corrosion of the other metal. This is the so-called
galvanic action or electrolysis that occurs when metals of
different position in the electromotive series are in direct
contact in the presence of an electrolyte. The common
metals used in construction are listed in the electromotive
series in the following order: 1-aluminum, 2-zinc, 3-iron
4-tin, 5-lead, 6-copper. When any two metals in this list
are in contact in the presence of an electrolyte, the one
with the lowest number is corroded. Also, the farther
the separation in the list, the greater the corrosion will be.
Thus with iron and copper contact in the presence of
water, the iron would be corroded more than lead in
contact with copper under similar any condition. Any
means that separates dissimilar metals will protect against
this action.
5-27. Perhaps you are beginning to wonder how
Figure 44. Glazing metal sash.
dissimilar metals can be used in layers as a single sheet of
metal. Let's take lead-coated copper as an example. The
like a flush door and may have either a hollow or
lead coating on the copper is of a lower number value in
insulated core.
the electromotive series and is affected by the corrosion
5-30. Metal doors seldom need repairing and
while the copper is being protected from corrosion. Also,
maintenance usually consists of tightening the bolts that
the two metals are consecutive (5 and 6) in the series,
hold the lock in place, or tightening or replacing screws in
and a minimum amount of corrosion is anticipated. The
the hinges and weatherstrip. Occupants usually correct
purpose of the lead coating is to protect the copper; in
the problem of loose screws and bolts, but you will
this case, it protects it in two ways, physically and
probably be called on to supply new or larger screws.
chemically.
When retightening of screws is required at frequent
5-28. Doors and windows. We have discussed the
intervals, you should substitute a screw that is one size
location and fastening of door post and window angles.
larger than the old one or relocate the hinge and make
Now let's look at the main units.
new screw holes. The weatherstrip on the jamb causes
5-29. Metal doors are preferred for prefabricated metal
very little trouble, but the strip along the bottom of the
buildings. There are two types of these doors. One type
door may get damaged or become loose. This threshold
has an angle iron, steel, or aluminum frame and a single
strip extends beyond the lower edge of the door and
metal covering that serves as the exterior surface. The
hooks into a groove in the threshold as shown in figure
frame is exposed on the inside of the building. The
43. Make sure that the strip is adjusted so that it fits into
other type of metal door has a metal frame with a metal
the groove. This type of threshold and weatherstrip is
covering on each side. This door is built
common in exterior doors that swing over a concrete
floor.
5-31. Window maintenance consist of tightening the
mounting screws in the frame, side panels, and the
U-shaped drip channel (gutter). Replacing glass in a
metal sash is a little different than working with a wood
sash. When you remove the old putty from the sash, you
must locate and save the metal glazing clips. Look at the
glazing clip shown in figure 44. This clip fits between
the edge of the glass and the frame. One end of the clip
fits into a hole in the frame, and the other end hooks
over the edge of the glass. Allow for the thickness of
these clips when you cut the new glass. Place a bed of
putty on the frame and press the new glass gently against
it. Use a screwdriver to install the glazing clips. The
clips will hold the glass in place while you are applying
the beveled layer of putty around the edge of the glass.
Figure 43. Weatherstrip installation.
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