Sweat equity has to be a major part of my upcoming project, so one of the appeals of AAC block construction is the DIY potential. I've watched professional brick, block and stone masons work (I had the thrill of handing materials up to them on the scaffolding), and I'm aware of how easy they made the real work seem. I've also stick-built room additions and a garage, and as a rank amateur I've helped lay CMU foundation walls. So I have a little concept of how differing materials affect construction time. My question is: for three able-bodied DIY'ers (weak minded enough to get roped into the project) how long does it take to lay a 16' course of 8x8x24 AAC blocks? Related questions might be: How long does it take to cut a block in half with a bandsaw? (Hey, I get to justify a monster bandsaw that'll come in use in totally different endeaver later!) How long does it take to drill a 3" core through a 8" thick block? Do you really have to give volunteers a lunch break? Seriously, I know I'm asking a lot, but I'm probing for the details that help me estimate project timelines (btw, I used to be a project manager in a former life...PMP certified and the whole 9 yards.)

I have had some training several years ago in laying Hebel AAC block.  I cannot begin to remember how long each task took but I do remember that laying the first course with mortar instead of adhesive took longer than the courses above.  Using mortar to get the first course perfectly level can be somewhat time consuming for a DIY.  After the first course has been established, the rest goes fairly fast.  At the time of my training, I was comparing the time with installing shotcrete panels and shotcreting them with laying the block.  It appeared to me that AAC blocks went up more quickly but both the blocks and the panels still needed another step such as stucco.

Alton, you may be describing another technology I considered: SCIP--shotcrete sandwiching a foam and wire mesh form. I received a bid for that, but at $24 / sqf it appears to cost almost 3x higher than AAC. I'm back to assessing whether I have the time or resources to build an AAC block house myself.

I've yet to master the art of sticking the head joint mortar on a concrete block. Is trowelling thinset onto the neighboring AAC block easier for the DIY'er? And won't the trowel teeth virtually assure a level bed for the block?

Maybe if I briefly explain some of the basics, the differences between building with SCIP and AAC will be more apparent.

I have built with SCIP and had only training with Hebel AAC.  The Hebel AAC house had experienced crews and inexperienced me.  Since most footers are not level, the first course of AAC block is usually laid on a fresh bed of mortar.  The mortar helps to level out the footer and get the top of the AAC block level.  After the first course is level, then thinset is used with a notched trowel to control the thickness of the thinset so each course of block will stay level.  No window bucks are required, especially if the windows are not surface mounted.  Threaded rods were used to tie the top plate of the wall to the footer.

SCIP panels are attached to vertical rebar dowels.  We found it was easier to drop a chalk line and then drill holes and epoxy the rebar on a straight line.  Each panel was lifted up and over the rebar dowel so that the rebar was between the wire mesh and EPS.  Additional rebar was installed to reinforce around openings.  We used a torch to remove some EPS behind the rebar so it would get proper concrete coverage.  The uneveness of the footer/slab did not matter.  No mortar required.  SCIP panels were placed side by side and joined with wire mesh with hog rings to the existing mesh.  We cut the wire mesh and EPS for openings and installed bucks.  The wall was shotcreted on both sides after all of the rebar was installed and the walls braced.  All of the shotcrete had to be troweled smooth enough to accept three coats of stucco.  (Some shotcreters say they can finish shotcrete smooth enough to be painted.  If so, then that saves the cost of installing stucco.)   

Summary:  I still think that for a DIY it would be faster to build a wall with AAC than SCIP although I would much prefer the strength and water tightness of a SCIP wall.  I think building the SCIP wall requires much more experience than building a AAC wall.  I have seen quotes from about $6 to $20 per square foot for finished SCIP walls.

My moonlighting mason and I put up the walls of my house in about 20 days -- spread over two months because he got called back pretty quiickly and dropped to weekends. My design was a particular PITA because of many many corners, a radius wall, architectural trim, a flat roof and a steel post and beam system carrying the second floor. The radius and the posts created a tremendous amount of cutting. Until we got above the second floor, I was practically running to cut blocks, stock them and mix mortar. (Dropped to my high school weight.)

As alton says, if the first course is near perfect, the rest of it goes up pretty quickly. The wife and I made sure of that over a day and half with a laser transom. The thinset gives you an eighth inch of play for blocks that are cut to a sixteen inch tolerance. There's a special trowel for AAC -- essentially an 8-inch scoop with raking teeth, sized to give you the right amount of mortar. Scoop. Plop. Rake. Place. Tap. Tap. Tap. TENDER!! (I can still hear his voice.) A DIYer will struggle most with thinset's memory. Set it down wrong, and it's very difficult to get it to stay where it belongs. Breaking the bond to reset it makes for a long tiring day. lThe three diimensions also take some some getting used to. You tend to concentrate on level and flush without checking enough on vertical. The best way to get the block down right is to bend at waist as you set it so you're sighting down the wall. I have no idea how masons can spend a day working in that position. My guy was 67 at the time. A shoutout to the best mason in Pa: John Sucik. Get a mason to go through the basics. (Example, when you break a course for a window, make sure to keep the same stagger so the first course above it picks up where the one below left off.)

SCIP is not diyable, and there's no way to get my finish on stucco without adding an abbreviated stucco step. The concern about moisture and vapor penetration is misplaced in my opinion. I should have mentioned this before. Aercon and Sider Oxydro told me that moisture content ebbs and flows in AAC in a manner similar to heat transfer, and in fact, can buffer humidity in the same manner. (i.e., the blocks will temper the occasional humid day.) It didn't occur to me because there is nothing occasional about humidity in Pa. Again, the longer you can leave the wall uncovered (but protected from rain) the better off you are. Blocks come out of the autoclave at 30 percent moisture. They lose more than half of it the first month, but don't reach a steady state 7-10 percent for up to a year.

At the end of the day, what makes AAC eminently DIYable is its unitary nature. A mistake with one block is only a mistake with one block as long as you catch it and fix it.

Todd, did you have internal AAC walls that figured into those 20 work days? You also aluded to your wife's involvement in this project: does that mean you really had about 60 person-days of work?

Also, does your post and beam structure support the flat roof over your garage, or the second floor structure?? I was planning to bolt a ledger through the AAC into the first floor bond beam to support the floor/ceiling joist system. What is the best approach. BTW, I doubt that AAC floor panels are within my capabilities.

Ok, one more question...did you mix your own concrete onsite for the reinforcement cores and bond beam?

Posted By AAC-curious on 15 Apr 2013 10:12 PM
Sweat equity has to be a major part of my upcoming project, so one of the appeals of AAC block construction is the DIY potential...

Have you considered ICF?  I built all of my full basement and main floor (62x34) myself using ICF except for the day of the pour when my ICF distributor provide three experienced guys to do the pour.  And this is my first home build.  My labor cost was ~$600 per floor.  My cost for all materials including the ICF, concrete, rebar, and concrete pump truck rental was ~$6/sq ft.  And I used quite a bit of rebar including grade 60 5/8" verticals 16" oc with 1/2" horizontals 16" oc in the basement and all 1/2" at 16" oc on the main floor.  I built my own wall bracing using 2x4s, a couple sheets of plywood, and treated 2x12 walkboards.  I reused all of that bracing material inside the house during interior framing, except for the cut up plywood gussets.  If this would have been a single story home above grade on a slab, this would have been an easy job - the basement including waterproofing and tying in the floor system, decks, and exterior concrete slabs added quite a bit to the effort in my home build.

Arkie6, which ICF did you go with? Yes, I know that ICF's are more popular in the US than AAC; I just haven't gotten comfortable yet with a foam exterior.

I used LiteForm ICF with 2.5" EPS foam panels. It is my understanding that the optional 2.5" thick foam is no longer available. 2" thick Type IX (2# nominal density) EPS is their standard.

The 20 days was how long it took to build the walls. We only had four sections of scaffolding, so it would have taken longer if I weren't doing prep work during the week. I had to build the garage deck and the second floor before we could move the scaffolding up a floor to continue. I mixed thinset with a drill paddle and concrete with a 3 cubic foot mixer. Hoisted it up in buckets using a hand-cranked Genie lift.

Steel post and beam is necessary to carry an AAC flat roof over a 23-foot span. It is not necessary for a normal 2-story house (which is to say not one designed by me.) I justified it as a $3k, counting the welder, belt and suspenders approach to DIY. If I had known how much work it would add, I would have thought about it longer before marching off after my personal drummer.

An AAC roof is less expensive than you think. The garage deck sits on two W8x21 steel beams welded to 3 inch sched 40 steel posts which in turn are bolted to the frost wall. Another two posts flag the garage door to hold a transverse W8x21 beam over the door, which in turn holds the two beams. Using the outside walls the beams carry three rows of two-foot AAC planks roughly 7.5 feet long. They are six inches thick and weigh 341 pounds each. If memory serves, I paid $1,500 for 40 of them. The rubber roofing cost more.

BTW, I cut through the foam to pour 8" concrete concrete pads directly over the outside walls and beams. I set posts on these pads, under multiple layers of EPDM, and bolted the deck joists to the posts. The pergola answers the question of what to do with the four interior posts. With a 7-foot span, I held the deck height to 11 inches over the AAC planks.

The second floor also sits on four steel beams, and I would have needed at least two because my 600sf second floor "floats" in my 1000sf first floor, carried by beams on two sides rather than exterior walls. Frank Lloyd Wright used varying ceiling heights to make rooms seem bigger. It works. Turning the joists to span eight feet between beams, I was able to use 2x6s.

The deck and the floor also hang on ledger boards bolted to the AAC. AAC comes in a U block that looks just like you imagine. You switch to this block at floor heights and fill the trough with steel and concrete, placing j bolts as necessary. These bond beams sit on 3-inch concrete cores every four feet -- the blocks come predrilled -- which are also filled with concrete and steel.

Just because pseudo-experts chap my a**, I will point out here that a 3 inch concrete core eight feet tall amounts to about a half a cubic foot of concrete. Placed every four feet, the cores would account for about 3 percent of the volume of an eight-inch wall eight feet high. Plus the core is insulated to the equivalent of ~ .75 inches of EPS on either side. So GBA's Martin Holladay should either break out his calculator or actually learn something about AAC construction. If the bond beam course were solid concrete it would amount to another 8 percent of wall volume, but of course it is not.

In short, if your design is a four corner box you could have it under roof in a month with one helper, assuming you quickly develop masonry skills. (Never happened in my case.) I would urge you to think bigger. With an electric chain saw and a very, very good dust mask, you could recreate the Cathedral of Notre Dame in central Indiana, complete with gargoyles.

Posted By arkie6 on 17 Apr 2013 07:44 PM
I used LiteForm ICF with 2.5" EPS foam panels. It is my understanding that the optional 2.5" thick foam is no longer available. 2" thick Type IX (2# nominal density) EPS is their standard.

The Type-IX / 2# EPS is pretty rugged stuff compared to the more commonly used Type-II goods, and holds up very well to the abuse/exposure on construction sites.  I wish more vendors used it!

It has a modest boost in R/inch too, at about R4.4-4.5/inch at ASTM C518 conditions (@ 75F center-temp, not the skewed 40F values ICF vendors often bandy about despite a credible rationale for using the 40F center-temp in a US residential app anywhere outside of zones 7 & 8.)  It's simply better stuff for the application.