I will be pouring a new concrete floor in my basement after digging it out deeper to increase head room. My question goes to preparing for the new pour. Should I place a layer of compacted gravel and if so, how deep?
I want to minimize the additional of material so as not to lose too much headroom when completed. The original floor (1916) had no base under the concrete. I suppose its worth noting that the floor will sit atop dense clay and that I will be installing radiant heat, thus a layer of insulation.
Replies
I think ya should do 3" gravel as a min. But, that's me. Don't forget the poly sheeting too.
Spheramid Enterprises Architectural Woodworks
Perhaps (?) more important than gravel under the slab is to make sure, especially in clay, that there are drain tiles on the outside of the new footings and these are covered with gravel and that you backfill with something that will let water drain to the tiles to prevent the clay getting wet, expanding and wanting to push the walls in. [You probably already know all this--but just in case you don't]
I added drain tile to the exterior perimeter when I underpinned the foundation. I also intend on placing interior drain tile feeding to a sump pump before pouring the flour. I mistakenly forgot to add a clean out to the exterior drain tile, so I figure it can't hurt to add an extra layer of protection on the inside, especially since this is going to become my office.
How about the insulation? Should the vapor barrier go on top of or below it?
compact the dirt with a jumping jack, no vibration sled
Stupid question, why the jumping jack and not the plate compactor..
Like FHB says "What's the difference?"
Thanks, I did not know that.
Spheramid Enterprises Architectural Woodworks
What sphere said,
I used a plate compactor to compact a 20yr. old gravel driveway
before we poured a slab over it. It seemed to work pretty good...
Here is an interesting article on placement of the vapor barrier. I poured on top of 4" 2 lb density (25 PSI compressive strength) borate treated EPS for the shop and 10 mill poly for the garage. Worked fine but tends to set slower so start the pour early if cold.
http://www.buildingscience.com/resources/foundations/sand_layer_under_slab.htm
I have used sleds for many years without any trouble you just have to lay the gravel in 2" layers and compact it in between for the best results. I would use wire over the vapor barrier or have the fiberglass reinforcement added to the cement for extra strength.
I have almost no cracks in 3 slab pours, all with a vapor barrier against the concrete. Pouring tile-up walls on a vapor barrier on top of a slab is also very common.
I have also cored concrete slabs poured on sand above vapor barriers. The sand is always wet, even when the ground below is dry.
All I am saying is my observations are inconsistent with some of your statements and I have had excellent results with the Building Science Corp. recommendations.