My boss told me to use portland cement to fill in the 2-3" deep swale for a drain drain in his basement, it hasn’t leaked in 20 years. (not my house, just doing as I’m told…)
Anyways, he wanted me to mix the cement real thick but it wouldn’t feather out so I made a thinner batch for the top coat (all made during the same session).
By over night it had 2-3 decent cracks in it but they would have been livable since we are covering the floor with tile anyways. Over the weekend it looks like the whole thing lifted a quarter inch and it’s basically junk.
My feelings are that I should have used actual concrete for the majority of it then came back and put a thin leveling coat on afterwards. I also think it dried too fast and I should have covered it with water.
What should I do now? Chisel it all out and start over? Chisel out the loose and above-grade stuff then do another coat of portland?
It’s basically cracked all the way around. Can provide more pics if necessary.
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you can kind of see the drain at the end of the caulk gun:
So a brief as I can you create the lip so that the cement fills under the surrounding slab. The surrounding slab is where all the strength is. One of the most important properties of Hydraulic cement is that unlike normal concrete it expands as it cures. That negative angle allows the cement to create a very strong seal as it expands and presses tight to the existing slab. It is not a perfect solution in wet application as there is always a chance of leakage but in a typically dry situation it will work perfect.
You cant use cement for this application. And since you did it in two batches, you have a cold joint between the two so that’s even worse. You need to remove the work you did, and fill the drain with a quick set non shrink grout. The dip itself is deep enough that you will also need to use non shrink grout to get it close to level. Then you can use a self leveling floor resurfacer (Quickrete 1249-51 or eq) to level the surface for the tile. Make sure to use a bonding adhesive before the resurfacing.
Sorry if my thoughts are disorganized, im working off a phone.
Source: I am an architect.
also, unless I’m not understanding this correctly, there is no need to pour concrete under the slab
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One more thing - the self leveling resurfacer is good for about an inch. If your dip is an inch or less, skip the grout
I need to read all of this a few more times but my first comment is that I didn’t do it in two settings, it was all wet, I just made a few batches sequentially and thinned the last one a lot because it wouldn’t feather out nicely.
So I should hammer it all out and start over? Then use a saw to cut a square out? How is the negative angle done?
Are there any sites that would explain this that I could send my boss? I tried searching but obviously that didn’t work.
I don’t think you need to saw cut anything. You should be able to remove most of what you already out in because I’m guessing you didn’t use a bonding adhesive. Once you do that you can fill the drain with non shrink grout, get the area close to level with more non shrink grout then use a bonding adhesive then the self leveling mix. Look up the quickrete number I gave you before and find the product specifications. That’ll give you all the info you need. It’s really pretty easy. As far as chiseling a negative angle, I don’t think that would be necessary because you don’t have any pressure below the slab. The goal here is just to plug the hole then fill the majority of the void with non shrink.
What is the drain connected to? If the sewer, I’d be really sure it is very well sealed before putting any flooring over it.
other than that, if the depression isn’t particularly deep there are many cement based floor leveling products that are meant to fill shallow depressions and feather down to near zero thickness. Personally I think the Ardex family of products is the most extensive and highest performing.
if the tile is then being directly set in thinset mortar over this patch, again you just need to be certain that no moisture is going to be being drawn up through the abandoned drain.
on a side note, there isn’t any good reason to use straight Portland cement in this kind of situation, so it wasn’t really your fault.
Usually, when mixed with sand and/or other aggregates and/or additives…otherwise it is just a paste or slurry that doesn’t work very well performing as a mortar or concrete would.
