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Unread 03-16-2008, 09:15 PM   #1
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water absorption on concrete + cutback

I have an old concrete floor with a thin layer of black cutback adhesive left on it - I scraped and that's all that's coming off. Tonight I spread the ~100 SF area floor with over two gallons of water with a little bleach in it. It served both to check for water absorption into the concrete floor, find any low spots that might need to be filled, and make the room smell better. My question is, how much water should be absorbed in how short a time? The puddles that remain after 2h are small and well under 1/16 inch deep. So I think I can skip the SLC step. Most of the water either was absorbed or evaporated (still winter here). I see on other threads that folks do a water absorption test, but I haven't found how much water should get absorbed in how short a time to be good to go ...

I'm hoping I'm ready to tile tomorrow. (no fingers crossed icon to choose from below!)

If so, should I damp mop the cutback again before applying thinset (Mapei UF2)?

Thanks, and thanks for your help on my other questions!

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Unread 03-16-2008, 09:22 PM   #2
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If the water doesn't bead up like on a waxed car, and absorbs, you probably got enough of the cutback adhesive off. You should be okay. I'd rinse the floor...not sure if the bleach helped or hurt things, but a rinse with clear water can't hurt.
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Unread 03-16-2008, 10:58 PM   #3
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When we talk about water absorbing, we are looking at sprinkling some water on the slab to see if the spots absorb or just sit on the surface. You are looking to see if they absorb in and darken the surface. With the bleach wash you did, I'd rinse it with water before you tile. And check to see if your cutback got gooey from the exposure to the water and the high alkaline bleach. If so, you'll still need to address the remaining cutback.

And whaddaya mean, no "cross-fingered" smilie? What about this one?
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Unread 03-17-2008, 09:49 AM   #4
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Thanks, guys!
Okay, all the remaining cutback definitely changed to a darker color when it got wet. And it's not at all gooey after bleaching. So I'm good there.
Rinse and go? Also I assume the surface should be damp- so I should rinse
right beforehand? Or doesn't that matter?

But there's one more small thing...
Now it's the next morning and there are 4 remaining puddles.
So maybe I should first level with thinset in those few spots?
The low areas are so thin (haven't measured yet, but certainly < 1/16") ... should I let any thinset patch dry all the way, (or just enough to trowel over) before the tiling begins?

And thanks for finding those crossed fingers for me.

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