Site Prep

[pg_rider]

We recently added on to our existing 10'x12' concrete patio by adding another 10'x12' section on either side. We did this partly in anticipation of eventually getting a hot tub, although we didn't tell that to our contractor. So, the pads are in and they're great; 4" thick, flat, with a very slight slope away from the house for drainage. My questions:

1) Will that slight slope affect the tub in any negative way? Like I said the pad itself is flat, it just has a slope to it (imperceptible to the eye). I REALLY don't want to have to shim the tub!

2) I just talked to the contractor and in his words "if you'd told me ahead of time it was going to be for a hot tub we'd have put some fabric or rebar in the concrete, but as it is it should still be fine". Should that make me nervous? I know they did a good job prepping the ground (tamping, etc) so I'm not too worried about settling, but could it crack or break?

Appreciate any insight!

Here's a pic of where it's going to go:

http://xxx.socalsportbikes.info/xmb/attachments/34475.jpg

And yes, we're going to take some measures to ensure privacy!!!

[Jim_The_Jim]

We recently added on to our existing 10'x12' concrete patio by adding another 10'x12' section on either side. We did this partly in anticipation of eventually getting a hot tub, although we didn't tell that to our contractor. So, the pads are in and they're great; 4" thick, flat, with a very slight slope away from the house for drainage. My questions:

1) Will that slight slope affect the tub in any negative way? Like I said the pad itself is flat, it just has a slope to it (imperceptible to the eye). I REALLY don't want to have to shim the tub!

2) I just talked to the contractor and in his words "if you'd told me ahead of time it was going to be for a hot tub we'd have put some fabric or rebar in the concrete, but as it is it should still be fine". Should that make me nervous? I know they did a good job prepping the ground (tamping, etc) so I'm not too worried about settling, but could it crack or break?

Appreciate any insight!

Here's a pic of where it's going to go:

http://xxx.socalsportbikes.info/xmb/attachments/34475.jpg

And yes, we're going to take some measures to ensure privacy!!!

Did the concrete at least have some wire mesh?

If you have a slight slope, some spas will work jsut fine as long as the skimmer is on the lower part. This limit the ability to position the seats exactly the way you want for your landscape and views.

If you want to check the slope take a straight 2x4 the size of the spa and place a level on top of it. Put it in the center of where the spa is to go and hold it level while you measure the gap on the low end. If it is more than 1.5 inches, you need to build a sub platform to put the spa on. I can send you the diagram on how to build it, but it is really for our spa customers.

Basically it is long wedges made from 2x4's treated lumber and a plywood top.

Nice sunny place. Where do you live?

[Dennis]

Concrete strength is dependent on the reinforcement (rebar, wire mesh, fiber mesh, ect.). Without reinforcement concrete has very little strength. If you have sufficient compacted base under the concrete you may be okay until the base moves, concrete is plenty ductile and the base would have to move quite a bit.

[pg_rider]

If it is more than 1.5 inches, you need to build a sub platform to put the spa on. I can send you the diagram on how to build it, but it is really for our spa customers.

Basically it is long wedges made from 2x4's treated lumber and a plywood top.

Nice sunny place. Where do you live?

I can picture the kind of wedge you're describing. Would rather not have to do that, but I'll measure and see just how much it slopes.

We live in Colorado Springs, CO. Mostly sunny, but you can see those wonderful afternoon CO clouds rolling in....

Concrete strength is dependent on the reinforcement (rebar, wire mesh, fiber mesh, ect.). Without reinforcement concrete has very little strength. If you have sufficient compacted base under the concrete you may be okay until the base moves, concrete is plenty ductile and the base would have to move quite a bit.

So if he didn't put ANY reinforcement in it, am I screwed? I'm just trying to picture how the slab could fail with such a spread-out load on it....

[wesj53]

We recently added on to our existing 10'x12' concrete patio by adding another 10'x12' section on either side. We did this partly in anticipation of eventually getting a hot tub, although we didn't tell that to our contractor. So, the pads are in and they're great; 4" thick, flat, with a very slight slope away from the house for drainage. My questions:

1) Will that slight slope affect the tub in any negative way? Like I said the pad itself is flat, it just has a slope to it (imperceptible to the eye). I REALLY don't want to have to shim the tub!

2) I just talked to the contractor and in his words "if you'd told me ahead of time it was going to be for a hot tub we'd have put some fabric or rebar in the concrete, but as it is it should still be fine". Should that make me nervous? I know they did a good job prepping the ground (tamping, etc) so I'm not too worried about settling, but could it crack or break?

Appreciate any insight!

Here's a pic of where it's going to go:

http://xxx.socalsportbikes.info/xmb/attachments/34475.jpg

And yes, we're going to take some measures to ensure privacy!!!

For those still undecided about a new purchase, pg rider's experience of installing concrete for his new spa is one reason why I went with an Arctic. No concrete, deck, or platform needed with their Forever Floor. Just level your ground, pour in 2" of #9 stone and you're done. Savings of time and $$ right from the start! I'm not rubbing anything into pg rider; rather just pointing out something that those undecided should consider.

[Trigger]

Wes,

While I like the idea of not having to put a poured slab down, the crushed stone didn't thrill me.

So, I'll gently counter your post and remind folks to remeber you will be walking around the tub to open it and clean it, and a poured slab or pavers do have thier advantages as well. Also, just so folks don't get the wrong idea. Regardless if you buy a tub with a forever type floor or base, if you are putting it on a deck, the deck will need to be modified to handle the additional load.

[Jim_The_Jim]

I can picture the kind of wedge you're describing. Would rather not have to do that, but I'll measure and see just how much it slopes.

We live in Colorado Springs, CO. Mostly sunny, but you can see those wonderful afternoon CO clouds rolling in....

So if he didn't put ANY reinforcement in it, am I screwed? I'm just trying to picture how the slab could fail with such a spread-out load on it....

I has the look and "feel" of Colorado. We have a few spas there.

The idea of the platform is to make it to a very thin piece on the front. You don't notice the front.

On the back and sides customers have painted it black and put a trim piece to match the bottom of the spa kick plate. It looks good. We build them on site sometimes.

I don't know of any concrete company that doesn't use some reinforcement and wire mesh is the bare minimum requiered. I did my shop area with fiber reinforced and it gets a lot of use and a fork life rolls over it.

[Jim_The_Jim]

For those still undecided about a new purchase, pg rider's experience of installing concrete for his new spa is one reason why I went with an Arctic. No concrete, deck, or platform needed with their Forever Floor. Just level your ground, pour in 2" of #9 stone and you're done. Savings of time and $$ right from the start! I'm not rubbing anything into pg rider; rather just pointing out something that those undecided should consider.

OK, this is where arctic and I differ. Unless the bottom is made from a minimum of 2x6 on 12 inch centers, lie a floor, framed with cross braces, the spa will sink on most land, unless it has bedrock at the base.

As my brother, said when we discussed this: "I is like having a "slow hammer" pounding down in the ground. The areas with the most height (highest water columb) will press down, because it is from 4000 to 6000 LB of LIVE LOAD." The hammering is the sloshing of the water in the vessel. This base of theirs has not been around long enough to satisfy the test. And as far as I know, from talking with Arctic they don't have engineers on staff, so they my have consulted an outside engeering firm, but I don't know. Maybe you should ask them. They are really nice people.

If it is not on concrete, it will settle in time and tha can cause the shell to crack. The time varies a lot depeding on the base soil and how compacted it is.

That is also the reason for the reinforced concrete for most any spa.

I had an engineer customer up in Toronto area who got his money back on his high end Arctic. They offered him a 1 year buy back and honored it. The problem was with the ozone system. They could not fix it.

The othe problem was that he had alread wet tested a Fallsburg in Tonawanda NY, near Niagara Falls. He told me that spoiled him and they were just not satisfied with any spa after that. He now has a SCF.

We totally spoil all of our customers.

[Altazi]

For those still undecided about a new purchase, pg rider's experience of installing concrete for his new spa is one reason why I went with an Arctic. No concrete, deck, or platform needed with their Forever Floor. Just level your ground, pour in 2" of #9 stone and you're done. Savings of time and $$ right from the start! I'm not rubbing anything into pg rider; rather just pointing out something that those undecided should consider.

Hello Wesj53,

Any idea how much money you saved by avoiding the need for a poured, reinforced concrete slab? Other readers, please feel free to "chime in" on the cost of concrete slabs!

Regards,

Altazi

[flibotte]

I made a wooden platform with pressure treated wood 2X6s and pressure treated plywood for like $80-90. It's been almost a year and it is still perfectly level.

[pg_rider]

Hello Wesj53,

Any idea how much money you saved by avoiding the need for a poured, reinforced concrete slab? Other readers, please feel free to "chime in" on the cost of concrete slabs!

To add two 10'x12' sections to either side of our original pad was $1600, or $800 per 10'x12' pad....

[wesj53]

Thanks much to Trigger, Jim, and Filibotte for their imput. I was going to butt some flagstone up to the stone and provide a clean surface to walk on, and in terms of Jim's concerns, the soil here in west suburban Chicago is a very heavy clay mix so there shouldn't be any settling. Plus, our neighborhood is about 35 years old and the ground where the spa is going to be placed has never been disturbed since our home was built. But I will share these constructive comments with my dealer and see if adjustments need to be made. I simply did not want to lay more concrete in my back yard. With my layout, it would not have worked well.

[Autoplay]

Concrete strength is dependent on the reinforcement (rebar, wire mesh, fiber mesh, ect.). Without reinforcement concrete has very little strength. If you have sufficient compacted base under the concrete you may be okay until the base moves, concrete is plenty ductile and the base would have to move quite a bit.

I'm a tile/stone mason....and what you say Dennis isn't entirely true. It's the aggregate,and how long the crystals grow in the cement/portland......that determines the strength etc. Rebar/wire etc is a form of an aggregate...it gives the portland something to bond to.

As he's not landing a helicopter on the pad etc....he should be fine My concerns in his area would be......if the contractor he had to do his pad,used plastic etc underneath the pad. He lives in a freeze/thaw area.....and in his case,you want a free-floating slab.

My spa pad has about an 1/8th per foot drainage/pitch. Been working fine for me for over 3 years.

[Jim_The_Jim]

Thanks much to Trigger, Jim, and Filibotte for their imput. I was going to butt some flagstone up to the stone and provide a clean surface to walk on, and in terms of Jim's concerns, the soil here in west suburban Chicago is a very heavy clay mix so there shouldn't be any settling. Plus, our neighborhood is about 35 years old and the ground where the spa is going to be placed has never been disturbed since our home was built. But I will share these constructive comments with my dealer and see if adjustments need to be made. I simply did not want to lay more concrete in my back yard. With my layout, it would not have worked well.

It is not that expensive to make a pad the exact size of the spa base. Then put the decorative rock up against it.

No other spa company on earth will let you put a spa on the ground unless you want to void the shell warranty.

[wesj53]

It is not that expensive to make a pad the exact size of the spa base. Then put the decorative rock up against it.

No other spa company on earth will let you put a spa on the ground unless you want to void the shell warranty.

I have just re-read the Arctic warranty Jim, and the only exclusion for a cracked shell would result if the spa was installed on "insufficiently prepared or unleveled ground". There is no other language in the contract that requires a pad of any sort, be it concrete, wood, brick, or plastic. In fact, their product catalog quotes the Forever Floor as being "composed of hand rolled fiberglass composites" and "completely eliminates the need for foundation materials like concrete, decking, or blocks" In terms of laying down a base of concrete (which in the Chicago area would probably cost about a grand), bricks or wood, would not the ground still tend to settle once the load of the full spa is placed on it? According to a concrete contractor friend of mine, that is why concrete (especially for driveways) develops cracks when weight is first placed on it. Once that concrete is removed and laid a second time, the ground has compressed to it's maximum and cracks tend not to develop again. We are on our second concrete driveway and this theory seems to hold true. So, I am not sure what the advantage of laying down base materials would serve in my case, especially since Arctic will (hopefully) stand behind any cracks that may develop in the future. But I appreciate your comments and bring them to the attention of my dealer today (and hopefully get something in writing to further protect me).

[Dennis]

So if he didn't put ANY reinforcement in it, am I screwed? I'm just trying to picture how the slab could fail with such a spread-out load on it....

Under compression concrete is very strong. That is why bridges have pre-stressed girders to carry the load. Under tension concrete has very little strength. So when you look at how a slab will be loaded you will have areas that are under compression and areas that are under tension. Without reinforcement there is not any thing to hold the concrete together. In short all concrete structures require reinforcement to carry a load without failure.

[Dennis]

I'm a tile/stone mason....and what you say Dennis isn't entirely true. It's the aggregate,and how long the crystals grow in the cement/portland......that determines the strength etc.

Concrete gains compression strength over a very long time as it hydrates. Although concrete continues to gain compression strength over a long period it is not linear relationship. Therefore, it was agreed that most of the strength was obtained at 28 days. At 28 days a concrete cylinder is tested to determine the compression strength of concrete. You can get concrete in many different compression strengths up to about 20,000 PSI. The mix designs to get different compression strength depends on the cement, aggregates, add mixtures, and water to cement ratios. This only determines the compression strength of the concrete.

Rebar/wire etc is a form of an aggregate...it gives the portland something to bond to.

Reinforcement is not called a form of aggregate because it is not. Under compression concrete is very strong and under tension concrete has very little strength. To properly design a reinforced slab you need to know the characteristics of the soil under it and what type of load the slab will have on it. With this information you can determine areas that will see tension. Once you know this you can determine the placement of the reinforcement within the slab so that areas under tension can be reinforced and create compression in other areas. Without reinforcement you cannot create compression and without compression you will have failure. Reinforcement does not have any thing to do with the compression strength of the concrete but it does have something to do with the strength of a slab.

[pg_rider]

So what you're saying is my slab is almost sure to fail? And that's because the soil underneath will, over time, have low points that will put the concrete in tension? How will this manifest itself -- will the slab crack and break at a low point in the soil? What if the soil was well-prepped prior to pouring the slab (i.e. tamping, wetting, etc)?

[Autoplay]

So what you're saying is my slab is almost sure to fail? And that's because the soil underneath will, over time, have low points that will put the concrete in tension? How will this manifest itself -- will the slab crack and break at a low point in the soil? What if the soil was well-prepped prior to pouring the slab (i.e. tamping, wetting, etc)?

I doubt it will fail. Compaction is 1 of the keys to it. Concrete compresses under it's own load while being poured.

When I float a shower pan/counter-top/floor etc.....I compact the mix I use with a mag float etc. I would be highly confident in my ability.....using 3"s of sand and portland,compacted and hydrated properly......to set a spa over,or even a car etc.

What dennis isn't mentioning,is the distances etc regarding the use of rebar. Just an FYI,expansion joints inside are every 20' outside,every 16' . Your pad is probably an 8x8 "free-floating" slab,and as you're not landing a heli on it etc and exposing it to constant vibration....you'll be fine. Trust me!

P.S. ... Having rebar/wire in it can't hurt,it can only strengthen the concrete,and give the "crystals" more to grow around. In your case,I wouldn't sweat it.

[Tom]

... And as far as I know....[at] Arctic they don't have engineers on staff...

Our R&D staff includes engineers and an award-winning engineering technologist.

Tom

[Autoplay]

HERES A COUPLE links of where I post/BS etc....

http://xxx.johnbridgexxx/vbulletin/showthread.php?t=39371

http://xxx.johnbridgexxx/vbulletin/showthread.php?t=39399

[Dennis]

So what you're saying is my slab is almost sure to fail? And that's because the soil underneath will, over time, have low points that will put the concrete in tension? How will this manifest itself -- will the slab crack and break at a low point in the soil? What if the soil was well-prepped prior to pouring the slab (i.e. tamping, wetting, etc)?

It would be difficult to say when the slab will fail. It depends on the soil under the slab and I do not know what you have clay, sand, rock, ect. It might last 1 year or it might last 10. But I can say that it will fail at some point. Will it support a spa, probably so? Will the spa have problems because of a failure I don't know? My point is that a concrete structure need to be reinforcement contrary to what any one else has stated previously.

[Autoplay]

I'm done with this thread. Having been a mason over 20 years,I guess I don't know wtf I'm takin about.

It's all yours Dennis!

[Jim_The_Jim]

I have just re-read the Arctic warranty Jim, and the only exclusion for a cracked shell would result if the spa was installed on "insufficiently prepared or unleveled ground". There is no other language in the contract that requires a pad of any sort, be it concrete, wood, brick, or plastic. In fact, their product catalog quotes the Forever Floor as being "composed of hand rolled fiberglass composites" and "completely eliminates the need for foundation materials like concrete, decking, or blocks" In terms of laying down a base of concrete (which in the Chicago area would probably cost about a grand), bricks or wood, would not the ground still tend to settle once the load of the full spa is placed on it? According to a concrete contractor friend of mine, that is why concrete (especially for driveways) develops cracks when weight is first placed on it. Once that concrete is removed and laid a second time, the ground has compressed to it's maximum and cracks tend not to develop again. We are on our second concrete driveway and this theory seems to hold true. So, I am not sure what the advantage of laying down base materials would serve in my case, especially since Arctic will (hopefully) stand behind any cracks that may develop in the future. But I appreciate your comments and bring them to the attention of my dealer today (and hopefully get something in writing to further protect me).

That is interesting wording that leaves them an obvious out. "insufficiently". Is about as vague and open as you can get. I don't know of any fiberglas that would be thick enough either. Really, I advise using concrete, because it is your spa and as far as I know, from talking with them, they don't have engineers on staff.

Try to imagine many thosands of pounds of water "pounding" on the base of the spa for 10 years. The other part is unless you put it on bare ground, the labor costs are about the same to put in rocks as to pour concrete. The concrete is about $200 here in Colorado for a 8 foot pad. If you get the fiber reinforced it doesn't require a lot of prep.

Our R&D staff includes engineers and an award-winning engineering technologist.

Tom

Can you tell me how this floor is structually strong enough to withstand many years of constant stress and the imbalanced pressures of water moving and sloshing? On a large spa that is about 5,000 LB of water in motion.

I am curious, because no other company has ever said what you say.

I'm done with this thread. Having been a mason over 20 years,I guess I don't know wtf I'm takin about.

It's all yours Dennis!

It's the "Caveman/Superman" that is throwing him off.

[Dennis]

I'm done with this thread. Having been a mason over 20 years,I guess I don't know wtf I'm takin about.

It's all yours Dennis!

I only gave basic information so one can understand the basic concepts as to the need for concrete reinforcement. Masonry experience is not relevant to sound structural engineering practices. You make some interesting statements; I hope you gained some insight on concrete reinforcement. If you do not grasp this concept, compared to all the other expenses of placing concrete adding steel is cheap.