How To Install Concrete Slab For Spa

[joeboo]

I've read a number of threads about concrete slab install. What I've learned so far is:

1) Minimum of 4" thick concrete, reinforced with rebar/wire mesh

2) As level as possible (maybe 1/2" grade for water drainage)

3) Minimum 5 days cure time prior to installing the spa.

My question is: Is no concrete footer needed for the slab? The few pictures I've seen (such as this one: http://www.poolspaforum.com/forum/index.ph...mp;hl=concrete) seem to just show putting up the concrete forms, and then pouring concrete. I've usually seen concrete poured with at least 4 - 6" footer on the exterior sides of the slab.

So is it really as easy as just buiding a form at ground level and pouring 4" of concrete on top of the ground? Any more details/recommendations are appreciated.

[KIALDA]

There are many ways to Build a small retaining wall for spa placement. There are also a few different good spa pads out there that I like better than concrete. You dont see them under the spa, frost is not an issue, and its easy to move the spa to a different location if you ever decide to.

[Wobbly]

I've read a number of threads about concrete slab install. What I've learned so far is:

1) Minimum of 4" thick concrete, reinforced with rebar/wire mesh

2) As level as possible (maybe 1/2" grade for water drainage)

3) Minimum 5 days cure time prior to installing the spa.

My question is: Is no concrete footer needed for the slab? The few pictures I've seen (such as this one: http://www.poolspaforum.com/forum/index.ph...mp;hl=concrete) seem to just show putting up the concrete forms, and then pouring concrete. I've usually seen concrete poured with at least 4 - 6" footer on the exterior sides of the slab.

So is it really as easy as just buiding a form at ground level and pouring 4" of concrete on top of the ground? Any more details/recommendations are appreciated.

What's below the slab is important. Depending on the soil, it may be wise to excavate 6" or more and backfill with compacted crushed rock. A vibratory compactor might be rented at Home Depot or other rental places.

The contractor who did my pad put in wire mesh at my request, but considered it unnecessary.

The slab doesn't need to be level, the hot tub does. Carefully determine where you want the slab to drain. The tub can be leveled by running tapered 2x4's under the base edges. Use treated wood.

Allow for contraction joints, or your new slab will decide for itself where it will crack.

If you want the electrical conduit to come up inside the tub enclosure install it before you pour.

Beware of concrete contractors on Craigslist with beautiful pictures . Check references and with the licensing authority.

An option is to use paver blocks over a suitable base. The slab can also be divided into a grid using wood dividers.

This makes it more feasible for a DIY project. Work on one section at a time using a portable mixer.

As to your question about the footer, I believe they are used to take the load from a structure. Don't think they are needed for a hot tub slab.

[Dnepr Dave]

I used fiberglass reinforced concrete on a 30X60 shop floor with no expansion joints. It hasn't cracked in the 15 years since I poured it. Though I really don't think something as small as a pad for a hot tub needs to be reinforced, it is cheap to do so it can't hurt.

The only reason for a spa to be level is for aesthetics. It might look funny for the water to be at a big angle across the tub, but an inch isn't noticeable and will not affect the water pump. The electrics can be in any position and still work fine. It is more important for water to be able to drain away from the tub so that the tub's wooden frame doesn't stay wet and eventually rot.

Dave

[spa_newb]

I've pretty much decided that when the times comes I'm using EZ Pads (http://www.ezpads.com) and saving most of the $1200-$1500 they charge around here for a slab.

[larrys1]

Just be sure to check your electrical requirements BEFORE you pour. I found out I was supposed to have the rebar EQUIPOTENTIALLY tied together inside the slab and now I have a couple of stray volts you can feel if you stand on the slab barefooted and put your hand in the water...

[Wobbly]

Just be sure to check your electrical requirements BEFORE you pour. I found out I was supposed to have the rebar EQUIPOTENTIALLY tied together inside the slab and now I have a couple of stray volts you can feel if you stand on the slab barefooted and put your hand in the water...

Look under Item 21:

2008 National Electrical Code Changes

[Pathfinder]

I've pretty much decided that when the times comes I'm using EZ Pads (http://www.ezpads.com) and saving most of the $1200-$1500 they charge around here for a slab.

$1,200??? We charge about half of that for a 10x10 8" thick with ground prep. As we only pay $320 for the concrete with the fibre mesh added.

[Raeven]

I have a concrete slab already poured, reinforced, etc. This is right next to my house, outside a sliding glass door. It is a continuation of a sloped walkway poured all around the house and a pad that had already been poured, but wasn't large enough to accommodate a standard-sized spa -- so I had an adjoining slab poured to increase the size by another 4 feet. Over the total length of the slab (about 14 feet), the slope is roughly an inch, perhaps an inch and a half. I know it's not a big slope, but I'd like to make the surface area level before installing a spa. I understand I should use treated wood and those 2 x 4s should be ripped to accommodate the slope.

My questions are these:

Should I rip the 2 x 4s on the wide or the narrow side? In other words, do I want 2" shims, or do I want 4" shims?

Should I nail the 3 sides together?

Do I need to fill in the shimmed area with something? I am assuming pea gravel. If so, how do I calculate how much of this material I will need?

Obviously I am not a handy person... I really appreciate all help and suggestions.

Thanks, Raeven

[Wobbly]

I have a concrete slab already poured, reinforced, etc. This is right next to my house, outside a sliding glass door. It is a continuation of a sloped walkway poured all around the house and a pad that had already been poured, but wasn't large enough to accommodate a standard-sized spa -- so I had an adjoining slab poured to increase the size by another 4 feet. Over the total length of the slab (about 14 feet), the slope is roughly an inch, perhaps an inch and a half. I know it's not a big slope, but I'd like to make the surface area level before installing a spa. I understand I should use treated wood and those 2 x 4s should be ripped to accommodate the slope.

My questions are these:

Should I rip the 2 x 4s on the wide or the narrow side? In other words, do I want 2" shims, or do I want 4" shims?

Should I nail the 3 sides together?

Do I need to fill in the shimmed area with something? I am assuming pea gravel. If so, how do I calculate how much of this material I will need?

Obviously I am not a handy person... I really appreciate all help and suggestions.

Thanks, Raeven

Not sure if we have the same situation. I used a level to determine the the height difference at each corner of the tub when it was situated on the slab. My tub is 8' x 8'. So I used four 8' 2x4's. Each 2x4 required a different taper to match my slab slope. ( My slab slopes in two directions) It's not practical to cut the 2x4 depth down to much less than 1" and still have enough "meat" in the board. So the minimum height of a shim was 1" at the high end and it tapered up to the height required at the low end. The four 2x4's are not fastened together. The edges of the tub rest on the tapered 2.x4's. The boards are installed on edge- not on side.

No fill material was used under the tub. I used a some wood blocks and a crow bar to elevate the empty tub enough to slide the shim boards under the tub edges.

[Raeven]

Hi, Wobbly,

Thanks so much for taking the time to reply. I know these seem like stupid questions, but I'm a woman on my own and I don't know a lot about things involving power tools. I considered it a major accomplishment when I learned to use a drill to set screws.

I think we do have the same situation more or less, and I think I understand most of what you shared with me. The spa I wish to purchase is slightly smaller than yours. But if I understand you correctly, you're saying the boards should be ripped for the entire length of the tub with the narrow side of the boards, not the wide side, supporting the tub (which is what I had intended to do); that it's not useful to rip the boards for under an inch in difference; that no fill material is needed and that the boards support the weight along the edges of the bottom of the tub. The shims should run parallel with each length of the tub directly under the edges, and not be placed at 45 degree angles to the edges.

Does all that sound right?

I plan to do more or less the same thing as you, except I want to have the shims ready before the tub arrives. I can measure the slope readily enough without the tub in place, so hopefully the installers will use them as they are settling the tub in its new home.

Thanks again for sharing your knowledge.

All the best,

Raeven

[Wobbly]

Hi, Wobbly,

Thanks so much for taking the time to reply. I know these seem like stupid questions, but I'm a woman on my own and I don't know a lot about things involving power tools. I considered it a major accomplishment when I learned to use a drill to set screws.

I think we do have the same situation more or less, and I think I understand most of what you shared with me. The spa I wish to purchase is slightly smaller than yours. But if I understand you correctly, you're saying the boards should be ripped for the entire length of the tub with the narrow side of the boards, not the wide side, supporting the tub (which is what I had intended to do); that it's not useful to rip the boards for under an inch in difference; that no fill material is needed and that the boards support the weight along the edges of the bottom of the tub. The shims should run parallel with each length of the tub directly under the edges, and not be placed at 45 degree angles to the edges.

Does all that sound right?

I plan to do more or less the same thing as you, except I want to have the shims ready before the tub arrives. I can measure the slope readily enough without the tub in place, so hopefully the installers will use them as they are settling the tub in its new home.

Thanks again for sharing your knowledge.

All the best,

Raeven

Hi Raeven,

You could also use the boards on the side, but ripping them would be harder. Connecting the boards at the corners might be an improvement. I like to use Robertson (square drive) screws, since they drive much better than Phillips head.

Another approach might be to pour self-leveling grout into 2x4 or 1x4 forms with 2 or 3 inch spreaders. That way you wouldn't have to be accurate with the level. The grout will level itself.

In any event, make sure that your wood or grout leveling doesn't interfere with your slab drainage (assuming an outdoor location)

I had to notch two of my shims to allow drainage flow under them.

Cheers,

Wobbly

[CantW8]

Wobbly,

With respect to the equipontential grid, the NEC refers to permanently installed pools or spas. Is a portable hot tub considered permanently installed? I am going to put in a cement pad the same size as the hot tub.

Thanks for your help!

[ChicagoMike]

$1,200??? We charge about half of that for a 10x10 8" thick with ground prep. As we only pay $320 for the concrete with the fibre mesh added.

So you make $300 for all that work? You have to have at least 3 trips to the site, time to make the forms, time to attend to the pouring and smoothing, come back and remove the forms. All to make $300?

[Wobbly]

Wobbly,

With respect to the equipontential grid, the NEC refers to permanently installed pools or spas. Is a portable hot tub considered permanently installed? I am going to put in a cement pad the same size as the hot tub.

Thanks for your help!

I'm not an electrician. At Mike Holt's Electrical Forum there appears to be much confusion about this subject.

I recommend that you ask your local building inspection department for a definitive answer ( or at least an answer that won't require you to tear out a pad)

[Pathfinder]

$1,200??? We charge about half of that for a 10x10 8" thick with ground prep. As we only pay $320 for the concrete with the fibre mesh added.

So you make $300 for all that work? You have to have at least 3 trips to the site, time to make the forms, time to attend to the pouring and smoothing, come back and remove the forms. All to make $300?

Mike, you make it sound like it takes hours upon hours to do a 10' square. I takes no time when you r organized. Proper fill, Packer & all wood for forms are brought on site morning of pour. It might take 2hrs of prep max. Cement truck comes, area is poured in less than 20. Top is prepped by me then forms wont come off until day of delivery. A large percentage of my customers come from referrals. I dont need too make huge mark ups on a tiny job when I get multiple jobs which will equate to more revenue without gouging my customers who r already spending thousands of dollars with me.

[CantW8]

Thanks Wobbly. That site does a nice job of clearing it up. It definitely applies to portable hot tubs. Unfortunately, I just had the contractor form up and install the rebar yesterday. I did have him extend one of the rebar so I can clamp a ground conductor to it but I didn't have him extend the grid 3 feet. I wonder if there is anyone out there that has actually done this. An awful lot of extra work for nothing!

Regards,

Dan