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ZIMMERIT:
by Donald Spalding
Production and Application Methods
From: AFV NEWS, Jan-Apr/1983 issue
This information is from a secret British Intelligence Objectives Sub-
Committee report. The information is now unclassified and entitled,
"Zimmerit" Anti-Magnetic Plaster for AFVs, which was reported by Major
J.W. Thompson and Mr. C.E. Hollis. The report is dated July 1945, and
is not complete due to insufficient information, or the failure to locate
persons with detailed knowledge of the subject.The investigation was
started with the hope that a way might be found to defeat magnetic mines
used against British armor in the war with Japan.
In 1943 the Germans adopted a thick coating for the vertical armored
surfaces of their tanks. This coating was designed to defeat the affects
of mines placed on armored vehicles, mainly tanks, by determined Russian
infantry assault teams. The mines were attached to the tanks and held in
place by magnets built into the bottom of the mines. The function of the
"zimmerit" was simply to provide a non-ferrous magnetic gap between the
steel armor and and the magnets, in other words a non-magnetic stand-off.
Early in 1944 samples of zimmerit were taken from captured vehicles and
instructions for its use obtained from prisoners of war. The composition
of zimmerit was analyzed by C.S.A.R. and found to be the following:
Polyvinyl Acetate-25%, as binder or glue Wood Fiber-10%, as filler
Barium Sulphate-40% Zinc Sulphide-10% Ochre Pigment-15%, for the
dark yellow color.
On August 14, 1945 the investigating team visited the Henschel Werke at
Kassel, Germany and interviewed the Director of Production and
Production Engineer. The following information was obtained. The
zimmerit was received in drums from Chemische Werke Zimmer in Berlin,
but they thought production had taken place in various centers because
of the large scale demands, and because of factory dispersal.
The material arrived in a consistency of soft putty (others have compared
it to paste, plaster or plastic). It contained a volatile solvent smelling
like acetone. No thinners were added before use as it worked very easily
even when handled by inexperienced personnel.
The surface of the tank did not need to be prepared before applying
zimmerit, but it was normal to coat the vehicle with anti-corrosive primer.
The zimmerit was applied to the surface in two coats, using a sheetmetal
trowel. The first coat was 5mm thick and was marked out in squares using
the edge of the trowel. This coat was allowed to dry at ordinary
temperatures for 24 hours. The second coat was applied thinner and
marked in wavy lines with a metal comb. The criss-cross squares increased
the adhesion of the second coat, while the comb markings gave a camouflage
finish, plus poor contact for mines.
After the application of both coats, the surface was treated by a gas
blow-lamp to harden it. This took about an hour per tank and no difficulty
was experienced in getting satisfactory hardness without the zimmerit
becoming brittle. (I have seen samples of aged zimmerit and it reminded
me of compressed sawdust.) During the hardening process the solvent was
removed by the heat of the blow-lamp on the surface. The chief thing to
watch was not to leave any soft spots which could be brushed off the
vehicle if not hardened properly. If the zimmerit was not heated with
a blow-lamp it took eight days to harden. This was impractical considering
the urgent need of tank delivery to the front.
The Production Engineer of Henschel Werke said that the company did not
help in the development of zimmerit, but simply applied it to vehicles.
He thought that zimmerit was dropped late in the war due to the development
of better anti-tank weapons. No mention was made of how successful zimmerit
was, however, when the British Army captured the Henschel Werke they
removed about 100 tons of zimmerit.
The investigating team next visited the Karl Freudenburg A.G. in Weinheim,
Germany and talked with the companyÍs Polyvinyl Acetate experts.
Again, this company had not helped in the development of zimmerit, but
did work on the P.I.B. mineral oil adhesives for sticky bombs. The Polyvinyl
Acetate was used as an emulsion in camouflage paints and as a solvent such
as Ethyl Acetate and Toluene during the war. It was mentioned that C.W.
Zimmer of Berlin was well known for paint manufacture during that time,
and probably used Polyvinyl Acetate.
On visiting I.G. Farbenindustrie A.G. Hochst, Germany, the Plastics
Development Manager and Production Manager were interviewed. They said
that they had heard of the C.W. Zimmer Co., but also knew nothing of the
development of zimmerit. It was also mentioned that such things were kept
secret. After referring to the companyÍs records it was learned that
Mowilith 20 (a Polyvinyl Acetate) was sold to the C.W. Zimmer Co. in
July 1943, but they had no idea if the company or its personnel still
existed.
The general properties of Polyvinyl Acetate were discussed. Mowilith 20
was 50% benzene solution (this is what smelled and was burned off with
blow-lamps). It had an average MW of 3500 (Staudinger viscosity method,
1 - 2% solution) and a melting range of 40 to 50 degrees C.
It was also confirmed that the blow-lamp would remove the solvent and
adhere the zimmerit to the armor, thus increasing its resistance to shock.
In regard to adhesion, it was suggested that a clean or just painted
surface would be better than a greasy or rusty one. Also, that Polyvinyl
Acetate with a pigment mixture (zimmerit had 15% ochre) were somewhat
water-resistant, but due to thermal behavior of Polyvinyl Acetate its use
was limited in plastics as it became brittle when cold.
In conclusion, the team decided that the C.W. Zimmer Co. was responsible
for zimmerit and every effort should be made to contact them. They also
were wondering if zimmerit, thinned down, could have been sprayed on
vehicles to speed up application time. However, no follow-up research was
done due to the end of WW2.
I wish to gratefully acknowledge the help of the staff of the Imperial
War Museum who made this article possible.
_____________________________
HL Panzer III & IV, HL Persing, HL Bulldog, T34/85 upgraded with HL, Tamiya Sherman and King Tiger.
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