# Problem with SLC?



## angus242 (Oct 20, 2007)

I poured some SLC to cover a heating element and within 3 days, I have cracks throughout. :sad:

Here are the floor stats:
Framed floor
Deflection L/1083
Subfloor: 3/4" ply
Underlayment: 1/2" ACX 

Subfloor screwed into joists
Underlayment laid perpendicular to ply, screwed to subfloor only

I installed a Laticrete heating mat. It has self adhesive on the mesh plus it was stapled to the ply.

I used Laticrete Admix per instructions to prime the floor and heating element.

Waited for 3 hours (admix was dry).

Mixed Laticrete Latilevel 86 with water as per directions. 

Poured immediately after mixing and worked it with a squeegee. Immediately mixed a second batch & poured. 

First problem I noticed was it didn't really self level very well. I worked the mix for no more than 5 minutes and left it to cure. The next morning, I noticed there were some of the squeegee marks left from the previous day. Because it looked as if it was not leveling very well, I dipped my finger in a section for a "test". The next day, the finger dip mark was still there.

I talked with my Laticrete rep and he suggested that maybe I worked it too long (only about 5 minutes after pouring) and that I used room temperature water to mix with. He suggested using cold water.

OK, so I could live with the fact that it didn't really self level. My main goal was to cover the heating element, which it did. However, 2 days later (3 days after the pour), I noticed cracks all over. The room has been blocked off so there was no foot traffic on it. The house has been conditioned so there shouldn't have been a big swing in humidity.

Any clues why it's cracking?


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## Jaf (May 10, 2010)

No idea, but I get the nightmare feeling looking at it. Sh!t happens, even to good people.

How do you fix it? Tear it up? or will that dimply stuff you use (name escapes me) make up for the cracks?


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## angus242 (Oct 20, 2007)

Jaf said:


> No idea, but I get the nightmare feeling looking at it. Sh!t happens, even to good people.
> 
> How do you fix it? Tear it up? or will that dimply stuff you use (name escapes me) make up for the cracks?


Not sure why it cracked. If it just shrank some, I'd feel fine using Ditra over it. However, if there's something else going on, I want a solution before going any further.


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## kevjob (Aug 14, 2006)

Not sure about laticretes but have used SLC and the one time i had hairline cracks was warm water to mix and had a bad batch as I had the rep come out. You might have the rep come out and take a look. Man what a bummer, i have gotten away from SLC with their finicky attitude.

We ended up putting ditra over it and had no problems so far.........


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## PrestigeR&D (Jan 6, 2010)

*doesn't look like shrinkage...*

to me Angus.... if that was the case it would be all over the field.. looks like stress cracks to me.. especially the slider..that is probably in the center somewhere I am guessing.. but I doubt that is shrinkage... to clean of a stress fracture to me.. what are the floor joists members and I am assuming 16" OC ..

B.


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## angus242 (Oct 20, 2007)

PrestigeR&D said:


> what are the floor joists members and I am assuming 16" OC


2"x10" SYP
16" O.C.
9' unsupport span

Room is a bathroom, totally gutted. I see absolutely _no _reason for stress cracks.


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## PrestigeR&D (Jan 6, 2010)

*that's accaptable,...*

just don't think it's shrinkage..but all that excess weight.. It may be causing those stress fractures - how many pounds of the SLR are on that floor...? You add the fact that you have heavier spotting due to leveling the floor and you have to think that the thickest area is going to be the middle..(center) just trying to think of this logically... I think it is definitely a weight issue Angus.. did you walk on it? ...jump up & down... you think I am kidding... when a floor goes in- better be able to handle that static load and then occupancy lifestyles. If you start to see some more cracks... you have a problem.. if not.. at least you know your floor is good.. otherwise you may have a product issue.. 

just does not look like shrinkage....

B.


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## angus242 (Oct 20, 2007)

Brian,

L/1083. No one has set foot on it. It can't be dead/live load.

SLC that can't support its own weight? :blink:


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## JazMan (Feb 16, 2007)

Hi Angus and all,

I noticed 2 things.

1. Plywood underlayment should be installed in the same direction as the plywood subfloor, face grain always across the joists. I don't believe this was the critical mistake though since the single 3/4" should be better than the L360 max deflection required. 

2. No mention of the lath required per Laticrete direction over wood for Laticrete Latilevel 86. It says.......*"Please note that wood surfaces must be exterior glue plywood and should have a metal lath attached prior to priming."*

Not sure whether it needs to be removed or not. Is it bonded well to be subfloor?

Jaz


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## angus242 (Oct 20, 2007)

JazMan said:


> 1. Plywood underlayment should be installed in the same direction as the plywood subfloor, face grain always across the joists. I don't believe this was the critical mistake though since the single 3/4" should be better than the L360 max deflection required.
> 
> 2. No mention of the lath required per Laticrete direction over wood for Laticrete Latilevel 86. It says.......*"Please note that wood surfaces must be exterior glue plywood and should have a metal lath attached prior to priming."*


1) The floor is only 5' x 8' and if I would have laid the 1/2" EGP in the same direction as the T&G, I would have had seams lining up. I didn't think it would be a big deal. There is no noticeable bounce in the floor (before the SLC).

2) I read the instructions and saw this exclusion: "Note: Galvanized diamond metal lath can be omitted when installing LATICRETE 86 LatiLevel™ over LATICRETE Floor HEAT."

The pour is roughly 3/16".

I'm seeing a section across the back wall where the SLC seeped under my perimeter barrier some. Not sure if that could be affecting it. 

The pour is adhered very well to the ply.


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## HS345 (Jan 20, 2008)

I would get a hold of Laticrete. 

Nice catch Jaz on the plywood. You should always, always always run 2nd layer of ply perpendicular to the joists, not the subfloor. Even if you have to cut it to avoid seams. I don't think this is your problem here though.


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## JazMan (Feb 16, 2007)

It actually says........

Note: Galvanized diamond metal lath can be omitted when installing LATICRETE® floor heat mat but must be used in areas where LATICRETE floor heat is not present.

I guess the mat acts as lath. OK, so maybe you may want to re-do it.

Jaz


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## Bud Cline (Feb 12, 2006)

I would forget about it and move on.

I think what you are seeing is nothing more than the natural adjustment of some surface tension. You obviously used the rapid set version (a slower acting standard version is also available). Air currents from A/C coming and going can add a little premature drying to the surface while the underside is slower to dry due to the primer and not as much air down there as is crossing over the surface. The surface dries first and as the core dries it tightens (shrinks) slightly causing surface cracks.

I'm thinking the bagged product was a little warm and the water was not cold enough but still no harm done. I see those sucker crack all the time. Hell I have been known to use ice in my mixing water in the summer time.

Keep going and *git-'r'-done*, no reason to call anybody and make an issue of anything that I can see.


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## angus242 (Oct 20, 2007)

Bud Cline said:


> Keep going and *git-'r'-done*, no reason to call anybody and make an issue of anything that I can see.


The cracks (from the ones that I can see) are all the way through. Still no worries about that? :sad:


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## Bud Cline (Feb 12, 2006)

> The cracks (from the ones that I can see) are all the way through. Still no worries about that?


Not that I can see!

I've seen that happen a lot.
If you consider you have several things going on...
such as: 
the structure make up and temperature
the primer coating
the plastic wire jacket and maybe plastic matting
the metal wire conductors
the cement (SLC) and components
SLC temperature
water temperature
interior environment
air flow

everything acting and reacting at different rates.

Not to worry.:thumbsup:

Now if things like air-pocks and blisters and pimples had developed in the surface that would be a different story, but that doesn't seem to be the case.

Besides...what can happen? The cracks will fill with thinset and the tile will bridge the cracks and other than routine temperature changes from now on everything will be normal. There can be no external forces on that strata if you allowed for perimeter expansion. Turn the heat on and see what happens. I can tell you tho - nothing will happen, I'm sure of it. 

Someday I'll tell you about the 3500 square feet of SLC we once poured over a wax-impregnated brick-paver corridor throughout a Holiday Inn. We mixed the SLC with ice water to slow things down and encourage the marriage of the many many mixings...and we used rapid set SLC. By six a.m. the next morning the SLC was nothing short of perfect. Oh hell yes it was cracked everywhere but none-the-less perfect for the tile application. We had a lot of sinks in the pattern of the brick and the Damned SLC found its way into a banquet room where a dam failed, but other than that everything was great. Looked scary as hell but still great. The tile went down without a hitch and is there today remaining flawless. That was twelve years ago.:thumbup:

*GO FOR IT!*


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## angus242 (Oct 20, 2007)

OK, upon further review, I did lay 1/2 of the ply underlayment perpendicular. I found incarnation #2 of this job (yes I am on the 3rd version). Joists run left-right in the pic.










I ended up pulling put the hydronic, replaced with ACX ply and installed the Laticrete mat in the area you see above with the PEX.

UGH 

This is what I get when "trying" new things. I have been pushed pretty soundly by a few folks from Laticrete to try their products. Since I was using the Laticrete heating, I figured I'd use the SLC too. I have successfully used Mapei stuff in the past. Hell, this past week, I even did a small bathroom with some Bostik SLC (Durabond 83P). 

I'm fairly certain I did something wrong here. I cannot imagine it's a problem withe the Laticrete Latilevel 86. Maybe it was my room temperature water. I'll go over everything again next week to verify my steps. 

There's a reason I use and stick with Mapei products (familiarity). 

Dammit


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## PrecisionFloors (Jan 24, 2006)

I'm way late to the party on this one but I'll throw my .02 in anyway. I think Bud is right on target. Combination of warm (room temp is warm in the summer  ) water, rapid set material, over worked, material and air temp variables, on and on. I would not have sweated it unless it showed signs of bonding issues. Cracks are really no biggie for a tile install...hell I've skimmed with Ardex Featherfinish and laid resilients over slc pours like that in high rolling load (hospital beds) with no issues whatsoever. We simply did not have time to tear it out and re-pour. I will say this. If I have a job that requires SLC it gets Ardex K-15 or I don't do it. Like you said familiarity of products goes a looong way. I also mix with ice water.


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## angus242 (Oct 20, 2007)

So far everyone keeps telling me about the water temp. There's _got _to be something to that.


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## PrecisionFloors (Jan 24, 2006)

There definitely is, trust me on that. Water temp has an effect on the working time and viscosity of the pour. I've witnessed it first hand on pours much larger. Count yourself lucky you learned it on little one. The finger dip mark not self leveling is a direct result of the water being too warm, I'd bet beers on it.


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## angus242 (Oct 20, 2007)

PrecisionFloors said:


> The finger dip mark not self leveling is a direct result of the water being too warm, I'd bet beers on it.


That's what Laticrete said too. Well, not the beers part :laughing:


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## PrecisionFloors (Jan 24, 2006)

angus242 said:


> That's what Laticrete said too. Well, not the beers part :laughing:


:laughing:

Precision Floors - More generous than Laticrete. :jester::jester::jester:

My new slogan arty:


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## jarvis design (May 6, 2008)

I have had the same issues (not with a laticrete product)- but with some SLC from flextile (owned by Olympia tile). I have used this product for a few years and love it, but, last year I did have the same thing happen on a job...in the middle of the summer...and it was damn hot. 
Did 2 rooms...no cracks..did the 3rd...cracks kinda like what your pictures show.
We were filling water buckets from the hose and after some thought, I asked my helper if he filled the buckets with "cold" water...not warm hose water...turns out, he did not "bleed" all the warm water from the hose. I checked to make sure it was well adhered (which it was), installed ditra, then tile...no problems


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## angus242 (Oct 20, 2007)

I ran over the top with my concrete grinder, just enough to rough up the surface. That thing will rattle your teeth. No more cracks appeared. The existing didn't get worse. I also ran my grinder around the perimeter to make sure I had a definite expansion gap.

I think I'm a go for the Ditra :shutup:


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## PrestigeR&D (Jan 6, 2010)

*Well...*

thats good news Ang.....:thumbup: progress may continue:thumbsup: Still curious as to what caused that.. you think it was the water temp? It's Just if that was shrinkage.. it certainly was an isolated event... none the less at least you know all is stable... 

B.


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## angus242 (Oct 20, 2007)

PrestigeR&D said:


> you think it was the water temp?


That's what I'm going with. My other error was 1/2 of the ply underlayment being installed in the wrong direction. If it was that, I wouldn't have gotten cracks across the entire floor, just on the 1/2 that was perpendicular to the subfloor. 

After beating up the SLC with the 2 grinders, I'm confident it's adhered. :thumbsup:


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