OK, the big day is here, pour day. Before the concrete pump arrives you should be double checking everything, making sure the formboards are firmly attatched and eyeballing the rebar grid to make sure that it is uniform in height and none of the barstock is protruding up to where it may be exposed to the atmosphere after the pour. Those bars should be lined up like a company of Marines standing tall before the inspecting general. Squared away and about one and one half inches above the plywood forms. Go inside and check all the vertical braces and make sure they are all tight. Double check the door forms to make sure you screwed them all together.
The concrete mixture should be 6 sack mix, which will test out at 3000 psi after setting up for 28 days. Most Maco and Thompson small line concrete pumps require 6 sack mix so the concrete will slide through the hose without binding up. There is a newer type of concrete pump built in Germany that pushes regular rock of 3/4" diameter. It is a Schwing pump. Check to see if they are located in your vicinity. The 3/4" rock will produce a stronger ceiling with fewer cracks in the long term. If you live in the northern states you will need to get air entrained concrete to help resist the freeze thaw cycle. Do not use any calcium chloride in the concrete as this will attack and destroy the rebar in a few short years. Call your concrete dispatcher to find out about the pump availability. Usually they will coordinate with the pump crew about the concrete mixture and time of pour, etc. Using a pump is cheaper and easier than trying to pour this by hand. Remember, the ceiling must be cast as one monolithic unit . You can't stop if the mixing crew gets tired.
When the pump shows up, let them decide where to locate the unit. The concrete truck must have enough room to back up to the pump. You want to start pumping at the low side of the forms and pour uphill. The rebar grid will act like a dam and help prevent the concrete from sliding down towards the low end. You will need 2 men to help move the pump hose around, 2 men to place and screed off the concrete and another person stationed inside the room who's job will be to tamp the underside of the plywood forms as the concrete is being poured. He can use a hammer if he is tall enough to reach the forms or a piece of 2x4 if the forms are out of his reach. This tamping will eliminate most voids and fissures around the rebar and will give a nice smooth surface to the underside once the plywood is stripped off. Once you have laid down all the concrete and screeded it off with a straight 2x4, you can use a wooden bullfloat with a long handle to bullfloat smooth the concrete. If you don't have a bullfloat you can make one out of a 3' long piece of wood siding or 6" one by material. Or use a metalic bull float. When the cement has cured some, run an edging tool around the perimeter forms to help with stripping these forms and then trowel the concrete. Six sack will set up faster than regular 5 sack so if its hot out, don't get caught asleep at the wheel. On a hot day you will need to mist the concrete after it has set up for several hours to help slow the cure. I mist it and then cover it with visqueen to retain the moisture and slow down the initial set of the concrete. If you pour during the cooler time of year and there is a threat of frost or freezing temperatures, cover the concrete with plastic visqueen and straw to keep from freezing.
Leave the forms on for at least one week. Then start stripping off the outside perimeter forms. BE CAREFULL they don't pop off and hit you in the head or land on your feet. Pull out all nails and scrape the cement from the form boards and stack for future use. Remove screws and pull nails from the door frame forms next. Put your hard hat on and then go inside and strip off all the small splice boards and diagonal braces. I always save the screws because they can be used again and cost too much to throw away. Remove the vertical braces. Listen for creaking and groaning and bolt out of there if you hear these noises. After one week the cement should be hard enough to withstand the strain and there should be no danger in removing the forms at this point. Next, remove the 2x6 joists and be carefull. The inside perimeter boards that support the plywood come off next. The best and safest procedure for removing the plywood is to hammer in a small, narrow starter bar between the seams in the middle of the room. You may have to get another set of hands on this while you insert a longer bar into the gap and pry off the first sheet of plywood. Sometimes it will pop right off; other times you have to scrape, yank, pull, yell and scream to get that plywood off of there. Again, be carefull it doesn't fly off and smash you in the head. Cart this material outside. You can use some of the plywood to make a door for the building.
The 5" thick ceiling with the 16" rebar grid that we have built will easily carry the weight of two feet of fill dirt. Before backfilling and burying the unit we need to consider a waterproofing treatment for the roof. I have had much trouble trying to waterproof concrete roofs and have had to go back and dig them up to redo them a year after completion. I spared no expense on waterproofing materials using acrylic cement and embeding fiberglass mesh into it. This worked fine for one year but the second year the roof was leaking like Niagara Falls. I had to dig up yhe entire roof by hand and discovered that there were cracks all over the roof that had pulled apart my waterproofing application due to the expansion and contraction of the concrete between the seasons. I wire brushed the entire roof and blew off all dust and debris and applied yet another coat of acrylic material. After it set up I covered the roof with 2 layers of thick black plastic visqueen, then broadcast a 4" thick layer of course sand before reburying the roof again. This layer of sand allows the rainwater to percolate through and run off of the roof. No leaks since I did this 18 years ago. Now they have a meterial called Bichathane waterproofing material that you roll out onto the concrete surface and this material allows the concrete to expand and contract and slip underneath the material so no leaks can develope.
Before backfilling you will need to install a 4" diameter PVC perf drain pipe around the outside of the walls of your building to exhaust the rainwater. Proper backfill material around the walls should be drainrock, but do to this materials recent skyrocketing price the second choice would be course sand to let the water perc through and get into the drain pipe. If you are forced to use the existing soil you may end up with damp or sweating interior walls because the soil is holding water just like a sponge.
You may also want to consider applying styrofoam insulation to the interior walls in your building to make it liveable during the winter months in an emergency. Several companies manufacture insulation designed to be applied over block and concrete surfaces. DRYVIT and STOWE are 2 of the most common. Google these names for more information.
Anyone who has actually constructed a masonry / concrete shelter knows how physically demanding it can be. You won't need weight watchers if you are bold enough to attempt this construction project. Once completed, there is nothing that exudes a sense of permanence like a masonry structure. Good luck with it. :mrgreen:

Proper rebar placement is necessary for the structural integrity of this concrete roof. Misplaced or convoluting rebar can cause cracks or even complete roof failure. From an engineering standpoint the LOAD will be from the top pushing down, which will force the bottom of the concrete roof to seperate and also push the top of the roof from the sides toward itself. (looking at the concrete from the side) This is why we must place the rebar towards the bottom of the pour, or approximately one and one half inches up from the plywood forms, where all of the pressure will be. With this placement the rebar will hold the bottom of the concrete from breaking open and it will prevent the roof from a catastrophic collapse. All free standing concrete structures are designed this way.
Clean off the plywood forms and scrape all the wet leaves and other unwanted organic material off of the forms. Get a 3' long piece of scrap metalic water pipe to use as a cheater bar to place over the rebar and bend them over. Start bending the uprights protruding up out of the longer level walls first. You may have to lay a piece of one by or a 2 x 4 down on top of the blocks and bend the bars over this to keep them from coming in contact with the blocks. This will give you the desired space above the forms, and help keep the rebar at a uniform elevation. They should correspond with the angle or pitch of the plywood forms. Line these bars up so they are all straight and at the right height. Make sure they are placed 1and a half inches above the plywood. After this is done, cut long pieces of half inch rebar and tie them onto the bars you have just bent over, from one wall to the opposite side. When all of these bars have been tied in place, start bending the bars over that are protruding out of the shorter walls, over the grid that you have just created. Tie them good and tight- you may have to use 2 ties doubled up to draw the opposing bars down tight. When this is done you should have a grid of rebar about 16" x 16". Bend all your tie wires so that they aren't sticking up or pointing down and hitting the plywood. MAKE CERTAIN that these rebars are about one and one half inches above the plywood forms everywhere in this grid. They may be as much as 1/2 inch out either way in elevation, but take your time and try to keep them as close as possible to one and a half inch specs.
If you have a clean tarp, throw it over the roof to keep leaves and other unwanted debris from falling onto the rebar/forms. Go into the room and check to see if you have forgotten to brace or screw any framing members and look for any loose formboards. Double check everything. There can be no mistakes as you get just one shot to do this roof pour correctly. Start thinking about how you are going to move the concrete up onto the roof. The bestest, fastest, easiest, safest way is to use a concrete pump. This may cost you another $300 to 400 but will guaranty that the job gets done without killing your crew or having them drop out from exhaustion. I have used everything from 5 gallon buckets to a backhoe bucket to move concrete from the redimix truck to the roof. Dumping the mud with a backhoe generates an awfull lot of pressure and vibrations onto the forms and increases the possibility of smashing the forms, ruining your job and liberating your money for no gain. In the mountains, depending on the terrain and how hard the ground is, you may be able to drive the cement truck up to the roof from a ledge or the upside of a hill and just dump the concrete using the trucks chutes. Several years ago I mixed the concrete by hand in a mixer and we wheeled it up a footpath that we cut into the mountainside by hand, but I will never attempt that again because it almost killed us. You will have to consider all the options before you decide, but like I said, the pump is the best way to go.

It will also be necessary to cut some 4" scrap pieces of half inch plywood about a foot long and then screw them onto the upright braces where they intersect with the 2x6 joists. There will be a lot of vibration when we pour the concrete and screwing a scab over the intersections of the braces will prevent them from vibrating loose during the pour. We don't need any forms to collapse on us while pouring the concrete.
Forms for the door entrance will consist of a 2x8 that gets cut nailed vertically on each side of the door jamb with a horizontal 2x8 nailed to the tops of these. Use just one common 8 penny nail from the top and nail down into the vertical boards. You will have to determine the height of the door but if possible, make it so that the forms do not protrude up into the roof concrete. You want at least a good solid 8" of concrete over the door opening. Make sure that this horizontal form is level. Cut a diagonal 2x6 brace and nail it from the center of the bottom of the door span form board, down to the corner on the bottom of the door opening so that you will have enough room to squeeze past this brace to gain access to the inside of the room. Also cut a spreader board and toenail it at the bottom of the door, between the vertical forms to keep these 2x8's from shaking free. You might discover that on the inside of the room, there may be an open space above the door forms. Nail a 2 by over this opening. Screws will work better if you have them and screws won't vibrate the 2x8's off like pounding nails will. Your portable screwgun will be worth the price you paid for it on this job.
Next we must cut nail a 2x10" board onto the outside of the building to contain the concrete. Start on the longer, level walls, making sure that there is 5 inches of board showing above the plywood on the inside of the form. The easiest way to do this is drive 2 common 16 penny duplex nails through the board, at 5 and one eighth inches from the top of the 2x10 and then use these nails to hang or rest the board on top of the block walls. This will make it easier to cut nail into the block. Make sure that these boards ase level. Cut nail about every foot or 16" and nail into the center webbing of the blocks if you can, for a better hold. Double check and make sure you have a good 5 or 5 and a quarter inches of exposed board showing on the inside, to hold the concrete. Next, nail the sloped sides in place and let the ends of these boards run wild. Screw a couple screws into the corners where the boards intersect and cut nail them onto the block walls the same way. When you are done, take some 2x4 scraps about 2' long and cut nail them below the 2x10's and flush onto the block walls. Nail these towards the bottom so that you can flush nail another 2x4 onto them, and over the 2x10 to act as a brace and help hold the outside forms on. Screw these 2x10's into the door header form so it can't split or seperate. Take some 1x4 and screw it diagonally onto the top of the 2x10's approx 2 feet from each corner. This will act as a brace and help hold the forms during the pour. (You might want to wait and do this after we have placed and tied the roof rebar.)
Are you wore out yet? Rebar placement is next. I'll bet you can't wait!

Be sure to wear your safety glasses/goggles while nailing hardened concrete nails. These nails are made from super hard steel and the heads can break off if not hit square on the head, and possibly strike you in the eye. Please be carefull.
Now that you have toenailed the 2x6's in place you should have a framed structure that resembles a floor joist system, but pitched so that one wall is 8" taller than its opposite wall to allow water to run off once the concrete is poured. These 2x6's now have to be supported by 2x4's running vertically from the bottom of the 2x6 down to the dirt floor and it is best to place a small 6x6 (approx) scrap of plywood, or a scrap of 2x6, under the 2x4 where it comes in contact with the ground. This will help distribute the weight and keep from pushing the 2x4's into the ground. Space these vertical braces every 2 feet under the 2x6's so you will have room to maneuver around in the room. This is going to take some time and if you can, it is better to use screws to secure the vertical 2x4 braces to the 2x6's. Screws are stronger, won't pull out and will speed up the disassembly of the forms after the pour. After this process is done, nail or screw a 2x4 diagonal brace across these vertical 2x4's from the top on one end to the bottom of the opposite end to insure that nothing shifts or pops while you are up there jumping around during the pour. It is not necessary to brace every row of verticals, but every other row should be fine. This is going to take many a man hour to do all of these braces, and when done you can sheet the top of these frameing members with the 3/4" plywood. To secure the plywood, nail it from the top with small 6 penny nails, just a couple nails per sheet so that you will be able to pull the plywood off from below after removing all of the braces and other form boards. If you use too many nails, the plywood will not want to cooperate when its time to come down. I never took any pictures of these forms so you are going to have to use your imagination to visualize it.

The easiest sloped roof is a flat roof raised on one side. On one of the 12 foot long walls, stack one extra block on top and fill with grout . This will raise the wall in elevation by 8 inches so when you build the form boards they will be pitched to allow for rain water runoff. Most of the masonry rooms I have built were buried on 3 sides and the roof for concealment and less chance of detection from aircraft. Its best to pitch the roof water runoff towards the exposed wall for better water removal. If you pitch the roof towards the backside where the walls are buried you are increasing the possibility of having a damp wall and room.
Take your water level and mark the corners 10" below the top of the block. Then snap a chalkline from corner to corner on the 12 foot long walls. Set a 2x10 on the wall so that the bottom of the board is directly above the chalkline. Drive cut nails through the board and into the block wall. Cut nails are hardened steel nails designed to be driven into block and concrete. There is a trick to using concrete (cut) nails. For securing a standard 2x10 you should use a 2 and a half inch long nail. Drive the nail through the board but pay attention that you only drive it about 3/8" into the block. If you drive it deeper than a half inch it will not hold. The nailhead should be sticking up and not flush with the board like a traditional wood nail. This will allow you to get a crowbar under the nailhead to assist in removing the formboards.. Nail that 2x10 about every foot and alternately stagger the nails from top to bottom so the nails are not all in the same woodgrain. This will help prevent the wood from splitting and cracking when we pour the concrete. Do this procedure on both of the longer walls and make nice square cuts at the corners. Next, snap a chalkline from the bottom of the 2x10s onto the shorter 8' long walls. Nail more 2x10s onto the 8'walls. These boards will be at an angle for the roof pitch. If there are any holes below the 2x10s on the short walls, nail some scraps of 2x10 or whatever else you have to cover these holes so concrete cannot leak out during the pour. Next step: cut nail a 2x4 vertically from the top of the concrete footing up to the bottom of the 2x10s, every 16 inches, all the way around the perimeter of the building. When we load these forms with the weight of the concrete, these 2x4s are going to help carry the weight. Cut nails by themselves will not take the weight of the concrete. After this is done you can cut some 2x6 and toenail them horizontally between the 2x10s, at the same angle as the 2x10 on the short 8' walls. These 2x6 should be nailed so that the tops are level with the 2x10 boards, every 16 inches to line up with the vertical 2x4 braces. Use 16 penny "DUPLEX" nails for this. Duplex nails have 2 heads so that they can be removed with a crowbar when stripping the forms.
Once again the sun has deserted me and I am almost out of power; will continue later.

After you have stacked block to the desired elevation and are certain that this elevation will be high enough to accommodate your needs, then go ahead and grout the walls but be sure to fill the top blocks only half full with grout. This is for those of you who wish to pour a concrete roof. If you have decided to build a conventional wood frame roof then you can grout the blocks completely full and you may have to set up some leveling form boards to level up the walls with grout poured into these forms. As you grout you will have to insert some 5/8" dia. galvanized bolts to be used to bolt down a mud sill for your roof rafters to rest on. Back to the concrete roof; you must have at least 3 feet of vertical rebar protruding through and above the tops of the block walls. On our 8' x 12' room we will be pouring a 5" thick concrete ceiling and the rebar will be bent over so that it will become a 16" grid. First we must build the forms to support the weight of the concrete. We will need approx 1- 1/2 cubic yards of concrete for our roof which weighs in at about 7,000 pounds. That is a lot of weight to support so our forms must be built without cutting any corners on the materials. You must think ahead and try to imagine the consequences of having the forms break under the weight of this wet concrete. This situation would be a total disaster and the prospect of shoveling out all that concrete before it sets up makes my back ache just thinking about it. This situation is unacceptable and we will insure that it does not occur on our jobsite. Take your time and build good solid forms.
Roof design: A flat roof is the easiest to build, and is suitable if you live in the desert, but if you live in a wet climate there is the possibility of rainwater seeping through the concrete and leaking down onto your survival cheerios, turning them into mush before you have the chance to eat them. This has happened even when the concrete was covered with a double layer of heavy plastic visqueen. All it takes is one tiny hole from mice or insects and you are in deep doodoo. So the best roof is a slightly sloped roof so that the water will run off. In this particular geographic area we have had winters with over 200 inches of rainfall so a sloped roof is a must.
Materials: We need 3/4" plywood for the platform to carry the concrete. Three sheets should be enough for our 8x12' unit. You will need about 82 lin feet of 2x8' for a roof with no overhang or drip edge and 122 feet if you would like a drip idge that protrudes out past the block walls an inch and a half to help keep the walls dry.
My house batteries are crashing so will continue later.

When the block walls have been stacked half way up to the desired elevation and have been grouted, you have reached the approximate half way point in this project. Remove the leveling form boards and scrape off all the concrete slobbers on the wall. If you poured a nice level footing you might not have to have used the leveling forms on your walls. Some people want to have running water piped into the room, or a chimney or stove pipe. These should be run near the top of the walls to prevent water from leaking into the shelter. A wet or damp room will become a tomb during the winter months so we want to prevent any leaks from occuring. Locating pipes or openings in the bottom half of the walls will guaranty leaks. One of the shelters I built had slit openings in the walls to stick a rifle barrel through, with half inch steel plates bolted over the openings.
You can proceed to stack blocks again, up to the desired height, laying horizontal rebar every course and if need be, tieing vertical rebar to the existing rebar in the walls so that it protrudes past the top of the finished walls by at least 3 feet. Apply waterproofing material to the backside of the walls every 2 or 3 course depending on how far you can reach over the back of the walls. Again, this should be applied AFTER you grout the blocks you have just layed. A well built wooden bench should be built to stand on for setting the last several layers of block, and to allow you to reach over and waterproof the walls. This will also save your back while bucketing the wall grout. Once you find it necessary to stand on the bench, you should have a second person to hand you block etc. Wherever the door opening is located, just stack and grout but leave it open with nothing on top. The concrete roof will be poured into formboards over the door opening to lock the walls in place. Decide where to locate water pipes, electrical, stovepipes etc and befofe grouting, stick some pieces of appropriate sized PVC pipe and angle it towards the outside so no rainwater can run into the room.