GLAZING

GLAZING AND FIXING - TECHNIQUES

The methods described in this section are those commonly found in practice. Variations on these methods may be used in certain circumstances and as agreed by the parties concerned.

5.1 EXTERNAL GLAZING - SINGLE GLASS

External glazing is any glazing in which either side of the glass is exposed to the outside of the building. It includes inside glazing, in which the glass is inserted from inside the building and outside glazing, in which the glass is inserted from outside the building. The essential difference between external glazing and internal glazing is that in external glazing one or both surfaces of the glass are exposed to the weather and the glazing seal is required to be weather-resistant.

External glazing can be carried out in a wide variety of frames and using a variety of methods. The methods themselves are essentially common to a variety of frames and situations, requiring slight variation to accommodate different conditions. For simplicity these methods will be considered individually and will show the variations required to accommodate particular conditions and frame types.

(a) Glazing with Putties, types 0 and 1

(i) PUTTY FRONTING

This method is suitable for glazing into wood and metal frames without beads or grooves. Putty is used for both bedding and fronting. When the putty has hardened, the fronting serves to retain the glass in position but, to prevent displacement during the setting time, the glass should be retained by sprigs, clips or cleats, which remain permanently embedded. 11, method is only suitable for use in frames where at putty fronting can be painted and where the frame and glass are subject to minimal degrees of movement. It is essential that the putty fronting is painted within the time specified by the putty manufacturer in order to prevent cracking and loss of adhesion.

1. Check glass and rebate sizes. The edge clearance should be at least 2mm all round. The rebate width; should be at least equal to the glass thickness plus 10 mm to allow for approximately 1.5 mm bedding and 8 mm fronting putty.

2. Clean and dry the rebate, removing all spillage and accidental contamination, dust, etc.

3. Prepare the rebate.

Painted softwood frames are normally supplied already primed. Where this has not been done or the primer has deteriorated severely, a coat of priming paint made to BS 2521-24, or primer having equivalent properties, should be applied to reduce the porosity of the timber surface. Shellac varnishes and gloss paints should not be used as they seal the wood excessively and prevent setting of the linseed oil putty.

Absorbent hardwood frames, which are to be painted, should have two coats of the manufacturer’s recommended sealer applied to the rebate area, allowed to dry between coats and glazing should then be carried out with metal casement putty.

Non-absorbent hardwood and softwood frames, which have been treated with certain types of primer or preservative, which reduce their absorption such that linseed oil putty will not set, should receive at least one coat of the manufacturer’s recommended sealer to ensure minimum absorption. Glazing should then be carried out with metal casement putty.

Galvanised steel frames normally require no priming provided the galvanising has been made passive or has weathered. If the frames have been primed with calcium plumbate or zinc chromate paint, these should be checked to ensure that they are fully hardened before glazing takes place. Rubbing the priming paint gently with a cloth moistened with white spirit will indicate, if the priming paint is not removed, that it has fully hardened. The paint having hardened, glazing can proceed, metal casement putty being used.

4. Glazing

(a) Sufficient putty of the appropriate type should be applied to the rebate, Figure 45(a), so that when the glass is pressed into the rebate a bed of compound, known as back putty, approximately 1.5 mm thick, will remain between the glass and the rebate upstand.

(b) Before actually offering the glass to the surround, where necessary, setting blocks are pushed into position in the putty on the rebate platform. Except for small panes, not exceeding 0.2 ml, the glass should rest on setting blocks to centralise the glass within the surround. These blocks should be 25 mm to 75 mm long except at the bottom bar of vertically pivoted windows where a single block not less than 150 mm long should be used. Location blocks should also be used in opening windows to prevent distortion of the frame. Setting and location blocks for single glazing should be positioned as shown in Figure 44.

(c) The glass is then placed on the setting blocks, centralised in the opening and pushed well back into the putty, care being taken to ensure that no voids or spaces are left. This action squeezes surplus putty out of the rebate and should leave the back putty approximately 1.5 mm thick. A cluster may be used to prevent putty finger marks appearing on the glass. Location blocks, as required, should be positioned at this stage.

(d) The glass is then secured in the opening, Figure 45 In wooden windows, sprigs should be tapped into the surround against the face of the glass at not more than 300 mm spacing. For metal windows, the glass should be retained by clips or cleats fixed into the holes provided. These fixings should hold the glass in position until the front putty hardens.

(e) Further putty should then be applied and finished at an angle from the edge of the frame up to approximately 2 mm below the sight line for painting onto the glass and so creating a seal between the putty and the glass to prevent water penetration.

(f) The surplus back putty should then be stripped taking care not to cause an undercut where water may lodge, Figure 45(c).

(g) All putties should be finished with a light brushing ‘n order to seal the putty to the glass. The putty should be allowed to firm for not less than seven days before being painted. Painting, including the finishing coat, should be carried out by other trades. Within the required time laid down by the putty manufacturer in order to provide the protection necessary to ensure satisfactory weathering of the putty.

(ii) GLAZING WITH BEADS

This method is suitable for glazing, other than curtain walling and ribbon windows, in sheltered localities and for glass areas up to 2 m2. The method is only suitable for use in frames where the frame and putty can be painted and where the frame is subject to minimal degrees of movement. Painting should be carried out within the time required for the protection of the putty. Weather-proofing is achieved by paint and putty, the layer of putty being sufficiently thin to be load—bearing. Experience has shown that, when bedding into normal setting putties, the putty offers substantial resistance to displacement when pressed back to a thickness of 1.5 mm. Used in this way there is no need to incorporate distance pieces. If thicker layers of putty are used they will not be load-bearing and it will be necessary to incorporate distance pieces to accommodate wind loading during the setting period of the putty.

1. Check glass and rebate sizes. The edge clearance should be a minimum of 2 mm all round for wood and steel frames; the rebate width should be at least equal to the glass thickness plus 3 mm plus sufficient bearing surface to enable the bead to be fixed without over- hanging.

2. Clean and dry the rebate, removing accidental contamination, dust, etc. spillage and accidental contamination, dust, etc.

3. Prepare the rebate.

Painted softwood frames are normally supplied already primed. Where this has not been done, or the primer has deteriorated severely, a coat of priming paint made to BS 2521-24, or primer having equivalent properties, should be applied to reduce the porosity of the timber surface. Shellac varnishes and gloss paints should not be used as they seal the wood excessively and prevent setting of the linseed oil putty.

Absorbent hardwood frames which are to be painted should have two coats of the manufacturer’s recommended sealer applied to the rebate area, allowed to dry between coats and glazing should then be carried out with metal casement putty. Non-absorbent hardwood frames and softwood frames, which have been treated with certain types of primer or preservative to render them non-absorbent, should receive at least one coat of the manufacturer’s recommended sealer to ensure minimum absorption. Glazing should then be carried out with metal casement putty.

Galvanised steel frames normally require no priming provided the galvanising has been made passive or has weathered. If the frames have been primed with calcium plumbate or zinc chromate paint, these should be checked to ensure that they are fully hardened before glazing takes place. Rubbing the primer gently with a cloth moistened with white spirit will indicate, if the primer is not removed, that the primer has fully hardened.