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Frequently
Asked Questions - Using Film Plastic |
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1.
Should I use a single or double layer of plastic for my high
tunnel? |
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2.
What type of plastic is used to cover a high tunnel? |
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3.
How do I repair small tears in plastic covering? |
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4.
Is it possible to use 4-year film plastic for longer than 4
years? |
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5.
Why does film plastic sometimes deteriorate where it contacts
the high tunnel structure? |
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1.
Should I use a single or double layer of plastic for my high
tunnel?
A double layer of plastic will significantly
increase your average daily
temperature. This may be of particular importance if you plan
to grow or harvest vegetables during late fall and winter. An
inflation fan will be needed to blow air into the area between
the two layers.
(Jett)
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2.
What type of plastic is used to cover a high tunnel?
Four
mil, 4-year, greenhouse-grade polyethylene is suitable plastic
for covering a high tunnel. (Jett) |
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3.
How do I repair small tears in plastic covering?
A
special tape is available for repairing ripped polyethylene.
It can be purchased in various widths from greenhouse suppliers
such as Hummert's and FarmTek. For most effective patching,
delay repairs until the sun in shining so that the plastic around
the tear and the tape are warm. Thoroughly clean the area around
the hole with glass cleaner. Patch with tape on both the inside
and outside of the tear, if possible. Alternatively, a patch
may be cut from a section of extra polyethylene. Place the patch
over the tear and tape the edges with poly repair tape, followed
by taping over the entire patch. These methods result in strong
patches that will hold air pressure. (Compiled by
Williams from
hightunnel.org listserv). |
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4.
Is it possible to use 4-year film plastic for longer than 4
years?
Greenhouse
location, ultra-violet light and temperature exposure,
greenhouse structure design, film plastic installation
practices, single-verses double-layer use, and maintenance of
the covering material are all factors that influence the
longevity of film plastic. Greenhouse polyethylene
producers include enough ultra-violet inhibitors to protect
the film plastic from degradation for 4-years of northern
exposure. While polyethylene manufacturers all know of
instances where growers report that their film plastic
outlasted the warranted 4-year life, additional longevity is
possible but not guaranteed. (Calabro) |
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5.
Why does film plastic sometimes deteriorate where it contacts
the high tunnel structure?
Film plastic is often weakened when in
contact with greenhouse structural components, especially PVC framing materials.
The background on this starts with the green tint greenhouse films produced
from 1960 through the early 1980s, which used a nickel-based
ultra-violet (UV) stabilizer that was not affected by free chlorine, fluorinated
hydrocarbons, and the volatile plastizers found in PVC. By
1983, long-life films were UV-protected not by the nickel-based
UV-stabilizer, but by clear UV-inhibitors called 'hindered amine light
stabilizers' (HALS). These films had high clarity and did not darken
with age. One of the drawbacks with the HALS UV-stabilizers is that as the
film is exposed to free chlorine, fluorinated hydrocarbons, selected
pesticides, sulfur, and volatile plastizers found in PVC pipe, the
stabilizer complex becomes inactivated. When this happens, the life
of the greenhouse film is shortened, especially where it contacts the
PVC. For this reason, all polyethylene manufacturers do not advocate
direct contact of long-life polyethylene with PVC pipe.
Sisal baler twine, which is often used for plant support and
may be tied to the purlins for this function, can also cause breakdown of
polyethylene. The petroleum-based preservative will,
over time, degrade the polyethylene. (Calabro)
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Nick
Calabro has over 20 years experience in the film plastics
industry and is currently Northeastern Territory Manager for Klerks
Plastics. He can
be contacted at calabron@klerksusa.com or (phone) 330-686-1207.
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