Low Mod Silicone
Used extensively the world over for several decades, low modulus silicone sealants (often known as low mod silicone or LM silicone), is a mainstay for many different trades in the construction industry for both installation and remedial works. As a result of low mod silicone’s reliability and popularity, there is now a wide variety of products available.
In conjunction with Simon Hodgson of Hodgson Sealants, we’ve co-written the following blog post regarding Low Mod Silicone Sealants.
Read an introductory blog post from Hodgson Sealants here.
Naturally, we find customers often wonder what’s the difference from one low mod silicone to the next? Hopefully in this article we’ll be able to shed a bit more light on the differences between the silicone technologies used in low mod silicones.
What is modulus?
Elastic modulus measures the resistance of the sealant being deformed elastically when a force is applied to it. Put simply; a low modulus (LM) silicone sealant offers less resistance to being stretched than a high modulus (HM) silicone sealant.
In general, low modulus sealants are preferred, especially in high moving joints such as window frames or expansion joints.
When a low modulus silicone sealant is extended, it puts less stress on the substrate and on the adhesion bond line than a high modulus sealant.
WIKIPEDIA explains modulus as so;
An elastic modulus (also known as modulus of elasticity) is a quantity that measures an object or substance’s resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. The elastic modulus of an object is defined as the slope of its stress–strain curve in the elastic deformation region: A stiffer material will have a higher elastic modulus. An elastic modulus has the form:
where stress is the force causing the deformation divided by the area to which the force is applied and strain is the ratio of the change in some parameter caused by the deformation to the original value of the parameter. Since strain is a dimensionless quantity, the units of λ will be the same as the units of stress.
Specifying how stress and strain are to be measured, including directions, allows for many types of elastic moduli to be defined. The three primary ones are:
- Young’s modulus (E) describes tensile elasticity, or the tendency of an object to deform along an axis when opposing forces are applied along that axis; it is defined as the ratio of tensile stress to tensile strain. It is often referred to simply as the elastic modulus.
- The shear modulus or modulus of rigidity (G or ) describes an object’s tendency to shear (the deformation of shape at constant volume) when acted upon by opposing forces; it is defined as shear stress over shear strain. The shear modulus is part of the derivation of viscosity.
- The bulk modulus (K) describes volumetric elasticity, or the tendency of an object to deform in all directions when uniformly loaded in all directions; it is defined as volumetric stress over volumetric strain, and is the inverse of compressibility. The bulk modulus is an extension of Young’s modulus to three dimensions.
What is Low Mod Silicone?
Silicone that is low modulus, offers less resistance when stretched making it a far better choice for stress joints that exhibit greater movement versus High Modulus Silicone Sealants which have less movement capabilities and almost always contain anti-mould fungicides to cope with high humidity.
A general distinction between Low Mod Silicone Sealants and High Mod Silicone Sealants is that Low Mods would usually be used for external works and High Mods would usually be used for internal works.
Are there different types of Low Mod Silicone?
Now we’ve ascertained the clear difference between HM & LM silicone sealants, recognizing that LM silicones are typically softer and have better movement capabilities than HM silicones, surely there’s not a big difference between the many various Low Mod’s available is there? … Actually there is…
Methyl Ethyl Ketoxime (or MEKO) is released with the Oxime curing systems, whereas, an alcohol is released with the Alkoxy curing systems, both technologies are neutral cure in nature and as such they are both non-corrosive substances. There are some subtle differences as a result of the chemical composition of each product which can affect the performance and declarations on the safety data sheets.
Physical characteristics – Oxime Low Mod Silicone v Alkoxy Low Mod Silicone
Skinning and working times with the two different products whilst curing.
Oxime: You would often find that Oxime based technologies typically form a skin quicker than Alkoxy based systems.
Many types of Oxime will form a skin in around 10 minutes in normal conditions and even faster in higher levels of humidity. This can have both advantages and disadvantages, it may well affect the tooling ability of the product, once a skin is formed the product can become unsightly to tool as the skin drags.
However, it can also protect the product on active construction sites with many different particles in the air.
Alkoxy: On the other hand, products produced with Alkoxy technology forms a skin slightly slower (15 – 20 minutes on average) allowing the user to tool the joints around, for example, window frames fully before a skin begins to form, thus giving the applicator adequate time to seal longer runs prior to tooling.
Judging by the comments of our professional applicator customers, many prefer the tooling characteristics of Alkoxy products as ‘they more body’ and with the extra working time, make them ideal when sealing externally on building façade.
The selection of which technology is in the low mod silicone used, (either Oxime or Alkoxy) comes down to personal preference.
Health & safety / environmental declarations
As previously mentioned the declarations on Material Safety data sheets can vary between the two technologies, whereas, in some cases Oxime sealants (which release MEKO) can have hazard warnings on both documentation and packaging, the Alkoxy sealants (which release alcohol) do not.
Fillers & extenders
With all sealants there can be differences in quality and LM’s are no different. One of the techniques to reduce the cost of the finished product is to add “extenders” to the base product which will reduce the performance, including loss of volume, extension and elongation (and ultimately the price!) so it’s crucial to remember that not all LM’s are the same when comparing “Like for Like”.
What is Low Mod Silicone used for?
As already mentioned, LM’s offer less resistance to stress, meaning that they stretch efficiently with movement. This is especially relevant for structures’ substrates which exhibit a consistent strain due to changing temperatures, weather and other variables.
With this fact taken into consideration, Low Mod Silicone Sealants are frequently used for external applications such as expansion joints between vertical brickwork, blockwork and render finished walls, with additional work being done in in horizontal joints such as sawn-cut expansion joints, perimeter floor joints and between poured concrete slabs.
With excellent adhesion on a multitude of materials such as glass, Upvc, wood, aluminium, steel and other metals, LM’s are the go-to choice for sealing around frames in windows and doors at the connecting joints where the frame meets the wall or other vertical substrate.
As well as the outer edge of framework, certain LM silicone sealants are used extensively for glazing applications, both at the production stage and in-situ. With a neutral (non-ac id) cure, Low Mod Silicone Sealants can be used for glass to glass joints and for waterproofing the gap between the glass and the containing frame.
You’ll often find the roofing trade preferring Low Mod Silicone Sealants over other materials for their compatibility with lead, excellent adhesion to tiles and again, for their superior movement capabilities. The joints between the flashing and the parapet wall or other vertical structures are often a weak link in the waterproofing chain and thus a silicone rubber seal cap works especially well as a belts & braces solution.
Quality LM silicones are commonly used for weathersealing the external facade (curtain wall) of all types of buildings where glass, stone, brick, timber, composite or other materials are used. These materials are attached to the outer shell of a building with a feather edge overlap or flat minimal joins which are usually then sealed with Low Mod Silicone to match or contrast the substrate. One such material we’re often asked to colour match is Marley Cedral weather board.
Although not commonly considered for internal sealing, LM’s can be used for many internal joint applications where appropriate. For example, lots of professional applicators and glaziers prefer to use Low Mods for internal glazing, with one application in particular being internal partitions.
Natural Stone sealing
Internal natural stone applications can be anything from swimming pool areas and sanitary ware in bathrooms/wet rooms, to kitchen areas such as worktops, trims and splash backs. All these high humidity areas generally require the addition of an anti-mould additive and where a natural stone is present (such as granite, sandstone, quartz, gneiss, slate, or porphyry and marble) a certified non-staining, neutral curing low mod silicone sealant is necessary to avoid leeching from the material to the substrate!
Low Mod Silicone is not just suitable for heavy duty construction joints but is also ideal for sealing and/or cosmetically finishing various fixtures etc. An example could be,, around the outside of a timber, metal or foamex sign on a brick wall, to protect the edges from weather decay and finish the aesthetics. (As per picture below)
A much overlooked use for a Low Mod Silicone Sealant is to make a final seal to the joints between wooden structures such as sheds and summerhouses to their concrete and/or timber bases where excessive moisture and rain travels and gathers. Applications such as these are serviced well by a large fillet joint and best applied when both the substrates are bone dry and free of dirt & dust etc.
Which Low Mod Silicone products are which?
There is no better or worse cure system for Low Mod Silicone products, just different characteristics that make the choice an individual preference. Below is a quick product guide to some of the most popular Oxime/Alkoxy LM’s on the market today. Please note; we don’t stock all of the products listed, some are merely for reference…
- 3C 380 LM Silicone Sealant (discontinued)
- Adshead Ratcliffe (Arbo) Arbosil LM click here to buy online
- Adshead Ratcliffe (Arbo) Arbosil XL1099 click here to buy online
- Bondit – WP100 Silicone Sealant
- Everbuild Tecnic 996 Silicone Sealant click here to buy online (popular)
- Everbuild Everflex 700T LMN Silicone Sealant click here to buy online
- Everbuild Everflex 900N Silicone Sealant click here to buy online
- illbruck FA870 Silicone Sealant click here to buy online
- illbruck FA880 Silicone Sealant click here to buy online (popular)
- illbruck FA600 Silicone Sealant
- Ottoseal S70 Silicone Sealant click here to buy online (popular)
- Ottoseal S117 Silicone Sealant click here to buy online
- Parasilico AM 85-1 RAL Silicone Sealant click here to buy online (popular)
- Sikasil WS605 S Silicone Sealant click here to buy online (popular)
- Soudal – Silirub N Silicone Sealant
- 3C LOW MOD Silicone Sealant click here to buy online (bestseller)
- Dowsil (formerly Dow Corning) C60 Silicone Sealant click here to buy online (bestseller)
- Dowsil (formerly Dow Corning) 791 Premium Silicone Sealant click here to buy online (bestseller)
- Dowsil (formerly Dow Corning) 796 Install & Go Silicone Sealant click here to buy online
- Everbuild Tecnic 825 Sealant click here to buy online (bestseller)
- Geocel LM Silicone Sealant (discontinued)
- Hodgson Sealants U8 Silicone Sealant click here to buy online
- illbruck FA500 Silicone Sealant
- Ottoseal S72 Silicone Sealant click here to buy online
- Ottoseal S120 Silicone Sealant coming soon online
- Ottoseal S130 Silicone Sealant click here to buy online
Our most popular, best-selling Low Mod Silicone sealant products
- 3C LOW MOD Silicone Sealant click here to buy online
- Dowsil C60 Silicone Sealant click here to buy online
- Dowsil 791 Premium Silicone Sealant click here to buy online
- Everbuild Tecnic 825 Sealant click here to buy online
- Illbruck FA880 Premium Matt Finish Sealant click here to buy online
- Ottoseal S70 Natural Stone Sealant click here to buy online
- Parasilico AM-85-1 RAL Sealant click here to buy online
You can see a comprehensive list of our entire mastic sealant range here.
Which colours does Low Mod Silicone come in?
In general the colour ranges of Low Mod Silicone Sealants accommodate the most popular materials used in the common applications. Pound for pound this would mean external frames and the substrates that surround them. You’ll find White is by far the best seller in any LM’s available with Black, Anthracite, Dark Anthracite, Grey, Mid Grey, Buff, Portland, Brick Red also selling well throughout the seasons.
As the natural stone sealants are designed to match a multitude of different shades and textures, they tend to have vastly extended ranges with a select few even offering matt finishes and/or physically textured materials.
We pride ourselves on offering many colour choices for our LM’s & HM’s with a very specialist, premium service that can match ANY physical sample required to both Low Mod Silicone Sealant or High Mod Silicone Sealant if there’s not a stock colour available.
A special thank you to Hodgson Sealants from County Construction Chemicals Ltd.
As mentioned at the top of this blog post, a large contribution was made by Simon Hodgson of Hodgson Sealants for the entire article, for which we thank him kindly.
Hodgson Sealants have their own Low Mod Silicone Sealant called Silfix U8 available directly online here. Simon signed off with the following statement…
“Hodgson’s new professional range is based on the Alkoxy curing systems, this is all part of Hodgson’s commitment to high quality product, service and innovation.”