protectionfromweather, rodent, insectand wateringress. Exterior wallsare
constructedof numerousmaterials suchas precast concrete, tilt up concrete,
cement block, metal,insulatedmetalpanelsor combinationsof the materials
depending on the size and functionof the facility. Precast, or tilt up (pouredin
place), concrete walls are usuallypreferredin my experience.Theyare more
durable, withstand morephysicalabuseand,in many instances, haveproven to
be aboutequalin cost to othertypesof exteriorwalls.
Whatevertypeor typesof wallmaterial and constructionusedtheyshould
conform to standards of sanitary design and construction according to
Katsuyama (1993). The walls should be constructed to be rodent- and
weatherproof. Thismeansthatthe juncturesof the roof/walland the floor/
wallmust be sealed to prevent insectentryas wellas outside weather.
Experiencehas shownthat the bestwallsfor a foodprocessing plantare
poured concrete that havebeentroweled smoothon the inside surface to a
standardof no morethan1/8 inch(3.20mm) diameter holeper square foot
(0.1 sq m). Pouredconcrete wallsdo not haveseamsthat requirecaulkingfound
in precast or tilt up construction.Pouredconcrete is usuallymore expensiveand
requires on-siteconstructionof formsand finishing. However, poured concrete
in areas where precastingor tilt up construction is not available or feasiblemay
be the onlytypeof concrete wallthat can be used.
Precast or tilt up walls haveproven to be a rapidand economical wayof
erecting a foodprocessingplant. Theirmaindisadvantagesare the timeand
expense necessary to adequately caulk all the jointsand seamsbetween panels.
The caulkingmust be periodicallymaintained.A relatively new(sinceabout
1990)innovationusing notchedbeams, notchedprecastwallpanels and double-
tee precastroof panelsis beingusedsuccessfullyon foodprocessingplants.The
technique(called pocketbeamconstruction)entails precastingthe wallpanels
and the roof support beams complete withnotches largeenoughto accommodate
the precast double tees of the roof panels.Whenlifted into place,the double tees
fit into the notchesratherthanresting on top of the beamsor walls.By fitting
insidethe notch, the dust-collecting flat surfaceson top of the beamsor wall
panels that are usually associatedwiththis type of constructionare eliminated. It
is thena simplematter to fill and caulkthe spaces around the double tees
creating a cosmetically attractiveand sanitarystructure.
A wordof cautionaboutprecast,tilt up and concrete blockshouldbe noted.If
a parting agent(sometimes knownas a releaseagentor oil) is usedto facilitate
the removalof the panelor block fromthe form,the agentshouldbe testedto
make sure it is compatible withany wall covering(epoxy,paint, etc.)beforeit is
used.If it is not compatible,peelingwill result and,as foodprocessorsknow
well, peeling paintsare not welcome in foodprocessingplants.
Rodents like to burrowunderbuilding foundationsto gainaccessto the plant
throughopeningsin the floor.Rodent-proofingshould be incorporatedinto the
initial design of the facility, especially the walls. For example, Graham
(1991a,b) reportedinDairy,Food and EnvironmentalSanitationmagazinethat
for a slab floorfacilities, the wallfooters should be constructedwitha rodent
186 Handbookof hygiene controlin the foodindustry