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Units should be measured to allow approximately 1mm to 1.5mm clearance all round where the rebate depth is 7mm. Allowance should be made where the opening is not perfectly rectangular. Where the rebate depth is in excess of 7mm, additional clearance can be allowed, but always ensuring that the sight line of the perimeter seal is below the sight line of the back rebate.

Glazing Timber Fore putty

All rebates should be clean and clear of minor obstructions and brushed cleaned and primed. The rebate should be bedded with a non hardening compound (butyl) to provide a bed between the back rebate and glass of approximately 1mm to 1.5mm. The unit should be placed into bedded opening and pressed equally around the perimeter until the 1mm to 1.5mm back bed is obtained.

However whilst the back bedding should be a non hardening compound such as butyl commonly used, silicon is sometimes used but mainly on metal windows.

The unit should be held in position by sprigs, which are thin metal shaped diamonds which are fixed into the rebate with a sprigging gun.

The use of a sprigging gun ensures that the diamond sprig is less than 1mm from glass, and prevents any scratches to glass surface. The sprig should be set at 150mm centres or as necessary for small panes.

The fore putty should be carried out with Linseed Oil Putty or Steel Sash Putty for metal windows, as BS6262 to the rebate depth sight line or just below to allow for paint finish line over putty. Putty should not be painted for at least seven days. The minimum fore putty on rebate width should not be less than approximately 6mm. The function of fore putty is to protect the frame by shedding the water from the frame, and protect the double glazed unit from ingress of water which will cause unit breakdown.

It is important that the fore putty should be brushed with a fine duster brush to ensure that there is a good seal on the putty against the glass, and painting should overlap the foreputty by approximately 2mm to provide an important final seal. 

Glazing Timber Beads

All rebates should be clean and clear of obstructions, brushed clean and primed. The rebate should be bedded with non hardening compound (Butyl) to provide a bed of approximately 2mm between the glass and back rebate. The unit should be placed against the bedded back rebate and pressed equally around the perimeter until the 2mm back bed is obtained and only trimmed flush when glazing has been completed.

The rebate width should then be bedded with non hardening compound to obtain a very thin bedding not exceeding 2mm or gun grade which has a much thinner consistency. The timber bead which should be angled to provide a water shed and should be bedded against the glass by applying the compound to the front edge of the bead in sufficient quantity to prevent voids when fitted against the glass and excess trimmed, matching the water shed angle of the bead.

The finished height of the bead should be 2mm below the back rebate height to allow the painter to paint over the trimmed water shed angle of the compound to match the angled bead. The paint finish is important to provide protection against the rain and sun and the compound should be allowed to cure for at least 7 days before painting, and within 28 days.


Where timber beads are to be pinned into the rebate width is particularly narrow the beads should be pre-drilled with a very fine drill.

Glazing Method

Slimlite Self Cleaning Double Glazed Units are supplied with taped perimeter edges for protection and safe handling and glazing. Slimlite is unaffected by Linseed Oil Putty. Linseed Oil putty has proved to be satisfactory over a long number of years and provided it is applied correctly as mentioned above should last a lifetime. It is necessary to paint over the putty at least every 5 years inland and 3 years in coastal areas. When putty cracks it is because of lack of paint protection.

glazing methods

Metal Windows

Glazing Slimlite Self Cleaning Double Glazed Units to existing metal windows, after removing single glazing, and primed with metal primer. The existing single glazing was held in place by metal clips fitted into metal holes in the rebate. As the holes are not re-usable, the best method of glazing is to bed the back rebate height with approximately a 2mm bed of silicone and the unit is pressed back against the silicone which when cured in approximately a day or two will hold the glass permanently in place. The rebate width can now be foreputted with a steel sash putty to finish approximately 2mm below sight line to allow painting to finish to sight line. It is important that the fore putty should be brushed with a fine duster brush to ensure there is a good seal on the putty against the glass.


Sprigs, Sprigging Guns and Duster Brushes

Can be obtained from any company selling miscellaneous glazing tools.

windowsDouble Glazing Breakdown or Misting

This is caused by failure of the glazing method which must protect the unit seal from the ingress of water or moisture. All double glazing sealants used in the manufacture of double glazing units have a moisture vapour transmission rate when exposed to water or moisture, which will cause misting or breakdown eventually over a period of time. Where units are foreputtied, the putty must be painted and on to the glass to provide a seal to protect the putty from moisture ingress. Foreputty should be left for 7 to 10 days before painting and within 28 days. Similarly when glazed with beads and non hardening compound, paint or protective coating should be applied over the bead and on to the glass. Where timber preservative has been used, Manufacturer's instructions should be followed to prevent reaction with glazing compound. All Slimlite Units are edge taped with a special waterproof adhesive tape which helps to avoid damage during handling and importantly added protection from moisture or water ingress, which would inevitably cause unit breakdown.

It is recommended that timber windows should be painted every five years Inland areas and three years Coastal areas. However it is recommended that the paint protection of the glazing including the overlap on to the glass face, should be repainted every three years to maintain the required protection particularly with putty fronting. Ultra Violet has a detrimental affect on most paints, particularily on south facing elevations. However more frequent 'spot painting' may be necessary to maintain the required standard of protection.

BS6262 Section

BS6262 Section


Optional Extra Glazing Protection

extra protectionMost causes of misting in the cavity of double glazed units are a result of the glazing protection failing and allowing water into mainly the lower horizontal glazing rebate.

All current double glazing perimeter sealants have a water vapour transmission rate when contacted by water or moisture and in time will appear as misting in the cavity. Water or moisture in the glazing rebate unless rectified will eventually cause decay in the timber section.

As an optional added protection a small bead of low modulus silicone which is resistant to water can be applied as a small bead 2 to 3mm around the joint. between the outer edge of the unit and rebate which must be perfectly dry to ensure good adhesion between unit and rebate (see sketch) See adjacent painting recommendation.


Slimlite Guarantees

Due to the successful performance of Slimlite Self Cleaning Double Glazed Units we are now able to provide Ten Year Guarantees to clients and specifier providing comfort and assurance.



Slimlite with Low Emissivity Hard Coat applied during glass manufacture forming part of the glass – 10 years guarantee.
Slimlite with Low Emissivity Soft Coat applied by vacuum deposition after glass manufacture – 10 Years guarantee.