Pouring A Thick Concrete Pad.....

[Utopia Texas]

I am putting the figures together to install a 27KW generator for our house. We live on water and though the creek has never fLowed over the bank I would like to have the top of the slab\pad 1 foot above ground level. Can I fill the center of the form with crushed cinder blocks to fill in before pouring the concrete or should the whole pad be 1 foot deep? The unit will weight in at 960 pounds. Am I being too cheap filling space with crushed material?

 

[crazyal]

What are the length and width of the pad? Are you planning on using rebar? The only issue I can see with using broken up blocks is that you could end up with voids because the cement didn't fully get down between them. Also if you are going to be standing in the form while pouring cement they will be difficult to walk on. The last thing you'll want to do is trip and fall into wet cement. You don't want to have the the cement watered down so it'll flow better either, as it will weaken it. If the pad isn't too big then you're most likely not talking much of a savings (that's why I asked). Not sure if this is something you are going to just buy bags of cement and mix yourself or having a mixer come in and pour it. If you're doing it yourself and you have plenty of help you could have someone putting the broken up blocks into the slab after you pour it.

 

[dusty3030]

I wouldn't pour a 1 foot thick pad period.


If a nat gas where the base of the unit is basically steel skids dig a hole for each corner, set 4 piers and if put it 2 feet off the ground with anchor bolts set in top of each pier and bolt it down to those - 1 each corner.

 

[Diamondpilot]

My hanger floor is 10" thick with rebarb and fiber. Not a single crack. We cut the floor open 24" wide 40' long to add a full bath. The cement was fully cured.

Chris

 

[Egon]

Should not be any problem if you keep the minimum depth of slab at four plus inches. Will you have bolt downs?

 

[Utopia Texas]

I wouldn't pour a 1 foot thick pad period.


If a nat gas where the base of the unit is basically steel skids dig a hole for each corner, set 4 piers and if put it 2 feet off the ground with anchor bolts set in top of each pier and bolt it down to those - 1 each corner.

Yes, This type unit is on a steal frame with a enclosed box type cover so just corner posts might work well. Or a "Rectangle Picture Frame" of concrete. With the center empty the electric lines to the house and propane line could be run easily and then the center section filled with gravel. This will be near the house so "The Boss" has to approve how it looks! I need to figure out cubic feet of concrete necessary for different set ups and call locally to see what minimum amounts can be delivered. This is by no means a huge pad....a little over 5 feet long and 3 feet wide and one foot tall.

 

[Utopia Texas]

Should not be any problem if you keep the minimum depth of slab at four plus inches. Will you have bolt downs?

Yes, I plan on bolts in the concrete through the lower frame just in case of vibration. Wouldn't want a thousand pound walking its way off its mount! This will probably be over kill. My brother already has a similar unit and it runs really smooth.

 

[Gary Fowler]

My hanger floor is 10" thick with rebarb and fiber. Not a single crack. We cut the floor open 24" wide 40' long to add a full bath. The cement was fully cured.

Chris

There is no issue with concrete thickness and curing. I have done inspections on slabs that are over 8 feet thick and they all cure in 28 days just like a 4" slab. Concrete will cure even when placed underwater. NOTE : studies have shown that concrete continues to cure and get harder for around 100 years but we only expect it to reach its design strength in 28 days regardless of thickness.
I have seen raised slabs poured when the perimeter is put in like a 6-8" thick wall (thickness depends on the height of the raised slab) and then it is backfilled with either sand or soil and compacted in maximum of 6" lifts using vibratory compactors of various sizes depending on the size of the slab. Small areas use whacker packer or vibra-plate and larger ones might use the large 15ton roller with vibrating drum.

For the OP slab I am assuming he will only make it 6-12" wider than the machine he is setting on it so he might just pack with a hand plate packer. What ever he uses needs to be solidly packed in so it doesn't settle.

Unless he is batch mixing it himself, a redi-mix company is going to charge him for minimum of 4 yards so he may as well set up for that amount and make his slab as big and as high so as to useup the minimum charge for the concrete. He can make one heck of a slab for a generator with 4 years of concrete.

 

[Egon]

Yes, I plan on bolts in the concrete through the lower frame just in case of vibration. Wouldn't want a thousand pound walking its way off its mount! This will probably be over kill. My brother already has a similar unit and it runs really smooth.

Sounds like you have it all played out. Now the SWMBO on looks factor is left.

 

[crazyal]

A 3x5x1 would be 15 cubic feet, less than a yard. That would be 25 80lbs bags. I'm lucky as I can get small loads, even as small as 1 yard. Anything less they might say no. I would just run the conduit through the slab for gas and power and then just pour around it. I would also look into cement coloring additive. Since you're going to have it up by a foot and you need to please the foreman showing her some optional colors to choose from will help get her approval. My garage is sitting on what's called an "Alaskan slab" It's 24" thick around the outside edges and about 6" in the center. You could do something like this but the savings would be pretty much nothing.

 

[jclaudii]

Could you not build a footer trench around the permiter that is the width of cinder blocks or even a knee wall if you chose to go native stone. Then fill it in with fill aggregate up to 1 foot and then poor slab on top of cinder block retainer wall/knee wall?

 

[rustyshakelford]

Build a pad out of select fill for use gravel to build the grade up. Set forms and poor

Brett

 

[Deere Dude]

I would frame it up to 3x5 an solid ground and start dumping and mixing and throwing hard head rocks or limestone or anything to take up space leaving the top couple inches concrete. I don't think I would use sinter blocks because of the air gaps it would leave, but then it probably would matter there either. Everyone has rocks and you won't need that many of them.

 

[the old grind]

3' x 5' using all of 4 yd would be 7' thick.

Been my experience when getting 'min order' that often it's a driver's last stop. Worst case, he shows up late with a 'hot' load (can NOT slake) and 1-2 yd give or take on the 4-5 yd expected. This should not be a discouragement. Have other things (pads, approaches) formed, their priorities arranged, and wheelbarrow or FEL bucket ready to distribute any largess if it's your day.

If you mix your own, have a helper squish stones, rip-rap, etc in between bags/pours. Rocks are much heavier that other stuff for the volume they displace (eg: to save several bags). Re-rod is more important than back-fill.

If it wouldn't be too much of an eyesore, ask the boss if she'd like one of those poly storage lockers (garden shed?) by the gen, or to block the view of it. (More slab if you order yards of 'crete.) For minimal-mix DIY, I like what dusty3030 suggested. Easy to keep clean/clear beneath and good service/hookup access.

 

[EddieWalker]

Are you going to just pour a slab big enough for the generator? or are you talking about the entire house?

If it's just the generator, wouldn't it be better to put it on top of a framed mount? Pretty easy to build a metal frame that will hold the weight of the generator and have some storage under it.

If it's the entire house, why not just keep building up the pad with compacted dirt until you get to where you want to be?

While there is nothing particularly wrong with thick concrete, it does become very wasteful and expensive without any benefit for the money spent.

Eddie

 

[jim_wilson]

Since we're on the subject of concrete slabs - I've got a related question.

I've got to pour a concrete slab in front of the side door to my barn. I'd pave it - but I've got limited space to get vehicles in thru this door - so I anticipate having to use something like Go-Jacks to line vehicles up to get thru the door (especially larger vehicles like my Suburban). I may also do things like roll an engine hoist around in this area. So I'm thinking that a slab is a better choice than pavement because of the small wheels which might not like hot pavement in the summer months.

Before I pour the slab - I've got to build the area up a good 18 to 24 inches.

What I'm thinking of doing - is using up some of the massive rock pile I've got to build up that base - what I'd do is lay down a layer of rocks - nothing more than say 5-6 inches in diameter, fill in the gaps with rock dust or smaller sized gravel - compact the **** out of it - and build that up until I get to the level where I want to pour the slab.

Is there any reason not to put down rocks like this under a slab? Drainage in this area is not a problem.