Sealants play an important part in cladding because AZ or paint coatings cannot be sealed using solder.

The purpose of sealants used in the joints between metal roof and wall cladding and flashings is to prevent the entry of rain or snow and to exclude dirt, debris, and moisture by capillary action. They may also have varying degrees of adhesive action.

Sealants are generally Neutral Cure silicone or Modified Silicone (MS) types. The latter is generally paintable. Proprietary self-adhesive tape sealants are also entering the market and give excellent performance in certain conditions. Acid cure sealant, designed to bond to inert surfaces such as glass, must not be used.

Designs using sealants to seal sheet components must always include a mechanical fastening such as a screw, rivet or a mechanical seam. 

Generally, the function of a sealant is carried out by that sealant being sandwiched in the joint. In most cases, the post application of sealant to the outside of a joint is both futile and unacceptable.

The sealant does not require significant total adhesive strength, but it should bond positively to both surfaces as a continuous layer. To ensure complete sealant cure, the width of sealant in a lap should not exceed 25 mm when compressed

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