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Glazing Recommendations for Double Glazed Sealed Units into Timber Frames.
Your Double Glazed Sealed Unit manufactured by RedKite Glass is to a high standard using top quality materials to BS5713 requirements.
Our Units are guaranteed for 5 years, with respect to edge seal adhesion to the glass, as long as they are glazed correctly as follows:
To ensure that your Unit performs as it should will only be achieved if it is glazed into a well designed frame, using appropriate durable glazing materials, and following the correct glazing proceedures.
The following document is set into two sections:
(a) The general principles of glazing
(b) Glazing methods of Double Glazed Sealed Units: Timber frames
(a) The general principles of glazing.
The fundamental principles underlying the correct glazing of well-made Sealed Units are :
* prevention of prolonged contact of moisture with the edge seal of the Unit (see notes 1.1) ;
*compatibility between the edge seal of the Unit and the glazing materials (see notes 1.2) ;
*protection of the edge seal of the Unit against sunlight (see notes 1.3) ;
*quality of workmanship (See notes 1.4) .
If water is trapped against the edge seal of a Unit for a long period, failure of the adhesive bond of the sealant to the glass will result, causing the Unit to "break-down".
Moisture can penetrate to the rebate area, either through or around the glazing system, or through frame joints into the glazing system, from a variety of sources such as :
*rainwater ;
*window cleaning ;
*condensation within frame sections ;
*condensation on the room side glass surfaces.
All glazing systems must protect the edge seal of the Unit, either by preventing access of water to the seal, or by ensuring that water which penetrates as far as the seal is soon removed by drainage of the rebate area by means of a specially designed frame.
1.2 Compatibility of Unit edge seal with glazing materials.
The edge seals of a Unit have different compatibilities with different glazing materials. An edge seal and glazing material are considered compatible if, when they are in direct contact with each other, the performance of either is not reduced in any way as a result.
The Hot-melt edge sealant used in Sealed Unit manufacture is not compatible with solvents, and because certain glazing compounds contain such solvents we recommend a good quality 'Low Modulus Neutral Cure' silicone sealant is used. (see 'solid bedding method' for more information) .
The edge seal on most Units will degrade if exposed to ultra-violet rays for a long period. It is essential, therefore, to ensure that the rebates provide full cover of the edge seal from sunlight.
Our Units will have at least 8mm of edge seal against the glass, plus 3mm for the glazing block (see 'Glazing methods' for more information') , which means at least a 12mm rebate depth is essential to cover the edge seal. It is normal practice for the spacer bar not to protrude past the rebate, for this at least 16mm is needed for the rebate depth.
Compared with conditions of on-site glazing, the manufacture of a Sealed Unit has the advantage of being easier to control as regards to workmanship, in a clean, dry atmosphere without problems of access (see 'prior to glazing' for more information) .
The glazing of a Unit has just as much a big part in it's performance as the manufacture.
(b) Glazing methods of Double Glazed Sealed Units: (Timber frames).
Prior to glazing.
An edge clearance is necessary to prevent frame-to-glass contact, and to prevent water from bridging between the rebate and edge seal of the Unit. The edge clearance should be sufficient to allow for thermal movement also, so, when measuring the frame you should allow 6mm on the width and 6mm on the height (3mm all around the Unit). (see 2.1 'solid bedding method' below) .
If the frame is in-situ and exposed to the weather before glazing commences, the frame must be kept adequately covered to keep the rebates and glazing beads as clean and dry as possible.
Glazing conditions are much better improved when there are no obstacles, such as scaffolding, around the frames to be glazed.
2.1 Types of glazing in timber frames.
The glazing of a Sealed Unit into a timber frame falls into two groups: (1) solid bedding method, and (2) drained method.
(1) A drained method is based on principle that some water may penetrate the glazing space; and while this is kept to minimum, provision is made in the design of the frame to ensure that any water which does penetrate is removed soon by drainage and ventilation. For more information on this type of glazing please contact us for advice.
(2) A solid bedding method protects the edge seal of the Unit by preventing moisture from coming into contact with the edge seal, by means of a sealed barrier. This is the most common type of glazing in timber frames which is shown below.
2.2 Glazing to timber frames.
2.2.1 Firstly ensure the rebates, beads and Unit are clean. Run a continuous seal of silicone around the back of the rebate and place two glazing blocks on the bottom rebate. The glazing blocks should be of a resillient, non-absorbing, rot-proof, compatible material; of which can be obtained from our factory sales counter.
Please Note: Silicone has to be of a 'Low Modulus Neutral Cure' type and of high quality. If you are unsure of your silicone type or quality, bring a sample to our office for a test for compatibility.
2.2.2 Sit the Unit on the glazing blocks and push gently against the back rebate and centralize, making sure not to push silicone out from the rebate. There should be a 3mm gap all around between the Unit edge and the timber, to allow for thermal movement and to prevent water from bridging between the rebate and edge seal of the Unit. (see fig 1)
2.2.3 Next fix the glazing beads around the Unit. The beads should be a snug fit, and fixed using suitable non-corrosive material (sheradized and brass glazing pins are available at our factory sales counter).
2.2.4 With a fine nozzle, run a neat continuous seal of silicone sealant between the face of the glass on the inside and the back rebate. (see fig 2)
2.2.5 Again, with a fine nozzle, run a neat continuous seal of silicone sealant between the face of the glass and the glazing bead on the outside, as in section 2.2.4, thus forming a water tight seal on the edge seal of the Unit from any moisture which may occur. Make sure any residual voids are filled. (see fig 3)
2.2.6 Do not work on or around the fixed Unit for 24 hours to allow the silicone sealant to cure.
Fig 1
Fig 2
Fig 3