crack isolation [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile

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jwmezzanotte
02-27-2012, 05:19 PM
I'm working on a job with an old concrete slab. There are a couple of small cracks in the slab, in plane movement only. less than 1/8".
The slab also has a bit of a slope so I want to use SLC to flatten it out. It's been cleaned and scarified with a diamond cup wheel. Nice clean concrete to bond to.

What are the typical order of operations here?
I'm thinking to take care of the crack-isolation (planning to use the mapeilastic hpg 2 coats with embedded mesh) and then when thats done use the primer and then SLC over top.
Should I rethink this?

thanks

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cx
02-27-2012, 05:52 PM
John, you'll wanna check with both the membrane manufacturer and the SLC manufacturer before you do that. Those two materials do not always play nice together.

And you understand about honoring the cracks up through the tile installation when using such isolation membranes, yes?

My opinion; worth price charged.

jwmezzanotte
02-28-2012, 12:30 AM
you'll wanna check with both the membrane manufacturer and the SLC manufacturer before you do that. Those two materials do not always play nice together.

Will do :tup2:. Planning to use all mapei product anyhow, but a quick call wouldn't hurt.

And you understand about honoring the cracks up through the tile installation when using such isolation membranes, yes?

I don't see how thats possible in this case? Short of letting the crack just break through the tile ;)
The cracks are random directions, not straight. How would I honor that?

There was some settling of the building in one corner (about an inch) because that corner is on piles. The rest is on rock. Pretty common problem here, and the cracks were likely caused by the original settling of the piles. Also pretty common here with some of the older buildings.
I don't think its moving anymore, there arent any signs of it and the owner says the cracks have not moved or gotten larger in the time that he's been there. (since he was a kid I beleive) This slab is at least 30+years old

I wanted to use mapeguard 2 since it claims protection up to 3/8", but I'm having issues with that product :bang:
(http://www.johnbridge.com/vbulletin/showthread.php?t=99459)
The other product we have here that could work is mapeilastic hpg. According to the directions it gives protection up to 1/8" with two coats and embedded mesh.
We have ditra as well, even though its not a crack isolatioin membrane I do suspect it helps :suspect:

Owner's solution
"I dont care, just order extra tile. If it cracks I'll have you or someone else re set them"
I'd feel better if I at least make an attempt at crack isolation though.

pics of the cracks:116583

PetrH
02-28-2012, 12:38 AM
always hard to tell from pictures, but those look like shrinkage cracks from the concrete curing, rather than structural cracks from movement. I've used Mapei Aquadefense in this application because it is much faster drying than the HPG. Normally you can start rolling on the second coat within 20 minutes of the first and if there are no thick areas start tiling in two hours.

jwmezzanotte
02-28-2012, 02:37 AM
crappy cell phone pics
I need to bring a camera, i just use the cell because I happen to always have it handy.

Definately old movement cracks. Hard to tell from the crappy pictures though, If you saw it in person you could tell.
I wanted to use mapeilastic CI (crack isolation), but not available here. Yet, working on it.
Never used the aquadefense though. I would try it if we had it here.
Any issues with SLC over it?

thanks

cx
02-28-2012, 08:12 AM
I don't see how thats possible in this case?Nor do I, which is why I wanted to be sure you recognized the limitations of the crack isolation product you planned to use. :)

jwmezzanotte
02-28-2012, 10:51 AM
Nor do I, which is why I wanted to be sure you recognized the limitations of the crack isolation product you planned to use.

gotcha :tup2:
Customer doesnt seem concerned about future cracks. This is in an office in his business downtown, not like its his kitchen or something.
I still want to try and give it some protection though. I dont know if it will prevent cracks or not, but its minimal added expense so why not? :shrug: