Traditional Paving Joint Technologies - Online Shop
In the UK, the most widely used paving joint materials today includes all the following different paving jointing technologies. We have given a short introduction and description of each type below, together with a summary of their key advantages, limitations, and disadvantages. Unfortunately, and as previously mentioned elsewhere throughout our website, it is important to realise that there is no universal ‘one-size-fits-all’ paving joint mortar and the variable requirements and exposure means that there cannot be one. As a result, the different paving joint technologies and systems in use around the UK and Ireland today are:
Natural Sand (with/without Sand Stabilisers / Surface Sealers)
The use of natural sand that is simply brushed into the joints between the paving elements is probably the oldest method, and is still a widely used approach, especially for concrete block paving with negligible joint widths and laid butt-jointed to the next element. The key advantages of sand filled joints are speed and cost, but the important key disadvantages are the ease of washout and ease of weed growth. These disadvantages can be partially negated, if not completely eliminated by the use of a so-called ‘Sand Stabiliser’, such as GftK’s vdw 870. This is roller or spray applied to the newly laid and jointed paving, where it penetrates. As the resin dispersion dries through evaporation, the residual resin acts to bind the fine sand particles together, thus very significantly reducing the surface resistance to sand washout or weed growth. A side benefit is that the impregnation of the concrete blocks also somewhat increases their stain resistance, by reducing the surface permeability. This can be a solution for this type of paving, but re-sanding and re-stabilising will likely need to be repeated every few years to maintain the protection and performance.
- Sand and Cement / Polymer-modified Sand and Cement (including site-batched mixes and factory pre-batched mortars).
As mentioned in the introduction to paving joint technologies, various forms of cement based paving jointing has been carried out for up to 6000 years, back to the origins of cement mortars and concretes by the Minoans, the Greeks, the Romans and every civilisation ever since. The key advantages of sand and cement are again that these materials are cheap and widely available everywhere. However the disadvantages of cement based materials for paving jointing works can be very significant and include surface staining and difficult or even impossible surface cleaning after application; plus all cement mixes shrink as they harden and this can result in cracks, from so-called short- and/or long-term shrinkage cracking. This is the primary reason that for the last 25-35 years or so, cement based paving jointing / pointing mixes have generally been ‘polymer-modified’ either by the addition of a liquid polymer, such as an SBR (Styrene Butadiene Rubber) to site batched pointing mixes, or by a freeze-dried acrylic / vinyl copolymer powder admixture in factory batched, prebagged paving joint mortars. This polymer modification is used to reduce the water cement content and so reduce shrinkage cracking, whilst also minimising the cement content and improving the flow properties for application. Today the most widely used polymer is polycarboxylate that is derived from the most widely used concrete superplasticiser.
In laboratory test and under ideal site conditions, these advanced polymer-modified paving joint mortars perform extremely well and have minimal or even zero shrinkage cracking. HOWEVER, as with all cement based mortars it is necessary to pre-wet and dampen, ideally to ‘SSD’ (Saturated Surface Dry), in order to obtain a good bond and prevent water migration from the mortar, BUT if there is any residual water from this pre-wetting, then the cement mortar’s precise water to cement ratio is immediately and very significantly altered adversely, so shrinkage and cracking will take place. This issue will arise whenever any free water / moisture is present, from pre-wetting, earlier cleaning works or recent rainfall. Overall, this problem of shrinkage cracking is by far the biggest cause of premature failure for all types of cement based paving jointing materials. These cracks are formed at the time of the pointing/grouting/jointing works, but they may be almost invisible at that time and the issues and problems do not arise for some time, sometimes several months or even years. Typically, the problems will be more evident after winter, when water penetration and freeze-thaw effects at low temperatures take place. These are greatly accelerated by the use of de-icing salts in any paved areas, especially public roads and pavements, but also domestic driveways, with salt brought in on the cars. You will see many areas of paving in public and commercial areas where there are many visible patches and areas of, evident re-pointing and patching being carried-out almost annually in some areas. The main reason usually being that the original paving joint materials were selected and used, primarily based on their material cost alone. “Buy the cheapest and pay twice” - is very real with paving jointing works, buyer beware!
W-C Ratio Problems with Cement-based Paving Joint Mortars
As outlined above, one of the key issues with any cement based paving joint mortar, be it traditional site-batched or a factory pre-batched product, is that any residual water in the joints from the paving installation and surface cleaning, or any pre- or immediate post-application rainfall, or any water run-off from adjacent surfaces, will always have seriously negative effects on the water : cement ratio of the product / design mix. These changes are negative because the increased water : cement ratio will significantly reduce the hardened performance and durability of any cement joint mortar. This is by greatly increasing the risk of both short- and long-term shrinkage cracking (by a factor of x 300% or more), plus an even more dramatic increase in the mortar capillary content (up by a factor of x 6 – 600% or more). The end result in practice is reduced performance and durability of hardened cement based paving joint mortars, due to significantly reduced resistance to water ingress, de-icing salts and frost damage, plus their resulting much lower strengths and resistance to load, stress exposure and cleaning regimes.
These two graphics are well known in cement technology and they can be used to Illustrate the dramatic changes in a cement based paving joint mortar, which will typically occur in the joints on site. This excess water can be from any residual water in the joints, or from rainfall just before, during or after installation, or as run-off from adjacent areas / structures etc.
- As can be seen in the first graph: Through the addition of any additional free water locally or along the whole joint, there can easily be 300% more shrinkage that will cause significant cracking (short and long-term), during curing and hardening of the product / design mix, than when precisely tested prebatched in a laboratory for the respective Product Data Sheets and/or any ‘Test Reports’ i.e. these are totally theoretical values and the real world is different.
- In the second graph: This graphic shows that as a result of any additional water, the resulting hardened cement based, paving joint mortar, will be anything up to 600% more permeable / porous than the laboratory test samples. Therefore, with this lower hardened density and much higher pore / capillary network in the cement matrix, the mortar will have much lower strengths and be very much weaker, with a severe loss of tensile / flexural strength. As a result, the joints will be far more susceptible to frost damage from freeze-thaw attack and de-icing salts, be more likely to stain and far less resistant to both natural erosion and modern cleaning regimes, especially jet washing and mechanical street cleaning machines.
These important differences are the reason that engineers can refer to Concrete as ‘Labcrete’ or ‘Sitecrete’ – These can be very different in performance when the environmental conditions for application are not ideal, which is never easy with the great British weather. Another thing to bear in mind is that defects and damage from this shrinkage and increased permeability may not be immediately apparent, because these damaging effects may take some time to develop and a couple of winters to show – But this damage definitely happened at the time of application.
So once again, buyer – beware! Can you control the environment sufficiently to ensure correct application of cement based paving jointing mortars? If so, then these are a great and very cost-effective solution. However, if this is not possible then you will be faced with awfully expensive repointing or worse, and within a very few years indeed. For signs of this just look around any public or commercial paved areas where the decision on the pointing mortar was likely made largely on the initial cost, even cost per pack or kilo, instead of on the overall long term sustainable cost.
The choice of paving pointing technology and products is yours!
Figure 1. Cement Mortar Shrinkage vs Water : Cement Ratio
Figure 2. Cement Mortar Porosity (as Penetration) vs Water : Cement Ratio
Traditional stone sett paving pointing with typically 3/4 to 1 cement to sand site mixes, are traditionally made and applied by trained and experienced craftsmen by trowel in small quantities, working on their hands and knees. They are cured correctly under damp hessian and plastic sheeting, but they do not do this work when it is cold and wet, or hot and dry. Today the larger areas of paving with cement based jointing, tend to be installed by pump or slurry and then the surfaces are mechanically cleaned to remove residual cement residue. However, once again this method is also temperamental and sensitive to environmental temperatures and humidity.
As some variation of water to cement ratio is almost inevitable with whatever method of cement pointing on any UK paving project there will always be some risk and some inherent defects installed from the beginning. This is not to mention the issues of inadequate curing and protection of cement mortars from direct sun and winds that causes the next biggest problem of excess evaporation. This can also result in the loss of surface strength and increased permeability, as well as cracks in cement paving joint mortars – though these will not be seen at the time, they come back to cause latent defects after a relatively short period of time.
Cement based paving joint mortars can also have issues with joints that have variable dimensions which can also lead to variable shrinkage and cracking. Plus it should always be remembered that cement mortars adhere most tenaciously to roughened, permeable mineral surfaces; their adhesion to smooth impermeable surfaces such as metals and plastic is much lower and not ideal for stress transfer or accommodating any form of movement, including for thermal variations – hence the reason that elastic joint sealants are used for the joints in concrete and brickwork structures. This is also a consideration for larger areas of exposed paving.
In summary we must stress that cement based paving jointing in many different forms, has and does provide a highly effective solution in many hard-landscaping situations. In fact, it should also be stressed that cement based paving jointing is used for somewhere over 80-85% of all paving joints, more in some markets and applications so it is not all bad. However, it is important to understand the limitations of cement paving jointing, as well as the fact that it is widely available in many forms and that it is relatively cheap. BUT please consider ALL of the parameters for your paving project and make the right technical and commercial decisions based on ALL of your requirements, which should always include the desired durability and what the ease of closure and repointing would mean on your project!
Polymeric Sand / Single-pack, Ready-to-use, Jointing Compound (acrylic polymer dispersion mixed with sand and vacuum packed).
These compounds were and still should be just for DIY and ‘Jobbing Builders’ and we do say that a bit disparagingly! These compounds are also frequently, but quite wrongly, referred to as ‘Resin Jointing Compounds, which is very annoying as they are nothing like the advanced 2-part Resin Paving Joint Mortars, outlined later on this website, but this does cause confusion for a lot of people – Sorry rant over!
These are all characterised as being one-part, vacuum sealed, ‘bag-in-a-tub’ materials, which have been around for 20 years and are now made by a few people in the UK and Europe but sold by many under their own brand name. Generally there is a better solution for most paving projects – avoid!
Geofix (now owned by Sika-Everbuild) was the original and once the most widely known of this type, followed by Cementone Wide Jointing Compound, but today there are many different varieties on sale everywhere, though mostly the difference is the colour of the tub. They are largely made as ‘3rd Party / Private label’ products by just a few companies and not sure if being this market leader is a positive accolade for anyone. The current variations of this theme that we have seen in 2020 include: Sika Pavefix, Easyjoint, Marshalls 365 Weather Joint, Joint-it and various (far too many!) others. The only real differences between these products is perhaps the percentage of polymer content.
However, we can only recommend this type of paving joint technology is used for limited DIY applications in domestic situations (excluding driveways) and where frequent cleaning and/or pressure jet washing is not likely to be used.
At NCC Streetscape we stock the only high-end version of this technology that we have found in our comparative tests, which is GftK’s vdw 840plus. Unfortunately, even this product should not be used for driveways, where one of our higher performance 2-part, epoxy resin bound, graded sand systems should be used for their far greater mechanical strengths, tensile / elastic recovery and resistance to direct jet washing.
Bitumen, Pitch / Tar based products (hot and cold applied).
The use of any type of bitumen or pitch / tar based products has pretty much disappeared for the obvious reasons of contamination, fire risk and their lack of temperature stability, as they are basically too soft on hot Summer days, and too brittle on cold Winter days) – so not a lot going for this approach! However, with joints 100 to 200mm deep, part-filled with stone chippings they have proved extremely durable over the past 300+ years or so, as a result that many areas of pitch paving still exist in some heritage areas. The installation and repair of these is for specialists and where absolutely necessary for heritage and conservation reasons only.
Epoxy Resin Mortars (2/3-part solvent-free resin + sand)
This conventional type of epoxy resin paving joint mortar has been around for some years and should not be confused or in any way considered to be the same as the latest technology, the epoxy resin coated and bound, graded sand products such as the GftK range of paving joint materials. Instead these conventional 2-part epoxy resin paving joint products are very closely related to the epoxy products and systems that are used for resin flooring repairs and screeds, as well as for concrete patch repairs. Indeed, they are so similar that for some materials the only difference we can find is the text on the labels…..!
These 2-part, epoxy resin mortars have long been used and are ideal for many resin flooring and concrete repair purposes, particularly making good areas of damage and producing high strength wearing surfaces, primarily because of their very high compressive strengths and rapid hardening, as well as their low permeability and good chemical and abrasion resistance. However, for use as paving joint mortars these are also the properties that can provide some disadvantages. These include significant dust that is generated from the fine sand ‘flour’ rather than graded aggregates that are used and released in the mixing process and their high compressive strength is inappropriate for sandstone and some limestone paving. Plus this makes the materials somewhat brittle like traditional cement mortars because they are also filled with a high ratio of sand to reduce cost.
Unfortunately, this also reduces the epoxy resin mortar bond to the joint sides, which is why in flooring and repair applications they would be used with a primer to improve this, but clearly this is not practical in paving jointing. Notwithstanding this there are still several manufacturers that market this type of products for use as paving jointing, though they are the same materials and can easily be recognised as they are always supplied as 3-components, the epoxy resin base (often called Part-A), the epoxy resin hardener (often called Part-B, which are supplied in sealed tins or bottles to be premixed together before being added to a bag of fine sand(usually called Part-C).
At NCC we also have specialists in resin flooring and concrete repairs, but for paving jointing, NCC Streetscape recommends the unique GftK technology of higher performance, 2-part, epoxy resin bound, graded pre-coated sand systems because of their far greater bond, mechanical strengths, tensile / elastic recovery and durability in service, with full resistance to direct pressure jet washing and even mechanical street cleaners.
Epoxy Resin Coated and Bound, Graded Alluvial Sand Paving Joint Systems (prebatched, 2-part epoxy resin pre-coated, graded alluvial sand).
This is effectively the ‘State-of-the-Art’ in paving joint technology. Although the original innovation was made in Germany nearly 25 years ago, the technology has also gained a huge track record in mainland Europe and around the world, including extensive references in the UK since 2007. These include successfully completed paving projects from domestic patios and driveways, to retail and commercial paved areas, to roads and highways in town centres, to historic market squares and conservation areas and heavy vehicle hard standings. This unique technology includes systems for all different types of paving and all different kinds of exposure. The advantages include wet slurry application, meaning that the pointing work can continue almost irrespective of the weather and that the application is made standing-up in an ergonomic position, rather than on your knees all day!
For more advice or assistance with your specific paving project, please call 01257 266696 for FREE Expert Advice during normal office hours, or you can email us at any time to: firstname.lastname@example.org and we will get back to you just as soon as we can. Thank you.