Pool Deck Rebar or no Rebar

[Carla_IL]

All,

After reading certain threads I am curious about rebar in the pool deck. I have a question out to the concrete subcontractor (I am GCing the job) but if he is not using rebar should he be? It is a 8 foot free form pool deck. Can he use copper mesh instead to make sure we have proper grounding?

Carla

 

[JohnT]

Depending on where you live, the copper mesh is probably required for safety bonding. The rebar is used to keep the concrete from moving at the cracks. I'd probably want both.

 

[Guest]

Rebar, or any steel for that matter, is fine as long as it stays in the middle of the pour! I can't tell you how many decks I have tore out, only to see a mat of rusty steel on the bottom, against the dirt! If the guys stand and walk on the material, it gets pushed down into the dirt, and it will do little, if any, good in the deck.

Personally, and unless you are in highly expansive soil, I would add the fibremesh to the mix. This is a non directional fibre that is mixed in to the concrete, and it tends to hold together better.

Lastly, I would not span the entire 8 foot area without score joints (expansion joints, tool joints, whatever you want to call them!). Have the finishers place a lot of the joints to control cracking, or you will end up with a cracked slab anyway!. And, if you are doing cantilever coping with the concrete also, pour the coping first, expansion foam between the coping/pool wall (bond beam) and then pour the deck last. Pools and decks expand and contract independently, and you will get a crack sooner or later if you do a single pour deck and cantilever!

Hope that is helpful!

 

[lborne]

I havea 12 foot wide cantilevered deck at the widest spot and it has fiber mesh and no rebar, but is tied into the pool walls with rebar out about 1 foot. They cut deep expansion joints. Here in Southern Florida, I've yet to see a concrete deck, sidewalk, or driveway that does not have cracks in it after a few years. Hariline cracks will show within a year. The expansion joints just help keep them from getting too bad.

 

[Bama Rambler]

I'd pay the extra for the fiber and the steel. I'd have them place control joints perpendicular to the pool wall about every 10 to 15 feet. And for the steel I'd go with 6x6x6/6 mesh set on chairs. The chairs are to keep the steel centered in the concrete.

The biggest thing they need to do is compact the soil. They should use a vibrating plate and compact it till it won't compact anymore (at least 95% proctor density). The number one reason people get severe cracking and settling on decks, walkways, etc is the base isn't compacted correctly. Because it's not a house or garage they don't think it's as important. They do need to stay away from the walls of the pool far enough to prevent deforming.

 

[bk406]

Yes, poorly compacted soil is the number one thing, IMO, that causes cracks. Not sure i agree with using both steel and fiber though. The fiber, by far, is the better choice for this application. All that being said, it doesnt matter what you do. In the end, the concrete WILL crack, no matter how much effort you put ito the job. all you can do is minimize the severity. The only way to avoid a cracked deck is to use pavers and deep six the concrete deck.

 

[Bama Rambler]

I agree that fiber is the best choice, but because I fear that they're not going to compact the soil properly I thought it worth adding some extra insurance. All I have is fiber in my 30'x40' shop and no control joints and no cracks. I did the backfilling and compacting myself, however, so I know it was done correctly.

 

[Guest]

Fiber mesh in my RV pad only as well, and an 18,000 pound RV sitting on it-no cracks! We did compact it well and add road base prior to the concrete also, which would not be the case in a deck. Pavers on my driveway (and the RV, as well as a lot of heavy machinery, has been on it!) though, and I am a big fan of them. Some day I will tear out the deck around my pool and install pavers in there place......

Do not tie the deck to the pool! That will just allow the two entities to be tied together, when they are two separate items, with different expansion and contraction rates. They need to be isolated and allowed to move independently.

 

[Henry Porter]

Hi Carla!
A good way to understand what kind of forces a concrete deck is exposed to, is to see the deck as an board which ends are placed on two pallets.
Without any force from underneath, the board will bend downwards in the middle. This is what happens to your deck when you strain it with weight. with that scenario is it stretch in the downside of the cast and preassure in the top.
Without weight on the deck is the relation vice versa, since you always have preassure from the ground. So then the stretch is on the upper layer of the cast and the preassure in the lower layer are you with me ........ Remember that concrete can whistand enormous amounts of pressure but not any stretch, almost! it's there the rebars comes in.
For the reasons above a proper made deck should have rebars in two layers of the cast and not just one........ with that being said many decks are poured with just one layer and doing ok anyway. I myself will use one layer on my deck and will place that on 2/3 of the cast's thickness.

Very importan though for every type of concrete pour, is to slow down the chemical reaction once the pour is made. Best way of doing that is to cover the surface with plastic which you constainusly keep wet with water, for as long as you can, the longer the better. That is an efffective way to avoid superficial cracks in the topplayer. How you finish the surface after it's poured is also important, just as the concrete mix itself. A good thumb of rule for that is..... less water in the mix, results in less shrinking and for that reason less intentions for the concrete to crack.

I have to add that I'm totally self taught when it comes to concrete, so take my advice for what they are, even if I know that they are pretty accurate

//Mats

 

[carolina pool]

A properly executed concrete slab will not crack. We warranty this in our contract even on cantilever patios. These are the steps we take:
1. Removal and replacement of highly expansive or unstable soil. Fill has to be properly compacted.
2. Installation of a 6 inch gravel base to minimize vertical movement from moisure variations in the subbase and frost heaving.
3. #3 rebar on 18inch centers
4. Prior to the pour water the subbase just short of puddling the water.
5. Use 3500 psi fiber reinforced concrete @ a 4.5 inch slump and 6% air. Never exceed a 5 inch slump as this is by far the largest cause of concrete cracking.6. Consolidate the concrete with a jitterbug or vibrating screed.
7. Bull float and hand float the slab. Never use wood floats on air entrained concrete. Tool or install contraction control joints at this time. These should be a maximum spacing of 2 times the width of the slab or 12 feet apart which ever is less.
8. Wait until the concrete slakes or skins over before finishing with a magnesium float and steel trowel. Attempting to finish prior to slaking will just lead to overworking the surface. Never splash water on the surface to aid in troweling.
9. Protect the finished concrete from severe tempature swimgs or dehumidifying conditions such as wind, sun, hot or dry ambient air conditions etc. with plastic, burlap, concrete blankets, sealer etc. Do not use plastic on dyed concrete. As Henry said, you want it to chemically cure, not dry.

Concrete can expand and contract as much as 3/4 inch over a 100 ft distance with a tempature swing of 40 degrees. With this in mind you can determine placement of expansion joints and control joints. Expansion joints are the full depth of the slab and should be placed against other foundations such as the pool bond beam and coping, house foundations or abutting slabs. On a rectangle pool you should use expansion joints where slabs are perpindicular. On a continuous run they should a maximum of 48 ft apart.

Control joints aid in preventing shinkage and contraction cracks and should be a minimum of 25% the depth of the slab and located as previously mentioned.

Cantelever patios: Understanding that the slab is always moving is the key to a catelever pour. The bondbeam needs to be slick finished from the top of the tile with a quarter bubble taper. After setting the forms cut 15lb roofing felt and fit to the top of the bond beam. This breaks any bond and allows the slab to float on the beam. As Bruce stated, never tie the pool steel into a patio slab as this does not faciltate movement.

Concrete is about proper preparation, timing and conditions. If you do it right, it only cracks where you want it to. If there is a crack there is a reason why.

 

[bk406]

A properly executed concrete slab will not crack. .

If you do it right, it only cracks where you want it to. .

I agree concrete prep work is essential. In 30 years around the construction business, i've never seen such a warrenty. The key to the above statement is that it will crack. Over time,any slab will. How long does your warrenty last? 1 year? 5 years?

 

[carolina pool]

5 years.

The opening statement was referring to uncontrolled cracking. Yes it cracks under the control joints.

Our warehouse floor is a six inch rebar reinforced slab with keyway joints on 24 ft centers. Its 26 years old and doesn't have a crack in it. Admittedly its inside and not exposed to the elements and thats why there are no control joints between the keyways.

 

[Brentr]

All,

After reading certain threads I am curious about rebar in the pool deck. I have a question out to the concrete subcontractor (I am GCing the job) but if he is not using rebar should he be? It is a 8 foot free form pool deck. Can he use copper mesh instead to make sure we have proper grounding?

Carla

Why not use pavers instead There are 2 types of concrete: :-D There is concrete and there is concrete that is going to crack Pavers do not crack Just my humble opinion

 

[polyvue]

2. Installation of a 6 inch gravel base to minimize vertical movement from moisure variations in the subbase and frost heaving.
3. #3 rebar on 18inch centers

You're in North Carolina. I wonder how much of what you suggest is applicable to regions without any serious frost. In addition to watching my pool deck being poured I've seen lots of patios and driveways done in my area. None of the installers appear to have followed your rigorous guidelines -- particually in regard to compacting soil, laying a 6 inch (!) gravel base and using 18 inch centers. Though the workers did elevate some pretty skinny looking rebar (24" centers) when they poured my pool/patio deck, there was minimal compacting and, at most, 1-2" of gravel placed. The finish work though was careful and control joint breaks well-spaced and deep.

 

[bk406]

You're in North Carolina. .

I missed the location. Nobody in their right mind would have a 5 year warrenty where i live. New England winters beat concrete slabs to death.


For all the prep work ( which is nice by the way) how much do you charge per sq ft for an install?

 

[huskyrider]

You guys will love my warranty.
We do everything in our power to provide a good sub-base and I try to keep my expansion joints to contain quadrants of 120 to 150 sq/ft.
I let the buyers know, if they ask, that we did all we could to prevent cracks but if you really want a warranty I'll offer it against theft.
Once you pour redimix nobody will ever steal it, you'll have to pay someone to remove it from your property.
Joking aside. I would not let a pool builders concrete man pour the pool deck without at least a #3 on an 18" center with the steel lifted anywhere from 1 1/2" to 2 1/2" off of the sub-base.

Reno, your attention to detail for the job at hand is AWESOME"

Henry hit on some important info in his reply.
Rebar is the only thing that transfers these forces acting against the concrete and distributes the energy in multiple directions away from the point where the force is exerted against it, the least amount of water necessary for working the redimix is best, and the longer you can allow it to cure the stronger the matrix is.
Concrete has an incredible compressive strength, picture a heavy weight placed on concrete with a good sub-base. But only has a fair tensile strength, picture the 2 boards Henry described at either end of the concrete pour. Tensile strength is also described as a yield or breaking strength. Picture picking up a 16' board from the last 6" and watching it warp in the middle as it flex's to absorb the weight and then splintering when it hits it's breaking strength.
I hope my descriptions assist you when making a mental picture of the forces causing the cracks in concrete decks.
Hairline cracks are usually due to shrinkage or crazing, these are only cosmetic issues on top of the pour and don't affect the structural strength of the redimix.
Supposedly the concrete matrix beneath crazing cracks is stronger than the material around it where there are no cracks. I've heard this several times over the years from several within the cement industry. I can't vouch for it being a fact.

See ya,
Kelly

 

[bk406]

these are only cosmetic issues on top of the pour and don't affect the structural strength of the redimix.

For clarification. I'm not concerend with the structural aspects of cracked concrete here and there. My basement slab has small cracks that dont concern me in the least. But you hit on the primary issue for a pool deck, COSMETIC. Any crack in my pool deck would drive me insane. Tens of thousands spent on the pool and the look can be ruined by cracks in the deck that, granted, are purely cosmetic.

 

[tsunami]

Cracking is one of the guarantees that comes with concrete. Expect it, and you won't feel so bad when it happens. We went the extra mile using a good base for compaction, compacted it well, used #3 rebar 18" OC , experienced concrete finishers from one of the better concrete companies in the area, and it still cracked. The rebar just keeps it from separating too much when it does crack. The control joints is where you hope it cracks, but the cracks have their own mind. I have a few cracks that followed the control joint almost all the way to the edge, then veered off. :grrrr:

If I had to do it over again, I'd go with the travertine pavers, if I only could afford it!

 

[carolina pool]

If you like lots of cracks in your paving, pavers are the way to go, they come with the cracks.

Concrete has been around a long time and is the most widely used construction material out there. If it was guaranteed to crack in mysterious places, they wouldn't use it for bridges, dams, high rises and highways. There is a reason for every crack and a way it could have been avoided.

I will respond to the other questions and statements later but we are starting a job thats in a swamp and I can't wait to get out there.

 

[bk406]

I dont think anyone here is really that concerned about the structural integrity of the deck. I would think for most, including myself, its a cosmetic issue.