Is Four Inches of Concrete Enough?

[2Yung2 Quit]

Originally Posted by Journey39n

As a construction engineer, I can say with certainty, that no one following this thread has enough info to properly design your slab. But there are a few things to keep in mind.

The more solid a subgrade, compacted, and with proper drainage you have, means a thinner slab can be poured. Rebar, or steel mesh works best (in the bottom third of the slab, that's where the tensile stress will break the slab from loading.

In large construction projects, lots of concrete means lots of dollars, so slabs are engineered to use as thin a slab as possible. Your one time project can be overbuilt for your personal peace of mind, and to help cover for a subgrade that may not be as compacted as it should be.

Without knowing the specifics of your climate or soil conditions, generally, with a properly prepared subgrade, a 3000 psi concrete mix with steel mesh reinforcement, can be poured to a 3 1/2" thickness and successfully support your motorhome. Keep in mind, 28 days to fully cure, keep moist for at least 7-10 days, and hopefully the pour is in a perfect 70 degrees. No problems, right?

It reaches 90% in 14 days. https://theconstructor.org/concrete/...-28-days/6060/

[pepacior]

We poured 6" with rebar and has worked well for our 40' Allegro Bus.

[RM Art]

Originally Posted by pepacior

We poured 6" with rebar and has worked well for our 40' Allegro Bus.

6" thick, 6 sac, 4" slump poured concrete slab with [tied or welded] 16" o.c. 60 grade deformed rebar cross hatch laid out atop 2" dobie elevators over a well compacted base having 1.5" of 3/4" crushed gravel embedded into the base will support more weight than any number of side by side RV's could ever amount to.

Deep cut or tooled 1.5" expansion joints should be placed at appropriate separation intervals throughout the slab. Cross hatched triple rebar reinforced, minimum sized perimeter grade beam of 12" wide x 8" deep should be poured at same time of slab pour [i.e. all around the edge underneath the slab].

Layout and scope of perimeter grade beam would be also determined by knowing what [if any] structure will be erected over the slab. Might be that a well designed rebar reinforced concrete stem wall is also required and could be formed out to be included into the slab/grade beam concrete pour.

My privately owned masonry and concrete and tile construction company has been been doing this type of building for decades. Again I recommend - get this engineered so you have plans to follow. I you are going to erect a prefab building atop concrete poured... get their plans for foundation and speak with their engineer reps.

Many good suggestions for pouring a slab have been offered on this thread by members to this forum. Best suggestion I can make: See this through from beginning to end. Don't make a mistake of producing an inferior product outcome by trying to save a couple bucks or a few hours work-effort!

[153stars]

Make sure you put in some super thick chain link fence ,so 50 years from now whoever is busting it up can up use every cuss word in their vocabulary toward you.

[RVRon]

Originally Posted by 153stars

Make sure you put in some super thick chain link fence ,so 50 years from now whoever is busting it up can up use every cuss word in their vocabulary toward you.

Now THAT’s FUNNY!!!!

[BazEnglander]

Don't think about the max weight, think about the point loading of the jacks, I've pushed through 4" before now, my advice put 4" compacted hardcore then 6" reinforced concrete, make sure there aren't any water ways that run through the ground, I've come across this too where the water has washed away the ground under the slab & gave way when I had my jacks down. Better safe etc.

[Dav L]

Originally Posted by RM Art

6" thick, 6 sac, 4" slump poured concrete slab with [tied or welded] 16" o.c. 60 grade deformed rebar cross hatch laid out atop 2" dobie elevators over a well compacted base having 1.5" of 3/4" crushed gravel embedded into the base will support more weight than any number of side by side RV's could ever amount to.

Deep cut or tooled 1.5" expansion joints should be placed at appropriate separation intervals throughout the slab. Cross hatched triple rebar reinforced, minimum sized perimeter grade beam of 12" wide x 8" deep should be poured at same time of slab pour [i.e. all around the edge underneath the slab].

Layout and scope of perimeter grade beam would be also determined by knowing what [if any] structure will be erected over the slab. Might be that a well designed rebar reinforced concrete stem wall is also required and could be formed out to be included into the slab/grade beam concrete pour.

Yup, what he said. The only addition would be a Rat Wall on the outside perimeter where the concrete goes down a foot just on the outside 4 inches or so. Keeps critters from digging under the slab and destroying all that material on top from sinking.

The biggest factor is what is the soil type under the slab. No topsoil. Ideally fully packed sand that has been down and rained on for a year for compaction.

[wbrewer]

I built a pole barn for our motorhome following are the steps I took to insure the floor does not crack. This is not the first time, I have built many concrete structures and I learned from experience.

1. Remove all organics material from the building site, add inorganic fill, if need, to level the site.
2. Rent a gasoline powered vibrator compactor, for the weekend, and relentlessly compact the site. Relentless mean running the compactor for two hours, resting ½ hour and running another two hours, Repeat this process until it is time to return the compactor to the rental company. This is key, no matter the thickness of the concrete, if the organic material is not remove and the site compacted any floor will crack
3. Add at least 4 inches of washed crushed stone. I always use 6 inches of number 56 stone, i.e. stone sized from ¾ inch up to 1 3/8 inch. Run the compactor over the stone at least six times. The stone is critical to keep water from pooling under the concrete floor
4. Place 15 mil thick concrete vapor barrier over the site. Overlap the joints by 12 inches
5. Rebar comes in 20 foot lengths. For structural strength, it is important to tie all of the rebar together. Place ½ inch rebar spaced 18 inches apart over the entire site.
6. Use rebar tie wires to connect where the rebars cross each other. Overlap the ends by 12 inches and use tie wires to securely join the overlapped joint.
7. Rebar laid on top of the vapor barrier adds zero strength to the concrete slab. Use concrete chairs under each joint where the rebar cross.
8. Use 2 inch chairs for four inch thick concrete and 3 inch chairs for six inch thick concrete
9. Most concrete is delivered with a PSI rating of 2500 to 3000. I always pour six inches of 3500-4000 PSI concrete. PSI is a measure of compressive strength, or the ability of the material to carry loads and handle compression. The cost difference between the two PSI is not that significant.
10. After the pour cover the concrete with plastic sheeting and keep the concrete water wet for at least two weeks. This increases the PSI by slowing the concrete cure time.
11. Remove the sheeting, allow the concrete to dry, sweep clean and coat the floor with a good quality industrial-grade, concrete sealer which will protect you floor deicing salts and oil intrusion.

[Mvkingfish]

I used 6” pour with fiberglass reinforcement for my 40’ HR Endeavor. Coach weighs 28000 and change empty.

[RM Art]

Mr./Ms.skitcharro

By now you should have a good idea in answer to your OP question!

So... Go build your needs!