Building Sealants: A Useful Guide

We commonly find significant problems with building sealants, problems range from:

  • Unsealed critical junction details
  • Poorly applied sealant
  • Poorly re-applied sealants
  • Incorrect choice of sealant
  • Premature sealant failure

A vast range of sealants are available but how do you choose the right product?
Sealants are possibly one of the most under-appreciated products in the construction industry and yet they often provide the critical technical detailing that will determine the long-term durability of you project. They can protect a multi-million pound external wall insulation project from failing prematurely, provide essential fire protection detailing or just be used as simple caulking to aid in providing a high quality internal decorative finish.

However, there are such a wide range of products available how do you choose the right product for your project? What are the dangers in choosing the wrong product, what supplementary factors also need consideration when choosing sealants and how should sealants be applied?

Sealant technology has progressed significantly over the last 30 years and we now have intumescent sealants available for sealing service penetrations in fire walls, lead sealants used as an alternative to mortaring lead flashings and even bacteriostatic cold room sealants to be used in areas where contact with food is possible.

Historically, ‘caulking’ was used to make heavy wooden ships watertight by soaking hemp in pine tar (Oakum) and driving it into the joints of the ship. The term caulking, is still used loosely to describe the sealing of building joints but more often it refers to internal decorative caulking, whereas we generally refer to ‘sealant’ as being required for external building applications. To my mind there have been some worrying developments in sealant marketing, rather than technology, in particular the marketing of lead sealants as a direct replacement for mortar and we are already encountering numerous cases of premature flashing failure due to premature sealant failure; particularly since the lead pegging is often omitted when sealant is chosen over mortar.  To  my mind lead flashing sealants should never be used for anything other than a temporary fix or at best you should accept that flashing durability will be significantly reduced when compared to mortar.


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