Concrete Pad

[D.P. Roberts]

We're about to get a concrete pad poured for our tub. Two of our estimates are for a 4" thick pad, but one recommended 6". He said that a big, heavy tub - especially one that's on one side of the slab, as ours will be - will cause a 4" pad to settle more on one side than the others over the years, or possibly even crack more quickly.

Is he right, or is a 6" pad overkill? We're getting a small, used tub now, but I want the ability to upgrade to a bigger tub later without having to worry about the pad.

[cplarsen]

Get the 6"

Concrete is cheap. Doing it over isn't.

[egbert]

4" reinforced concrete pad is all you should need.

[Brulan1]

We're about to get a concrete pad poured for our tub. Two of our estimates are for a 4" thick pad, but one recommended 6". He said that a big, heavy tub - especially one that's on one side of the slab, as ours will be - will cause a 4" pad to settle more on one side than the others over the years, or possibly even crack more quickly.

Is he right, or is a 6" pad overkill? We're getting a small, used tub now, but I want the ability to upgrade to a bigger tub later without having to worry about the pad.

Screw it Go 8" with rebar and sleep better at night!

[mark2550]

I would say a 5 inch pad with some type of re-inforcement would be the way to go like with wire if there usining re-bar 4 inch would do the trick but dont use what they call wire-mesh it's sorta like synthetic type of re-inforcement but most contractors don't prefer it

[soakerman]

Do I hear 4 1/2 fiberglass inlayed with Kevlar? ??

[D.P. Roberts]

Do I hear 4 1/2 fiberglass inlayed with Kevlar? ??

Kevlar? I don't plan on anyone shooting at me while I'm soaking, it would detract from the relaxation experience.

[pg_rider]

So am I completely screwed with my 4", non-reinforced pad? When we had our patio poured we didn't plan on putting a hot tub on it so we didn't reinforce. Plans changed and we now have 5000lbs of Optima sitting on it. So far after a year in Colorado it hasn't cracked; is it only a matter of time though?

[cplarsen]

Depends. Is your hot tub centered on the pad? How's the soil underneath? Etc.

Almost all concrete cracks eventually. I wouldn't lose sleep over it.

[pg_rider]

Is your hot tub centered on the pad? How's the soil underneath? Etc.

Centered? Not really. Soil? Not sure... wish me luck!

[tony]

Depends. Is your hot tub centered on the pad? How's the soil underneath? Etc.

Almost all concrete cracks eventually. I wouldn't lose sleep over it.

Exactly. Its not so much the pad, but whats underneath. With the right soil properly compacted the pad will not fail and makes an ideal base for your spa, even at 4 inches.

[kevinv18]

concrete is commonly cracked by the roots of trees so if there are no trees near don't worry about it

[Sdr_27]

Here is mine..just poured it.....concrete is 110 bucks a yard here with a three yard min.

OUCH.... so me and a buddy pitched in for the three yards..

9' x 9' x depth (in ft) devided by 27 will give you your yards to order ..also get the concrete with fiber added, make sure your ground has good compaction.....you will not see it crack..

if you use 4" with a 9'x9' pad it will look like this 9'x9'x.33'(4"/12")=26.73cuft/27cuft per yard= .99 yards of concrete..

Water weighs 8.34 lbs per gal. so if your tub holds 400 gal. and the dry weight is 850lbs its 8.34x400=3336+850=4186lbs

A 4" pad will support this with no problem...however I would go ahead with a 5-6" pad for extra support..you might want to smelt lead in your tub.....

[duck_man]

[i did a 10x10 pad, 4" thick with 5x10" radius 4 foot deep sonotubes. One on each corner about 8" in and one in the middle. I also did rebar. At my last house I hired a concrete company to do the whole thing and this time I just copied what they did to prep it. That pad didn't move at all, or crack. This time it was $700 for the concrete and 2 guys to finish it all nice (better than I'd probably do). I was going to do it but I don't have the tools, experience, etc. I added the concrete into a load for a basement floor being done down the street so I avoided the small load charges etc.

[Brulan1]

Here is mine..just poured it.....concrete is 110 bucks a yard here with a three yard min.

OUCH.... so me and a buddy pitched in for the three yards..

9' x 9' x depth (in ft) devided by 27 will give you your yards to order ..also get the concrete with fiber added, make sure your ground has good compaction.....you will not see it crack..

if you use 4" with a 9'x9' pad it will look like this 9'x9'x.33'(4"/12")=26.73cuft/27cuft per yard= .99 yards of concrete..

Water weighs 8.34 lbs per gal. so if your tub holds 400 gal. and the dry weight is 850lbs its 8.34x400=3336+850=4186lbs

A 4" pad will support this with no problem...however I would go ahead with a 5-6" pad for extra support..you might want to smelt lead in your tub.....

Thanks for the great info and calculations. Now I know how to determine how much yardadge someone needs to pour a slab.

[Saskman]

So am I completely screwed with my 4", non-reinforced pad? When we had our patio poured we didn't plan on putting a hot tub on it so we didn't reinforce. Plans changed and we now have 5000lbs of Optima sitting on it. So far after a year in Colorado it hasn't cracked; is it only a matter of time though?

I have bad news you will have problems but they will be slow coming and should take years. First your house looks new. I suspect that when the house was built the contractor backfilled around the foundation. Depending on the type of soil backfilled the ground may settle as much as 2 feet. Count on a foot at least over the next 20 years. Your pad will fail as the ground settles on the house side. This will probably take a while. A well reinforced pad would still tilt. If it was anchored to the house then a void would form underneath. This is the gift that every contractor leaves behind when they build a house. There is no weight issues with the concrete. Good concrete can hold 4000 PSI and up (32 MPA for the Canadians). Your spa will be less than 1 PSI. You will have to watch it. Look for movement. Any pad next to a new house is doomed. The posts that say its all about whats underneath are correct. I was a tech for an engineering company and a CSA certified concrete tech for years. I would suggest to anyone putting in a tub not to do it right next to your house if your home is newer. Most basements are backfilled and the ground next to your foundation will settle. This can easily last for 20 years with some soil types. Most yards are graded with some excavated soil. The ground will settle everywhere if this is the case but to a lesser extent. Now the part about rebar. Use rebar...it adds a major amount of shear strength to concrete. Shear strength is important when the base under the pad fails. If you use rebar ( the more the stronger ) the pad does not have to be as thick. I poured a 10 ft sq pad for mine. The pad is about 8 feet from the house (mine house is over 30 years old). I went 4 inches thick with rebar on 16 inch square.

[Saskman]

Here is mine..just poured it.....concrete is 110 bucks a yard here with a three yard min.

OUCH.... so me and a buddy pitched in for the three yards..

9' x 9' x depth (in ft) devided by 27 will give you your yards to order ..also get the concrete with fiber added, make sure your ground has good compaction.....you will not see it crack..

if you use 4" with a 9'x9' pad it will look like this 9'x9'x.33'(4"/12")=26.73cuft/27cuft per yard= .99 yards of concrete..

Water weighs 8.34 lbs per gal. so if your tub holds 400 gal. and the dry weight is 850lbs its 8.34x400=3336+850=4186lbs

A 4" pad will support this with no problem...however I would go ahead with a 5-6" pad for extra support..you might want to smelt lead in your tub.....

Thanks for the great info and calculations. Now I know how to determine how much yardadge someone needs to pour a slab.

This should last forever. The ground should be firm and no settleing taking place underneath at all

[kengorman]

Should a slab (or pavers) that a tub sits on be pitched? If so, how much?

Thanks,

Ken

[sker]

We're about to get a concrete pad poured for our tub. Two of our estimates are for a 4" thick pad, but one recommended 6". He said that a big, heavy tub - especially one that's on one side of the slab, as ours will be - will cause a 4" pad to settle more on one side than the others over the years, or possibly even crack more quickly.

Is he right, or is a 6" pad overkill? We're getting a small, used tub now, but I want the ability to upgrade to a bigger tub later without having to worry about the pad.

I have a question about the pad, also. We bought a house last December that has a hot tub. The house was built in '94, and the date on the hot tub is 1997. So, I believe the pad has been there 10 years. The previous owners had somewhat "let it go", and the gutters were leaking on the back of the house in a way that caused erosion (there is a general slope away from the house) around this area and under the rest of the deck. I've since fixed the problem and have done some grading work so that the runoff water now goes where it's supposed to, and no further erosion will take place in this area. Some dirt around the perimeter of the slab is gone, probably around 2 of the four sides. The slab is at least a foot thick, probably less thick where it meets up with the sidewalk that runs directly next to (parallel) the concrete block foundation of the basement of the house. I'm wondering if this bit of erosion will hurt anything? I had filled the old hot tub, a 91" x 91" Caldera. It held water, and I didn't see any problems. Everything seems level to me, as in, I don't think it is sinking one direction or the other. The erosion probably extends 6 inches, maybe up to a foot or so in places. I jammed some river rock up under the one side I could get to. Once I get the old tub out of there, I can do a better inspection to see if the concrete has any cracks. I don't think I have anything to worry about. Or do I? Got a brand new tub coming in a couple weeks...

Thanks,

sker

[Saskman]

We're about to get a concrete pad poured for our tub. Two of our estimates are for a 4" thick pad, but one recommended 6". He said that a big, heavy tub - especially one that's on one side of the slab, as ours will be - will cause a 4" pad to settle more on one side than the others over the years, or possibly even crack more quickly.

Is he right, or is a 6" pad overkill? We're getting a small, used tub now, but I want the ability to upgrade to a bigger tub later without having to worry about the pad.

I have a question about the pad, also. We bought a house last December that has a hot tub. The house was built in '94, and the date on the hot tub is 1997. So, I believe the pad has been there 10 years. The previous owners had somewhat "let it go", and the gutters were leaking on the back of the house in a way that caused erosion (there is a general slope away from the house) around this area and under the rest of the deck. I've since fixed the problem and have done some grading work so that the runoff water now goes where it's supposed to, and no further erosion will take place in this area. Some dirt around the perimeter of the slab is gone, probably around 2 of the four sides. The slab is at least a foot thick, probably less thick where it meets up with the sidewalk that runs directly next to (parallel) the concrete block foundation of the basement of the house. I'm wondering if this bit of erosion will hurt anything? I had filled the old hot tub, a 91" x 91" Caldera. It held water, and I didn't see any problems. Everything seems level to me, as in, I don't think it is sinking one direction or the other. The erosion probably extends 6 inches, maybe up to a foot or so in places. I jammed some river rock up under the one side I could get to. Once I get the old tub out of there, I can do a better inspection to see if the concrete has any cracks. I don't think I have anything to worry about. Or do I? Got a brand new tub coming in a couple weeks...

Thanks,

sker

If you are asking about replacing ground that has washed away from under the slab then the answer is yes you can. Pack damp material into the void and use something to pack it from the side like a 2x2. If the material is to wet then it will shrink and not pack as dense. If it is to dry if won't pack well either. If the slab has good rebar then a little wash out shouldn't hurt it. If it has none then replacing the washed out material will make it as good as it ever was. I would pack in the same material that is under the rest of the slab if possible.

[anewspa]

http://picasaweb.google.com/ghalge/HotTubP...143906557674626

This is how the contractor did my pavers/slab (4"). He also sold us the hot tub.

[Sdr_27]

Find someone with a post bar, they are heavy and are no fun to run....trust me I know....use the round end and beat that moist dirt back in there, make shure you bring the dirt all the way up to the edge of the pad....plant some good ol Kentucky blue garss and you are in.........

If any one is going to have pad poured just be sure to remove all the old grass, then its best to find a whacker packer (these also suck to run...don't ask me how I know.... ) beat that ground down till your teeth rattle..then you will be safe.

As stated above, a new house rarley has good compactoin around it.. so if it were me, and I was going to pour next to a new house I would dig down a few feet or more depending on your foundation, then start compaction whacking it in one foot lifts.

Sdr_27

[sker]

What exactly is a post bar? Can you describe it? Is it possible to rent one?

My pad is below a deck, so it's not the easiest to get at. I used a level on the top sides of the existing, 10-year old tub, and it seems to be level.

I am a bit concerned about the erosion. Like I said, it's around the perimeter. I didn't pour the concrete so I don't know if there's any rebar in it. There IS rebar tieing the sidewalk into the side of the house foundation, and this is right next to that sidewalk. It's very even (no noticeable settling) going from the sidewalk to the pad, so there is a chance that there is rebar there. Also, that sidewalk HAS settled a bit, due to this drainage problem that existed. It is sloping away from the house a bit now. I know it has also been undermined, but with the rebar I don't think I'm going to rip it all out and re do it until it starts cracking or deteriorating.

Thanks,

Rod

Find someone with a post bar, they are heavy and are no fun to run....trust me I know....use the round end and beat that moist dirt back in there, make shure you bring the dirt all the way up to the edge of the pad....plant some good ol Kentucky blue garss and you are in.........

If any one is going to have pad poured just be sure to remove all the old grass, then its best to find a whacker packer (these also suck to run...don't ask me how I know.... ) beat that ground down till your teeth rattle..then you will be safe.

As stated above, a new house rarley has good compactoin around it.. so if it were me, and I was going to pour next to a new house I would dig down a few feet or more depending on your foundation, then start compaction whacking it in one foot lifts.

Sdr_27

[cplarsen]

If you have large erosion voids, look into having it mudjacked. Probably the cheapest fix.

[D.P. Roberts]

Okay, here's a followup question to my original post. Part of our new concrete pad will be over an area that is currently compacted stone. We're expanding the patio, so part of it is going be over an area that is currently dirt. We have two estimates:

1) One involves excavating the whole area, putting down 4" of compact stone, and then pouring rebar-reinforced concrete.

2) The low-bid guy is going to keep the existing base, and just redo the part that's currently dirt. He's only going to rebar the outside part (that's over dirt).

My question is if we go with lowball guy #2, is this "new" part going to settle differently than the existing base, or are we better off redoing the whole area, as guy #1 suggests? The existing base has been there for about 10 years, if that helps any.