pouring slab for existing foundation?

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Old 03-23-13, 06:25 AM
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pouring slab for existing foundation?

I have an outhouse at my cabin thats about 6x8. About half the floor is already concrete as it sits on a septic tank. The rest is packed dirt with some rock. Should be easy as the base is already formed and all I have to do is throw the mix down. Question is, how do I skim, screen, level the top with a 2x4 since the building is already there?
 
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Old 03-23-13, 07:01 AM
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Is it sitting directly on the septic tank? Or does it sit on bricks/blocks, etc? Is the wood below grade? Ideally you would have a footing around the perimeter of the building for it to sit on and disperse weight. You will have to blind screed it with a straight 2x4 about 2/3 the shortest dimension of the building. Rest the screed on the existing concrete and fill up and screed off the edge.

Gotta remember this is an outhouse, and although a quality job is always best, do the best you can.
 
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Old 03-23-13, 07:18 AM
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Yes it sits on top of a concrete tank but the top of the tank only take up about 1/4 of the floor. Basically I want to pour concrete around it. The sides of the floor are 4x4 on the ground. I was gonna dig down a little further then pour. How many inches should the floor be? How should I level it around the tank if I have no room to screed with a 2x4?
 
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Old 03-23-13, 07:30 AM
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If you make your concrete a little loose, it will seek level pretty much on it's own and screeding will be done with a shorter 2x4 as mentioned. You can put a level on top of your screed to keep things level, too. Floor should be a minimum of 3" if not 4". Foot traffic is all you'll have, right?
 
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Old 03-23-13, 04:46 PM
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Yes light foot traffic bu tI do store things like pushmower and small log splitter in there.
 
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Old 03-23-13, 05:25 PM
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If you can snap some chalk lines on the walls to represent level, you will want to carefully place some concrete along the edges of the walls, and hand pack it with a trowel, patting it flat until it closely follows your line. Then use that concrete as a reference to eyeball how much concrete you are adding in the middle. If there is a doorway into this area, work your way out of the room through the door, just lightly screed the floor by resting your screed on the level concrete you have patted down on each side. You just have to be careful not to drag too deep.

Alternatively, some guys will install a pair of wood stakes and a metal pipe on top (held between a pair of nails) to help guide the screed back and forth. You then have to pull those pipes, beat the nails over and bury the stakes as you smooth the spots the pipe left. I'd do it the former way, though.
 
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Old 03-23-13, 08:58 PM
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Or you could establish a level line all the way around the perimeter at top of finished grade, using a carpenter's level and pencil mark. Then nail some 1/2" x 4" joint filler to the 2 x 4s, tops along the pencil lines (you may have to temporarily block the joint filler between studs, to prevent concrete from causing it to bulge outward). Pour, consolidate and finish your concrete to the tops of the joint filler, using a long wood float or darby to float the mud into place.
 
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Old 03-24-13, 01:23 PM
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A chalk line around the outside will help lead you to level, but you will lose them in the process of placing the concrete. Use a 6" roll of painters tape. Let the bottom of it be your level and place it along the chalk line. It is be a visual reference and also make for easy clean up.
 
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