Home driveway thickness

[Shawn Christ]

The driveway at my home has settled and cracked near the garage, and has been undermined which causes siltation at the bottom of the driveway following any measurable rain. It's about a 12% slope. I'm getting estimates for both mudjacking and also full tearout and replacement. I intend to be in this house for awhile, so I'm leaning toward replacement as a long-term fix. The contractors have said 4 inches of concrete is standard for residential driveways, placed on a 6 inch crushed rock bed to help eliminate the undermining and siltation problem I have now. But other folks, including my dad, suggest 6 inches of concrete.

Is 6 inches worth the extra money?

[Matt Meiser]

I know for my shop floor that was just poured today, they asked what I might park in there. The comment was "Unless its a triple axle dump truck, 4" is fine."

[Greg Portland]

4" is OK for cars. If I was planning on having trucks on the pad (even 1/2 ton) I would pour at least 5". 6" can handle larger trucks (delivery trucks, etc.). Make sure that this is a -real- 4" or 6" (not the height of a 2x4 or 2x6 which are 3.5" and 5.5"!).

This is with a standard 4000psi mix. Different mixes may greatly increase the strength...

[Scott T Smith]

Shawn, ditto the other comments re 4" being sufficient for cars, 6" required for trucks (such as if you get propane or fuel oil deliveries).

Be sure that all organic matter is removed from the subsurface area (ie - no topsoil, roots, etc), and backfill with rock or road base.

Very important - specify a low slump concrete mix, and do not allow them to add water at the site. Usually for a slab I spec a slump between 3.5" - 4.5". The more water, the higher the slump, and the more likely the slab is to crack in the future.

[Harry Hagan]

My subdivision is about twenty years old and full of four-inch thick driveways. Every single one of them has cracked in multiple places with the exception of those that have been replaced—some of them with 6” slabs. It only takes one heavy truck one time to crack a driveway that didn’t have a proper foundation installed or wasn’t poured properly. Four inches should be OK for cars if it’s installed correctly.

My take on it is that the contractors did a crappy job thinking that they’d get future business replacing their shoddy work.

[Larry Frank]

I had the apron in front of my garage mud jacked back up and it was great. I watched and it does take a good operator to do it properly and not crack the slab. For just doing the apron, it was the best option for me. My drive way is 80 foot long and 24 ft of concrete and 56 feet of blacktop. The concrete is great but the black top is starting to need replacing after about 10 years.

[Chuck Saunders]

If you can swing it, 6" will handle everything in stride and concrete is one of those things you can't add later.

[Greg Just]

no matter how thick you make the driveway, it is very important to keep water from getting under the driveway. If the underbed washes away and there is no support, the drvieway will settle no matter how think it is. I have ad to replace the seal between the driveway and the garage floor a couple of time to prevent this. Also, if you live in a cold climate, heaving can take place if water gets under the driveway and then it will settle in the spring.

[Shawn Christ]

Thanks for the comments so far guys.
Greg, you're right, I think water under the driveway has caused my cracking and settling problems. What do you use to seal between the driveway slab and the garage floor? And would you use the same stuff to seal any cracks that develop?