whether it's correct or not.

And I'm in San Diego too up in Vista.
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Unread 06-24-2021, 12:11 PM   #13
SDQS
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Gents,

It's been a busy few days since last time I was able to get logged in and create a reply. My wife recently took her dream job at a VA Hospital in the central part of the country, so it's just me and the dogs here now. Sometimes it's not so bad, but other times it's tough.

Well tomorrow is a big day, going to rent the EDCO concrete grinder from the orange box store and spend every waking hour tomorrow till I drop getting the mastic and thinset off and then trying to work on the high spots. I spent last weekend going around the rooms that only have mastic and working with that 10' aluminum screed - it's super straight - and marking high spots. Oddly enough, they corresponded with my heat chart and it was significantly faster, although not quite as accurate. But good enough for the initial go at getting this floor to a point where we can see what's really going on.

Jim: I have heard you mention Henry's liquid backerboard in other posts over the years, in addition to Ardex liquid backerboard, as well as one more that I have written down at my desk at work which I can't remember right now. However regarding the moisture problem, I did read the 5 gallon pale of Drylok and that looks like it could be promising. I just need to contact them as ask if it's ok to lay tile onto it. I want to verify that thinset will properly adhere to it. I also will have to use an etching product where there is bad efflorescence and I'll need your guys advice on the slab cracks when we get to that point, but for now we'll just see how tomorrow goes. SD doesn't have much of a rainy season anymore, but when it does rain it rains quite a bit over a few days it seems and since the dirt here doesn't drain very well and the water table under my house is so shallow (along with no vapor barrier under the slab), all those things combine to create a pretty moist environment.

Regarding the photos - I'll just use the sideway method as much as possible now. That's typically how I take pictures anyway, except for when the subject matter demands a portrait orientation more.
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Unread 06-24-2021, 04:58 PM   #14
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Cement isn't particularly bothered by being wetted, but not all products like high water pressure coming up through the slab...so, maybe a call to the tech support line of the people you're interested in trying might be good.

Many of today's products are a mix of lots of things, so it's not always that easy to know without some technical help.

Since much of CA is in drought, trying to evaluate your worst case situation may be difficult to next to impossible, so you can only try to make your best guess. Trying to stop it from coming up through the slab is a tough call that I'm not up on.
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Unread 06-27-2021, 12:41 PM   #15
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Friday was interesting. I would call it a success, but I didn't get as far as I had wanted. Spent 10 hours behind that machine and got all the old thinset off. It was ~500 sq ft of thinset and some of it was close to 1/2" thick in spots. No joke. I was able to really work on the master bath since that was a 4'x7' slab patch of raw concrete my neighbor and I poured after redoing all the DWV, and it wasn't flat or level so I spent nearly 1.5 hours in that little bathroom working the high spots down and making it nice and smooth. I got that to where a little bit of Ardex liquid backerboard would make it just right.

The blade on the machine I rented wasn't great at getting the mastic nor the topical waterproofing layer someone did in the 2nd bedroom off. It had smaller, rectangular diamond covered bits and if I had like 5 more hours with that machine it probably could have gotten it done, but it would have been really painful. That mastic just gummed up the diamond bits and it slung little balls everywhere, so I need to rent a floor polisher type machine with a disc containing the little sandpaper type paddles to remove these surface coatings. Then we can work on the highs and lows. Would like to find a high speed concrete grinder. The one I rented was as low speed machine and while it worked good on the thinset, once you set it on actual concrete, it really took a while.
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