Concrete slabs & steps

I'd like to replace all of this wood decking walkway located at the back of the house with concrete.

My question is, can I concrete the landings without fill (dirt and gravel) with just rebars and cement blocks? Or should I fill the voids as much as I can with dirt and gravel and pour the slabs on top?
Thanks!!

 

You should first lay your block foundation, and then fill it with stone, allowing for a final 4 inches of concrete. If you poured it all with concrete, not only would it cost a lot extra, but the sheer weight of that chunk of concrete would make it settle. It looks like you've got plumbing of some sort below the deck. If you poured it all solid concrete, the settling would break those pipes underneath eventually.

 

Thank you for your quick response!

Yes, the first thing I intend to do is to lay a block foundation for each landing. When I mentioned without dirt and gravel fill I did not mean fill the entire void with concrete instead. I was wondering if I could lay rebarred slabs without any gravel fill underneath for solid support......just emply space underneath the slabs. I know it can be done but is it practical?
I was just trying to avoid filling all the emply space with dirt and gravel.

 

Like you said, it's possible...but not practical. Unless you are a skilled form carpenter, rodbuster, and concrete finisher it would be far more difficult (and expensive) to pour an elevated, reinforced slab. Just out of curiosity, why do you want to leave a void underneath? Is it just so as not to have to buy and place the fill stone?

 

Well, yes, I was trying to save a little money by not having to buy several tons of gravel.
But you're right, on second thought, it's not practical.
I will fill them with gravel and pour 4" slabs on top.

 

I have some follow-up questions:

Above the first course, can the blocks be dry-stacked, and the cores rebarred and filled? They won't be taller than 3 blocks high at the highest landing.

Also, should the forms for the risers be placed right up against the blocks or should they be placed such that the concrete will form 4" above the top of the block foundation and overlap in front as well, completely covering the exposed block face?
I hope I'm explaining this as well as I'm visualizing.

Thanks!

EDIT: I just drew a quick sketch here at work to show if this is proper...

 

The sketch shows the way it should be done. However, it would be a good idea to place several pieces of rebar bent in an "L" down the face of the step risers. That way, the re-entrant corner you create with the blocks under the slab is re-inforced and will hold together if/when it cracks.

 

Thank you Pecos, I will add the rebars as you suggest.

 

I also demolished the small decking which was part of and next to the above mentioned walkway.
This area would require a considerable amount of gravel to support a slab. Would a suspended slab make any sense here? Or is there any other option?
Thanks again!

 

I just posted this morning and noted that our questions are similiar - you figure anything out yet? - Nick

 

Re: post #9 photo

I dug across the front there for the footing and will be erecting a 2' foundation wall.

I got rid of that disconnected 4" rain pipe laying there. It will be re-routed above the new slab.

 

More progress. During the week I mortared the first course to the footing and just yesterday I laid horizontal rebars and stacked the rest of the blocks.
I will toss in a few vertical rebars and fill most of the cores this week.

So far, this has been a great practice project for me before moving onto the main patio/wood brick oven project.

 

Should I fill every core or can I get away with filling every other?

 

Every other core has been filled with concrete and vertical rebars placed in them as well with at least a foot protruding out the tops of every other core.


Going back to my original inquiry when I started this thread regarding suspended slabs, I have seen city street maintenance workers repair old collapsed sidewalks over large storm drain entries. Sheets of suspended plywood forms are placed under pinned criss-crossing rebars and concrete poured onto that. The plywood forms are left there indefinitely as there is no way to remove them.
I can probably do the same thing here and not have to deal with filling the areas with tons of solid fill material.

Any thoughts on this would be appreciated.

 

On the smaller triangular area I decided to fill with compacted dirt, layed rebars, and poured concrete. And that small area took a lot of fill which I don't look forward to doing again.

I will most likely suspend the slabs on the other areas which require a lot of fill material.

This is what I accomplished today:

 

It sounds like you've got your mind made up. I still think it's a bad idea. The suspended slabs you've seen are professionally engineered and contain grids of rebar (usually about 1 foot on center each way) professionally tied into supporting walls. If you don't have everything tied in right and the slab cracks, it could fall. This is especially true down the road when the wooden supports you left in have rotted or deteriorated. Someone could be walking on the slab when it comes down and be badly hurt. If you place the slab on fill, where's it going to go? You'd also need to use a LOT less rebar if placed on fill.
Fill is about $12 to $20 per ton. A single sheet of treated 3/4 inch plywood is probably around $30-$45. You'll need 3/4 inch plywood because of the weight and probable deflection, and it should be treated to last longer than a couple of years. You're looking at a huge cost to do it elevated (rebar is expensive too these days) and if not professionally engineered, it's a big risk to take. Have you checked with your insurance agent to see if they would even insure such a DIY project? I seriously doubt they would.

 

Well, I'm having seconds thoughts (AGAIN....sigh) on going suspended. Several others have advised me against doing this as well...
You do make some very good points. I should just go ahead and order a truckload of fill and get this whole area over with as I still have to move on to the main patio area in the back yard.
So far, this has been a good practice run for me as I have never worked with block walls and concrete slabs before.

Thanks!

 

I'm sorry, I keep changing my mind like I change underwear....

Since I've got hundreds of crappy 2x6's strewn everywhere in my back yard from my current demolition of our main deck I decided to put some of that scrap lumber and plywood to good use and let them rot underneath over time...

I think prepping for a suspended slab was far less labor intense than filling and tamping/compacting that area will fill material for that particular area I'm working on. I might have over done it rebars though....I'm not sure.

 

Looks good so far, but you did not overdo the rebar. Typically on an elevated slab they would be 1 foot on center each way. Yours look to be about 2 feet on center. Are you going to do the whole thing elevated? If so, make sure to brace the hell out of it, especially on the joints between the plywood.

 

Thanks for the encouragement, Pecos!
I'm looking forward to pouring the slab this afternoon and moving on to the next area...

 

I'm very happy with the way the slab pouring went yesterday. That little wheelbarrow mixer definitely was a good investment and a huge time saver.
I'm also getting the hang of using the surface finishing tools. Using the little hand float is very soothing to the mind and a nice way to end the day...

The next area will be the 8'x12' area. If I go suspended here I think I need to erect another foundation wall or block columns on the other end to support the slab. (...but I'm secretly wishing I'd wake up one morning and find that whole area filled with compacted fill material... )

 

Progressing slowly, but I'm slowing getting the job done...

I poured a couple more slabs yesterday, (not seen in these pics)
I'll pour some steps tomorrow.....

 

Here's a little before and 'current progress' shots.

I estimate I've poured over 210 90lb bags of concrete so far for the footings, slabs, and steps. I still have a long ways to go as this area leads to the main patio area below where I'll be pouring more slabs.

 

So anyway, when I eventually get to the main deck area I'll be pouring a corner foundation slab for my wood fired, pompeii brick pizza oven. Yes. Pizza for everyone.

 

Hello! I have a question:

I have on hand several bags of Portland Cement and Plastic Cement, over 500 lbs of each.
Can I add aggregate to Plastic Cement to make concrete mix?

 

What is your definition of "Plastic Cement"?

In over 40 years and 37 countries, I have not heard that term except for concrete that is mixed and not set, so it can be referred to a "plastic concrete".

I can remember the old days when your local stadium was known as "Chiveze Ravine" when both the Dodgers and Angels played there. - Still a good ballpark.

Dick

 

This is what I have:

Colton Plastic Cement 94 Lb. Plastic Cement - 0010294000 at The Home Depot

I have several bags of these. I regularly pick up pallets of damaged/torn bagged goods at Home Depot, looking for cheap concrete & mortar mix, and the pallets almost always include items I really don't need. But it's part of the deal as the pallet is hugely discounted and you must buy everything they threw on the pallet.