Concrete on raised deck

southtownicemanAugust 19, 2008

I am considering installing a free standing deck off the back of my house. The deck only needs to be about 18" off the ground. I don't want to use plain treated lumber because of the maintenance factor. Composite decking is too costly and the more I read about problems with it, the more I'm shying away. I'm thinking along the lines of possibly using pavers, or 16x16 concrete patio blocks

(available from Home Depot, Lowe's etc.)My question is how to support it safely. I have to consider the weight of the pavers, people, and snow load. I'm not an engineer and don't understand span tables. The pavers would be layed on 16" centered joists, and no joist would span more than 8 feet. Would 2"x8"'s work or 2"x10"'s or should I use maybe 4"x4"'s for the joists? I visited a couple of sites that used a similar system, but the materials were purchased from them. Just trying to save a few bucks and do it myself. ANY INPUT?

Tom

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deckman22

Pavers or the like do not go on a wood frame, they go on top of the dirt. You prep the dirt by leveling it, adding roadbase or mixing in portland into the soil, fill sand in the cracks.

Al

    Bookmark   August 19, 2008 at 10:45PM
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southtowniceman

I realize that, but why couldn't they be installed above grade? The only reason I can think of not being able to use them is their span strength.
Tom

    Bookmark   August 20, 2008 at 6:10PM
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aidan_m

Pavers will not span. They are only for laying on grade. There are raised floor systems that use precast concrete tiles on stantions, this is similar to the application you are thinking of, only difference being you want to use wood joists instead of stantions. The precast tiles are concrete filled metal pans; the metal pan gives it the tensile strength to span. Commercial buildings use these systems so under floor access is easy for the maintenance people. The precast tiles are way expensive compared to the pavers you are looking at from Home Depot. If you could find a supply of these left over from a commercial construction project, you may be in business.

Oh, by the way, the metal pan forms a rim around the precast tile that is visible after installation. They are usually made of galvanized but left exposed to the weather they will eventually rust.

    Bookmark   August 20, 2008 at 6:31PM
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egor_sb

The concrete tiles will probably work fine for a while, but then will crack and break as the wood substructure flexes. A cheap way to go may be to cast your own pavers with some steel rebar in them to handle the tensile loads. Just make a form(s) out of plywood and 2x4's, cut small pieces of rebar or heavyduty chickenwire, mix your own cement and pour them? I am an engineer and physically, that will work. I am just an amatuer at deck building so am sure there are probably problems doing this I am not thinking of. But structurally should work and apart from your labor time, very cheap. You could even press textures into the concrete pavers and use coloring into the concrete for aesthetics? Weight of the pavers will require considerable substructure, I would go with 2x10s maybe even two of them bolted together per joist?

    Bookmark   August 21, 2008 at 3:54PM
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sturgeonguy

Southtowniceman,

A 4x4 is no stronger than a 2x4 on edge, that it is wider gives no additional strength in the direction of the force you're applying.

Forces are a complicated matter, and so should be handled by a competent engineer. If you draw something up with sizes as recommended by your local building center, an engineer should be able to work out the actual forces and properly size things (and space supports) for a relatively small amount of money (my 20x20 sunroom cost me $200 to have reviewed by an engineer.) Go to them with a flimsy sketch on a napkin and it will be more.

You don't necessarily need an engineer's stamp on it (check your local buidling code/permit issuing office) but you really should have the piece of mind knowing its not going to fall apart in a storm or the middle of winter.

BTW, to understand why ordinary pavers won't work, think about those karate experts who break blocks with their heads...;-] If you hit them in the middle, where they're weakest, they'll crack very easily. Now imagine dropping a clay pot that you were placing on the deck...

Cheers,
Russ

    Bookmark   August 21, 2008 at 8:38PM
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southtowniceman

Thank's to all for the advice. These are just ideas going thru my head right now, and I can see where regular pavers have a span strength problem, so that may not be the way to go. The thought of using grateing underneath the pavers also crossed my mind, but I think the cost would be prohibitive.
Right now I'm just taking in information and then draw a conclusion as to what is the best way to go. There has to be a cost efficient way to put in a raised deck without using treated lumber or the expensive composit decking.
Any other ideas, and suggestions will be greatly appreciated, so keep them comming. Thank's
Tom

    Bookmark   August 21, 2008 at 10:10PM
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sturgeonguy

Plywood and astro-turf.

Cheers,
Russ

    Bookmark   August 21, 2008 at 10:54PM
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gvgemtp

IPE TILES WOULD BE IDEAL FOR THIS.

    Bookmark   August 22, 2008 at 3:48PM
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jgmcinnis

I too have pondered this quite a bit... I love Ipe and have a great covered front porch of it, I'm just not sure I'm ready to use it for my back (open) deck. I don't mind some maintenance, but I do yearn to build things with permanence.

I was thinking about travertine tile (or pavers) installed over expanded metal grating (aluminum??) or perhaps fiberglass grating if I could find some used at a reasonable price (see gratedex.com for an incredibly expensive commercial version of this). You would be covered if a tile split - no one would fall through. Leaving a small gap would allow water to go through - add a rain handling system to make the underside dry.

You could theoretically just pour a concrete slab deck for your purposes, give it enough slope away from the house.

I'd love to see more discussion on all of this...

    Bookmark   August 24, 2008 at 9:35PM
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riles_j

Tom,

Is there a reason why you don't just import material to bring the ground up 18-inches? Pavers typically need 4-6 inches of base material anyway. Just bring in the extra material and put pavers or travertine on grade.

Riles

    Bookmark   August 25, 2008 at 12:49PM
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hendricus

Crushed concrete in SW Mich. was $125 delivered for 10 yards this summer. Probably be cheaper than framing lumber.

    Bookmark   August 25, 2008 at 11:09PM
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southtowniceman

Well, here's why raising the grade isn't an option. Backfilling 18" would cover about 16 feet of siding on the house. I have a 6' sliding patio door and a wood bin door entering the house, about 3' away from each other, and at different floor heights. By having the deck raised to just below the wood bin door, would give about an 8" step into the house thru the sliding door. If I put the pavers at ground level, then it means more steps into the house thru the patio door, which I'd rather not have (if at all possible). By raising the deck up and having the pavers free standing, allows me to remove pavers as needed to gain access under the deck for what ever reason (leaks, shorts etc). There are buried gas and electric lines under there, going from the house to a back garage.
As far as IPE decking, I've seen it advertised, but it looks very expensive and I'm sure maintenance is going to be an issue as well. I'll have to do some serious checking on that.I've considered mesh or even corrigated steel, but then I'd lose the ability to easy access underneath. Keep on thinking people! And thanks so much.
Tom

    Bookmark   August 26, 2008 at 10:39AM
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riles_j

Tom,

Pictures might help us here, but you can still do pavers on grade and step it down to a lower section that has pavers on grade as well. It doesn't all have to be the same grade.

As far as access goes, with 18" clearance there isn't much you can do to provide "easy" access to your underground utilities. Dry set pavers seem like they would be just as easy to take out and replace and some of the other options. Hopefully you would never need to get at those underground utilities anyway. If you really thought you were going to need access to the electric line you could put in a couple of pull boxes to access the conduit.

Riles

    Bookmark   August 26, 2008 at 1:36PM
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dooer

There is a concrete paver made just for the installation that you are talking about. It's costly though.

http://www.stepstoneinc.com/deck.htm

Here is a link that might be useful: Deck Stone Pavers

    Bookmark   August 26, 2008 at 8:06PM
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southtowniceman

Riles:
Thanks for the input. In the area I'm planning the deck, isn't all that large, at least to me. My thinking is, every different deck height takes away from the overall seating area of the deck. But that may be the only way to go. Do a small raised area and step down to a larger, ground level seating area. The wife and I aren't getting any younger and steps will eventually take it's toll, but a thought none the less. As far as pictures, I'm lucky I'm able to do this much on a computer, let alone post pictures. I may just try though, with no guarantees. Maybe I'm just to fussy?
Tom

    Bookmark   August 26, 2008 at 8:08PM
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mikec4w

I will add my 2 cents worth. Composites are expensive but they are worth the expense. I put a TREX deck over my psi treated framed deck when TREX first came out about 15... years ago of so... maybe more. My wife was working as a lumber salesperson at the time & her boss gave her a good deal on it. It still looks as good as the day I put it down. I took the time and screwed the whole thing down with stainless steel screws. all countersunk. There is nothing like walking out on this deck in your bare feet....
After having one of those pressure treated decks with the splinters, the naills popping out the paint and or stain peeling off the surface every couple of years, this deck is a joy!!! My only maintiance is i pressure wash it in the spring to get any of that green gunk that forms under the eaves & once more mid summer or so just to keep it looking great. Worth the money.....

    Bookmark   August 26, 2008 at 9:51PM
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gardenmax-2008

We are so scared to built a composite deck. They all seem to have problems. milkec4w I am glad your Trex worked out for you. But when you read the shared information on this site it scares you. Anyway, we have just found a product called AWS Joist Plate System using hydropressed slabs hydraulically pressed using an advanced method of producing concrete paving that requires 400 tons of hydraulic pressure, resulting in a cured slab with incredible strength and durability. I copied that from the manual. It is an Abbotsford, B.C. Canada product. It looks really nice and should only need a real good power washing a couple of times a year. We hope. Here is the website for any of you who are interested. wwwpavingstones.com Keep my fingers and toes crossed

    Bookmark   September 20, 2008 at 2:32PM
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deckman22

The first Trex was actually pretty good stuff. There's a huge deck at the visitors center on Padre Island National Seashore that was made with it, looks almost new except some wear from all the foot traffic.

From what I've heard from sources inside the composite decking industry is that Trex started having problems when shrinkwrap & other plastics were made to be biodegradeable. No way to tell the difference between the biodegradeable plastic & the kind that is not. Since Trex uses recycled plastic this would get into their boards which caused them to fall apart. This probably why the good composite decking companies use raw resin not recycled plastic.

Maybe Pat the Trex man can verify that or set me straight.

Al

    Bookmark   September 21, 2008 at 1:04PM
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gardenmax-2008

deckman would you use a cement system like we are thinking of using or would you go to a Timbertech or some other reecommendation you can make? They all seem to have at least one problem or more don't they. So much money you want to make sure you buy the right product.

    Bookmark   September 22, 2008 at 2:21AM
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deckman22

Only you know what's best for you, just depends on what you want, deck or patio. I can say timbertech has never disappointed me.

Al

    Bookmark   September 22, 2008 at 6:14AM
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rembrandt

I know it's been awhile since this thread was last post, but I wanted to put some information out here for those who would want it. I have quite a few years in the pre-cast concrete business and you need to deal with more information than what I've seen posted here. First, in most parts of the country, your 'deck' only needs to be engineered to 40 psi loads. Most wood and composite decks that are passed before building departments meet this minimum. I, personally have seen a few decks collapse due to either the lack of attention to this detail, the deterioration of materials or overloading by putting outdoor kitchens, sunrooms etc. into the space after the deck was built. Always with people on them. Over engineer. It's smart.

Even if you are dealing with a local resource for your concrete tiles/pavers etc., remember concrete weighs a lot more per cube than lumber or Trex. That really adds to the shipping costs! IE: Stepstone is in California. Putting a load on a truck to Ohio could cost more than the product. Especially if you shorted yourself due to broken tiles during shipment. It would also require, most likely, two drops. Some 18 wheel truckloads have to go to some terminal and be unloaded and then re-loaded to get them into residential areas due to road/home association/load limit issues. Plus you may need a forklift on site to unload. These issues are called the 'warts and hair' part of making bad decisions.

As far as hydro-concrete anything. That's marketing. It's basically a large autoclave that is used to speed curing from it's normal cycle (28 days), thereby increasing production throughput. Done poorly, it can actually decrease the material's performance while getting the product out the door. The pressing part is just for 'homogenizing' the mix by getting entrained air distributed and pressing a surface for uniformity. It's about the look.

Concrete as a surface material or structural material; it has basically three important factors to be measured: compressive strength, tensile strength and modulus. there are others, but for what I see here, these are the three that matter. Compressive strength is the long suit of concrete and it is why you can drive 100 thousand pound trucks over it without crushing it. Exceed the compressive strength and it crushes. Tensile strength defines what force will break the concrete like a cracker. Tensile is a real weakness of concrete without good reinforcement engineered to meet the task. Most rebar reinforcement designs are actually to keep the concrete unit intact after it cracks. Think of a concrete counter top cantilevered on an island by 14 or more inches overhang. Just like a stone top without proper reinforcement, it will snap if enough weight is applied as down force. The closer to the edge that you apply the force, the less down force required to create the cracking. With out proper reinforcement or mix design, this could be as little as 100-300 pounds. Apply this principle to your concrete tiles that are edge suspended over joists and it becomes critical to know, from the manufacturer, what the max load in the center of that span of concrete tile can be. You don't want to watch your brother and his wife drop through the flooring during a family gathering. The modulus is a measure of the flexibility of the concrete unit. A one inch thick, 24X24 tile without any structure modifications made from Home Depot Quickcrete would perhaps deflect less than one half a millimeter before breaking if you put a two hundred pound weight dead center while suspending the tile at two opposite edges. Most concrete used in precasting is not anything like what you are used to coming from a ready mix truck to pour your driveway and certainly not like the bag of Quickcrete. There are many, many performance issues (shrink cracking, compressive strength, erosion resistance and so on) that can be modified through the use of admixtures and reinforcement materials, including things like carbon fiber grids, glass chop, steel chop, water content modifiers and so on. It's quite the chemistry lab.

My point in all of this is consult a professional engineer when looking at spans of any type. Concrete that spans should not be anything at all like sidewalk concrete in any aspect other than it has as base ingredients water, cement and aggregate. Not all pre-cast is the same. Like bread. Different day, different cook, different recipe. Get structural data for products you aren't knowledgeable about. Don't guess and above all, don't take the word of DIY'ers. Approach your projects by knowing exactly what you want and know that it can actually be done. Then find who you want to do it. Then work out the price. Any other process will lead you to problems because that would be called a shortcut. Problems always cost extra.

    Bookmark   December 4, 2008 at 2:21PM
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ncrealestateguy

Here is what I am thinking of doing...
I have a 16 foot long by 10 foot wide deck off of the master br. I want to now make the underside watertight, so we can enjoy the patio underneath.
Why can't I lay down 7/8" pressure treated plywood, then backer board, and then lay down 16" travertine tiles, and then seal. I would use trex decking as a border on all outside edges to give it a finished look.

1. Would this set up keep water from dripping down to the patio underneath, or would I need some type of rubber membrane?

    Bookmark   December 21, 2008 at 8:42AM
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john_hyatt

Everyone would like to do that including my ownself. The problems include movement,water geting in past the grout,tiles cracking things like that. It only takes a small leak to ruin the whole project just like a roof.

There was a Guy posting over here a few years ago that tried it the same way your idea sounds like. Full sun/weather exposure upstairs project. The tiles started coming up in a few weeks as the pictures showed.

Never use trex for anything but mabey fire starters in the wood stove.

Fastening tile to a torchdown modified roof wont work either. Way too much movement.

J.

    Bookmark   December 21, 2008 at 10:01AM
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ncrealestateguy

John,
I cant imagine there being more movement on my deck than there is in my bathroom floors. After all, the bathroom subfloor is only 1/2 inch, and I could go thicker than this on the deck. AND then lay down the thickest backer board possible. I would "glue" the plywood joints so they would be watertight. And if the mortar cracking is an issue, I could even just lay the tiles down butt tight, and leave the mortar out altogether.
I was told by someone that he has done it to several customers decks.
Any other ideas about this type of setup?

    Bookmark   December 21, 2008 at 11:17AM
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john_hyatt

Man Man Man.....Sigh.......

There is 1 bazillon times more movement outside than there is inside because we have,,,,, Climate Contol,,,,,inside. Ya know like the Roof and that little thing on the wall you turn up and down.

There is no plywood glued up joint that is watertight, in fact there is no plywood that is watertight. 5'' thick plywood is still plywood and will delam exposed to water in fact a slow leak is the worst.

Creet board is fine for water contact geting it sealed up is a little tricky. You could use fiberglass/webing like they do on boats. Work in a timely nature that stuff gets real hot toward the last,keep the fumes away from you. And of course the tile mastic wont stick to it.

Butting up the tile is so stupid...just leave that one alone John

Tell you want Mon go get that guy and have him do your job. Dont even ask to see some of those jobs. Im sure he has done it to a lot of Folks.
ghessssssss

    Bookmark   December 21, 2008 at 4:34PM
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ncrealestateguy

John, bazillion is not a real number.

    Bookmark   December 21, 2008 at 7:40PM
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sierraeast

Even if you could get a watertight underlayment, you would have to come up with a funky drainage system, the water has to have somewhere to go.

Correction....bazillion is a trillion to the thousandth power. That's a lot of movement!

    Bookmark   December 22, 2008 at 10:26AM
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cherstaf

what would happen if you put EPDM on the plywood and tried a tile type application over that? Or, has anyone here ever used EPDM on a raised deck as the "floor"

    Bookmark   December 23, 2008 at 8:37PM
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john_hyatt

Its the nature of tile/grout. Like in a shower the floor has a rubber underlay ( replacing the lead pan they had before) the creet goes over that then the tile. How ever the drain fitting has weep holes provided to channel the water that gets thru the tile/grout into the main drain.
Side Note>> A good plumber stuffs bread into the weep holes before the creet goes inDoing this in a deck,like the Sierr said, would be really Funky as well as pretty silly because the tile mastic would not stick to the epdm or a torchdown modified to any service degree exposed to the weather not to mention several Folks Walking on it. J.

    Bookmark   December 24, 2008 at 9:04AM
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rembrandt

Any of these three systems for diverting rainwater from raised decks are going to be cheaper and work much better than your Rube Goldberg approach to mucking up a perfectly good deck. If I were you I'd spend the extreme money to do it your way, then when you're really disappointed in how your idea worked out, you can purchase one of these and appreciate what a good product that is based on a good idea can do for you.

Investigate these and pick the one that matches your 'style'. Find a local installer with some experience. Negotiate a price. Enjoy your deck. Enjoy your dry patio. Pat yourself on the back for being so smart.

Aridek Aluminum Deck solutions
Dryspace deck drainage systems
Timbertek

    Bookmark   December 30, 2008 at 3:57PM
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john_hyatt

Those prducts look good and leak like a sob. J.

    Bookmark   January 1, 2009 at 2:12PM
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ncrealestateguy

So John, is there ANY product out there that does what we are trying to do?

    Bookmark   January 3, 2009 at 7:51AM
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john_hyatt

Google up stone deck. You wont be saving a few bucks,movement will still happen and puting any weight on them like two people standing on one tile is a little ife I would not do it.

Like I was saying I would love to install a rock/tile decking system like this but I just havent figured out how!!! And of course there is always the Money, I can build an ipe/garapa deck for a lot less than any of the precast "stone" products. J.

    Bookmark   January 3, 2009 at 9:14AM
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celestial

Why not just poured concrete? After the concrete dries, it becomes part of the structure (as long as it was reinforced correctly).

Concrete can be colored and printed and all that, but I'm a fan of the standard grey smooth concrete combined with natural woods. Below is a link to a picture of a concrete deck, made to look like stone. There are lots of great concrete deck ideas online.

Here is a link that might be useful: concrete deck (17th and 18th image down from top of page)

    Bookmark   January 4, 2009 at 11:21AM
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john_hyatt

That Jeff Mon puts down some mighty Fine work!!! J.

    Bookmark   January 4, 2009 at 6:16PM
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