GRC (Glass Fibre Reinforced Concrete) has stood the test of time in proving it is arguably the best material for making commercial grade planters and troughs. It looks good, strong and lasts for decades in all weather conditions. However, if GRC planters are so strong, durable and weather resistant – why would you bother having them sealed? Well, in most commercial projects we believe you should. To explain why, let’s have a closer look at the value that sealing GRC troughs and planters provides and which sealants are the best to use.
The value sealants provide
GRC is fundamentally concrete and even good quality concrete will absorb some moisture. This moisture can create problems such as:
Creating blotchy wet patches on the outside of the planter walls – which detract from the aesthetic appearance of a planter.
Highlighting non-structural hairline cracks (that are usually not visible but present in almost all concrete surfaces) – which also detracts from the appearance of a planter.
Facilitating moss and algae growth on the outside of planter walls – which is ugly and difficult to remove.
Facilitating freeze/thaw structural cracking – that is caused by absorbed moisture freezing and expanding within a planter’s walls.
Nevertheless, keeping the moisture out of the walls of GRC planters to avoid the above problems can be easily achieved by simply having them sealed. Sealing is not expensive, can be virtual invisible and is an important element in defining the quality of GRC planters, providing the right sealant is used.
What types of sealants are best to use
Since concrete is such a widely used material, and GRC is a subset of concrete, there is a multitude of concrete sealant technologies on the market today that all have their own advantages, disadvantages, applications and quality variations. However, in a very broad sense, and without getting too technical, there are four fundamental groups of sealants on the market that are typically used on GRC planters: -
Topical sealants, as the name suggests, form a protective layer over the top of a planter’s surface and are usually the least expensive of the sealant groups. However, they tend to darken the raw colour of a planter and create a glossy appearance. Therefore, they are most appropriate when cost is the key consideration or when the change in appearance they create is not a significant concern. Topical sealants are most often used externally on cheaper quality GRC planters or for sealing the inside of planters where the natural aesthetic appearance is not an issue.
Bitumen based topical sealants
Within the context of this document, bitumen-based sealants are basically a high-performance topical sealant that generally costs more than general-purpose topical sealants. They are only suitable for sealing the inside of planters but are an excellent option for “tanking” GRC planters for commercial planter installations.
Like topical sealants, penetrative sealants form a protective layer on top of a planter’s surface, but they also penetrate the surface to seal the surface capillaries of the concrete to provide a more comprehensive sealing process. Penetrative sealants generally have minimal impact on the natural appearance of GRC, so they are excellent for the external walls of planters. However, they are typically more expensive than topical sealants.
Graffiti protection sealants
Graffiti sealants are generally more expensive than the other types of sealants. However, they not only provide better protection against graffiti permanently marking a GRC surface, they also facilitate the removal of the graffiti after it has been applied. Therefore, this type of sealant is appropriate for public spaces.
Below is a brief table-based summary of the four groups of sealants that are generally appropriate for the sealing of GRC planters and troughs. It is worth noting that the on-site application of sealants can be significantly more expensive than if the sealing is done at the time of manufacture because GRC factories are generally more efficiently setup for this than on-site tradesmen.
Type of Sealant
Typical Usage on GRC Planters & Troughs
To seal the outside of planters
To seal the inside of planters
Reason for usage
When the cost of the sealant is more important than the change in the aesthetic appearance of the planter made by the sealant
To suppress moisture penetration from the inside
Bitumen Based Topical Sealants
To ‘tank’ the inside of planters
When a higher level inside moisture resistance is required
To seal the outside of planters
When the cost of the sealant is less important than the change a topical sealant would make to the aesthetic appearance of a planter
To provide graffiti protection
When a planter is to be installed in a public space
In some circumstances, suppliers/manufacturers of GRC planters may not highlight the value of using sealants in the sales process as a means of keeping their competitive pricing low. However, from a purchaser’s perspective, the value of sealing GRC planters should not be overlooked. Sealing adds genuine value to the quality of GRC planters and generally the cost is minimal and worth it when reputations and warranties are on the line.
Also, as a word of warning, not all sealants on the market in each of the above described types are the same. Like most other applied materials, sealants come in different qualities, based on different technologies and applied in different ways. Good quality sealants do a great job, but poor-quality sealants and poor application processes can result in peeling, yellowing and moisture permeability. Therefore, unless you can do a lot of investigation and testing yourself, you are very dependent on the supplier/manufacturer to ensure that the sealants they provide are well tested and proven.
Satu Bumi, as a GRC planter manufacturer, has spent significant time and investment in testing dozens of sealants to ensure we provide sealants that are fit for purpose and of the highest quality. And since we apply our sealants in the factory at the time of manufacture, we are able to provide the most cost-effective application processes.