Preparing for the Gravel Sub-base
The plumbing rough-in bunched the conduits together so tightly, especially those going to the bathrooms, that air space existed under them and any downward pressure on many caused them to flex. Since the 3/4" clean gravel of the sub-base would not find its way
Under load-bearing walls and posts, the thickness of the slab had to be doubled in order
Finally, the operator of the slinger truck needed reference points for spreading an even thickness of gravel at the proper depth. Accordingly, grade stakes in the form of 12" spikes were pushed into the soil to form a grid that more or less positioned them 15' apart. The rotating laser and a hammer was used to position the tops of the spikes at the +/-5" fill level for the gravel. The spikes were then sprayed with marking paint to give them visibility. The spikes that delineated the grade beams and piers were driven much deeper so as not to be confused with the grade stakes.
Slinging the Gravel
It took four truckloads of gravel and a long half-day to sling the gravel into place.
The slinger truck in action |
Compacting the Gravel Sub-base?
Our plans called for 5+" of 3/4" clean gravel under the concrete. Apparently, usual protocol calls for pouring concrete over the the slung gravel without compacting it first. Our
Compacted gravel sub-base; burlap covers the black plastic over the PEX tubing to protect it from wind damage |
The designated pour day was too windy due to an approaching cold front and had to be postponed for a couple of days in the span of which rain was forecast. In order to keep the soil dry for the concrete trucks, we spread 6 mil plastic sheeting and weighted it down with enough junk to withstand the stiff winds . Unfortunately, the effort proved fruitless because the rain was minimal.
Two of Jamie Schulte's crew appeared the day before the pour and used a laser to snap chalk lines on the concrete wall and set grade pins designating the height of the pour. As soon as Jamie and his crew had unloaded their equipment on the day of the pour, they used the plastic sheeting to fit a
The inaccessible areas were poured using a conveyor truck; the accessible areas were poured directly from the chute; notice the plastic moisture barrier in place |
Pouring the Floor
The depth of pour was targeted to be 5" and level with the top of the foundation wall. The square footage was 1,680. In lieu of metal reinforcing mesh, the mix was
Beginning the final finish 6 hours after beginning the pour |
Wrapping Up the Floor
Concrete shrinks as it sets, causing random cracks. Control joints are used in an attempt to direct the cracks to where they will be least problematic. They are sawed into the concrete to a depth of about 1/4 of the floor thickness after the the concrete has had time to set but before cracking. Jamie and a helper snapped chalk lines and used both a walk-behind and portable concrete saw to make the cuts. Fortunately, we were able to hide most of the control joints under future partitions and a couple could be partially hidden under the future stairway and kitchen island. Since it will be quite a while before the finished floor goes in, I am hoping all the cracking will have occurred, whether in the control joints or not, and the ceramic or porcelain floor tile will hide them without the crack expanding more later and cracking the tile.
The pour was done in mid-November and would be susceptible to cold weather damage if not protected. Accordingly, Jamie recommended a product called "Cure & Seal" as a temporary coating lasting about three months before letting loose, which will get us through the winter, and one that does not compromise the bond of the thin set to the concrete when the tile is laid. I tried applying it with a cheap garden sprayer but found it faster and easier to roll it on. Five gallons cost $120 and was only a tad more than we needed for 1,680 sq ft.
Insulated Slab Edge
A final note. The advantage of pouring the floor flush with the tops of the insulated concrete forms is that the slab edge is separated from the exterior environment by 5" of expanded polystyrene insulation. Without the slab edge insulation, heat would be conducted in and out through the exposed concrete (thermal bridging) and alter the floor temperature adjacent the wall accordingly. All energy certification programs require slab edge insulation (see first post on certification and second post on certification (the latter is more germane to slab edge insulation)).
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