[MT Stringer]

I'm thinking about expanidng my dinky patio slab by pouring additional concrete over it and adding additional square footage. The existing slab is about 8X10 - 80 sq ft.

The finished slab will be 14 x 15 - 210 sq ft.

So, 80 sq ft 3 inches thick plus 130 sqft 4 inches thick = ______ cubic yds.

Does 2.5 - 3 cubic yds sound about right?

Since this is located in the back yard in a subdivision, what method would you suggest?

1) Contract it out to someone else.
2) Have a mini-gathering of a few strong backs and a couple of weak minds! That would most likely entail a fish fry or BBQ or something...maybe tuna fish sammiches!
3) Concrete mixing machine (UGH!) or tow trailer. With the trailer I guess it would have to stay out at the street and tote it via wheelbarrow (thus the strong backs!)
Note: I can prepare the site for the pour. It's the actual get the concrete and get it poured that is the problem.

Lemme know what you think. What has been your experience?
Thanks
Mike

 

[Badhabit]

Tuna fish sammiches ??? Are ya nuts ??? Start talking CRAWFISH boil and I might consider driving cross country to yer casa....LMAO

 

[Badhabit]

Oh, forgot the cold adult beverages in massive quanitys......LOL

 

[JettyJumper]

yup dat sounds bout right. get a second opinion though. my math is horrible LMAO

 

[troy merrill]

Try this

http://www.onlineconversion.com/

 

[Guest]

Well, the way I do the math:

80 sq ft x 3 inches = 80 x 1/4 = 20 cubic feet.

130 sq ft x 4 inches = 130 x 1/3 = 43.3 cubic feet

grand total of 63.3 cubic feet.

divide by 27 for cubic yards = 2.34 cubic yards.

Be aware that since the sub-base of the new 130 sq foot section is softer, settling will occur and the concrete may crack all around the old section, unless proper precautions are taken before pouring.

 

[ComeFrom?]

Mikey, Do You Know What I Was Doing The Last Time I Broke A Sweat?

Her name wasn't slab, it was Tina or something like that. Go with #1. Sue 'em if it's wrong. CF?

 

[CoolChange]

Mikey, the math is right but if you are going to tie an existing slab to a new one, you need to tie them together by hammer drilling short lengths of rebar into the existing slab and coating the top with a binder. CF may have the right idea. I know the talent is here, but I'd like to be your friend long after the slab cracks. LOL!

 

[MT Stringer]

Good feedback...

Thanks for your thoughts. Yeah, I was gonna beat the heck out of the existing slab to make some chunks fly so the new stuff would have a place to grab ahold.

Hammerdrill, huh? UGH. Maybe ComeFrom? is right afterall!

I'm still thinking on it.
Mike

 

[BertS]

I would suggest

A. Hire a concrete truck...(even 2.5-3 yards, is alot of mixing).....us two sets of wheelbarrows (preferably the two wheel type), if the truck can't make it to the back yard (you'd be surprised, what they can do, or how close they can get with their chutes).....they will also do the math for you......

B. Get about 1/4 to 1/2 more yards, than what you think you'll need.

C. If you are tieing into an existing slab, be sure to dowel in, using slick bar. Every 12 - 18 inches, depending on usage of new slab.

D. Plan for early morning. Concrete works sux, and is tough.

E. Save the adult beverages, until AFTER the work is completed.

F. Be sure the forms are level and square.

G. If the slab isn't gonna have anything load bearing, which only 3" with a 4" thickened beam doesn't sound like it, use the mesh reinforcement.

F. Be sure to pull the mesh up, to get concrete between it and the dirt below.

G. Rent a vibrator.......it will help spread the concrete more uniformly..settle out the air bubbles, and help to make the new slab stronger.

H. Relief cuts, or expansion joints, to help prevent cracking.

 

[Guest]

Mikey,

I think that pouring on top of your existing slab is asking for trouble down the road (and a lot of prep work at the very least). I'd try to add to the existing slab, using expansion joints and hog wire.......and avoid pouring on top of the old slab. You may need to tie-in the new with the old with some rebar spikes by drilling into the sides of the old slab about every foot or so.

What sort of finish is on the old slab? You may need to know that so as to duplicate it on the expansion. To me, forming and pouring are the easy parts. Achieving a good finish is the hard part.

Finally, if it were me, I'd contract it out.

 

[BertS]

oops.....

sorry, I didn't see the part about pouring on top of the existing slab?!?

hmm.......I'm sure it would save you some excavation, but I'd agree, probably not a good idea. There may be some serious settling of the existing slab, due to the added weight of new concrete on top. Unless there is some drainage problems, I'd shy away from that.

If you're set on doing that.....jeez......um, I guess you could chip some holes in the existing slab, use a post hole digger, to give you some piers to help support the weight of the new concrete???

That would seem like a lot more work, than excavating, to get the same elevation as the existing slab.

 

[Profish00]

80 sq feet 4" thick is a yard of concrete

 

[MT Stringer]

Thanks for the feedback. Y'all brought some good things to think about/consider. I think I will give this project some additional thought and get a couple of bids from local contractors and see what they suggest.
Thanks again
Mike

 

[WilliamH]

Those are all good suggestions. I have a couple more.

Demo the existing slab. Don't take the risk of something happening. Concrete is going for over $60 per yard right now.

Pour a turn down around the perimeter of the slab. You don't want any undermining to occur when it rains. 12" deep x 8" wide would be good.

Use #3 rebar at 16" o.c each way. Center it in the slab with rebar chairs at 48" o.c. each way. Tie the rebar together at each intersection. Wire mesh would be o.k. but for the do-it-yourselfer it usually comes in rolls. Rolled mesh is very difficult to get flat. If you can get flat sheets that would be the way to go.

You want to tie the new slab to your house slab the way that has been mentioned before. Drill holes into the existing slab, 4"-6" embedment should be good. Make sure you have at least 12" of rebar from the face of the existing slab into the new slab. Use epoxy grout to "glue" the rebar into the existing slab.

Cut contractions joints in the new slab. Contraction joints are just scored lines in the surface of the new slab. They help to prevent shrinkage cracks. Keep the new slab wet / moist for as long as you can stand it. The longer it cures the better. Ask for a 3000 psi mix.

Last but not least HIRE A CONTRACTOR!

Concrete work is hard. From the prep work to the finished product, and in this heat . . . . Hire someone to do it and just sit back and play superintendant!!

 

[On A Mission]

Thanks for the feedback. Y'all brought some good things to think about/consider. I think I will give this project some additional thought and get a couple of bids from local contractors and see what they suggest.
Thanks again
Mike

Mike,
I have put in a few slabs in my time and with a little prep it is no problems.

First you can go over existing concrete and score/ruff it up as best you can. I would recommend going at least 4" above the existing slab. Rebar stands are standard height and you want to get that in the middle of the concrete as best as you can, so go 4" if you can.

Wherever the new slab will be overlapping the existing slab you will need to put a grade beam approx 6" wide by 10" deep . This will provide additional support around the existing slab in case you get a little setting.

You also need to put the same grade beam around the perimeter of the new slab and a stiffner in the middle of the new slab. A stiffner is the same as a grade beam 6" wide by 10" deep. I would make the new slab a minium of 5". This will not add much to the concrete cost because most companies will require a minium of 3 yrds. Use a factor of .4 sq. ft. per lineal foot to calculate the amount of concrete for the grade beams. Measure the perimeter and the length of the stiffner X .4 then /27 to get yards.

Probably the biggest mistake that most people make when pouring new concrete is that they do not properly prepare the subgrade (ground below the slab). This is usually the major cause of cracking in a slab. You will need to excavate a minimum a 4" below the bottom of your slab and fill it back in with sand and compacted down with a hand ram. This will provide a cushion so the speak between the concrete and the gumbo clay that we have here in Texas.

If you pour when it is real dry, water the night before so the the gound in moist not wet. This will allow the concrete to dry slow and not have the water suck out of the concrete by the surround ground.

A stated before use #3 rebar on the existing slab and overlap that at least 12" into the new slab area. I would use #4 in the new slab. Set at 12" O.C. Each way. Also use #4 in the grade beams and stiffner. One misconception the most people have is rebar gives the concrete strength, but it help keep it from cracking by reliefing and control the heat stored within in and controls the expansion/contraction of it. Also, when placing the rebar don't go any closer than 2" from the sides and bottom any exposed grades.

Get 3500/4000 PSI 5 sack concrete with 1 1/2" rock, do not mix your own. The size of rock give the concrete strength. You just can't get that in the sackcrete.

When calculating the amount of concrete add at least an additional 15-20 % for waste and usually most people can't get the depth just right, so this will give you extra.

If you decide to go with a contractor, make them follow the same specification stated above and be there when they do the pour!

Remember the As* Chewing for to much is better than not having enough!

If you have any other questions I will be happy to help

Good Luck!

 

[BertS]

grade beams may be a bit of over-kill, and add additional cost, for a patio slab, as will the rebar? I do agree with getting the mesh in sheets, versus the rolls. I would also very seriously reconsider pouring new concrete over an existing patio slab. I'm sure, that when this slab was poured, that there weren't any beams, and mesh waus probably used. Be sure, that on any bars into your existing slab, either be slick, or sleeved.

 

[flatsfats]

Lenght x width x heighth / 27

for example for a 10' x 12' four inch slab. 10 x 12 x .33 divided by 27= 1.46 cubic yds. the .33 is the decimal for 4" thickness. .54 is decimal for 6" thickness. to find the decimal for any thickness divide the thickness by 12 because you are working in feet.

demo the existing concrete. placing thin concrete over concrete is asking for trouble. drilling in tie bars will be good for the patio, but be aware that this could void some warranties on the house slab.

as metioned above #3 (3/8") rebar on 16" centers. i would personally stay away from the mesh. it tends to end up on the bottom of the slab if your not REALLY careful. it doesn't do much good down there and rusts away in a few years.

the purpose of deformed rebar (the kind you always see with the ridges on it) is to pull the concrete back together after it cracks. and it will crack. the purpose of saw cutting green concrete is to make the concrete crack where you want it. another big plus with the rebar is that you can hold it up with chairs as mentioned above. this will place your reinforcement in the proper place in the slab and you can pretty much forget about it and worry about pouring and finishing. also don't forget to wet your bedding down really good just before the pour. this will keep the ground from sucking the water outa your concrete too fast.

put an expasion joint on any adjoining concrete. a 1x4 for 4", 1x6 for 6" etc. this will allow for the expansion and conctraction that happens with temperature changes. this will also give you a good edge to run you edger along. a tooled edge looks much better and gives a more durable edge.

when you're all done with the finishing you can use some curing compound to slow down the curing process. the longer the cement in your concrete stays hydrated the higher compressive stengths you'll get. curing compound makes a thin membrane on the surface of your slab and keeps the water in longer.

oh yeh the 15-20% overage is a rule to live by with concrete. order at least 15% more than the math says you'll need. i started doing this stuff for a living about ten yrs ago and thats the first rule i learned.

good luck. if you're somewhere in the houston area and need a finisher just holler. will work for budweiser & a sandwich. but i ain't touching no wheelbarrow

doing concrete right is a bear if you don't know what your doing. a good conctractor (yes there are some) could be well worth the money.
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