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Elkwood, VA 22718 USA
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Construction FAQ

What type of foundation do I need?

Generally, you need a standard strip footing, with some simplifications.

The standard procedure for am-cor Foundations is:

  • Review Structural Set (i.e.: am-cor engineering drawings) provided with your am-cor Kit.
  • Pour standard reinforced concrete footings: footer dimensions vary depending on region, but generally are 8" (20cm) deep by 1'-4" (40cm) wide.
  • Install reinforcing bar in the footer, but do not provide hooked bars sticking up out of the footer.
  • Fasten am-cor wall panels directly to the top of the concrete footing using the powder activated or pneumatic driven pins, as specified in your am-cor Field Manual.
  • Depth of footing below finish grade depends on site location; your am-cor Kit's wall panels will be designed & structured based on building code for your region.
  • These am-cor wall panels act as the slab edge formwork when you pour the floor slab; the wall panels are then embedded & integrated into the floor slab, not just pinned to the slab surface.
NB: The am-cor System simplifies foundation contracts, as you only need to provide a level, smooth footer to start shell & floor construction.

For details, see the Foundation phase in our Comparisons section.
What R-Value / U-Value does the am-cor System have?

The am-cor System is a structural system, and does not include insulation. The Ferrocement skin has an R value of 0.6.

Why we don't include any one particular insulation as part of the system:

  • Designing your structure around your insulation choice is a Bad Idea™. Insulation technology is constantly improving; why constrict your building's design to an insulation type?
  • The am-cor System allows for much more flexibility than other systems which mandate an insulation type (e.g.: SIPS, ICF).
  • The cavity (hollow) walls, floors, and roofs of the am-cor System allow for any type and depth of insulation, from high performance polyisocyanurate & aerogel assemblies, to very green & low VOC insulations.
  • Standard North American am-cor Kits range from 6" (15cm) wall cavities to 8" (20cm) & 12" (30cm) wall, floor & roof cavities.
  • Depending on your needs, you can achieve R100 or Passive Haus ratings with the right assembly, such as double wall designs & high performance thermal breaks.
See also:
What kind of interior insulation should I use?

Over the years, our clients have installed a number of different types of interior insulations, from just fiberglass batts, to to 10" (25cm) solid of closed cell spray foam. Our current favorite balance between performance & expense is a combination of:

  • At least 2" (5cm) skim coat of polyisocyanurate spray foam insulation (vapor-barrier),
  • High-performance aerogel thermal breaks,
  • Low-VOC "eco" batts,
  • Low-VOC blown cellulose.
For the price, this combination performs quite adequately in walls, intermediate floors, and roofs. It's not too expensive nor difficult to install. In colder climates, one option for additional performance is a double-wall, separated by thermal breaks (in some cases, just slight a slight furring out is required for a reasonable performance gain).

See also:
What's the maximum height of an am-cor building?

The am-cor System can be built to any height reached by either standard steel or reinforced concrete construction. Basically, we can go as high as anybody else.

An am-cor building shell will be stronger and lighter than its standard structural counterpart at any height. The am-cor System is a life-saving construction method, incorporating both a monocoque steel frame encased in and integrated with a seamless structural Ferrocement (highly reinforced thin cement) skin. As such, it is a composite & redundant structure, highly resistant to lateral forces such as wind, storm surge, and earthquake. For instance, in a standard high-rise steel or concrete structure, if several major columns are removed, the building will collapse. If several of the columns in an am-cor high-rise structure are removed, the unibody Ferrocement stress-skin shell transfers the load to the remaining members without collapsing.

Are am-cor Panels the full building height?

Wall panel height depends on the building type. Generally, am-cor exterior wall panels are the height of each story:

  • Ground floor wall panels start at the top of the footing and reach to the floor above.
  • Upper floor panels reach to each successive story, so that the panels remain light and easily handled and placed at each level.
Average wall panel height:
  • Residential/Commercial/Retail = 10' (3m) to 14' (4m)
  • Industrial/Warehouse = 14' (4m) to 32' (10m)
If you have a special structural/dimensional need, we can design for it. Contact us.
Is the am-cor System strong enough?

Yes. The am-cor System is definitely as strong as, if not stronger than standard construction. To compare:

  • am-cor vs. wood construction = Far stronger.
    • The am-cor System's Ferrocement structural skin is orders of magnitude stronger than wood construction.
    • Ferrocement is made of steel, which flexes under applied force, while wood splinters.
    • Wood components (studs, beams, rafters, poles, etc.) are usually connected with fasteners (nails, screws, bolts, etc.). Both these fasteners and their wood substrates fail over time, under repeated applied force.
    • As soon as a wood building is completed, its structure becomes progressively weaker, through:
      • age & mold/mildew/rot
      • moisture damage
      • consumed by termites, vermin, other insects, bacteria, animals, etc.
      • expansion & contraction of metal fasteners
    • In comparison, cement strengthens as it ages, and steel & cement expand & contract at the same rate.
  • am-cor vs. SIPs = Far stronger.
    • Structural Insulated Panels are generally made of a non-durable inner and out skin, separated by foam insulation (e.g.: polystyrene).
    • They are actually not significantly stronger than polystyrene (not a rated structural material).
    • Their strength is further limited by the strength of the adhesive holding the foam to the exterior panel faces.
    • Facing material is often made of chipboard or gypsum board (low structurally rated materials), which have many of the same issues noted above re: wood.
  • am-cor vs. Reinforced Concrete and Blockwork = As Strong/Stronger.
    • Reinforcing bars are not stiff by themselves, but will bend under their own weight; by themselves they will not hold up a building.
    • Bar spacing is often 2" (5cm) to 6" (15cm) apart; the concrete between such bars is actually dead weight, since it receives no help from the bar to withstand tension.
    • Failure in a reinforced concrete building is often due to the excessive weight of the structure itself, and its inability to resist cracking.
    • am-cor light weight galvanized steel frame members are stiff yet flexible; they will not bend under their own weight, and they can hold up an entire building.
    • amcorite Ferrocement structural skins are thin and light, there is no cement more than 1/8" (3mm) away from Carbon steel reinforcing
    • An am-cor building will not collapse under its own weight, even under extreme loading conditions; instead, it the unibody stress skin will flex, whereas a reinforced concrete building would crack and fail, or even worse, collapse.
  • am-cor vs. Structural Steel = As Strong/Stronger.
    • The amcorite Ferrocement skin protects its inner steel framework from rupture, and strengthens it against bending.
    • The compatibility of steel and cement are maximized in the am-cor unified composite structure, where steel and cement are keyed together as well as bonded together, creating a unibody shell.
    • This composite assembly increases resistance of each member by joining them all together, not just with bolts, but along the entire length of every steel profile.
    • The composite am-cor assembly configuration increases the strength of the steel frame, by adding the compressive strength of cement. Again, an am-cor Ferrocement structure will flex, whereas a structural steel's connections between components will fail.
What are the fire ratings for the am-cor System?
We're fully fire rating compliant:
  • UL 2-hour assembly: am-cor walls and ceilings coated on one side with amcorite Ferrocement mix
  • UL 4-hour assembly: am-cor walls and ceilings coated on both sides with amcorite Ferrocement mix
Standard fire retarding assemblies (e.g.: fire-rated gypsum) can also be installed increased protection.
See our Code Compliance page for details.
How are windows & doors installed?
am-cor prefab Wall Panels are framed with openings sized to accept your specified windows and exterior doors.

To mount openings in the wall panels, perform the following procedure on site, after panels have been fastened in place, and before coating with amcorite Ferrocement structural skin:
  • Unfasten the Carbon steel expanded metal sheathing around the window and door jambs.
  • Temporarily pull back the Carbon steel mesh.
  • Place the window or door into the opening, with its nailing fin against the steel frame jambs, sills, and heads of each opening.
  • Fold the sheathing back in place, and fasten the window to the frame, through both sheathing and nailing flange.
  • Usually openings are sized to leave a 1/2" (1-2cm) gap between window/door unit and frame, to allow an interior drywall return around openings.
  • If this is the case in your am-cor Kit, place a shim of 1/2" drywall, plywood, or aerogel thermal break, between the unit and the frame when mounting the unit, to ensure an even gap right around the interior face.
This procedure and others are covered in the Field Manual included with each am-cor Kit.  See Kit Contents and Construction Sequence for more.
Do I need to decide on my windows beforehand?
Yes. It is very important that your window and door units fit properly during Kit assembly. We customize your Kit to suit your choice of windows and exterior doors, and it's expensive to modify your Kit after fabrication.
How are openings flashed?
Requirements for flashing vary depending on region & local code. The general rule of thumb is: you should flash openings however they are normally flashed in your region, depending the building's exterior surface.
In this respect, the am-cor System is no different from standard light gauge steel framing.

The typical method:
  • Once window and exterior door units are installed in the am-cor Panels' galvanized steel frame, and before coating with amcorite Ferrocement,
  • Position flashing along the top of exterior openings and secure it with self tapping screws.
  • Coat the wall panels with the amcorite/Portland cement/sand mix.
  • Flash as normal, with your finish surface (brick, stucco, stone, siding, etc.)
If the exterior surface is another stucco coat, do the following after completing the above steps:
  • Make a V-shaped groove in the stucco along the head of the window/door unit.
  • The finish coat is not to cover this V. The unfinished V allows any vapor between the amcorite cement coat and the finish coat to escape, rather than be trapped at the window/exterior door head.
This procedure and others are covered in the Field Manual included with each am-cor Kit. Contact us if you have questions on a specific installation or project.

For increased thermal performance, openings can also be flashed and insulated at the same time, and covered with a weather-resistance stucco finish.
Window with exterior stucco insulationWindow with exterior stucco insulation
Are am-cor flat roofs really flat?
No. Our "flat" roofs are always slightly sloped for drainage.
Do am-cor walls need housewrap?
No. When properly installed, the am-cor Ferrocement structural skin is seamless and should not allow air infiltration.

A good insurance is to install at least a skim coat (2" or 5cm) of closed-cell spray foam insulation (e.g.: polyisocyanurate), which will fill in microscopic cracks and act as a vapor barrier. Customers who have constructed "tight" houses have had success with this method.

Another popular method is to use a good, weather-resistant synthetic stucco as a finish coat, thereby adding another layer of protection.

See also:
Do I need to drill for wires & pipes?
No. Prefabricated am‑cor panels include wall studs, floor joists, and roof rafters, which are factory punched to allow fast and easy installation of service runs. Plastic grommets are provided with your Kit. Place the grommets in the factory punched holes, then run your pipes and wires through the grommets, to avoid chafing on the galvanized steel.

See also:
Is there any waste with am-cor Kits?
No.  There is no cutting required with am-cor Kit assembly, and therefore no structural waste or cartage required on am-cor building sites.
What's the difference between a structural stucco coat & a finish coat?
The amcorite Portland cement and sand Ferrocement structural coat is the first coating to be applied to your am-cor galvanized steel frame building shell upon completion of panel placement.  This structural coat is mixed according to your am-cor Field Manual, and forced through the Carbon steel expanded metal mesh sheathing on the factory prefabricated am-cor steel frame panels. In forcing the amcorite mix through the small holes in the expanded metal you are unifying two compatible materials: cement and steel, to create a single composite structure. This unibody structural coat creates a seamless skin which joins all panels and steel frame members together into a single cemented piece. This action creates am-cor's redundant, life saving structural shell.

If your building's exterior finish is a stucco surface, we call this the finish coat.
This second (or optionally third) coat is usually a standard cement and sand stucco mix, which is thinly applied to smooth out any variations in the amcorite structural coat. This coat can be a mixture of Weather resistant white Portland cement, tinted and textured for appearance, or commercial weather resistant cement or synthetic mixtures may be used as well.

Additional coats may be added to create ornamental relief on walls such as: trim, cornices, quoins, keystones, sills, etc. Trim is often finished in a different color and texture from the wall surface for accent.
What kind of exterior finishes are available?

Customers have installed the following exterior wall finishes:

  • siding (wood/vinyl/metal),
  • stone/masonry,
  • brickwork
  • stucco,
  • etc.
We recommend weatherproof acrylic stucco finishes; there are a number available from different suppliers. To the installer of the exterior finish, the substrate of Ferrocement structural stucco acts, looks & feels just like a standard, rough concrete surface.


See our Galleries for examples of different exterior surfaces on am-cor Kits.

What kind of interior finishes are available?

Customers have finished the interiors of their am-cor Kits with:

    • gypsum drywall/sheetrock (cheapest, most prevalent)
    • interior wood paneling
    • interior plaster/stucco (more labor intensive, most durable & professional)
    • cement board (similar to drywall, but stiffer, stronger, more moisture resistant, more expensive)
    • tile (marble, ceramic, etc.)
    • interior laminate/polycarbonate paneling/boards (usually used in commercial/retail, sometimes residential)
    These surfaces are applied in the same manner as typical light gauge steel framed construction.
    Basically, any standard interior finish product can be applied to the interior frame of an am-cor Kit. Often the drywall, cement board, and plaster stucco surfaces look the same from a distance, but stucco & cement board are more durable: they feel more solid and do not scratch or dent as easily as drywall.
    Do I need formwork for my floor slabs?

    No. Your am-cor Kit's exterior wall panels act as the slab formwork. See also:

    How do I weatherproof exterior surfaces?
    Basically, the same as you would weatherproof any concrete surface.
    A number of materials can be used for weatherproofing amcorite exterior wall and roof surfaces. Virtually any finish material which is weatherproof, and is applicable for use on concrete and cement surfaces will be effective. Beware plastic based finishes subject to deterioration from Ultra Violet (UV) sunlight exposure, as they will eventually crack shrink and peel, leaving points of moisture penetration. Compare advertising claims with product warranty limitations. amcorite is extremely durable and you want an equally durable finish coat.
    Below grade, standard concrete vapor barriers are used.
    Can EIFS be used over am-cor Ferrocement surfaces?
    Yes. EIFS (Exterior Insulation and Finishing Systems) can be used with the am-cor System. To the EIFS installer, the Ferrocement structural skin is the same as a poured concrete or concrete block wall surface.
    Is experienced labor required for am-cor construction?
    NO!

    Contractors & Builders
    You don't need to rely on highly-skilled, but expensive tradesmen. Our prefab Kits provide the business opportunity for builders and contractors to:
    • Perform work faster & collect payment sooner
    • Bid competitively
    • Greatly reduce site time & labor
    • Generate greater & faster performance from building crews
    • Do more work in less time = greater net income
    • Lower site overhead costs: no cutting, no measuring, no cartage fees, no shell construction waste
    • Higher profit margins: consistently high quality and life-safe buildings at low cost
    The am-cor Field Manual is easy to read, fully illustrated, and is a great help to the supervisor. He does not need to pore through complicated architectural & engineering drawings in order to assemble the building structure.
    This leads to:
    • greater field efficiency
    • less chance of error
    • higher production levels
    • predictable cost
    Please see our Professionals section for more information.


    Owner-Builders
    If you are inexperienced with normal construction methods you can still successfully assemble and coat your am-cor Kit.  No measuring or cutting is required.
    Your Field Manual has a full description of the Construction Sequence, as well as detailed illustrated instructions on how to line out your building, excavate, pour footers and concrete floor slab, etc.

    Check out our DIY section for more.

    am-cor Kit assembly is easy, fast, and fun. am-cor prefabricated panels are light weight and clearly marked. Their positions are shown on the Panel Placement Diagrams of your am-cor Field Manual.

    Coating the assembled panel Kit with amcorite Ferrocement mixture is done either with by trowel or spray. DIY applicators quickly become proficient with either method.

    Subcontractors usually install roofing, insulation, drywall, electrical, plumbing, and mechanical services; however, you can purchase how-to books on the internet and at building supply stores, to learn these trades as well.
    Do I need to run electrical wires in BX cable?
    No. BX cable, aka armored cable or metal sheathed wire, is not necessary in am‑cor Kits. Electrical conduit is also not required.
    The am‑cor System conforms to the IBC, IRC, and NEC, which do not require armored cable in steel studs if grommets are installed before running electrical wire through stud service holes. am‑cor Kits come standard with grommets, just so you don't have to worry about this!
    Do I need a crane?
    For light residential: No.
    For multistory commercial/multifamily: Not required, but it helps speed things along.

    am‑cor Panels (wall, floor, roof, etc.) are designed to be placed by 2 able-bodied people. Panels are fabricated from lightweight carbon steel, so they're easily transported, and do not require a crane.
    Panel Crane DeliveryPanel Crane DeliveryDrywall Crane DeliveryDrywall Crane Delivery

    However, if you have a large project with multiple floors, consider using a crane to quickly place the panels on the next story. If you have a big project, you'll most likely use a crane for moving other material as well (e.g.: drywall, etc.).
    Do I need to frame out on the interior for services/finishes?
    No. The Ferrocement skin of an am‑cor wall goes on the exterior of the panel, leaving the interior hollow for running services and applying finishes.
    Electrical wire in am‑cor Wall CavityElectrical wire in am‑cor Wall CavityElectrical conduit in am‑cor Wall CavityElectrical conduit in am‑cor Wall Cavity

    No "Floating Corners"
    You wont have extra/remedial work on the interior before installing electrics, plumbing, insulation, and drywall. For example: all wall, ceiling, and floor corners and panel junctions are preframed; you won't come to a corner and find nothing to screw to!

    See also:
    How is continuous insulation installed in an am‑cor structure?
    In order to meet ASHRAE requirements for continuous insulation, you have a number of options. Customers have accomplished tight, continuous insulation in am-cor buildings by using assemblies detailed under Super and Passiv in our Insulation section.
    Also, am‑cor ExoStructures can wrap the exterior of an existing building in a complete weatherproof, structural and insulating Ferrocement barrier.

    Poor Man's PassivHaus

    The Super Wall & Super Roof assemblies, aka the "Poor Man's PassivHaus", provide excellent insulation performance for a minimal price increase: the building's structure is completely separated by thermal breaks from interior conditioned space. See these assemblies and more in our Insulation section.

    See also:
    How are air barriers installed in an am‑cor structure?
    Generally, your am‑cor building has a number of air barrier assemblies, which conform to the relevant ASTM E standards:
    • The amcorite Ferrocement unibody exterior skin forms a continuous barrier, eliminating air infiltration around your walls, floors, foundation, and roof (if a Ferrocement roof).
    • We recommend a water-resistant exterior finish coating over the structural Ferrocement skin, for added protection.
    • We recommend the Super level of Insulation for walls & roofs. This includes at least 2" (5cm) of closed cell foam insulation, forming a continuous interior air & vapor barrier, and covering all wall/roof/floor intersections.
    Do you use expansion joints?
    We specify expansion joints with the same requirements as standard concrete construction, at approximately every 120 lin.ft. of wall.
    Don't stucco homes have cracking problems?
    You're probably familiar with stucco finishes over wood framing. This particular method of construction has unfortunately given stucco exteriors an unwarranted reputation in the USA over the past few decades.
    Cracking and structural problems in wood & stucco buildings is directly related to moisture and the incompatibility of these two materials: the building's wood frame expands and contracts at a different rate than the stucco exterior. The problem is exacerbated by moisture, as the wood will swell and rot.

    Since steel and cement have approximately the same thermal expansion coefficient, we don't have these issues. The oldest am‑cor structure is approximately 17 years old, with no reported problems.

      Have a question that's not answered in the FAQ? Let us know! You can also search this site for your question.