Concrete floor leveling

Ok, so I'm renting the scarifier to remove the latex paint on the concrete slab. I have a new problem, though.

There appears to be a heave resulting in a crack down the middle of the floor that is higher than the rest of the floor. It appears to be a small hump or hill along the crack. If I put a 4' level on it, it teeters up and down by about 3/16" inches.

So, a couple questions:
Can I use the scarifier to level that section?

How does one determine the level in a room short of moving a level around? I read a post where someone stated they had a 1/4" rise over 10' or something like that. Are there nifty tools that do that type of measurement? Just want to make sure I don't blow this tile install.

The folks at Lowe's recommended a product for filling the cracks and other divets in the slab. Is there a particular product you recommend or would advise avoding for filling the cracks & divets.

Thanks in advance!

Jamboaz

I should add that the crack at its widest (which is also roughly the center of the room) would snuggly fit a penny. So I'm guessing it is at worst about 1/8" wide and tapers in width as it gets to the walls.

Thanks,

Jamboaz

[Jerry Thomas]

Ok, I will try to offer some guidance but I difficulty explaining stuff at times so bear with me.

A scarifier will take take down high spots about 1/16" each pass, but we need to back up here first.

Lateral cracks in a slab can be fixed by using a crack isolation membrane. But the crack you describe is a vertical crack where one side is higher than the other. I don't any sure fire way to fix that. You could grind it down even but it will likely reappear and result in the tile cracking. How long has that crack been there?

[Bradley Bitter]

have you looked into ardex k-15 it works wonders in large areas and stays very flexible

My bad, I haven't done a good job describing it. It is a lateral crack, if I'm following this right. Both sides of the crack are at same height, just separated apart and both sides are slightly elevated, forming a very slight hill on each side. When I place a tile perfectly on the middle of the crack, it teeters back and forth, the crack length forming the fulcrum or pivot point. Does that help?

The house is 14 years old, no telling when the crack formed, I presume early on.

I looked at Ditra and will take a peek at Ardex. My little project keeps growing :')

Thanks for any suggestions, I'm baffled on how to proceed.

Jamboaz

[Jerry Thomas]

Read what the TCNA has to say on handling cracks in concrete TCNA - Technical Services: FAQ

Ditra will work. The few times I have repaired lateral cracks under an 1/8" wide I used Laticrete 9235. You need some kind of anti-fracture membrane that will bond to the concrete that will isolate the crack from the tile above when using a thinset method.

Originally Posted by Jerry Read what the TCNA has to say on handling cracks in concrete TCNA - Technical Services: FAQ Ditra will work. The few times I have repaired lateral cracks under an 1/8" wide I used Laticrete 9235. You need some kind of anti-fracture membrane that will bond to the concrete that will isolate the crack from the tile above when using a thinset method.

Thanks Jerry. Are there other membranes you would recommend? I looked at Laticrete 9235 and it appears to be both the crack filler and the membrane. Is that correct?

Would I need to isolate the entire room with something like Ditra or just the area around the crack?

Thanks,

Jamboaz

[Jerry Thomas]

Just around the crack Jam. The 9235 is the only one I have any personal experience with and it does come with the fabric needed to isolate the crack. Ditra would be too thick imo to use here unless you decided to cover the whole floor.

[Bud Cline]

Laticrete 9235 is primarily intended to be used as a waterproofing membrane, Laticrete Blue 92 is their liquid crack isolation membrane. This isn't to say there wouldn't be some benefit in using 9235 for crack isolation. It may even be the same product with a different label.

DITRA would have to be used throughout the area if you used it and I would recommend doing just that.

However if all you intend to do is to address the crack a membrane like Noble CIS would work for this purpose but there again, it would be better to use it on 100% of the floor area. If you only address the area of the crack the membrane should go out in all directions equal to two tiles.

No matter what you do I would first use some cheap caulk to fill the crack to keep the thinset out of it. You could also look at some of the newer flexible thinsets available. Some boast of allowing a 1/16" lateral movement and others claim a 1/8" lateral movement when using the thinset alone.

If all you choose to do is to grind the high spot along the crack then you could use thinset to fill any of the low places that exist, this doesn't require a high-dollar filler such as Ardex, it would be a waste of money in this application. I think.

[Jerry Thomas]

I hear you Bud. I been using 9235 for years and probably because I build showers in my work. It works very well for isolating smallish cracks in slabs. They list it as one of the advantages of using it ....

Advantages ▪ Inhibits stain causing mold and mildew growth in the substrate with Microban® antimicrobial product protection ▪ Safe—no solvents and non-flammable ▪ Interior and exterior use ▪ Vertical and horizontal surfaces (including ceilings) ▪ Thin—only 0.02" (0.5 mm) thick when cured ▪ Anti-fracture protection of up to 1/8" (3 mm) over shrinkage and other non-structural cracks

It is expensive so it's probably not the best choice for him. But.... my hands get tied when asked to comment on something I have never used before.

I couldn't find Laticrete 9235 at Lowe's or Home Depot. Any thoughts about RedGard for the same purpose? Otherwise, what stores might carry the 9235 or other suitable product for isolation? I'm in the Phoenix area.

Thanks, this is a great forum!

Jamboaz

[TFP Admin]

Originally Posted by Jamboaz Thanks, this is a great forum!

Thanks, Jamboaz, and we're glad you are participating. Unfortunately, unregistered visitors may have to wait a while before their messages are approved to be seen on the forum. This isn't the case with registered members (although there is a wait for the first few messages of new members who post links, but that too goes away very quickly). So, if you would like your messages to be seen as quickly as possible and also to be able to take advantage of features and content only available to registered members, I invite you to join for free. It will also make you eligible to win contests and give-aways.

In any case, thanks for being here.

T

[Jerbo]

My company distributes Laticrete, Custom and Mapei. Blu92 is a great crack isolater. 9235 works as a crack isolater when used with the fabric. Both of these isolate horizontal cracks up to an 1/8". RedGard also works for cracks up to 1/8". Custom's Easymat works for cracks up to 1/4". Mapei's Mapeguard works for cracks up to 3/8". Easymat and Mapeguard are new this year and aren't as well known but are starting to sell well for not only their performance characteristics, but also for their extreme ease in handling and installation. They come in 300 and 150 square foot rolls, respectively, and can be read about at their websites. I don't profess to be a concrete specialist, so I won't comment on the crack if it's still moving. I just wanted to suggest a couple of products that are new to the market.

[Jerry Thomas]

Thank you very much Jerbo and glad to have you here.

[Jamboaz]

Excellent info! I'm now official and registered.

I took some time off and ignored the house for TDay break, going to hit it next week.

One quick question as I figure out crack isolation. (Sorry, I should probably start a new thread, hopefully I'm not breaking the rules.) There are holes in the concrete from where I pulled up the track strip. They are relatively shallow (at most a 3/16" inch), and around the size of a silver dollar. Should I worry about filing them or just apply the thinset and tiles over them?

Thanks,

Jamboaz