Secondary Glazing


Acrylic Glazing
Acrylic sheet is naturally UV stable and with careful cleaning and handling it should easily stay clear for a minimum of 10 years. Other products such as polystyrene are sometimes confused with acrylic as they look similar when new but these can quickly yellow or mist over. Acrylic is much lighter in weight than glass, safer to handle and especially good where children and the elderly are a concern. More about glass – acrylic is much warmer to the touch and is 4 times more thermally efficient. It has a higher light transmission and a lower sound transmission.

There are generally three thicknesses of acrylic sheet that are used in secondary glazing: 2mm, 3mm, 4mm. 3mm being the most popular.
Acrylic sheet is not as rigid as glass and this should be one of the considerations when choosing which thickness to purchase. If you are intending to fit glazing in your main rooms (i.e. lounge, dining room, kitchen) you may prefer to have a clear undistorted view through to your surroundings. (4mm or possibly 3mm depending on size). Alternatively in a little used bedroom 2mm/3mm might suffice. In general terms, the larger the glazing panel the thicker you would need to go for least distortion. Insulation does increase with thickness but only marginally. If you are hoping for noise reduction 4mm should be your choice.
2mm sheet is often bought on price but is usually the least aesthetically pleasing as it only lays flat across windows of relatively small size.
Having read all of the information, have a measure up according to the guidelines and call or email us for a quotation. All acrylic is cut to size for you, it’s then just a matter of installing the fixing system. If you have an unusual situation and require advice you can email a picture or diagram.

All plastic sheets should either be stored flat or supported by a board leaning at an angle of 80 degrees to the ground. If sheets are leant against a wall unsupported the downward pressure may cause distortion. Do not store in conditions of excessive heat.

Please contact us to request a small sample of any stocked material.
A demonstration panel is available for viewing in our shop.

Magnetic Fixing System
Possible applications: Listed buildings, Character residencies, Rented accommodation. Any situation where the existing window is best left unaltered. A financially economic option to replacement windows. Acceptable as an insulator towards your “Energy Performance Certificate”.
Benefits: Saves energy by keeping heat in and the cold out. Helps to cure condensation problems. Eliminates draughts (a few turnbuckle clips around the edge may also be required).

Information & fitting tips

The system consists of two self adhesive strips
1. A thin white finished metal strip that adheres to the window frame.
(This can be painted over at decorating time with an oil based paint – also recommended in rooms which have little heating to avoid the metal shim getting damp and corroding)
2. A black magnetic strip which adheres to the acrylic panel.
(The adhesive side of the magnet which shows through the
acrylic is coloured white.)
Both strips are 12.5mm (1/2”) in width so you will need a flat area around the window to accommodate this. Some older sliding sash windows have a moulded beading and it may be necessary to fit the panels beyond this point. Once fitted, the magnet provides a reasonably sealed air gap to help reduce condensation, provided that it is neatly butted up together at the corners. The joints of the window frame should also be checked as any unevenness will cause a weakness in the system allowing warm air to get into the air gap either beneath the metal shim or between the magnet and shim. Any problem areas can be levelled with normal filler and painted. The objective of secondary glazing is to create a gap between the cold outside air and the warm inside temperature. When the two meet, condensation occurs.
Simple tools for installation: Sharp Stanley knife, scissors (I have found that blunt scissors actually cut the metal shim better), pen, pencil. A small set square can be very helpful.

There is generally no advantage in taking the acrylic panel beyond the outside of the window frame any further than the required ½”. In fact it is by far easiest to measure the inside of the frame and then add 1” to accommodate the magnet on either side. You then know exactly where the metal shim has to be fitted to line up with the magnet on the panel. Watch out for any protruding window furniture. Check as to whether the frame is square and if not it would be wise to make the panel slightly larger to compensate.

Level out any uneven areas in the frame. Draughtproof the outside window as much as possible. Any cold air coming into the air gap may create condensation on the room side of the acrylic panel. Also, a very draughty window may cause the acrylic panel to “pant”. All surfaces around the edge of the window should be clean, dry and grease free to allow the shim to adhere properly (try methylated spirits). Any dust/dirt left on the existing window may be attracted to the acrylic panel after fitting due to static between the acrylic and its protective covering.


Carefully peel back about 1” (25mm) of the protective polythene covering all around one side of the acrylic and trim it off. Now orientate the panel so that you can work on one edge that will form the vertical side of the panel. Peel back about 2” (50mm) of the magnetic tape backing strip (red) and starting at one corner of the panel lay this end gently into position. It helps to keep your thumb on the outside edge of the acrylic to help line the tape up. Continue to peel off the backing as you gently “roll on” the rest of the magnetic strip. Try to keep your fingers off the exposed acrylic as much as possible to avoid extra cleaning after fitting. Once you have completed one side, using the Stanley knife trim the end of the magnetic tape off squarely (this is where the set square comes in handy). Continue to fit the remaining sides in the same manner making sure that you butt the corners of the magnet together as neatly as possible. After checking that the magnet is aligned correctly, using a clean cloth smooth down the strip, applying pressure and making sure that it has adhered properly.

Metal shim
With the glazing flat in front of you orientate it so that you can work on the edge that will form the bottom side of your glazing panel. Lay the metal shim white face down on to the magnetic tape, starting at the edge of the acrylic and mark the end with your pen to match the length of the magnet (again the set square can be helpful). Carefully cut the metal shim squarely along this line with your scissors. Leave this strip in position while you continue to cut the opposite end in the same manner. Then cut the remaining two sides to fit between the first two strips. On completion remove all four lengths of shim.

Fitting to the window – This section is much easier with two people – teamwork!
Hold the glazing panel up in position against the window. Looking through the edges of the glazing you should be able to make out the opening of the window frame. Try to centre the panel so that an equal amount of frame is showing along all edges (or none at all if your window is really square and the panel is the exact size for the opening). Once you are happy with the position take your pencil and mark around each side of the panel particularly at the corners. Remove the panel. It is sometimes difficult to draw the pencil line exactly on the edge of the glazing and it can therefore be slightly over size. You need to take this into account when applying the metal shim and sometimes use the line for a directional guide only. It is best to fit the bottom metal strip first as this will determine the positions of the other sides. Before you remove the backing strip (red) from any of the metal shim lengths always hold each one in position first to make sure that you are using the correct length and that you know exactly where it is going to go. Peel back about 2” (50mm) of the backing strip (red) and starting at one corner lay the strip very gently into position. If two of you are working together one person can hold the centre and opposite end of the shim to help keep it in line. Continue to peel off the backing as you gently lay the rest of the metal strip in position. Immediately check to see if the alignment is correct. At this stage, if there is a major problem you may still be able to remove the strip carefully before it adheres completely. If the white adhesive backing starts to come away from the metal STOP. Any minor inaccuracies are best accepted as they are as they will generally be hidden by the magnet on the glazing panel. In the same manner now fit one of the vertical strips starting at the bottom making sure that you butt the two strips together. As you progress around the frame you can keep holding the panel up to make sure that things are going in the right direction. After fitting the remaining side and top strips and checking that the shim is aligned correctly, using a clean cloth to avoid cutting your fingers, smooth down the shim, applying pressure and making sure that it has adhered properly. On completion place the panel into position. The magnet will “grab” as the panel gets close to the window. You can now remove the protective film from both sides of the glazing. The more you can keep your fingers away from the face of the glazing the less you will have to clean it. Don’t forget to clean your pencil marks off the window frame.

The acrylic may be cleaned at any time with a soft cotton cloth (j.cloths are abrasive). If very dirty a small amount of washing-up liquid can be added to warm water. If you have access to any anti-static cleaning fluid, a small amount of this applied with a cloth with help to reduce static and the attraction of dust (available over the internet).
Extremely draughty windows that cannot be sealed may require the addition of a couple of turnbuckle clips which I can supply. Wind entering the air gap from the outside can cause the corners of the acrylic panel to pop on and off or the entire panel to move slightly down the window frame. This also applies to doors which are closed without turning the handle/lock as the vibration can shake the panel downwards. There is no danger of the panel coming away completely.

Back to Top