need to build an indoor sunken concrete pond for a water feature. pond is basically 15 feet long x 6 feet wide x 18 to 20 inches deep. top of pond equals finish floor.
concrete is the chosen material!
How thick you think i need to pour the bottom and the sides? rebar?
This is indoor so freeze/thaw necessary…plus it’s in florida.
Thanks,
bob
Replies
Bob,
I built a few small outdoor ponds in deep frost areas, using rebar and concrete, most of them larger than what you have in mind. The most important consideration for strength, IMO, is to avoid any angles/corners. If you can do that, you won't need more than three inches of concrete in Florida with 1/2" rebar spaced about 12"-16".
The excavation should be well compacted soil, no loose fill. Renting a small plate compactor is advisable if the soil is soft. Remember not make the sides of the pond too vertical or the concrete won't hold, no matter how stiff it's poured. 45 degrees is safe. Florida suggests that you may be on sand. If so, I'd forget the compactor and add an inch of concrete.
The rebar should be bent to fit your excavation, laid out in a perpendicular pattern forming squares, wire-tied at each intersection, then supported by bricks or flat stones so that it will be midway in the concrete. 1/2" rebar can be bent by hand. It can also be easily cut with a hacksaw. Cut more than half way through, then bend to break it off.
Remember that you'll be wearing large rubber boots when you pour the concrete and standing on the rebar so be sure that it's well supported with flat stones or bricks. Do some testing with two people to make sure that the supports don't sink under your weight. The rebar is very significant to the long term success of this pond.
Don't worry about the pour, it won't help. ;-) If you have any experience with concrete, it will come in handy. If not, find someone who's done a few sidewalks or patio slabs to help you. Your not looking for a polished finish, just a good float and a decent final trowel to get it fairly smooth. So you don't need a concrete finisher, just a couple of strong backs to shovel the concrete into place for half an hour.
The finish isn't terribly important because it'll be underwater and covered with algae.
I'm trying to remember what strength concrete I ordered for the landscape ponds I did in NY and PA. It wasn't more than 3000psi. At last report, none of those ponds have cracked.
Pour the concrete as stiff as you can make it, starting with the bottom and working up the sides.
When the concrete has set, a few hours after pouring, fill the pond with water and leave it like that for a week. That will help to cure the concrete to it's maximum strength. Use a sump pump, a swimming pool cover pump will work fine, to pump out that water.
Edited 5/28/2007 11:45 am ET by Hudson Valley Carpenter
Agree with much of that exept to add that there should be a PVC or EPDM liner laid before the conrete because crete is not waterproof.And
This crete should be placed, or pounded, not poured. It needs to be way too stiff to pour.
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Agree with much of that exept to add that there should be a PVC or EPDM liner laid before the conrete because crete is not waterproof.
AndThis crete should be placed, or pounded, not poured. It needs to be way too stiff to pour.
As I said, I installed several of these pools/ponds, three large ones and a couple of others, using the methods described, during the years that I was installing in-ground swimming pools. There was never any evidence that they were porous.
I've also built concrete forms for much larger upright, above ground, concrete tanks at two federally funded sewege treatment plants in the Catskills, in the county where I live. Those tanks aren't porous either. And, at sixteen feet high, they are under much greater pressure than a shallow pond will ever be.
As regards how stiff the concrete should be in order to "pour" it in this shape, I've already said that it should be as stiff as he can make it. If that's not an adequate description for him, I'll be happy to provide a more detailed explanation.
Edited 5/28/2007 7:47 pm ET by Hudson Valley Carpenter
You know less about concrete than you think then.
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Yer both right!Concrete is porous, but not very.Above ground, the minerals left behind in the surface pores by evaporation will quickly seal the surface. Even before then, the seepage is not enough to notice.Underground, the moisture effectively doesnt evaporate, so it will continue to, very slowly, seep out.If one doesn't want to mess around with a membrane, add some Zypex or other admix to the 'crete.SamT
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True - crete is porous by definition.
In a sewer plant it is not mesureable to aany practical amount.But for the interior of a residence, any seepage is critical to control. That is my basis for thinking it is important to liner it.
Add to tt the fact that almost no concrete, especially not done by an inexperienced person, is without cracks.I was mildly amused by the reference to "pouring" it.
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If you're going to be contentious, how about providing some personal credentials regarding your experience, as I have. All I'm getting from your posts is your desire to dominate the conversation. Blowing smoke adds nothing to the thread.
I'm not blowing any smoke, and you didn't give any references. The professional term for putting concrete where you want it is "placing" not "pouring" and concrete is porous by definition. To claim otherwise is pure imagination on your part. You can look at any reference on the subject for both of those facts
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OK, you stick to your "references", I'll go with my experience.
Me too
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Hudson Valley Carpenter- "As I said, I installed several of these pools/ponds, three large ones and a couple of others, using the methods described, during the years that I was installing in-ground swimming pools. There was never any evidence that they were porous."
HVC I've got to go with Piffen on this one. We've done repairs to three concrete ponds over the years that had slow leaks that we attributed to either a crack in the concrete or the water moving through the concrete itself since concrete is porous (otherwise why would we waterproof foundations?). The way we dealt with the leaks was just to install a thin layer of fiberglass. Those ponds we repaired that way haven't leaked in some 7 or 8 years now.
You said in your earlier post "The finish isn't terribly important because it'll be underwater and covered with algae." With a concrete pond that's not entirely true in that the finish is often what makes the pond waterproof.
As for concrete being porous with outdoor ponds that's not necessarily a critical problem since the seeping water isn't going to do any real damage provided it's minimal but with an indoor pond it's terribly important that the pond in 100% watertight.
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I have been told by people who should know as well as having read that brick should not be used to support rebar in concrete but that dobies (dampened) should be used. Any opinion on that?
Bricks do weaken the structure somewhat. When used, they should be removed as crete is flowed in around the rebar.
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CaseyR - "I have been told by people who should know as well as having read that brick should not be used to support rebar in concrete but that dobies (dampened) should be used. Any opinion on that? "
I'm not sure if you really meant to direct your question for comment to me but I'll reply anyway.
We fabricate our ponds and tubs out fiberglass and we don't fabricate ponds or pools out of concrete ourselves (we'll sub that out to pool companies when that's the prescribed method) but from my own somewhat limited knowledge of that kind of work I would concur. In fact if I saw a masonry/concrete contractor was using brick or stone to support rebar instead of the dobies (I call them rebar chairs) that are designed and intended for that purpose I would think they were either inexperienced or disorganized and sloppy in their planning and/or not really quality conscious with their work. The brick or rock used to support the rebar is an obvious weak point.
I recall however from one project a few years ago that had a (concrete) reflecting pool in the courtyard that the rebar chairs they used were specifically designed for compatibility with the waterproofing membrane they were using underneath the pool so that the rebar chairs wouldn't or couldn't puncture the membrane under the weight of the pool with the water in it.
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thanks for everyones input. no rebar support with bricks is worth passing along. actually my preferred method is to have no channel thru the slab accomplished by suspending the rebar grid with wire druing the first portion of the pour.
Sure concrete cracks...thats a given. but if your getting the amount of cracks it appears you guys are referring to...your doing something wrong.
again thanks for all the good ideas.
"if your getting the amount of cracks it appears you guys are referring to...your doing something wrong."You don't seem to realize this even after being warned by several members here, but one invisible crack 12" long is enough to cause you a lot of grief in an interior location like this. That is as clear as I can make it. After that,
Good luck!
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Jerrald,
You haven't been called on to repair any of my work, have you?
As regards the finish making the concrete nonporuous...the sixteen foot high concrete sewege treatment tanks I mentioned were poured in forms and, other than patching a few voids, never received any finish.
As I said, I stand by my experience.
Edited 5/29/2007 3:57 am ET by Hudson Valley Carpenter
"HVC I've got to go with Piffen on this one."Thanks. I don't have an ego investment in this tho. Just pointing out basic facts about properties of concrete.I would not have thought of fibreglassing it, tho there is a lot of that up here with all the boats. I know a couple of FG decks that seem to work fine
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I don't have an ego investment in this tho.
Thirty-eight thousand posts and counting. Naw...no ego investment here. ;-)
I'll try and get Jerrald Hayes here...he's a true expert on that.
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Andy called this to my attention since he knows we've done a couple of indoor ponds both for pet stores and private residences.
You say with emphasis that "concrete is the chosen material!" and I have to ask you why? Most of the time that's not going to be best material for the project and I see some of the other posters here are telling you why. There are just a lot of other steps you need to take to make a concrete pond both water and crackproof.
Our ponds are built using either polyester or epoxy FRP (fiberglass) techniques. You form the pond basically using carpentry techniques with wiggle ply to form the the curves you need. So that we don't have a 90º at the bottom of our tubs we spray some foam in at that joint and and then shape it when it's set to make a filet and then we lay in the fiberglass matting and impregnate the glass with either polyester or epoxy resin. It's like building a custom fiberglass bath tub only because it's a 'pond' you don't need the fancy gel coat to finish it off.
Here's the one we did out in Hewlett Harbor years ago.
I can give you more details on the framing and the glassing if your interested but I not going to kill myself here tonight if you are wedded to using concrete.
The pond in that Hewlett Harbor job I linked too is on the second floor of a garage addition and some engineering was involved in designing the building structure that holds the weight of the filled pond but the pond framing itself is pretty basic and easy.
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I mentioned in an earlier post my assumption that this is a residence. In re-reading your post here, I wonder if that is true or not. You do not clearly say.
In any commercial job, there would be several paragraphs of specs as to exactly how the designer and engineer want this detailed, which is why I assume it is a less controled environment of a residence.
Anytime waterproof conrete is required, special mixes and additives are called for to make the mix less porous than it's common state, the wonderfull experience of the Hudson carpenter aside. Interior mudpans for showers and tiled baths are always lined as well, in recognition of the fact that some moisture will always migrate through concrete. That is also why we always lay moisture stop under a slab before pouring concrete, so it will not wick water up from the ground into the living environment.
If your pool ever developes the slightest crack, it will add a lot of moisture to the soil underbearing it. Where that will travel to is anybodies guess and how much the traveling water will undermine the supporting soil or what other damage it will do is open to conjecture. Placement of a liner before concrete is a better safe than sorry insurance.
Other than the deletion of the liner, Hudson outlined things pretty well. The less water added to a concrete mix, the less chance of shrinkage craks, and the stronger it may be.
Rebar yes
This water surface will also be a sourcce of a lot of evaporative moisture added to the interior air. I would hope that measures to control that are included in the HVAC systems, but since you have been given no design details for the pond, I wonder if the rest of the structure is as carelessly thought out.
Good luck.
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Concrete is considered by the electrical code to be a 'wet' location, due to it's porosity. Simply laying a sheet of plywood on a garage floor will often result in ground moisture accumulating under it ... proof of the porosity.
I believe that the 'gunnite' type of concrete used in pool construction is 'waterproof.' I still see most pools covered with a layer of plaster, so perhaps even gunnite is not enough by itself.
I have just completed an indoor pond. While the size is quite a bit smaller than yours, and the construction is different, I believe my single experience has suggested some details for you to consider:
Ponds will need regular water changes, as well as evaporation replaced. Make sure to provide for draining and filling ... and in accessible places. The fill water will likely be passed through a de-ionizing filter, and the circulating water will be passed through a series of filters, including a UV light to control algae. Make sure the design allows for this equipment.
Pond people use a 'sponge on a stick' to wipe algae off of surfaces. Interior finish does matter.
pH, or the relative acidity, of the water is critical to many fish and plants. Concrete will make the pond a bit too alkali; again, you need to seal it somehow.
Plants need a LOT more light than you would expect. Make sure that the design not only has lots of lights ... make sure the bulbs can be changed after the pond is filled.
I would suggest some sort of rim around the pond; this will help define the area, and keep floor sweeping from entering the pond.
The pond will have a major impact on humidity near it. Make sure windowsills, etc., can drain... or they shall become little moss farms.
Now that you've been given plenty of things to worry about...don't. As long as the soil under your pond is more porous than concrete, your pond won't cause any problems. Unless it's all hard clay, it'll surely absorb the small amount of seepage which will come through concrete.
If you're really concerned about porousity at this point, I'd advise you to follow SamT's suggestion and spend a few bucks on an appropriate concrete additive. The redimix company should have it on hand.
Edited 5/29/2007 2:45 pm ET by Hudson Valley Carpenter
concrete is the chosen material!
Oh boy. Who chose it?
Concrete will work, cipher up the cutout in the floor, and square that off neatly. Lay in a "turn down" around the edge and allow for a 4" slab below the lowest depth of the pond. Provide a sump in one corner of this. Rebar everything together (I'd make slab and turndown one bent bar if possible).
Ok, so that makes for a big box in the slab, which is not a "pond"--what gives? Well, you then take and shape the pond in soft sand cut about 5:1 with sharp sand so it will hold an edge. Then use a stock pond liner to make the waterproof bottom for the pond. The edge of the pond liner can be glues to the slab, or, what I'd do is set a decorative stone edge in.
Why go to all that trouble? Well, custom-shaping an irregular concrete structure tied to a floor slab is not for the faint-of-heart at the best of times. "Doing" a pond, tha aquaculture of it, can also be complex. The materials used can be critical to the success of the pond.
So, let's suppose you go a diferent way. You get the irregular hole cut in. You get the bar shaped "just right." You get that hole gunite-ed in (or do a lot of hand work with very-low slump concrete. That all goes good. Next comes the waterproofing.
Well, most of the fish and almost all of the plants are very picky about chemistry. That cuts out using most of the asphalitc coatings. Ok, do like an outdoor pool, marble plaster. Well, the plasterers can't use several admixes (and will need to know in advance). The real issue, though, gets to that joint between the marble plaster and the floor. Any uh-ohs there at all, and water gets underneath and vanishes into the complicated concrete . . .
"Liner in a pit" solves a number of shaping and contouring issues. The membrane defines the water's edge (even being a tad higher if need be). Many win-wins that way.
But, that's just my opinion; others' differ.
thanks for all the responses.
This is a residential application and has been extensively thought out.
The reason for concrete is a more formal look is required than a liner or fiberglass provides.
Exterior lined concrete with a waterproofing additive and rendering is a proven method.
It baffels me how you all talk about cracking concrete..I've poured miles of walls and dozens of slip form towers and never had a visable crack yet (that I'm aware of). Maybe your pouring to thin. This is one application where I feel thicker is better.
bolanger - "This is a residential application and has been extensively thought out."
If this has been extensively thought out why didn't you give us more of the details that went into all of this "thought" in the first place and come to think of it if it has been "extensively thought out" why are you asking us here what "How thick you think [you] need to pour the bottom and the sides? rebar?"
"The reason for concrete is a more formal look is required than a liner or fiberglass provides."
A 'more formal look'? Well that is just absolute sheer nonsense and baloney or a failure of any kind of creative vision on your design team's part. A fiberglass tub can be made very easily to look like it's concrete . Duh,... you just add sand as aggregate to the final coat.
We've used fiberglass in other applications and have made it look like tree bark, palm tree leaves, splashing water, wave foam, patinized copper (all for a themed restaurant), a bullet ridden wall, sawdust on a floor, rotten stone (for The Poland Invaded exhibit for the Intrepid Air & Space Museum years ago), and Pennsylvania flagstone for the pond I linked to above. And more....
"Exterior lined concrete with a waterproofing additive and rendering is a proven method."
For an outdoor pool, tub, or pond yes but not for an indoor one and I would think in this age of mold paranoia you'd have to be crazy not to care about being 100% certain your pool, tub, or pond is 100% waterproof. In fact in the commercial spaces we did we installed our fiberglass tubs within pond liners just so our client's ( and our insurance company) would be happy with our backup redundancy efforts.
"It baffels me how you all talk about cracking concrete..I've poured miles of walls and dozens of slip form towers and never had a visable crack yet (that I'm aware of). Maybe your pouring to thin. This is one application where I feel thicker is better."
You've just got to be kidding me. Are you a real concrete professional or just someone who has been around some jobs where concrete has been placed? A fact of life well known to all the folks I know who do concrete is that concrete cracks. And I will tell you from my own experience with a waterfall we created that a microscopic crack invisible to the eye still will leak water. We had a concrete waterfall we did leak that way but were fortunate in that the waterfall was within the tub perimeter so the feature leaked into the pond but so that there wouldn't be a mold or mildew problems behind the waterfall we waterproofed the waterfall feature with a coat of fiberglass resin, glass fiber, and sand.
Another problem is concrete will crack from vibration too. One pet store we did our fiberglass repairs to a concrete pond in was located right next to a superhighway and exit ramp intersection and we (the insurance company people, the building's engineer, the building's owner, and us) all attributed the leaking micro cracks to the near constant ground vibrations.
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I get fewer cracks than most, and some of the guys who work with me get pissed when I won't let them add water to make it easier on them, but anyone who says they have never had a crack in concrete either hasn't poured much crete or is only kidding themselves. There is only one way to have perfect non-cracking crete and that is to have aperfect mix, perfect placement, perfect curing temperature and humidity, and perfect alignment of their stars in heaven.As for extensively thought out, you must have a different definition of extensive than I do.
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Piffen: Wasn't there a guy from Canada (who seldom posts here any more) who said he could pour massive foundations and floors without a crack in them?
[grin]
I'll have to take your word for it!
;)
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Nope. That was/is me.SamT
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