what is Double Glazing?
Put in simple terms, a window with two layers of
glazing. There are two types of double glazing, the earliest type is
Secondary Glazing whereby a second glazed frame, which is usually made from
aluminium, is fitted behind the main window. There is not much call for it
nowadays but there are still some useful applications for this type of
double glazing, (commercial installations, listed buildings, sound reduction
and for those that simply do not wish to change their windows). The second
type is called a sealed double glazed unit or D/G unit for short.
what is a double glazed unit?
A double glazed unit consists of two pieces of glass
separated by a spacer bar and hermetically sealed all around the edge. The
spacer bar is a hollow tube which contains desiccant (moister absorbing
granules') which will absorb any moister which is sealed into the double
glazed unit during manufacture. These tubes vary in width from 6mm to 20mm
and more, when this is sandwiched between two pieces of 4mm glass it will
give the makeup description for the double glazed unit i.e. 4-20-4 will give
the highest general specification used to-day for a 28mm unit. The
insulation value of double glazed units can be further increased by
replacing the air inside with Argon gas, this is done during manufacture
just prior to sealing. The edge of the double glazed unit is sealed with a
hot melt polysulphide sealant. Edge tape may also be used to cover the
edges, this does not form part of the sealing arrangement and is used to
provide comfort and a degree of safety during handling and installation.
what is a failed unit?
The symptoms of a failed unit is condensation forming
BETWEEN the panes of glass. This indicates that
the sealant has failed and allowed the ingress of moister sufficient for the
desiccant to become saturated and therefore ineffective and the moist air
will condense into water. The risk of premature failure is why it is so
important to use packers correctly during installation. I have seen all
sorts of inappropriate material used for packing, wedges of timber,
folded up cardboard even foam travel pads used during transportation of
units. Worse still is using no packers at all, never fit a double glazed
unit without packers as this can allow the unit to sit in water which may
gather quite normally in the rebate of your frames, this is why PVCu frames
have integral drainage slots machined into them.
Some people mistakenly think that condensation on the
outside is an indication of a failed unit. THIS IS NOT THE CASE if you can
wipe away the condensation the double glazed unit has not failed.
Installing double glazed units
These instructions are for installing
double glazed units into PVCu frames.
Starting with one of the
longest beads first, remove the glazing beads by pushing a sharp chisel or a
rigid paint scraper between the bead and the frame joint at approximately
the centre point. A sharp tap on the but of the tool should allow the bead
to be freed. It is most important to refit the beads in the same positions
as they were removed, they may vary in length slightly due to the
into position the glass packers approx. 100mm in from each corner.
(Intermediate packers should be used if the double glazed unit is wider than
the double glazed unit into the frame ensuring correct positioning on the
on one of the shortest lengths, fit 3 of the beads using a rubber mallet,
finally fitting the last bead by bending into position.
N.B. It is always best to
leave one of the longer beads until last as a long bead will locate and bend
Toe & Heeling
is essential that glass packers are used to support the double glazed units
to prevent them from standing in any water that may collect in the frame
rebate. This can cause failure of the seal of the double glazing and will
invalidate your guarantee if packers are not used. Packers must not cover
the drainage holes in the frame. Both leaves of the double glazed unit must
be supported by the packer, do not allow the packer to support one leaf only
as it may ?bed? into the sealant and cause failure of the unit.
Fixed glass and
top hung openers.
Side opening vents and doors
The objective of
?toe & heeling? is to transfer the weight of the glass onto the hinge side
of the frame. Correct use of this technique will give trouble free operation
once the vents have been set correctly. The vent should be flexed upwards if
necessary to allow the insertion of the top packers.
N.B. Adjustment of hardware should not be
attempted until the frames and glass has been correctly packed and
All double glazed units supplied by
Easyfit Window Warehouse are manufactured to B.S. and C.E.N. standards and
are of the highest quality available. All frames are supplied with the
appropriate glass packers.