Foam Core Stress-Skin Shell Method for Insul-Tanks This   method   creates   two   very   thin   and   strong   shells   that   are   comprised   of   a   unique,   ultra   high-performance cementitious   composite.   This   special   high-strength   coating   and   is   hand-applied   with   a   trowel   to   both   sides   of   2 inch   thick   extruded   polystyrene   insulation   panels   and   embedded   with   layers   of   fiberglass   grid   reinforcing   and finished with a brush-on glaze of similar material. The   rigid   blue   foam   panels   are   often   called   ‘Dow   Board’   and   they   come   in several   thickness   and   varieties   such   as   High-Load   Dow   Board   that   has   a   higher compressive   strength   than   the   regular   15   psi   Dow   Board.      The   Insul-Tanks   use 2   inch   thick   regular   Dow   Board   that   comes   in   the   4   feet   by   8   feet   by   2   inch sheets. The   two,   very   thin,   surface   shells   transform   the   foam   into   very   rigid   and damage   resistant   material   because   the   high-strength   composite   and   reinforcing create a stress-skin, or structural sandwich, effect.   The    composite    wet    mix    plaster    and    the    finish    glaze    are    both    made    by combining   special   additives   that   are   used   for   Ultra   High   Performance   Concrete with        pre-bagged        polymer-modified cement.      This   polymer-modified   cement   is readily    available    in    Building    Materials Supply   Outlets   that   carry   plaster   supplies.      It   is   used   as   a   base-coat   for   EIFS (Exterior   Insulation   and   Finish   System)   as   is   the   special   fiberglass   mesh   that is   used   with   it.      Typically   the   base   mix   and   glass   make   a   sturdy   shell   for EIFS   but   adding   the   water-reducer/superplasticizer   called   Eucon   SPJ   and   a refined   pozzolan   called   Micron   3,   greatly   reduces   the   porosity   and   increases the    density    of    the    cement    based    shell    resulting    in    a    harder    and    more chemically resistant shell.  Adhesive   Base   Coat   Mix:       This   usually   comes   in   50   #   bags   and   is   used   as   plaster   for   embedding   fiberglass   mesh onto   foam   board   for   the   exterior   of   buildings.      It   is   called   adhesive   base-coat   because   it   adheres   the   fiberglass reinforcing   to   the   foam   while   making   a   hard   protective   shell.      The   finish   system   that   goes   over   the   adhesive   base coat   is   usually   a   sprayed   stucco   texture   of   rubberized   sand   to   make   a   nice   smooth   sandy   finish.      The   adhesive base   coat   mix   is   a   true   polymer   modified   cement   that   consist   of   about   50   percent   Portland   Cement,   40   percent fine   quartzite   sand   and   10   percent   dry   (high-solids)   acrylic   usually   an   acrylic   vinyl   acetate   co-polymer.         Some common   brand   names   are   Dryvit   Primus   and   UltraKote.      They   come   in   50   pound   sacks   that   cost   between   24   and 35 dollars each.  For this high strength version of this mix, it is necessary to only mix up a small 64 ounce batch. Crack-Free   Fiber   Glass   Mesh      This   mesh   is   specially   engineered   for   a   cementitious   matrix   because   it   is   has   a light   rubberized   coating   to   prevent   alkali   chemical   attack   on   the   fiberglass.            This   fiberglass   mesh   comes   in   150 feet rolls that are 38 inches to 48 inches wide and that cost between 85 and 125 dollars each.  The   fiberglass   mesh   is   cut   to   match   the   layouts,   the   planned   plaster   area   for   a   batch,   so   that   two   or   three   layers will   be   used.      The   layout   is   drawn   onto   the   foam   with   a   marker.      The   layout   is   between   6   and   10   square   feet   and will   use   the   mix   that   is   about   ½   gallon.      An   additional   line   that   is   inset   one   inch   from   the   edges   of   the   layout   is drawn   to   denote   the   overlap   area   to   the   adjoining   pieces.      On   the   overlap   area,   the   fiberglass   is   not   covered   with extra   composite   material   or   a   glaze   so   the   overlap   can   be   seen   and   so   the   overlap   area   is   not   thicker   than   the   rest of the shell. Other Uses of this Foam Core Stress-Skin Shell Method Besides   the   Insul-Tanks      this   basic   shell   method   can   be   used   for   many   things   where   a   durable,   water-proof   and easy   to   shape   and   smooth   surface   is   desired.      The   insulation   really   helps   the   material   to   serve   other   important purposes.  Some of the other uses for this Foam Core Stress-Skin Method are: Cantilevered Countertops and Shelves  – The base material is easy to shape and sand.  (Insert Image)    The   enhanced   shell   material   is   very   durable   and   easy   to   repair.      A   2   inch   shelf   can   be   fully   supported   from   one side,   provided   it   is   bonding   with   the   same   material   as   a   backing   that   is   mounted   to   the   wall   or   a   self   supporting unit that sits on the floor. This   allows   more   open   designs   for   counters   such   as   counter   tops   that   do   not   need   cabinets   below   for   supports.     Open shelves can be placed below and above. Self-supporting   Prefabbed   sections   can   be   brought   inside,   or   used   as   durable   outdoor   kitchen   elements   and assembled   to   make   beautiful   counter   top   and   shelf   assemblies   transforming   a   bare   room   or   patio   into   a   functional and   beautiful   kitchen   The   cantilevered   shelves   attach   to   the   backing   with   a   small   radius   instead   of   a   sharp   corner so   it   does   not   dark,   recessed   and   dusty   corners   where   spiders   can   build   webs.      That   web-free   corner   combined with   the   more   open   design   enabled   by   the   stress-skin   effect,   makes   the   kitchen   and   bathroom   designs   easy   to clean and brings in a new element of simplicity to design that was not available before. Bath    &    Shower    Details     –    The    material    is    well    suited    for    bathtubs,    showers    and    bathroom    sink    &    shelf assemblies   the   same   as   the   kitchen.      Finishing   the   smooth   glaze   on   the   high-strength   composite   with   chlorinated rubber paint makes for an easy to clean and durable surface.  Cabinets,   Doors   and   Windows    –   This   is   a   great   medium   for   making   decorative   doors   and   windows   that   have complex   shapes.      For   making   hatch   designs   that   are   more   curvy   than   square   doors,   the   medium   allows   you   to sand   precise   shapes   that   will   make   a   good   weather   seal.      You   can   make   conventional   doors   and   window   frame designs as well, but the insulation here makes this medium better. Surface   Paint    -   The   surface   shell   is   very   dense   and   hard   but   bonds   to   the   chlorinated   rubber   paint   better   than other   cement   shells   such   as   swimming   pool   concrete.      This   is   because   the   sand   aggregate   in   the   enhanced polymer-modified   mortar   mix   is   much   smaller   and   so   will   not   flake   away   or   weather   away   as   quickly.      The harder   mix   allows   the   swimming   pool   paint   to   endure   warmer   temperatures   because   of   the   better   bond.      If   the paint   does   show   signs   of   weathering   over   the   years,   a   fresh   coat   can   be   applied.      If   an   epoxy   paint   is   preferred   for longevity,   the   composite   can   be   sanded   and   prepped   for   an   epoxy   paint,   that   will   endure   heat   better   and   is   what   is typically   used   for   hot   tubs,   but   the   epoxy   paint   could   fade   in   the   sunlight   whereas   the   chlorinated   rubber   endures ultra-violate   better.      The   chlorinated   rubber   swimming   pool   paint   may   last   longer   on   this   particular   composite design,   even   though   epoxy   based   swimming   pool   paints   will   last   longer   on   conventional   concrete.   Both   are   good options   but   on   this   shell,   it   is   easier   to   prepare   the   rubber   painted   surface   for   a   new   coating   of   epoxy   swimming pool paint. Installing   Hardware,   such   as   hinges   and   latches    -   Hinges   and   latches   bond   differently   to   this   medium   that   to wood.   The   bond   is   more   durable   because   the   anchor   into   the   shell   material   on   the   surfaces   rather   than   in   the middle.      The   pins   or   bolts   that   support   the   hinges   or   other   hardware   go   from   one   side   of   the   stress-skin   shell   to the   other   and   anchor   to   the   plane   of   the   shell,   by   using   washers   that   are   layered   into   the   composite   and   fiberglass.     In   wood,   a   screw   will   rely   on   a   friction   bond   on   the   inside.   This   bond   can   loosen   over   time   as   repeat   strains   are placed   on   the   screw   or   as   the   wood   shrinks   and   degrades   over   time.   Plastering   the   hardware   into   both   of   the supporting   shell   makes   it   so   that   bending   strains   placed   on   the   hardware   will   not   weaken   the   connection.   This   is because   the   strains   are   more   in-line   with   the   direction   of   tensile   and   compression   reinforcing   on   the   hardened shell. The   expected   deflection   caused   by   strong   bending   strains,   such   as   hanging   on   a   door   or   cabinet   door,   strains strong   enough   to   damage   the   stress-skin   shell   surround   the   hardware,   are   not   likely   to   dislodge   the   hardware because   the   pull-out   resistance,   the   twisting   resistance   are   all   fully   countered   better   than   the   breaking   resistance around the hardware, meaning the stress-skin hull would break before the hardware pulled loose.
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