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03-02-2007, 12:05 AM
Hi all, this is my first post ever. Thanks in advance for reading it and trying to help. I have a problem that's similar to a few other posts in these forums, but with a twist. So far, I haven't found the same situation, so I don't know what to do.

My plan was to lay Thermosoft electric radiant heating mats on my 300 sq.ft. concrete basement floor, then cover it with Custom's LevelQuik RS so that I would have a nice flat surface for laying 12" ceramic tiles without fear of snagging the trowel on the wires or mesh. The concrete floor was in good shape, solid, dry, and with no moisture problems. A little uneven in spots, but nothing that the slc wouldn't fix. So far, it's a good plan, right?

So, I properly prepared the concrete floor (scarified it, vacuumed off all the dust, primed it with LevelQuik Primer), then layed out the electric radiant heating mats.

Over the top of the mats, I poured 7 bags of the slc. A day later, I decided that I hadn't poured enough to safely cover the wires, so I primed it again, and poured another 8 bags. This was enough to cover the wires, but the floor wasn't as flat as I had expected it to be (self-leveling, right?). So, a day later, I primed again, and poured another 6 bags, concentrating on the low spots. All of the mixing and pouring for all three pours was done exactly like it said to on the slc bags (6-1/2 quarts of water for each 50# bag, mixed for 2 minutes, worked fast, etc.). The last pour still didn't make the floor perfectly flat, but seemed to be close enough to be workable. So, I was finally ready to snap some lines and throw down some tile. :king:

Not so fast. The next day, I noticed there was a big area right in the middle of the room (about a 5' circle) that had a bunch of hairline cracks, and sounded hollow when I tapped on it. Same thing in a few other smaller spots. Not good.

I called Custom's tech support to see what they had to say, and the guy said to pour more primer on top of the slc and let it soak in, to try to fill the air pockets. :shrug: That didn't seem to make sense, but what the heck, I tried it anyway. Not surprisingly, it didn't help.

I am now assuming that I'm going to have to break the slc and take off the loose sections, then reprime and repour more slc to fill the holes. My question, though, is how can I do this without destroying the radiant heating mats? I'm afraid that if I try to break up the cracked slc and peel it off back to where it's solid, I'll do all kinds of damage to the wires. I'm not even sure which of the 3 layers has the poor bond. I don't know what to do. After spending $1800 for the radiant heat and $600 for the slc (not to mention the $800 worth of tile that's sitting there waiting), I'm pretty worried now. My good plan has suddenly turned into a nightmare.

Very sorry for the long post, but I wanted to make sure I included enough detail to help you help me. Any suggestions at all would be much appreciated. Thanks again. -Mike

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03-02-2007, 03:19 AM
I'm not an expert, but I think your problem is/was too many layers. How thick approx is each layer? Thin layers will tend to crack I think.

03-02-2007, 09:05 AM
Welcome to the Forum... :nod:
Sorry bout your problem....
LIke GHR says, how thick is each pour? - prox...
You let the primer dry prior to the pours?
The hollow sounds are generally lack of adhesion..

We'll wait for FlatFloor to come along and weigh-in...

03-02-2007, 04:11 PM
I'd say the bottom pour is around 1/8" thick, the second pour ranges from feather edge to 1/4" in spots (but mostly 1/8"), and the last pour is like the second. Yes, I allowed the primer to dry to a thin film for all pours.

Thanks again for your input. -Mike

03-06-2007, 10:13 AM
Hi Mike, found you, you may be OK, hairline cracks are not unusual and the hollow sound don't always indicate a lack of bonding. Find a hollow spot and give it a good whack with a hammer. let us know what happens.

03-06-2007, 06:18 PM
There seem to be more cracks and more hollow sounding areas every day. If I hit those spots with a hammer, it sounds like I could break them apart if I really wanted to (but I don't really want to, so I'm not really laying into it). The cracks don't seem to get any bigger as I hit them, though, for whatever that's worth.

In my original post, I had mentioned that the guy from Custom suggested I try pouring more primer on top to let it soak in to try to fill the voids, and I originally said that it didn't work. However, after trying it again, it actually did seem to work in one particular area. It was an area that had some 'bounce' to it (when I stepped on it, I could feel it sink a little, and I could hear air hissing out of the surface holes around it). I poured the primer on that area, and worked it into the holes and cracks by bouncing on it and pushing the puddle of primer around with a paint roller. Eventually, it worked it's way in there, and whenever I bounced on it, the primer would seep up out of the holes, so I figured it was pretty well saturated. The next day, that area no longer bounced, even though it does still sound hollow.

Even though there aren't any more bouncy areas, I'm now tempted to pour primer all over the floor and do a repeat performance of my bouncing and rolling act :yipee: since it doesn't seem like it would make things any worse, and may actually even help, but I don't know if that would be a waste of time, or if somebody has a better idea. I guess I'm still just wondering what kind of trouble I'm asking for if I ignore it all and tile right over it.

By the way, I'm not crazy, for those of you who may be starting to wonder.

Sorry again for rambling on so much.

03-06-2007, 07:19 PM
Not at all crazy, your using the proper amount of caution.

I'm dubious about the primer trick but the again? Worth a shot. I would whack it though it bonded and won't get any worse or it will crack completely. Either way you need to know now not after the tile goes down.

03-06-2007, 07:38 PM
Darn Mike,
I came back hoping to see what had happened with the Whack!!!!
That will give you the info ya need... Like FlatFloor said - Ya needs to know... :nod:
If it ain't stickin you shouldn't put tile down on top of it... A good whack will tell ya if it's stickin or not... Don't be shy - Whack it!!! :bonk:

when I stepped on it, I could feel it sink a little

Tile doesn't like to move..

03-06-2007, 08:47 PM
Ok, I picked a typical hollow sounding area and whacked like I was trying to kill a fleeing cockroach. I hit it about 50 times in a 2 sq. ft. area that already had some cracks, and all it did was leave about 50 indentations from the hammer head. I'm pretty sure I didn't introduce any new cracks, but I can't say for sure. In any case, it didn't all break apart like a sheet of ice on a sidewalk would if I was hitting it like that. For comparison, I was hitting it about as hard as you would if you were trying to drive a 10 penny nail into a 2x4.

It's almost like a big jigsaw puzzle that's sitting on a table, where if you tap it with your finger you can feel (or hear) where it's not flat against the table, and no matter how hard you hit it with your finger, the pieces won't come out. Does that make sense?

03-08-2007, 05:04 PM
Mike I hate to give up on this. Call Custom and get a rep out to check the floor. We are at the point where it's impossible to diagnose from here.

03-08-2007, 06:42 PM
Yea Mike,
That's a great idea Jim has.. Since you already have one communication with their support, just axe em to come an look...
It's just that the movin, and hollow sound but not crackin up, is somewhat bafflin... Let us know what they say.....

Just like Barack Obama n Ross Perot - we're all ears..... :nod:

03-10-2007, 09:30 PM
Well, I contacted Custom again, and the guy suggested I drill small holes (3/8" dia.) with a masonry bit through the slc where the hollow sounds are, then pour more primer into the holes to let it fill from the bottom.

Since a similar technique worked pretty well on that "bouncy" spot, I figured I'd give it a try. The problem, however, was that I didn't want to drill right through a heating wire, which meant I could only do it where the wire is close enough to the surface for me to actually see it.

So, I found a hollow spot with the wire visible, drilled the hole (with a vacuum running to keep it clean), dribbled the primer into it until it wouldn't take any more, then I let it cure. It took about half a quart in that one spot. Well, it seems to have worked well enough to continue doing it. That's the good news. The bad news is that all the rest of the problem areas don't have any wire showing, so I don't dare drill any more holes.

So, if anybody can suggest a clever way of locating the wires (like a stud finder for wires or something), that would be great, because I actually think this might do the trick.

By the way, the guy at Custom thinks that the reason I had the problem in the first place was that I waited too long between the primer coat and the first pour. He's saying that you need to pour the slc a few hours after you prime (which I didn't), and that if you wait too long (overnight, for instance, which I did), you need to re-prime. Nowhere in the instructions does it say there's a time limit for the primer, so that kind of sucks. It just says 2 hour drying time. In any case, he also said that based on my description, he doesn't think the slc is moving enough to cause the tile to crack, and that he'd just tile over it. Of course, it's not his floor, so I'm sure he doesn't really care if the tiles crack.

And I suppose when you get right down to it, I'm getting to the point where neither do I.

03-11-2007, 12:42 AM
Hi Mike. I'm not positive about this but shouldn't the heating mats have been set in a watered down thinset and pressed into it before using SLC??

03-11-2007, 05:21 PM
Not according to the heating mat instructions from Thermosoft. They offer two installation techniques. The first one is to lay the mats on the floor, then thinset and tile right over them. The second one is to lay the mats, pour slc, then thinset and tile over that.

03-11-2007, 06:23 PM
OK, I stand corrected. I wasn't sure about the type you used, sorry!

03-11-2007, 07:47 PM
Nothing you are doing has any lasting value..Tear it out and start over!!

Custom's trying to satisfy you but latex saturations simply so not work when youve already had the SLC debond. All you are doing is creating a pressure balance not fixing the problem.

WHY did the SLC debond is the question & without knowing Why we cant fix this.In order to find this out you will have to remove a bad spot.

You say you scarified the floor.........With what??
How did you prepare the floor afterwards EXACTLY!!

Sorry, you will not get a quick fix out of me because there are none!!!
If you want to do this right however, I will be glad to help!

03-15-2007, 06:44 PM
Hi Todd. Thanks for reading this and contributing your thoughts. Sorry for the late reply on my end, but I've been away from the computer for a few days.

You're probably right, I'm guessing I didn't prepare the floor correctly. I originally said that I had scarified the floor, but now after learning more from reading this forum, I'm thinking that it wasn't even close to being scarified. I originally thought that 'scarified' simply meant roughed up, or scratched. There was originally a coat of paint on this floor. We used razor scrapers that were only 3/4" wide, and scraped the entire floor hard to get it all off, so I was thinking that that process in and of itself could be considered 'scarifying' the floor. However, from the sounds of it, using a power scarifier would have actually removed about 1/8" off the top of the slab, so we weren't even close.

On top of that, I had primed the floor using the LevelQuik Primer on a Friday night, put down the heating mats the next day, then made the first pour of slc either late Saturday or early Sunday morning (I actually can't remember). In any case, I think it was too long between prime and pour.

Then, to make it even worse, I had cut the primer to 3/4 strength. The reason for that is that on the bottle, it said to use it half strength on rough floors, or full strength on smooth floors. I figured my floor was somewhere in between the two, so I split the difference. I probably should have left it full strength.

Plus, to top it all off, the room temp was in the low to mid 50's most of the time, which means the floor was probably too cold for everything anyway.

So, the more I learn, the more it seems that this had little chance of success right from the start.

If it wasn't such a big area (meaning $2400 worth of stuff already on the floor), I'd definitely just rip it up and start over like you suggested. But since I really don't want to do that, I've convinced myself that I'm willing to live with the consequences and just finish it.

The question is what's the worst that will happen if I do just continue, and how long is it likely to hold up?

05-05-2010, 06:30 PM
Mike 01331, how did this all turn out? I just posted my own question re SLC which sounds not nearly like what you had going on, but has us a bit on frayed nerves because we don't know exactly what's going on under there.

05-05-2010, 07:33 PM
Hi Raj.

I'm happy to report that the whole thing worked out just fine. The floor has survived with no signs of cracking anywhere, and the electric radiant heat works great (although it can be fairly expensive to run during a cold New England winter). It's been in for around 3 years now. The only sign of anything out of the ordinary is that in one spot (in a seam, where the grout is), every once in a while a small pile of white powdery stuff appears (about the size of a dime). It's very similar to efflorescence that you may see on a concrete basement wall, but it cleans off easily. In any case, I'm really happy with the whole thing, and wouldn't be afraid to do it again. I'd be happy to answer any other questions you might have, but keep in mind that I'm no expert.


05-07-2010, 06:38 PM
it's always great to hear a happy ending.

Can you tell me more about how you used the primer on the cracks to get it in? Sounds like that made a big difference.

05-07-2010, 08:45 PM
Sure, no problem. I'm sure I'll forget a few details, seeing as this was 3 years ago, but this is the way I remember it.

There were big hollow sounding areas and "floating" sections in the SLC that flexed underfoot. We went around and marked them off by making big circles on the floor with a pencil to get a better visual. The idea was to drill holes through the SLC in those areas and then fill the voids with primer. The problem was that we didn't want to drill through any of the heating wires. There were a few areas where the wire was still showing near the surface, so in those areas, it was fairly obvious where not to drill. In other areas, it wasn't obvious at all. Luckily, however, we had taken pictures as we went during the different steps, and we also had a pretty good "map" from the original layout when we were calculating how much wire we were going to need. Using those pieces of information, we made a bunch of measurements and then made our best guess as to where we could safely drill. Then we crossed our fingers and drilled little holes (I think they were 1/4" but they may have been 3/8"). We also checked the resistance of the wires before, during, and after to make sure it didn't change as we went, even though it would have been too late anyway. While we drilled the holes, we had a shop vac running to keep all the chips from dropping into the holes.

To get the primer in, we started with a technique that was very slow going. We would pour the primer right into the hole until it puddled up around it (which didn't take long at all), then bounce on the floor to get it to "suck" into the hole. The problem with this is that the primer kept spreading out around the hole, while not much went into the hole, so we had to keep squeegee-ing the puddle back into position and then start bouncing again. Not only did we look and feel foolish, but it wasn't working too well.

What we ended up doing was way better. We took my son's silly putty and made little donuts around the holes, and pushed them down tight to stick to the SLC. We then took some small empty squirt bottles and cut them into cylinders about 2" tall, and pressed those into the donuts. What we ended up with were little reservoirs that we could pour the primer into to keep it contained directly above the holes. That way we wouldn't have to worry about the puddles getting away from us anymore, and we could just bounce. Or better yet, we could go have a beer and a sandwich and come back later to see how things were doing. This worked pretty well, but it still was somewhat slow.

The last thing we did really helped things along. We used the reservoir technique, but we also put the shop vac nozzle down against one of the other holes in the same penciled area to suck the primer down into the hollow areas. We continued like that and kept refilling the reservoirs until we were comfortable that the air pocket was full, then we'd move to the next pocket and do it again. Yeah, we're brilliant. hahaha.

So that was pretty much it. It was time consuming because of all the trial and error, but if we had gone right to the final technique first it probably wouldn't have been so bad.

I hope this helps.

05-15-2010, 02:05 PM
We're going to get started on that today.

I suggested in another thread that we're at the point of paralysis though, as constant reading and rereading other threads suggests my SLC pour was wrong to not have expansion joints along the wall base plates. The sheetrock was high, so it's not a matter of just cutting that back.

Thanks for the reply on this. The method you describe sounds like a good way of moving forward. I realize the easy thing to do is to simply say "rip 'er out" but after investing in the best substrates it's hard to just do that without trying innovative measures.