Criteria for Paving Jointing

Criteria for Paving Jointing

Paving Jointing – Key Selection Criteria

1. Type of Area

Different types of areas have different requirements for paving and the paving jointing, especially in terms of the traffic loadings and exposure. For example, the substructure support for a garden patio or pathways, is lower than for a domestic driveway, which is lower than required for a busy commercial parking area with more frequent and potentially heavier traffic, that in turn is lower than the roads and town centre market squares etc., with regular heavy vehicles and articulated truck traffic. What type of area is your project:

• Domestic Patios & Pathways
• Domestic Driveways & Parking Areas
• Retail & Commercial Areas
• Highways & Town Centres
• Historic Areas (Market Squares)

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2. Type of Paving

Different types of paving can have significant differences in their nature and requirements for secure bedding and long-term durability in service. For example, sandstone paving is much ‘softer’ than granite and other igneous stone (basalt, porphyry etc.), with low compressive and flexural strengths (typically around 20Mpa and 2Mpa respectively), and as a result ,will be less durable under vehicle traffic, plus the sandstone jointing should ideally have a lower compressive and higher flexural strength than the stone, in order to prevent restrictive cracking and best accommodate thermal movement. What type of paving are you using:

• Natural Stone
• Reconstituted Stone
• Concrete Pavers
• External Porcelain Tiles
• Brick & Clay Pavers

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3. Paving Format

There is a basic difference in the requirement of paving units depending on their size. Basically, larger format paving (typically units larger than 400mm x 400mm) can be considered more ‘bedding dependent’, whilst ‘small format paving’ (units less than 400mm x 400mm) can be said to be more ‘jointing dependent’. Generally, this is especially important to accommodate and transfer thermal movement, vehicle loadings (both static and dynamic), and to resist freeze-thaw action, as well as cleaning regimes such as high-pressure jet-washing, and/or mechanical street cleaning equipment etc. For larger format paving the joint material is still very important, as the ratio of joint surface area and volume to the paving element surfaces is very low, meaning any lateral movement or stress on the joints, including thermal movement, will be limited by this capability in the joints. This is also one of the reasons such larger format paving should not be used for heavy vehicular trafficked areas without special measures including thicker slabs and wider joints etc. For smaller joints, one key difference from larger format paving is their much greater thickness, in domestic driveways these maybe only 50mm, with the traditional stone sett thicknesses used in the UK’s town centres and market squares being from minimum 100mm, up to more than 200mm deep, according to the type of structure and requirements, as well as history, though much of this was before the development of 40 tonne articulated vehicles. Successful small format paving requires that the jointing material has the capacity to allow and accommodate lateral movement and stress transfer under the anticipated traffic load, with flexural tensile strength being far more important than the compressive strength, as all the load is imposed on the paving units, whilst the movement and environmental exposure must be accommodated in the joints.

The number, size and shape of joints in paving varies considerably due to the size and shape of the paving elements, and not all jointing materials are suitable for all sizes of joints, plus most importantly, any significant changes and variations in the dimensions of the joint width and joint depth, may not be suitable for all types of paving jointing materials. For example the sloping sides of rounded cobblestones, means that cement based materials may suffer increased shrinkage and cracking due to differential drying etc., additionally, as these joints would be varied and very wide in places due to the nature of cobbles, which also means that 1-part, air-drying, vacuum-packed, paving joint compounds will not be suitable, because of their relatively low strengths and limited resistance to point loadings, depending on the anticipated traffic exposure etc. What size and format of paving are you using:

• Larger Format Slabs
  (> 400 x 400mm)
• Smaller Format Slabs
  (< 400 x 400mm)
• Setts
  (Square and/or Tumbled)
• Cobbles
  (Rounded)
• External Porcelain Tiles
  (min. 20mm thick)

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4. Paving Substructure Permeability

In an ideal world, all paved surfaces would be permeable or use falls to direct water to soakaways to support groundwater management and flood prevention wherever possible. However, the compacted build-up of multiple historical layers of paving substructures reduces permeability in urban areas such as town centres, but for domestic paving the substructure should be permeable wherever possible and the simple glass of water test can be used to assess this i.e. pour about 250ml (approx. half a pint) of water onto the built-up substructure and see how long it takes to disappear – if the water is fully absorbed in less than 5 minutes it can be classed as permeable, if it takes a little longer, say within 15 minutes, technically it could be classed as semi-permeable, which in paving jointing terms, is effectively still classed as ‘permeable’, because the water does drain within a relatively short time. However, if there is minimal absorption within 30 minutes then the substructure is impermeable, and the jointing mortar should be selected accordingly. What is your paved area substructure permeability:

• Impermeable (negligible absorption)
• Semi-permeable (significant absorption in 5 minutes)
• Permeable (full absorption within 5 minutes)

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5. Paving Joint Dimensions

The specific joint dimensions should be known i.e. the joint width and equally importantly, the joint depth, and is this uniform – what is the likely variation of these dimensions across the paved area? The reason is that in paving jointing we are dealing with a relatively small cross-section and just like with concrete, and especially thinner layer concrete and mortars, the joint mortar materials and their component sand, aggregate and other fillers size and grading, must be suitable for application and then long-term performance in the joint dimensions. In the same way as we need to use different sized sand and aggregates, as well as different sand and aggregate grading to produce different thicknesses and sizes of concrete elements, it is also necessary to do the same at a more micro-level for paving jointing mortars. This is a function of basic building physics to prevent shrinkage cracking during curing and hardening, which is especially important with cement-based mortars, even in so-called ‘shrinkage-compensated’ or ‘plastic’ non-shrink materials. Always check the joint dimensions, especially the width that governs the exposed surface area, and select a material that is suitable for the joint dimensions. The depth of jointing mortar is also important for them to be able to function and accommodate thermal movement and transfer imposed load stress across the joint and/or into the substructure.

Different jointing material technologies also behave very differently when the joint dimensions are variable, in either width and/or depth along the joint, which creates additional stress in the jointing material during curing/hardening, as well as in service, creating differential shrinkage and/or imposed loadings that can increase the risk of cracking and disbonding. This is a particular issue in repointing works, where the dimensions are already fixed in terms of the joint width along the joints, and therefore it is always essential to check these dimensions and their variations in advance, including to ensure that when repointing there is sufficient depth for the new jointing material to function correctly. This will typically be a minimum of the full depth of the paving unit i.e. a minimum of 20mm - 30mm according to the type of paving. This physical requirement is very important and applies to all different paving joint material technologies; the selected jointing material must have a maximum particle size, with suitable grading and granulometry, for the joint dimensions and the range of variation to be expected. What are the joint dimensions and variations on your project (width and depth, level of variance):

5.i. Joint Width:

• Less than < 5mm
• From 5mm to 20mm
• More than > 20mm
• Consider levels of variation?

5.ii. Joint Depth:

• Less than < 20mm
• From 20mm to 30mm
• More than > 30mm
• Consider levels of variation?

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6. Performance & Exposure in Service

The paved area's type of traffic and frequency of use, as well as any other mechanical and environmental exposure in service, must all be fully considered in selecting the most appropriate jointing material i.e., what loadings and exposure must the jointing material be resistant to….? What other potentially aggressive influences will the joints be exposed to simultaneously or independently, as an integral part of the paved surface in this area. For example, consider:

6.i. Type and Frequency of Traffic

The type and frequency of traffic is a major factor for joint specification, foot traffic generally imposes much lower static and dynamic loading and stress on the paving than normal passenger cars, which impose less than larger vans and commercial vehicles, and so on up to the highest loadings imposed by heavy articulated trucks. The key points here are that whatever the traffic loadings are, the weight of traffic as a static load is imposed vertically as compressive force on the paving units and transmitted directly into the substructure, whereas the dynamic loading from traffic movement is imposed vertically and then transversely by transmission to and through the joints. The jointing materials must therefore be able to safely accommodate and /or transfer this load to the substrate, and/or the adjacent paving elements. This capability is largely dependent on the jointing material’s flexural tensile strength and e-modulus (modulus of elasticity), rather than their compressive strength, because as stated, any static loading is taken by the paving elements themselves and transferred directly to the substructure. What type of traffic exposure will there be:

• Domestic Patios etc.
  (Pedestrian incl. bicycles)
• Domestic Driveways
  (light cars & vans)
• Public Paved Areas
  (frequent cars & vans)
• Town Centre Roads & Highways
  (frequent vehicles - incl. heavy trucks)

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6.ii. Mechanical Impact & Abrasion Resistance

As outlined above regarding traffic loadings, there is not normally a requirement for paving joint materials to have high compressive strengths, as the traffic load is taken by the paving units and transferred directly to the substructure, which must be designed to accommodate the intended loading. However, the paving joint mortar may still have to be resistant to point loadings from anything with a small ‘footprint’, such as stiletto heels or metal furniture legs etc., which could be imposed directly on it, within the joints. Where this is a requirement, the jointing material should be of sufficient strength to withstand the loading i.e., this will generally mean a minimum compressive strength of 10+ Mpa (1 MPa = 1 N/mm2), and a flexural tensile strength of at least 2.5+ MPa, must be achieved Note for info: a compressive strength of 10 MPa is the minimum required for pedestrians (only) to walk on a concrete floor slab, or to strike (remove) the concrete formwork in a precast plant. The relative strengths of the paving elements and the jointing material should also be considered in the joint material selection process; this is because many types of natural stone paving used for domestic patio paving projects (some sandstone and limestone for example), will have a compressive strength of around 50 to 60 MPa or less, and typically these are also somewhat rigid, even brittle, with a flexural tensile strength of only around 2 Mpa or less. These values are typical for garden sandstone and limestone slabs or setts, which are probably the lowest strength natural stone options, but they are undoubtedly attractive, and the popular types of natural stone paving used around the UK and work well when installed and jointed appropriately. The most important consideration in relation to their jointing, is that to function correctly in accommodating load transfer and movement in the joints, the jointing material should generally have a lower compressive strength, but a higher flexural tensile strength than the stone paving elements. The old builders saying, ‘the higher the compressive strength the better’, is most definitely not true for sandstone and limestone paving jointing materials. Therefore, always consider the strength of jointing mortar required, as well as the type and level of loading by mechanical impact or abrasion is anticipated in the paved area. For example, will there be:

• Standing Equipment / Structures
• Garden Furniture Legs
• Stiletto Heels
• Other loads…..?

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6.iii. Paved Area Cleaning Regime

All areas of externally exposed paving require regular cleaning to keep them safe and attractive, free from green growths, and to remove spillages and stains, as well as the build-up of dirt and grime. The type and nature of this paving cleaning should also be considered in advance to ensure that the selected jointing material can resist and withstand the use of the cleaning materials and methods.

Important note: Outdated, dangerous, and potentially very damaging use of brick acid, and other acid-based cleaners should be avoided, as should strong alkalis such as sodium hypochlorite (strong bleach), which can all seriously damage and/or badly and irrevocably stain many types of paving and/or the paving jointing materials. This is in addition to these chemicals being classed as hazardous and potentially harmful to people, pets, and garden plants, as well as to the natural environment.

However, fortunately, there are now a lot of safe and efficient cleaning solutions that are produced specifically for cleaning paving without any such issues - for more information on modern paving cleaning solutions, please see the Paving Cleaning pages of this website: where you can get full details, determine the best solution for your specific paving cleaning requirements, and you can also buy these advanced, safe solutions in our Online shop.

To select the most appropriate paving jointing materials always consider the cleaning regime for the paved area, i.e Is the area to be cleaned by:

• Garden Hose & Brushing Only
• Domestic Jet-washing
• Commercial Jet-washing
• Streetcleaning Vehicles / Machines

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6.iv. Chemical Resistance

In different types and areas of paving, almost by definition, there are also different levels of chemical liquid exposure and use, in fact there are many paved areas that are or can be exposed to quite a wide range of ‘chemicals, though we might not initially think of them as chemicals. These chemicals can vary from food and drink spillages, including the ubiquitous red wine and BBQ fats, on domestic patios, to de-icing salts and/or automotive fluids on driveways and other car parking areas, plus just about anything can be spilled on our roads and pavements in town centres and market squares. The paving jointing material should always be assessed to confirm that it is resistant to the anticipated chemical liquid exposure(s) in the area. For example, will red wine stain the paving grout and spoil the finish, and will the de-icing salts lead to accelerated freeze-thaw damage in winter months…? Typically, it is sensible to consider the resistance of paving jointing materials to any ‘chemical’ liquids and cleaning solutions that could be spilled or used. What chemical liquids could be used / spilled on your paved area:

• De-icing Salts
• Hot & Cold Food & Drinks
• Automobile Fluids (Petrol, Deisel, Engine Oil, Brake Fluid etc.)

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6.v. Boring Insect Resistance (Ants, miner bees & beetles etc.)

Most domestic paving areas can be at the risk of damage from various types of burrowing insects. The best known in the UK are the many different types of ants, but there are also many different types of ‘Miner’ bees that live solitary lives or colonies in underground burrows, as well as the countless different types of burrowing beetles that are found in the UK - Interesting fact – Did you know that there are more different types of beetle than there are of any other animal...! Generally, there are more of these burrowing insects in Southern areas of Britain, and they prefer dryer environments (if there are any left in the UK nowadays!), so under a garden patio makes a perfect home! Most of the time these go about their business unnoticed, but several types are very capable of undermining and burrowing though paving jointing materials, unless these are specifically selected to be fully resistant to this form of attack. None of the widely available 1-part, air-drying joint materials are fully resistant to boring insects, though some such as GftK Patio grout are very much better than all the rest due to its increased strengths. Cement-based jointing is also at risk, especially when there are cracks in the mortar and / or debonding from the edges of paving units, which typically happens when the product has been applied in unsuitable conditions with residual water in the joints etc., meaning that the water to cement ratio has been disrupted, leading to shrinkage cracking and the creation of many access points that are ideal for insect access. What resistance to boring insects is required:

• Highly resistant
• Somewhat resistant
• Limited resistance

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6.vi. Weed Growth / Root Resistance

One of the biggest dangers to the long-term stability and durability of paved garden patios, pathways, and domestic driveways, is from plant roots, not just the roots of larger trees, but also the many other popular shrubs, bushes, and feature plants, as well as some invasive ‘weeds’ (such as the dreaded Japanese Knotweed), which have root systems that are naturally spreading, invasive, and therefore potentially damaging to paving. Plant root damage usually starts with growth under and/or through the paving substructure build-up, which is why it is that for new patios, pathways, and driveways, it is always important to ensuring that sufficient depth of top soil is removed, along with any existing roots, and then that a suitable membrane and compacted MOT type sub-base has been used to prepare sound, stable foundations for the new paved areas. However, another ‘plant root’ issue is paving damage caused by smaller plants; the so-called ‘weed growth’, on and in the paved surfaces, which can easily start, when for example, there are shrinkage cracks in the paving jointing, allowing wind-blown and bird-poop carried seeds to enter, germinate and grow expanding the cracks and causing more damage as they grow. Small plants often regarded as weeds, such as the common dandelion for example in the UK, evolved with the ability to spread seeds in the wind and for these to settle and colonise other areas by settling in fine surface cracks in dried mud or stone, then germinating when water and warmth creates the right conditions – Shrinkage cracks in your paving jointing makes a perfect alternative! Evolution has led to these plants being able to select the path of least resistance to grow and can generate huge forces with their leaves and their roots. This is another reason to avoid any shrinkage cracks in the jointing i.e. by ensuring there is no residual water in the joints for cement-based jointing materials, or to select paving jointing products that do not produce shrinkage cracks during installation. This strategy also then requires a jointing product with higher flexural tensile strength (>3.5 Mpa) and e-modulus of elasticity (>4.5 GPa), to easily accommodate the anticipated levels of thermal movement without debonding and cracking in service, long-term. This movement accommodation capability becomes increasingly more important the larger the paving units, and conversely, the smaller the joint widths, where selecting the right jointing material, with correctly optimised strengths and e-modulus, producing high cohesion and adhesion in the joints, will greatly assist the prevention and/or significant reduction of any such cracking cracks long-term, thereby also helping to prevent weed and root growth in your paving. Therefore, in selecting the most appropriate paving jointing material, it is also always important to consider the importance and need to prevent weed growth. What resistance to weed growth in the joints is required:

• Highly Resistant
• Somewhat resistant
• Limited resistance

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6.vii. Any Others exposure to consider…..?

Are there any other exposure in service requirements to consider……………???

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7. Site Environmental Conditions for Installation

The environmental conditions on site during new paved area construction and for refurbishment and repointing, can place restrictions on the use and application of paving joint materials, depending on the material technology. For example, all paving jointing technologies and products have minimum and upper temperature limits for their successful installation and curing, plus some jointing products require dry conditions for successful application and curing, or they cannot be used immediately after or during rainfall, when there is any residual water in the joints. The temperature and moisture limits for paving jointing materials must therefore always be considered in the selection process. Dust and dusting are also increasingly restricted for health and public safety (H&S / HSE) reasons in public areas etc., plus any wastewater run-off from paving works containing cement must increasingly be contained and prevented from entering the drainage system to avoid build-up and sedimentation / consolidation of the network reducing flow and flood risk etc.

7.i. Temperature for the Paving Jointing Installation & Curing

Generally, all around the UK, no bonded natural stone, concrete or ceramic paving (including external porcelain tiles) paving should ever be laid or jointed below +3o C on a rising thermometer. In fact, most paving substructure build-up, bedding and laying is safer at +5 o C on a rising, to be sure of avoiding micro-frost pockets, and reducing the additional overnight protection and covering required, and not just for the cost saving, but to avoid physical damage. It is always essential to check that the jointing material’s temperature limitations for installation and curing are within the site conditions, as not all jointing materials are the same and some jointing materials will present more of a risk, particularly at lower temperatures around 5 o C, and at higher temperatures above 25 o C. Therefore, it is important to understand and plan the works to keep safely within the limitations of the selected jointing materials, to do this assess what the temperatures for installation and curing will be on your project along the following lines, then check the materials technical data sheet (TDS). Do not assume! What will the temperature be for installation of the jointing material in your project:

• Very Low (less than < +5o C)
• Low (5 to 10o C)
• UK Normal (10o C to 25o C)
• Higher (Over > 25o C)

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7.ii. Precipitation (Rain) & Residual Water

Some paving jointing materials must only be used in dry conditions, and only with a dry weather forecast for 1, 2, or more days. Other jointing materials should not be used if there is residual water in the joints, including cement-based products, because this can seriously disrupt their water to cement ratio, which significantly reduces the hardened cement jointing material’s properties, performance, and durability, primarily this water to cement ratio disruption can lead to shrinkage, cracking, and an overall lack of strength and faster erosion. Check and monitor the weather conditions, should you delay the paving jointing works, or use a material that is not affected by rain and/or water in the joints:

• Dry Conditions
  (Joints are dry)
• Dry, but Rain Forecast
  (Joints are dry)
• Damp and Rain Forecast
  (Risk of residual water in joints)
• Wet & Rain Forecast
  (Residual water is in the joints)

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7.iii. Water Run-off Restrictions

Cement grout from run-off has caused blockages and other problems in drainage, as well as polluting groundwater, which means this is increasingly tightly controlled by local and environmental agencies. Today, this should always be prevented and there is a strategy and cost to be considered for any necessary cement containing wastewater run-off, prevention, and collection works, even where there are no stated restrictions in the paving specifications, as this is no longer allowed anywhere in the UK under groundwater protection regulations. What cement water run off restrictions must be complied with:

• No Risk of Cement Water to Drainage
  (i.e. No water run-off restrictions)
• Risk of Cement Wastewater to Drainage
  (i.e. Temporary cement wastewater collection to be provided)

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7.iv. Dust & Dusting Restrictions

The preparation and mixing of some paving jointing materials is dust-free, whilst others always create dust e.g. from cement and fine sand/fillers in their powder components, which obviously require appropriate PPE to be worn, to protect against health risks. This can also cause additional problems and lead to claims for damages from the public, as well as businesses and their employees adjacent to the works. Dust and dusting from paving works is therefore being increasingly restricted in public areas, such as in Town Centres and retail developments. These issues can be prevented by selecting a dust free jointing product. What are the dust and dusting restrictions for your project:

• No Dust Allowed
  (e.g. adjacent areas occupied)
• No Dust Restrictions
  
  

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7.v. Any Additional Site Working Restrictions

Are there any other requirements or restrictions that could be relevant, for example are there working time restrictions….? If closure of the work is mandated by a certain time, then application must be stopped in good time to allow all necessary finishing and cleaning to be completed within these restrictions. Alternatively, selecting a paving jointing material that requires minimal additional finishing and cleaning can be an advantage, allowing a greater area to be completed in the given time…….???

8. Site Application of Paving Jointing Materials

8.i. Method of Application

Different paving jointing products are applied using different methods and equipment, which can significantly influence the time and cost of the product installation, as well as the skills and experience necessary for the method and the application, finishing and cleaning equipment required. Is the method of application suitable for the jointing material and vice versa, is special equipment or training required etc.

• Hand Pointing by Trowel
• Gun Applied
• Dry Brush-in + Tooling
• Wet Slurry + Tooling
• Wet Slurry - No Tooling

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8.ii. Specialist Equipment Required

Different paving jointing products require different tools and equipment for application, which can obviously add to the cost of the works, as well as the ‘skills’ required in using them. For this we exclude ‘standard’ hand tools (e.g. trowels, brushes, squeegee, hose with gun/nozzle etc.). What specialist tools and equipment are required / available:

• Cement / Concrete Mixer
• Drill Mixer & Paddle
• Washboy & Sponges
• No Special Equipment

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8.iii. Tooling & Finishing

Some paving jointing products are manually ‘pointed’ in the joints by trowel to finish them, others are brushed or wet-slurried to fill the joints but must then be ‘tooled’ to compact and finish them, with many needing additional filling and tooling again as they are tooled and compacted. Alternatively, some wet-slurry applied products are fully self-compacting, so no tooling or additional finishing work is required, saving time and money. Does the selected paving jointing material require tooling and finishing:

• Dry Brush-in + Tooling
• Wet Slurry + Tooling
• Wet Slurry - No Tooling

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8.iv. Surface Cleaning

After the jointing material application and finishing works, the paved surfaces must be cleaned to prevent staining and remove any material residues. The amount of cleaning required, the cleaning process and equipment needed, are all dependent on the paving jointing product used. This can be a simple as a quick rinse with clean water and brushing off any loose material, or this can be a critical part of the installation process, requiring specialist equipment and expertise, with an additional one, two or more steps in the installation process. Some types of porous natural stone surfaces can be particularly sensitive to this. How much surface cleaning is required for the selected paving jointing material:

• Simply Brush & Rinse Clean
  (with clean water and a coconut bristle brush)
• Remove Cement Slurry Residue (Step-1)
  (with a Washboy machine & sponges)
• Remove Cement Haze (Step-2)
  (with a clean washboy & sponges, and/or light jet wash)

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8.v. Risk of Staining

As mentioned above regarding surface cleaning, some paving jointing products are prone to staining porous and sensitive natural stone surfaces, such as sawn and ‘rainbow’ sandstone, or certain light granites etc., This should be checked for the specific paving selected, and a suitable non-staining jointing product selected where possible, if uncertain a test on a representative stone sample / limited area of the paved surface is recommended. What is the risk of staining the paving surfaces with the selected jointing material:

• High
• Medium
• Low

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9. Curing & Protection

Different types of paving jointing materials require different types and levels of protection from the elements during application and then hardening / curing. Therefore, it is important firstly to consider what protection is possible and available, for the selected paving jointing products. The issue on many areas of failed paving / jointing is directly related to good paving joint products being used in conditions for which they are not suitable, and/or not being given appropriate time and protection for their curing. Always check that the curing time and the protection required when freshly applied, is correct and in synch with the protection available, and that this is available and used on site. What are the weather protection and curing requirements for the selected paving jointing materials:

9.i. Rain & Weather Protection Possibilities

• Covering and Protection Possible
• Limited Protection Possible
• Surface Protection Not Possible

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9.ii. Curing Time Before Opening to Service (@20°C)

• 24 Hours
• 48 – 72 Hours
• 7 Days

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10. Durability and Longevity

The level of durability in terms of years of service required is always important, but this is not always correctly or fully considered. For example, is the owner happy to refresh and refurbish their paving with deep cleaning and repointing every few years, or do they want the paving and jointing to be log-lasting and the only maintenance to be frequent cleaning, with jet washing and cleaning solutions etc. What is the overall longevity and durability required for the paved area, before maintenance other than cleaning is necessary:

• From 1 - 4 Years
• From 5 – 10 Years
• More than 10+ Years

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