Nightmare with concrete pad.

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Old 04-30-20, 05:18 PM
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Nightmare with concrete pad.

This was such a simple project. A 2' x3' 4" thick concrete pad to mount a heat pump compressor on. Unfoirutnately I did several things wrong, leading to the pad hardening fine but tilting in the muddy earth. I mud-jacked it up with a pick axe and shoved stones under it, getting closer to level. (I really needed an extra pair of (dispendable) hands. Originally, this mud was so hard it took a pickaxe to break it. But now it is squishy, so I want it a little lower on one side that it is. To accomplish this, I loaded that side with two 5 gal buckets of water and topped them with a rubbermad tub also filled. I have about 200 pounds on that side. I am thinking that the constant weight will work in my favor. If I see any effect mat all, I can make adjustments.
But as a reliable level surface to mount anything on, I can't see it so far. If I had just dug a 4" hole and filled it with concrete, I would have had no trouble.
Will my pad settle into a level position, sink, or do otherwise? There is no frost.
The roots of the trouble is two fold. I over excavated and filled with dirt and rocks uncompacted and 2) I poured the concrete onto a piece of cement board thinking this would strenghten the whole thing. What it was good for instead was sliding. The concrete itself would have conformed. My experiment was a failure and I the laughing stock like all great experimenters.
 
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Old 04-30-20, 06:38 PM
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I think your biggest problem was pouring on top of a piece of cement board.
If what you have is solid...... maybe you could lift it up on its end and backfill under it with rock.
It needs a solid level base.

I'm sure there will be other helpful replies.
 
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Old 04-30-20, 07:29 PM
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Well, there is no sense crying over spilled milk, but I think you might want to bite the bullet and break out the sledgehammer. If it's not level and on a solid base, you will likely be sorry.

Yes, as you now know, you don't overexcavate a hole if you want the pad to be solid. If you do, you must fill it with rock and compact it. And finally, if you are pouring a pad, you make a FORM for it.

What that means is you build a box out of 2x4's that is the exact size you want the pad to be. You dig it down so that the top will be at the right depth in relation to the lawn. Not so low that it floods. You don't just pour it on top of the ground because you don't want the surrounding soil to erode and expose the bottom of your pad. So you usually dig it into the ground so that 3/4 of it is below ground. You probably don't want the top so high that it's hard to mow around.

You level the 2x4 form and the drive in stakes around it. You assemble the form with screws and you secure the stakes to the form with screws. That way, after the concrete has cured for a week or so, you can disassemble it and remove the form.
 
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Old 05-01-20, 11:59 AM
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I think I would get a good big pry bar and lift it off and away. If it breaks then break it again to make it a size you can handle. This pad weighs about 300#. Then excavate and fill and compact and level the base and slide the pad back into place. You know now that I write this I think it might be less work to pour a new one. I just like the challenge of tryingto move it.. You have to decide if the few bucks of form and new concrete plus that work is worth the savings of lifting. moving, filling compacting and moving. Makes me sweat thinking about it either way.
 
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Old 05-04-20, 01:43 PM
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I did over excavate and I did fail to compact it. I did use forms. I have to agree Xsleeper, that removing the whole thing might be the only answer. But in the meantime, the coMbined forced or gravity (think how even my slab is with the board) evaporation, temperature changes, centrifugal force, speed of the planet, and any other forces acting on it, the slab has righted itself to a large extent. Since my surface is pebbly it might not be possible to perfectly level the compressor without washers anyway, so the question is how stable it will prove long term. And then there will be the vibration of the compressor.
But since it is now level I will just stall on proceeding with the job and watch it for stability. If I were working for someone else there would be no choice but redo it from scratch. But at some point the thing will probably stabilize. I am in no real rush to proceed with the installation.
I started out to do a really good job, with gravel forms, sand, rebar, but I blew it anyway. If the slab is not doing the hurdy-gurdy this will be an anthill in the long service of the heat pump. The heat pump! Thass pretty classy. Not everyone has a heat pump. Most are jackassing wood. I would too, gladly, but with no freezing temperatures and triple digit summers, wood heat is less and less useful. So far I have used an electric heater and a window A/C. But this will be better and cheaper. I haven't yet examined the plights of forum users in the heat pump category.
 
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Old 05-04-20, 01:55 PM
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Since we don't know where you are..... it's hard to comment on the virtues of a heat pump.
Since you are using a heat pump...... can we assume you don't have natural gas service ?

Heat pumps are better than electric resistance heating.
 
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