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Detailed Instructions for Inserting Double Glaze Unit

06/07/2020 Double Glazed Window 0

Unless you are an expert painter, it is recommended that all beading is painted before installing the window. You will just need a single coat of paint to touch it up when installed.

Step 1. Ensure frame is clean

It is important to remove all traces of the silicone. This can normally be done best by dragging a chisel or putty knife along the edge. Use a brush to remove all dust and debris.

Step 2. Check and clean the window unit

Often there will be small amounts of sealant on the front or rear of the window unit. This can be removed using a razor blade in a window scraper. There also may be lumps of adhesive on the edge of the unit. These can be gently shaved of using a putty knife, chisel or window scraper.

Step 3. Check the window fits

Lift the new window into the frame at the top, resting it on the edge of the window sill. Make sure you wear gloves to reduce the chance of cutting yourself on the glass. Place 4 rubber setting pads, 3 mm thick, at the bottom of the window frame for the glass to rest on. Use a suction cup to lift the unit and place it in the frame. If it doesn’t fit, you will need to use a chisel or router to enlarge the window frame. Push on diagonally opposite corners of the glass unit to check it does not ‘rock”. This could be because there is some residual cement on the frame or the window frame has warped. If necessary you may need to chisel out some of the frame, or add additional sealing tape.


Always wear gloves. It is recommended that you use a proper glazier’s suction pad rather than a cheap one. They cost more ($130) but lift twice the weight and have a safety feature that indicates if the seal is failing. It is difficult to handle the window unit on your own and it is recommended that two people ease it in. A normal unit weighs 20 KG per sq metre. If the unit is over 1 square metre, a second person is essential. If the window exceeds 2 square metres, some mechanical lifting device will be required. When the window is removed again, ensure it is placed on a clear soft surface, both on the bottom and on the rear. Resting the unit on concrete or leaning it against brickwork will cause chipping or cracking.

Step 4. Add the sealing tape

This should be attached to the frame on all 4 sides. Do not stretch the tape. It is easiest to hold the tape roughly in position with one hand and use your finger to line it with the edge of the frame and your thumb to push it down. When all sides are done, remove the white tape.

Step 5. Add the Setting Blocks

Add 4 setting blocks on the sill, 2 under each piece of glass. These blocks are approximately 3 mm thick and will ensure the base does not sit in moisture and that each sheet of glass is supported. Often the window frame is sloped to allow water to run Off. If so chisel out the frame so that the rubber supports are flat and support both sheets of glass. If the glass is too tight to fit supports, don’t worry, they are not esential.

Step 6. Insert the window

If you wish, place a bead of silicon along the base for the glass to sit on. Insert the window as per step 3 and add a stop so that it can’t fall out. Seal around it with silicone, making sure that it is “Neutral cure” silicone not “Acetic Cure”. The Acetic cure silicone can react with the seal and lead to failure.”Neutral cure” silicon is the one used on metal downpipes.

Step 7. Cut external beading (recessed)

In most cases the window frame will extend beyond the glass unit. In these cases it may be possible to reuse the old beading, provided it is wide enough. Otherwise, use the 12 mm tri-quad. I got this tip from a builder. Cut the top and bottom bits of beading at right angles, then cut the verticals at 45 degrees so they cover the horizontals. It looks neater and it is less likely for water to enter the joint. I use a drop saw with a fine blade to cut the wood, but a mitre board works well.

Note: It is best to use the 12 mm quad to ensure the black spacer in the unit is covered to protect it from direct sunlight.

Note: If the window frame is sloped at the bottom, an improved seal is obtained by trimming the quad at an angle so it sits better against the glass and the frame – but its a lot of work!.

Step 8. Add external beading (recessed)

Hammer small nails into the wood, making sure they come out on the side of the wood that sits against the frame, not the glass. This is the wood that has a right angle cut, not the edge that has a 45 degree cut. Push firmly on the glass when hammering in the nails. Be careful not to hit the glass with the hammer as it can crack. It is worth wrapping a piece of rubber around the hammer to minimise this risk and use a nail punch.

Step 8(a). Using a nail gun


now use a nail gun to do it. It is much faster, but you can break the glass. Using 20 mm brads reduces the risk of the brad hitting the back sheet of glass.

Step 9. Cut external capping(Overhang)

It some cases the glass unit will extend beyond the window frame. While you build up the frame using thin pieces of 4 or 8 mm rectangular wood, a better solution is to use a small hand held router to increase the rebate to 21 mm so that the glass extends a little beyond the frame. You can also order the window with a 8 or 10 mm gap although this does reduce the thermal performance slightly.

Step 10. Add external capping (Overhang)

Use a 30 mm cap to cover the frame. If you are capping all the way around, cut the capping at 45 degrees. If you are using capping on only one side, join it at 90 degrees. It is best to use screws as nails can pull out, although I find the nail gun holds it quite firmly.

Step 11. Paint the frame

You will normally need to paint the whole window frame on completion. Depending on your skill as a painter, you may wish to paint the beading before attaching it then just touch up any imperfections. If you get paint on the glass, allow it to dry and then use a razor blade and paint scraper to remove it.

Step 12. Remove excess silicon

This is the bit that most people miss out, but it makes a big difference. I normally allow 3 – 4 hours so that the silicon starts going off. Use a knife or chisel to remove the big bits of silicon. Then use paper towel and methylated spirits to remove silicon at the edge or in the middle of the window. Methylated spirits will also remove any black sealant on the glass. Often you find that silicon gets onto the paper and so you get more smears as you try to clean of existing smears, so changing paper regularly is important.

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