Placing Concrete In Our ICF Foundation Walls
To keep your ICF walls plumb, don’t skimp on the bracing
[Editor's note: Roger and Lynn Normand are building a Passivhaus in Maine. This is the 23rd article in a series that will follow their project from planning through construction.]
We’ve been at this foundation business for about three weeks now. It seems longer!
After we worked through several snafus detailed in my previous blog, the crew resumed stacking the block. Other chores included:
Erecting ICFInsulated concrete form. Hollow insulated forms, usually made from expanded polystyrene (EPS), used for building walls (foundation and above-ground); after stacking and stabilizing the forms, the aligned cores are filled with concrete, which provides the wall structure. bracing on the interior side of the block. This steel bracing includes an adjustable turnbuckle to push or pull an errant wall back into plumb. The bracing also served as staging to allow the crew to stack the block to the full 12-foot height of the wall, and later as a platform to control placing the concrete into the block’s hollow core.
Framing a concrete retainer and nailing surface for the four window wells on the south side. We will be using Timbersil rather than pressure-treated lumber where wood meets concrete. PT lumber has associated health and corrosive concerns. Timbersil is a manufactured (and more costly) lumber made by infusing glass into the wood fiber, rendering the wood impervious to rot or decay. It looks identical to dry PT lumber, but the glass barrier in the lumber is permanent, non-toxic, and not corrosive.
BLOGS BY ROGER NORMAND
Spray foaming any gaps between cut block. While this will seal against air leaks and thermal losses, the more practical goal is to prevent any leaks and potential block failure while placing the concrete.
Nailing temporary horizontal 1-by wood bracing at weak points on the interior and exterior surfaces where less than full-sized block were used, e.g., around window openings, where shorter blocks were needed, or at the two odd angle corners in the foundation.
Finally, we were ready to place some concrete!
When the pump truck arrives, everyone becomes alert
Our Logix block has a 6-inch-thick concrete core. But the horizontal and vertical rebar, plastic zip ties, and plastic webbing in the block present many obstacles to using a mechanical vibrator during the pour. Instead, the crew would bang the ICF walls with hammer and block to vibrate and level the concrete within the block, particularly at the bottom courses.
A trailer-mounted boom concrete pump truck arrived at the appointed hour and set up station, followed by the first of an eventual seven concrete delivery trucks. There was a sense of focus and some tension on the faces of the crew as the concrete began to flow from the delivery truck to the pump truck, up the long boom before emerging from the end of the hose and flowing into the bottom course of block.
Only a few of the crew had experience with ICF block, and none with Logix brand. I guess all “concreters” live with an element of fear that they might have overlooked some detail in the concrete forms, and suddenly there’s a breach letting concrete flow onto the ground. That can be a very expensive repair and even messier cleanup.
Not enough bracing
There were no breaches, and we saw little sign of water seeping out of any joints. Nonetheless, it wasn’t a completely uneventful pour.
We had to await delivery of concrete twice – once because it was being pumped into the Logix faster than deliveries could be made, and then at the end when the crew realized we were short about 4 yards of concrete. Uh-oh. It’s after 5 p.m.
Fortunately, the concrete plant remained open, and quickly dispatched another truck to complete the pour.
Some of the block rose up a bit during the pour but settled back into position as more concrete was added above. It will be interesting to see whether we maintained a uniform elevation at the top of the foundation when it comes time to set the bottom plate of the walls.
A few of the walls bowed out of plumb as we neared the top courses of block. Much of that was because we had 10-foot tall bracing for a 12-foot-high wall. The crew had strung lines at the top corners of the foundation and quickly noticed the problems and brought the offending walls back into plumb.
Convincing the concrete to flow under the windows
It was tricky to get the concrete to flow under the four window openings. The crew tweaked the slump, vibrated from below the window with block and hammer, and above using long poles. The sound from banging the block immediately below the window confirmed the cavity was filled.
In retrospect, perhaps a better way would have been to initially leave out the bottom of the window frame, flow concrete into the cavity until it is filled, then toe-nail the the bottom frame into place.
Overall, we are very pleased the Logix Platinum Series ICFs and the efforts of the foundation crew.
Here’s a video on assembling the block and placing the concrete.
- Roger Normand
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