Need to make concrete pad bigger for A/C unit

Old 06-29-05, 04:10 PM
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Exclamation Need to make concrete pad bigger for A/C unit

I have a concrete pad upon which sits my current outdoor air conditioning compressor.
I am putting in a new unit which is physically larger than the current unit. The current unit sits upon a 30" x 30" pad, about 7" thick. This pad sits on another pad right next to the house that incorporates a planter box and a brick box around a basement window.
The new pad needs to be about 46" x 34"

My plan is to:
1. build a form of the appropriate dimensions around the existing pad
2. clean and then apply a concrete bonding adhesive to vertical edges of the existing pad
3. run some long (6"-8") bolts about halfway into the vertical edges of the existing pad. The idea is the half of the bolt sticking out will provide an anchor to hold the new concrete to the old concrete
4. fill the form with new concrete, finish it, etc.

The existing pad cannot be demo'd since the current A/C unit is on it, and this unit needs to stay there right until the new one is seconds from being installed. So I plan to only add concrete around the edges to make it larger, and do not plan to add any concrete over the top. I know this plan will create a seam where the new and old concrete meet. Since I am adding on such a small amount of concrete, it doesnt seem like using a fiber expansion joint is necessary.

Any thoughts, ideas, or critisicm of this plan are greatly appreciated.

FYI I am a carpenter, but work along with a general contractor so I am familiar with, and have some experience pouring concrete pads.

Old 06-29-05, 08:16 PM
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Location: Rockland, New York
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You could try to raise the unit a foot off the ground and then do the whole slab over, or better yet make a mold and pour the new pad close by and the set it over the top of the old one after you remove the unit.

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