Self leveling underlayment snafu?

I'm in the middle of installing a 5" wide plank floating engineered floor over a premium underlayment pad. I'm doing this room by room, and as I prep the concrete slab in each room, I'm pouring self leveling underlayment (TEC EZ Level) to address low spots that I come across.

So far, I've done 5 of these small pours for different areas, and run into no issues. Because I don't need the whole bag of underlayment for a single pour, I'm having to pay careful attention to the consistency I mix in my bucket, and I shoot for a runny milkshake. As far as I can tell, this has worked out pretty well thus far. However, today, I guess I pulled a bit of a dumb move. I don't know if it was the weather outside (about 32 degrees) or just my lack of attention, but for one pour I did this morning I couldn't seem to figure out why my mix wasn't thickening up enough in my bucket to my liking. But after moving ahead with the pour anyway (yes, dumb), which was fairly watery and not at all uniform like the other ones, I got back to my outdoor faucet and then figured out the problem:

I had a slug of damp mix at the bottom of my bucket.

After enough self-flagellation (didn't I mix for 2 to 3 minutes? didn't I scrape the bucket sides?), I checked out the pour six hours later. Here are some pics:



The pour itself is ugly, no doubt. My question is, is it still usable? I've scratched the surface in various spots with my fingernail and tapped with a hammer in places, and I don't see or hear anything seriously odd. And as it happens (no surprise, I guess), because the pour was so thin I'll have to do another pour on top of most of this to get the height I need (which I will prime first).

But what's the verdict here... am I safe to keep this underlayment, or do I have to dig and/or grind it up?

 

Since you have to do another pour anyway, I suggest you try to remove a small part of it by smacking it flat with a hammer. If it doesn't crumble and come off the substrate, you should be ok. If it does, well, you now know how to remove it.

It will be weaker than the proper mix, but hard to say how much weaker. If it's just going to be foot traffic in the area and not, say, rolling big machines back and forth, then strength is not as critical.

Best thing might be a call the manufacturer; I'm sure they've handled that call before. Most have a tech department that can advise you.

 

If it stands up to a scratch test you should be OK. If it is sandy and crumbles, remove it and start over. Way thinned down cement or SLC is not structurally sound. Bite the bullet and chalk this up to experience. Don't want a crumbling substructure AFTER the floor goes in.

 

Thanks guys. So an update... in various spots, I've taken my hammer as CarbideTipped suggested and smacked the surface fairly good. The underlayment does not crumble... but it does dent ever so slightly. Because of this I have the impression that it isn't fully set up... but who knows? Although it's been 7 hours now, this pour was definitely more watery than my others and so maybe the standard 2-4 set-up time goes out the window here.

As for the fingernail test, let me make sure I'm clear: should this leave no detectable mark whatsoever? Or just no score in the surface that can be felt afterwards?

I like the suggestion of calling TEC to inquire. My guess is that they'll err on the side of extreme caution and tell me to yank it up & start over, and unless that's necessary, I'd prefer not to (obviously!).

 

Not sure about a finger nail, I would test is with something a little stiffer like a putty knife or the point of your trowel. Hitting it with a hammer is more of a compression test. You want to make sure it is well adhered and solid. Cut at it around an inch from the edge of the pour and see if it flakes a chunk off.

 

So this morning I took another look at the pour. In the first few photos, you can see that I used a wide chisel to get a bit more aggressive with the surface to test its strength:



At this point, I'm just not feeling good about this second pour. So I bite the bullet and start smacking it with the claw of my framing hammer. I soon realize that this pour was just not right:



So clearly, this has now become a lesson in how to recognize when pours go bad.

However, I began to notice something I didn't expect. This bad pour was actually a second pour on top of a previous one I did the day before. That first one seemed to go just fine for me, and I didn't notice anything weird about it compared to the other four I'd previously done. However, in the interest of full disclosure, I did NOT prime over that first pour before doing the second one about 24 hours later. I mention this because eventually, as these next photos show, the first pour started to come up as well, and at this stage I'm getting down to the original slab:



A question I now have is, did my first pour start coming up as well here because I didn't prime over it before doing the second? Or was my first pour also bad from the start for whatever reason? If the latter, I'm going to start getting nervous about using self leveling underlayment in general.

 

Did you wait until the primer was completely dry on the first pour - say 2 hours at a minimum depending on temp and humidity?

 

I'd think so. I waited about 3 hours, when the indoor temp was about 67 degrees and in the neighborhood of 40% indoor humidity.