Concrete Patio Depth

Discussion in 'Homesteading Questions' started by BCR, Feb 21, 2005.

  1. BCR

    BCR Well-Known Member

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    Well, we are having a patio poured and I am requesting recommendations on the depth of the pour. The same guys put in our 70 foot sidewalk and foundation for our shed (22 X 18 feet) and they are 5 inches deep. What do you recommend a plain patio be? 5 inches as well? Less or more? We will have a picnic table and grill/chairs on it, approx. 12 feet X 12 feet.
     
  2. moopups

    moopups In Remembrance

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    4 inches should be adequate, would be here in zone 9, central Florida with no freezes. The edges should be thicker, about 7 to 8 inches if you are ever going to put a vehicle up on it.
     

  3. mtman

    mtman Well-Known Member

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    i agree with 4 inches with wire of course
     
  4. Jena

    Jena Well-Known Member

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    4 inches, with footers if you plan to build a cover over it.

    Jena
     
  5. crashy

    crashy chickaholic goddess

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    Depends on your winters and if you are going to cover it or not. I would at least put chicken wire to strengthen it. Your concrete guy should let you know what you need even call around never hurts.
     
  6. Cosmic

    Cosmic Well-Known Member

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    Assuming you are happy with this contractor's work from prior projects and he does adequate preparation and buys a reasonable grade of concrete.

    View the problem from this angle.

    A 12 x 12 foot pour will require 1 cubic yard of concrete for every 2.25 inch thickness. So what is the difference between a 2 yard order and a 3 yard order.

    2 cubic yards will give 4.5" patio thickness.

    3 cubic yards will give 6.75" patio thickness.

    A good guessimate is the concrete is something in the $40 - 60 range per yard in some quantity. Depends on who supplies, how many jobs he has, size of the order, time for the truck to unload, etc, etc but just rounding it off, say an extra yard of concrete only adds $100 total to the real price of the job.

    Would you rather have 4.5" or 6.75" thick patio. I will go 6.75" every time for the nominal difference. The real price of a contractor concrete job is primarily in labor and profit. The concrete material is a small fraction of the total price.

    Just for chuckles I would request the contractor to give me a quote based on say 4, 6 & 8 inch slabs. If he is wildly out of hand for extra thickness, tells you a lot about him in general. Extra thickness should add only nominal to the total price. The labor gets a day's pay, no matter the hours worked in most cases. Most good contractors will schedule enough pours to get the best use of labor and a truck for a given day. Adding additional thickness to a pour should have only a very minor upward adjustment in price. The time to pour the extra thickness is again nominal, they pump at a quicker rate and in the end comes out about even.

    Extra thickness in a slab is a prime factor in its service life. Also might want to ask for things like a chopped fiberglass thread additive or even some color. Again should add very little to the final price. The little extras like strengthening agents again add greatly to service life. Some of this of course will depend on how many orders he is doing out of the truck. Around my way, most small jobs are done by a "Dry Mix" truck. The cement, sand, gravel are in dry bins and actually mixed in quantity exactly to order on the site via an extrusion type deal. You can have color in very small quantities. Can even supply your own.

    If paying for primarily labor / profit, you always want to go first class on materials. Have the contractor explain what options he has available from this concrete supplier and how much they cost. I would get a super good patio for a few dollars more. Part is understanding what makes up the pricing in masonary type projects. Asking the right questions also shows the contractor you can speak "Concrete".

    The quality and strength of concrete are far more important than thickness. Ask what he orders for strength and what slump. In general you want a dryer mix for a higher quality slab. Some of those garbage sidewalk mixes might only be 300# or 600# mixes. Again adding reinforcing wire mesh should add only nominal extras to the total price.

    One of those subjects that can get complex but about like cooking. Get the best ingredients and hope the cook know exactly how to make the best of them.
     
  7. Steve

    Steve Well-Known Member

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    Here in central Illinois, last May, I poured a 12x15 patio pad attached to the mobile home slab. To attach, I hammer-drilled 1/2" rebar into the edge of the mobile home slab about every 18".

    The patio pad was a nominal 4" depth over a 2" deep gravel bed. For frost control, water control, and rodent control I dug a 9" wide x 18" deep footing on the 3 sides not attached to the mobile home slab. I used Home Depot remesh in the footings and across the pad. I did a broom finish to prevent slipping in the winter.

    One rule-of-thumb is pour 4" deep if you know for sure you'll never put a vehicle on it, 5" if you think you might. And always make it deeper around the edges for rodent control. Those little buggers will undermine a concrete slab in a hurry if you don't make it deeper around the edges. Their burrows channel water right under the slab and if it freezes in your area, the slab will begin to break up.

    Most concrete ready-mix companies have a minimum yardage for delivery. Our local company has a 2 yard minimum. I've heard of some having a 3 yard minimum (about a half truck). On a job as small as yours, you might want to compute and adjust your surface square footage and maybe even the depth to make the most use of their minimum delivery yardage.

    One final note, have about a dozen clean patio paver blocks on hand in case you or your concrete contractor run short of concrete. Just shove them down in the mix to add volume.
     
  8. gobug

    gobug Well-Known Member Supporter

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    This past summer I made a raised porch (5x13) that is 1/2 inch thick and supported on wood beams. It is waterproof, flexible and appears to be holding up well here in Colorado. It was like ferrocement, except only one metal layer.
     
  9. Quint

    Quint Well-Known Member

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    Listen to Cosmic when he talks about the strength of mix. (well listen to the rest of his post for that matter cuz he knows what he's talking about) I helped a friend put in a large driveway and patio about 2 years ago and he already has the top layer flaking off and cracks all through it. In fact when shoveling snow this winter you could actually see the surface coming apart. He didn't know what he ordered but told the ready mix company what he was doing and they said they would give him the proper type.
     
  10. BCR

    BCR Well-Known Member

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    This is great advice, thanks.

    It won't ever be covered because where it is that would just look very bad in regards to fitting in with the deck/house. And there won't be a vehicle put on it since it is in an odd location in relation to where any vehicle might be. Plus said vehicle would have to cross a sidewalk or a long garden bed--won't happen.

    He put in some seriously heavy duty mesh stuff last time and then put grooves in the sidewalk to guide the shifting/cracks. Hasn't cracked elsewhere so it must have worked. I like the idea of a 6.75 inch pour.....I never thought about rodent damage under a patio, so I will mention that to him.
     
  11. stanb999

    stanb999 Well-Known Member

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    Above all else when doing concrete work don't add water to the mix. Yes it can be sometimes difficult to finish, But concrete wear has everything to do with the "water/cement ratio. What happens often when flat work is done by Doit Yourselfers they think they are to add water to the trowel or work surface to get a good finish. This is not the case. You must work the surface to attain the "cream" by pushing down the stone and bring up the sand and paste. The other Big thing to do is proper curing. With proper curing the strength can be fully achieved.
    Steps to good quality concrete.
    1. Don't add water to the mix. It was made at the plant with the proper amount. (Ready mix companys love when you do it removes the liability from them.)
    2. Properly prepared forms and clean reinforcing. Don't skimp on forms. If they move it really makes it diffucult to repair after the concrete is inplace.
    3. Have enough help!!!! The weight of concrete is over 2 ton per yard and it must be placed quickly.
    4. Finish the concrete as quickly as possible. This can take several hours to all day with larger areas.
    5. Cure it. Cover the concrete to protect it from moisture loss,sun,wind.
    Wet curing would be best. But plastic will do. Ask the ready mix company the time suggested to cure with the mix used.
    6. Stay off until the curing is through.
     
  12. gobug

    gobug Well-Known Member Supporter

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    Fiberglass fibers do NOT strengthen the cement, it only helps prevent cracks during the initial cure. These fibers do not bond with the cement, and the cement actually corrodes the fiberglass over time.

    There are fibers made of polyvinyl alcohol (PVA) that do add significant strength, but they are difficult to find. The manufacturer is from Japan and there is only one distributor in the states. Steel fibers are also very good for strength and much more available.

    Once the initial set has occurred, regular concrete must be damp for at least 48 hours.

    The rodents that do the most significant undermining are 7 line squirrels (chipmunks). They are paranoid about predators detecting their burrow and will fill their cheeks with dirt and carry it far from the porch. A family of them can move more than a cubic yard of fill in a few years. Regular mice aren't very good diggers. Rats are, but usually people are aware of them against the house before they do any structural damage.

    Concrete delivered ready mixed in Denver is $90 and up per yard. The ratio of portland cement to sand is the biggest determinant of the strength. The ready mix plants refer to the portland by bags per yard. Like, 7 bag mix is 7 bags of portland per cubic yard of concrete and that is pretty rich and much stronger than 4 bag mix which is about as dilute as I have heard. You might inquire about the addition of Flyash. It is now a requirement on government work because it makes the concrete stronger, replaces some of the portland, and makes the concrete more plastic. Most flat work does not require great strength.

    Distance from the plant will influence the mix and the delivery price. (if you are a long distance, they must add special chemicals to retard the set time) In some rural areas, they use dry mix trucks that add water at the site. This is the best insurance for a good concrete.

    If you have the cash, it is easiest to have a single contractor do the formwork, order the concrete and do the installation. Flatwork contractors can be pretty reasonable because they get a break on the materials, have the equipment and skilled labor and get it done quickly.

    My half inch thick 5x13 deck was done in 3 hours with 2 people. I mixed it with a drill mixer in a 5 gallon bucket. It took about 6 buckets. I used 2 bags portland, 1 bag flyash, and 6 bags of sand with Acryl60 bonding agent mixed with an equal amount of water. Initial mix water content will determine the strength of the final concrete and it must be minimal.