By following these basic guidlines to good glazing you can be assured that every project will result in a good sealant application.
Guidelines to Good Glazing
Gunnable sealants, when applied as a cap bead, should form a bevel or watershed away from the glass. When tape is used to the sightline, it should form a watershed when compressed. Do not undercut a sealant, compound, or tape below the sightline. Minimum cap bead depth should be from 1/4" to 3/8". For banded insulating units, a minimum of 1/8" sealant contact above the band is recommended. Tool and finish the sealant with a Tooling Spatula or Stick Tool as required. Do not use liquid tooling aids such as water, soap, or alcohol (such as IPA). These materials may interfere with sealant cure and adhesion and may create an unpleasant finished look.
Always glaze above 40°F
It is always a good practice to glaze above 40ºF. Below this temperature, condensation and frost can contaminate the surface and interfere with its adhesive capabilities. If you have no choice and you must glaze in colder temperatures, make sure to wipe all surfaces first with a recommended solvent, then wipe dry. Isopropyl alcohol and Methyl Ethyl Ketone (Caution: both hazardous materials), are soluble in water and may be more appropriate for winter cleaning as they help remove condensation and frost. Xylene and Toluene (also hazardous materials) are not soluble in water and may be better suited for warmer weather cleaning. (See our Blog "Guide to Cold Weather Caulking and Sealing" for additional information.)
Form a Watershed To Achieve Positive Contact
When applying a heel bead, lap onto the glass a minimum of 3/16" and make certain that you have a positive contact with the sash. When applying a toe bead, whether continuous or a corner seal, make certain it is large enough to make contact with both the glass and the sash and be sure to inject the sealant prior to installating or replacing the glass.
Setting Blocks
Setting blocks should generally be made of Neoprene, EPDM or Silicone with a Shore "A" durometer from 80 to 90. When used in combination with heel and toe beads, they should be first buttered with sealant, then placed before installing the glass. This ensures an uninterrupted seal between glass and sash member. As a general rule, setting blocks should be centered at quarter points, however, they can also be moved out to eighth points or to a point 6" from the edge of the glass to the end of the setting block, whichever is greater. Setting block widths should be 1/16" less than the full rabbet width and high enough to provide the recommended minimum bite and minimum edge clearance for the glass. Length of setting blocks should not be less than 2".
Surface Preparation
Now for the real important stuff! The key to achieving excellent sealant adhesion is applying the sealant to a clean surface. Clean the sash surface and glass edge just prior to glazing with proper cleaning solvents such as CRL 2032 General Purpose Solvent and Adhesive Cleaner. Non-porous surfaces must be cleaned with a solvent before the sealant is applied. The solvent used will depend on the type of dirt or oil to be removed and the substrate to be cleaned. To avoid damaging the construction material, make sure that the cleaning procedures and solvents you are using are compatible with the material. Non-oily dirt and dust can usually be removed with a 50% solution of IPA or isopropyl alcohol (yes; another hazardous material) and water or a 70% solution of IPA and water (rubbing alcohol) or pure IPA. Excessive oily dirt or film generally requires a degreasing solvent such as Xylene or Methyl Ethyl Ketone (the last of the hazardous materials on this page)
Now for the Cleaning Part
Be sure to use the "two-cloth" cleaning method. What I mean by this is using a solvent wipe followed by a dry cloth wipe, such as our BX15 CRL Lint-Free Glass Wipes. Allowing the solvent to dry on the surface without wiping with a second cloth negates the entire cleaning procedure because the imputities are re-deposited as the solvent dries. As work progresses, remove all excess sealant and smears.
Air Seal
Observe minimum face clearance, edge clearance, and glass bite as recommended by the appropriate glass and sealant manufacturers. This allows the glass to freely float in the opening without undue restriction by the framing piecess that allows the sealant to perform within its designed capabilities.
Weep Holes
When glazing a pressure-equalized system, it is necessary to install a vapor barrier around the perimeter of the glass piece. This will equalize the pressure in the void around the edge of the unit with that of the building's exterior. A heel bead of applied sealant accomplishes this best since it dependably bridges the space between the interior face of the glass unit and the sash.
Clearances
When glazing insulated and laminated glass, sills must be wept to the exterior. A minimum of three weeps per sill, separated by the setting blocks, is recommended. Refer to the appropriate glass manufacturer for their recommended size and placement.
Tape Installation
Do not install glazing tapes more than one day ahead of glass placement. This helps avoid potential damage to the tapes by the other trades. Remove the release paper from the tape only when the glass is ready to be installed. Do not stretch the tape to make it fit or overlap the ends of the tape. Instead, butt the ends together and when the corners are butted together, apply a dab with your sealant to assure a positive seal.
If you should have any questions regarding any of these general guidelines, please feel free to contact the CR Laurence Glass and Glazing Technical Sales Department at (800) 421-6144.
Reference: CRL Sealant Requirement Estimator Chart