TECH TIPS —
Sealant success Sealants aren’t magic. These well-produced products have a definite place in building construction but can be (and often are) misused. Some basic rules for the successful use of sealants include: 1. Attach the sealant to two edges of the joint only; 2. Always use a backing rod or separation tape (to prevent three-sided adhesion); 3. A 2:1 width to depth ratio is a reliable guide; 4. Always clean the joint surfaces, and always use a primer for high performance joints; 5. Keep the sealant slightly back from the outer edge of the joint, and arris the corner of the edge of the element to be sealed; 6. Check that the sealant is compatible with the substrate; and 7. Above all, never squirt and hope. It is apparent from this list that sealants must be used in conjunction with the appropriate primers, backing tapes and PEF backing rods. These ‘support’ products are critical to sealant performance.
Cleaning Cleaning is vital. Wipe down the joint surfaces before application of primers, separation tapes, PEF backing rods and sealants. Unfortunately, the application of sealants directly to dust covered surfaces is common – and it does not work. The adhesion in these areas will be directly to the dust, or loose abraded material of a cut edge. Joint failure occurs at the weakest point – which is obviously the dust or loose surface material. In many building inspections sealants have been pulled away from windows with ease. Most often the sealant is clinging to dust particles, board particles or wood fibres. There is no bond between the sealant and the substrate and there was likely to have been a capillary track for water to gain entry.
Priming Many sealants will bond to clean, dry, sound and homogeneous substrates that are free from oils, grease, dust and loose or friable particles without primers and/or activators. However, for optimum adhesion and critical, high performance applications, such as on multi-story buildings, highly stressed joints, extreme weather exposure or water immersion, priming and/or pretreatment should be considered to ensure the best possible result.
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Joint design While sealants have a definite place in the building industry, they are not a fix all for all situations. • They do not stretch to double their size and they are not gap fillers. • They do not and will not replace good weathertight design. • They should not be relied upon as a complete cure to all water ingress problems, but as one part of a total solution. Correct joint design and installation are essential.
Painting And one final tip... and it’s an important one. While many joint sealants may accept paint or coatings, the key point to be aware of is the joint sealant is flexible and will move with the joint. The paint or coating is usually rigid and will not move. This may cause undesirable side effects such as cracking of the paint film, and movement accommodation ability may be reduced. Always check your product’s data sheet for information prior to use. For more information visit https://nzl.sika.com/en/46072/sealants-fillers.html
This Tech Tip was supplied by Sika (NZ) Ltd. Sika is a NZCB National Partner and a global supplier of construction products. Sika has more than 100 years of experience and combines strong international product R+D with quality, kiwi expertise. Call 0800 745 269 or email info@nz.sika.com for product help or enquiries.
