subject: Are sealants really a help, or rather a hindrance? [print this page] Are sealants really a help, or rather a hindrance?
A sealant is a viscous material that changes state to become a durable solid, once applied: its purpose is to prevent the penetration of air, gas, noise, dust, fire, smoke or even liquid from one location through to another.
Sealants are typically applied to minor openings, rather than greater cavities, which are particularly difficult to fasten using other materials, such as concrete. Desirable properties of sealants include insolubility, corrosion resistance, and adhesion which are rarely found in other products. Sealants are widely used in many industries, from construction through to aerospace industries.
Sealants are commonly confused with adhesives as they have similar properties and are used in identical ways. However the principle differences between adhesives and sealants are that sealants have naturally lower strength but higher elongation.
The main objective of a sealant is to essentially seal up joints, therefore they must have sufficient adhesion to the building, and be able to resist environmental conditions for the bond to last for a long period of time. When joint sealants are used between buildings, with contrasting thermal coefficients or expansion and differing elongation under stress, therefore they need to have sufficient flexibility.
Generally sealants have a paste consistency to allow an easy application, which means they have a low shrinkage after application.
Some sealants are considered more effective than others, so here are some sealants which the basic pros and cons.
Waterproofing coatings:
Tar or asphalt coatings are generally the cheapest sealant but are only effective for damp roofing, rather than waterproofing, like their misleading title suggests. Polymerized waterproof coatings are suggested to last much longer and also come in an easy apply spray-on version.
Both tar and asphalt are brittle and will eventually flake off after times, as the foundation settles and the concrete contracts, resulting in cracks and degrading after several years. All three coating get attacked by lime in the concrete, causing them to separate however a neutraliser can be added to the mixture to prevent such process.
Acrylic Sealers:
acrylic sealers form a shiny film which enhances the appearance of coloured and decorative concrete. Plus the materials have a UV resistance therefore making them beneficial to the exterior of a building.
These sealers are relatively soft and need to be consistently applied due to surface wear and tear. In addition to this, solvent-based acrylics pose health and fire hazards.
Epoxy Coatings:
Strong and durable, the epoxy coating bonds well with concrete surfaces' and also forms a transparent glossy layer, which in turn allows for easy cleaning.
Though the coating is not permeable to water vapour, therefore trapping moisture, unable for the building to breathe': this then causes bubbling and cracking. A secondary sacrificial' coating is recommended to protect the inner epoxy coat against scratching.
Polyester Sealers:
Penetrating deep into the pores in concrete and bricks, it hardens similar to plastic. It is a permanent deep-seal which helps strengthen the building. It is also waterproof against side water pressure unlike many other sealants. Contrasting to epoxy coatings, this sealant allows the building to breathe'. Polyester sealers are water-based, paintable and will never need to be re-applied.
Unfortunately it only reduces vapour and gases rather than completely stopping them from entering the building, and has tendencies to cause efflorescence.
Whether you are using sealants for concrete repair or to simply fasten a joint: some joint sealants carry more advantages then downfalls, yet each sealant is unique in comparison to another, and depending on the building, a certain sealant may be beneficial to a particular project, but a hindrance to another.
