May 24, 2011
By Ben OBrien
by Mike Marsh.
Tom Kamper of Thomson, Ill., hunts a 30-acre family-owned parcel in northwestern Illinois. The property has three cells: two have above-ground box blinds and the third serves as a rest area.
"My goal was to build a permanent pit blind at the water's edge that would not leak to replace one of the above-ground box blinds," Kamper said. "I wanted the dimensions to be 14 feet by 6 feet inside, with a 52-inch to 54-inch height. I also wanted a two-sided roof, pitching down to the front and back walls of the blind. The pit needed three shooting ports and one hole for dogs to exit and enter the blind."
Kamper's idea resulted in a comfortable, leak-proof concrete-block blind ideal for hunting geese in freezing conditions, and earned an honorable mention in the 2010 Wildfowl Boats and Blinds Contest.
A Solid Base
"The first problem that had to be solved was how to go about constructing the walls and floors," Kamper said. "I looked into pre-cast concrete septic tanks, but the biggest one I found had 10-feet by 5-feet outside dimensions and was only 6 inches thick. I was told it could collapse if there was a lot of outside pressure from the soil backfill and from frost heaving."
Kamper considered pouring concrete floors and walls, but the estimated cost was $3,000, and the excavated hole would have to be completely dry to perform the job.
"I also looked at custom-made pit blinds made of fiberglass and steel, but they were not really the size I needed," he said.
Kamper found a former union mason looking for a side job, and he formed a plan to build the pit blind out of concrete blocks.
"We decided to pour a concrete floor that was 6 inches thick and reinforce it with woven wire," he said. "The slab would have a 4-inch outside lip at the edge of the walls, making the slab's outside dimensions 16 feet by 8 feet."
They excavated the hole to 18 feet by 10 feet with a depth of 4 feet, allowing room to work around the walls. Water seeped into the hole and maintained 4 inches deep. A small gasoline-engine pump dried out the hole. The concrete floor was poured and cured underwater. The men used a form of 2-by-6-inch lumber with 1-inch-by-2-inch stakes screwed in. Keeping the floor level was difficult. For sure footing, Kamper broom-finished the slab. After the slab cured for a week, masonry work began.
The walls required 204 full-sized and 34 half-sized blocks. After laying the first row of blocks, the men drilled â'µâ'„â‚'-inch holes into the slab and inserted 4-foot-long reinforcing rod stakes, with four stakes in the 14-foot walls and two in the 6-foot walls. To hold the rods in place and create a tight seal around the wall's base, they filled the first row of blocks with mortar.
Block walls were laid on the base. A mixture of one part Portland cement, 10 parts sand and water filled the walls. Sill plate anchors were inserted into the mortar, with four plates in each long wall and two plates in each short wall. The inner wall slurry set for five days.
"The slab now had an edge of 4 inches outside of the blocks," Kamper said. "A mortar mix was made and a curb built from the edge of the slab up to about 2 to 3 inches on the blocks all the way around, providing an additional seal between the blocks and the slab. Once this set up, the outsides of the walls were coated with a thick coating of foundation sealer, applied with a trowel."
Four-foot-by-8-foot foam boards bonded to the outside walls with the foundation sealer, providing a cushioning effect against the backfill pressure. A brush-on sealer finished the inside walls. Made of 2-inch-by-8-inch lumber, sill plates were installed along the 6-foot walls. Along the 14-inch walls, the men attached 2-inch-by-12-inch lumber sill plates, with the extra 4 inches for roof overhang to keep precipitation runoff away from the pit.
After installing the sills, Kamper backfilled the hole with a small tractor and an excavation bucket, pouring bentonite chips around the bottom 4 inches deep. The remainder of the hole was sealed with soil.
Building the Top
Roof ends were cut as one-piece units from a 16-foot piece of 2-inch-by-12-inch treated lumber. To ensure the roof would lay flat on the sills, wood was cut at angles in each direction from the 12-inch center peak.
For roof supports, two pieces of 2-inch-by-4-inch treated lumber connected with 4-inch truss plates were built to have a 12-inch center height, also with angled cuts all the way to the ends. On each side of the shooting ports, Kamper added lumber supports, one on the outside edge of the dog hole and one along the front roof seam. He installed cross braces of lumber laid flat between the supports on the front and backsides of the roof.
At the back of the roof is an entryway for hunters, made of a cellar door that opens toward the front of the pit. Framed out of treated 1-inch-by-6-inch lumber, the door is covered with a ¹â'„â‚'-inch fiberglass panel that overlaps the roof by 4 inches at the top, keeping water from getting into the pit when the door is closed.
The rest of the roof is covered with more ¹â'„â‚'-inch-thick fiberglass panels, leaving a 2-inch overhang along the front that is flush with the sill plate in the back. The men fastened the roof material with barn screws with gasket seals.
The front of the roof required two full sheets of ½-inch treated plywood. To allow for the roof supports, which have a centerline spacing of 16 inches, the men placed the sheets on sawhorses, marked holes and then cut them with a power saw.
The dog hole spans 16 inches wide and 18 inches long, while the shooting ports measure 28 inches wide and 30 inches long.
Before installing wooden edges, Kamper placed a foam-rubber seal around the hole. During positioning of the front part of the roof, he pushed it tightly against a 2-inch overhang of the back of the roof. He then fastened the roof's front portion with the same type of screws as the back, using aerosol foam insulation to seal the joint between the two roof sections. The pit's inside has a 2-inch-by-12-inch shelf along the length of the shooting area, mounted on T-braces fastened to the base of the sill. Additional legs support each end of the shelf.
A stairway by the entry boasts 32-inch-wide steps cut from 2-inch-by-12-inch treated lumber. Braces attached to the sill plate and the framework of the dog box support the stairs.
The dog box is an elevated plywood platform measuring 40 inches by 40 inches, covered with indoor-outdoor carpet. The side and front walls of the pit shape two walls of the dog box, and a 16-inch fiberglass panel forms the other wall. The inside panel is short enough to allow a hunter contact with dogs. To enter, dogs step from the hunter access stairway onto the platform and into the back of the box. Canines can see forward through the dog hole, but are hidden from the top and sides.
Space beneath the dog platform provides storage. Hunters sit on high-backed, swiveling stools.
To close up cracks, Kamper used aerosol foam insulation. He also draped military camouflage netting over both sides of the roof.
Artificial Christmas tree limbs painted in camo colors add concealment. Held down with electrical wire, the faux limbs were tied into bundles and placed over the blind. The weight of the artificial branches holds them in place. They can be shifted or easily removed and stored, yet they don't blow off in strong winds.
Electrical power from a nearby farm building runs an aerator to keep a hole open and also lights the blind. Future plans include propane heaters and shotgun holders.