ReddiForm’s Screen Grid approach to Insulated Concrete Form design is the ideal concrete masonry unit (CMU) replacement. Screen Grid Insulating Concrete Forms (ICFs) were initially conceived as replacements for cinder or concrete blocks since they actually resemble large concrete masonry units.
Screen grid ICF layout, and the tasks related to getting started, are the same as standard CMUs. You start from the corners and work towards the center to establish the bond.
The major differences between screen grid insulating concrete forms and actual CMUs are product size (1′ x 4′ ICF vs. 8” x 16” CMU) and product weight (3 pounds for 4 square feet of ICF vs. approximately 280 pounds for 4 square foot of CMU wall space).
Coupled with the fact that CMU block work is not as strong as reinforced concrete – most codes now require them to be grouted and reinforced – hence ReddiForm’s ICF building system is an ideal alternative for current and future concrete building technology.
Stability. Screen grids are a very stable ICF building system. Due to their design, they do not flex when concrete is poured into them, and the connection of one side to the other eliminates bulging, virtually eliminates blowout issues, strongly encourages straight walls. The form design distributes pressure developed by the concrete; reduces the pressure against the corners and reduces wall distortion. Less overall bracing, and no corner bracing is required.
The fact that the “liquid head” pressure of the concrete needs to be calculated in each column only, versus the entire wall, allows ReddiForm concrete foundations and walls to be poured in lifts of up to 10 feet – less pump truck time, less labor, no bulges or blowouts, and no cold joints. The integrated web design eliminates lateral movement between the sides of the form, which increases the form’s stability and insures flat and plumb walls and corners!
Versatility. Because of their stability and strength, screen grid insulated concrete forms can be used for “slab-on-grade” and “frost walls.” Simply place and level the forms on the footing in the trench and evenly back-fill both sides so as not to move them off the building line. Then pour the floor and wall monolithically.
Accuracy. Because of the larger foam surface area of the foam ties, concrete flow over the top of these ties creates pressure, which holds the form down. This makes gluing unnecessary throughout most of the wall. Only at the very top of the wall is extra adhesion necessary where there is more concrete under the tie than over which may cause the top form to float. Another benefit of the large “distributed” ReddiForm ICF interior is that as the concrete flows it pushes the blocks deeper into the locks of the adjoining form, causing the wall to actually straighten under pressure!
No Moving Parts. Pure screen grids are much easier to work with since there are no dissimilar parts (plastic or metal). The design makes cutting simple. Since the forms are easy to cut, slopes, angles, curves and elevation changes are simple to produce. Since the form is reversible, cutoffs can be used rather than becoming waste.
Lighter Weight. While structurally stronger, filled screen grid ICF blocks are actually lighter in overall weight than other ICF concrete building systems. This factor makes them better for buildings in seismic areas as well as being of great benefit in high-rise building construction.
Angles. Any angle can be achieved by first cutting the block at one half the degrees of the desired angle, then flip the cut off piece over and since the form is reversible there is no top or bottom simply glue the pieces together to create the angled form you need.
Curves. One cut between each cell does it. With your hot wire cutter or saw, cut the block almost all the way through between the cells (on the line outside of the block), leaving about ¾ of an inch. Layout the arc and bend the block to conform to the arc. A foam insert to hold the opening precise is helpful, or use wood inserts for later attachment points. Once the first row is established, repeat.
Brick and stone shelves. Cut a standard block on a diagonal lengthwise (you will get 2 pieces from one block). Then cut holes in the wall at the desired height to allow the concrete to flow into the brick shelf. Then glue the angled piece to the wall. This capability allows you to place the shelf where you need it which can reduce the need for extra brick or stone.
T-walls. Simply run your outside wall and where the “T” occurs cut out the foam in that cell then butt the perpendicular block at that point. Plumb both walls and glue each side of the block vertically. No bracing is required. If the “T” falls on a cell line, use a corner block and cut out the foam on side opposite the corner cut then interlock teh ‘T’ form you have created into the straight wall starting on the second course. Butt the next row into the straight wall, then alternate to form the “T”.
Design Simplicity. Openings for doors and windows are simple and easy. Glue 1 ½” or 2” rigid foam to the sides of the opening and use a 2×10 or 2×12 as the header. This can only be done with screen grids because of the reduced pressures of the concrete. Once the wall is poured and the concrete has set, strip the foam and wood from the opening to complete the process. All major window and door manufacturers have masonry clips to fasten directly to the concrete eliminating extra costs for labor and pressure treated wood or plastic. Additional savings can be realized by finishing up to the door or window unit with sheet rock rather than using wood extension jambs and wood casing.
Plastic buck and ¾ plywood materials are available and work well too. Metal door bucks are very simple to install. Just install the frame in the opening prior to pouring and glue it to the foam, making sure it is plumb and level in the wall.
Remember: ReddiForm concrete blocks are all foam, with no moving parts so the wall doesn’t move either!