Is Four Inches of Concrete Enough?

[DegoRed]

Love concrete topics, the advise that comes forth is the gift that keeps on giving

Skitcheroo, here is the only question you have to ask yourself, how much do you like money? If you hate money and just like to spend it as fast as you can, then some solutions offered will help you accomplish that. On the other hand if you want a good quality slab that will last you a very long time at a reasonable price, follow this advice that has been given so far.

Originally Posted by Nohurry

4” should be plenty, especially re-bar reinforced.

Originally Posted by Hoosier14

Our coach is 50,000 lbs. We built our garage 7 years ago with 4” concrete and we don’t have any cracks whatsoever.

Originally Posted by sbleiweiss

My contractor swore that 4 inch was plenty after good site compaction and floated rebar. Haven't had a crack in two years with 22K motorhome.

I pour hundreds of thousands of yards of concrete per year. We build all sorts of commercial facilities, things like Costco's & Home Depot's for example, but our main business is commercial & industrial business parks, that handle heavy loads day in and day out. Give you one guess as to what thickness we typically pour? If you guessed 4" thick with standard 3000psi concrete, no rebar but 6 guage WWM (in sheets, not that stuff on a roll), you get a gold star

Now to give some of the other experts in this thread some cover, 25 years ago, the trend was heavy rebar, thick high psi concrete. However, over the years they have discovered that thick high psi concrete does not prevent cracking. If a slab is going to crack, it will do so the same at 6000psi as it will at 3000psi.

Some have mentioned Fiber Mesh for reinforcement, fiber is great stuff, big fan, but typically the concrete batch plant charges an arm and a leg to use it, its and extra step for them as they have to manually dump it into the trucks. Now if you all really want to get your mind blown, another trend we are seeing right now, is no reinforcement used at all just straight concrete with standard 3/4" aggregate, poured 5 acres this way for Sunbelt Rental in Arlington, TX and they run 30K-80K lbs equipment on it all day.

Obviously if you are pouring on top of a swamp, different rules apply. But on typical soils, typical conditions, 4" of concrete is plenty sufficient, especially for parking a motor home on.

Good luck!

[CountryB]

Originally Posted by DegoRed

Obviously if you are pouring on top of a swamp, different rules apply. But on typical soils, typical conditions, 4" of concrete is plenty sufficient, especially for parking a motor home on.

Good luck!

Who installs the base at your job sites? If you, what are you using and how thick?

[Dutch Star Don]

At 4", you could park a tank on it. Your garage floor at 4" will be fine. The transition to that floor is where you need to be concerned. If you pour a 4" slab on TOP of a dirt lot and then drive your RV over the edge every month, you'll snap off that edge. Pretty simple to understand.....look at a lot of RV campsites where the front edge/corners are snapped off. In those situations, a thick footing around the edges was needed.

So.....if you have a driveway, that will be level with your garage floor, you won't have issues with a 4" slab with reinforcement.

[DegoRed]

Originally Posted by CountryB

Who installs the base at your job sites? If you, what are you using and how thick?

On the project we are pouring 250 yards tomorrow morning, we are using 6"-8" of base rolled and compacted down to 4"+/-. This is fairly typical for drive & parking situations, after all, this is what the OP originally asked about, we are not discussing building slab/foundation type applications.

One could cheat on the 6-8 inches and still be ok depending on your native subgrade. I did for my own driveway at my house, used nothing, 15 years later its still good. But always recommend at least a couple inches minimum to give some cushion/flex below.

[slabman]

So...where are you located? Here in Texas we wouldn't dream of going less than 5-6 in. with #4 bars at 16" O.C.E.W. But there are so many variables, some of which have been outlined in this thread. 5 in. of fiber CC is OK in Florida, a bit more with non-expansive soils like in the Midwest, but for expansive clays, you'll need more. This is not a simple question to answer for ALL applications. (Ask me how I got my name...) :-)

[Busskipper]

Originally Posted by skitcharoo

I am in the process of obtaining bids for a concrete floor in an new garage that will house at 39 foot class A diesel pusher with no tag axle. The manufacturer of the motorhome says the front axle GAWR is 14,320 pounds and the rear axle GAWR is 24,000 pounds. The GVWR is 38,200 pounds. I can not find anything on the manufacturer's web site that states what the unloaded vehicle weight is. Since the coach is not in my possession yet I can not take it to a weigh station.

With the above information do you think four inches of concrete with rebar is sufficient, if not, how thick? I am looking for answers from people who have built their own garage, or who had it built for them, with the above approximate weights.

The key to the question is the Base and the Subgrade - a good subgrade with 6-8" of CR-6 compacted would be fine - IMHO - with 4" of 3,500# concrete.

But if the subgrade is suspect then you will need to Bridge the problems and 4"'s will not likely work - more/thicker base may be needed with a higher strength/thicker concrete to bridge over the issues.

Best thing to do is to talk to a GOOD local contractor and follow his Advice.

JMHO,

[Deucenut]

I had a slab poured for my motorhome. It is about the same weight as yours, 14000 lbs front axle and around 20000 lbs for the rear. When I had my slab poured, I was worried about cracking. My contractor said 4" would be plenty and he reinforced it with rebar. 7 years later, there are zero cracks. And I park the wheels on the driver side directly on the edge of the slab(kinda made a mistake and didn't make it quite wide enough). The edge has held up no problems at all. The contractor used 3/4 crush I believe as a base and compacted it to 4". As is said above, the base is important as well.

[NXR]

Originally Posted by Busskipper

The key to the question is ...

Best thing to do is to talk to a GOOD local contractor and follow his Advice.

Based on my sample size of having done this precisely once in my life I second this. If I were doing this over I would have researched contractors far longer and better.

The company I used had good references and I had used them before for some pads for a shed and a hot tub. They did excellent work, were respectful, timely, kept us informed of delays in the schedule due to weather, kept the work area clean, the price was competitive and the work held up. They also do a lot of residential driveways but not a lot of commercial work.

Live, learn and share.

Ray

[red300zx]

Concrete is only as strong as the substrate foundation, improper compaction an concrete thickness won't matter. I would go 6" 4500 psi with an 12 min-18" compacted base.

[Ivylog]

DegoRed ^^^^ gave you good advice and in KY you probably have clay soil which has good load bearing when dry. 10 years ago I poured 1000’ of 4” 3000 psi 10’ wide driveway on GA clay...no cracks other than where I sawed it every 12’ to control where it’s going to crack. I did increase the depth to 6” along the edges (after forming) for 12”.
In the MH bay the floor is 4” except where the tires go so again 6” thick but 24” wide. Did use fiber for this floor.

[CountryB]

A Civil Engineer friend of mine (roadway and runway construction), said the fiber strands used in concrete will not do much good as far a preventing cracks from loading. The fiber stands are too short to preventing structural load cracking.
It is only useful to prevent "plastic and drying shrinkage" cracking. And it make it more difficult to float and achieve a nice finish.
Wire mesh and/or rebar is still the best choice for structural slabs.

[Chargerman]

I’ve utilized the fiber mesh on a few projects with great success. The base is so important for long term success. If filling an area be sure to compact it every 6 inches of rise and not with one of the small units. A vibratory compactor is needed. An easy way to remove the cider hairs after curing is to flame the surface with a propane rosebud torch.

Good luck!

[jacwjames]

Long before I ever thought about owning a motorhome I redid my asphalt driveway at my previous house and poured concrete. Poured it 4" think with concrete mesh.

We had a Class C first and parked it without a problem. We then acquired our Class a ~ 32K pounds and parked it there for ~8 years without a problem other then the transition to the road in front of the house. I would usually back the motorhome into the driveway and would run right on the corner. Over the years a ~2' X 3' area cracked.

A lot depends on where you live so I would talk to some contractors to see what is standard for the area. I live in East TN and the base is clay which stand up well. Built a new house and the contractor dug a 6" deep foundation. They were going to use 2 each 1/2" rebar, which is normal around here, but I had them use 4 pieces. It just looked better.

[Tysco]

I built a 20x70 RV Garage last year and used 6" concrete with rebar. I also used it on the driveway. It has worked well with no cracking.