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Joint Definitions
On This Page... jointing and pointing definitions
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Terminology

There are certain terms used with regard to the pointing and/or jointing of pavements and it can be a bit confusing, to say the least.

There are three main types of joint: butt; close; and open.

This page makes a stab at trying to sort out just what is what, explain the reasons why we use one width of joint rather than another, and to dispel a couple of common misconceptions.

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Butt jointing:

This is effectively no joint. The adjacent paving units are in direct contact with one another; they are 'butted' together.

Depending on the type of paving unit involved, there may be a very narrow strip of fresh air between the units, but to all intents and purposes, the gap between them is a minimal as possible and there will be numerous points of direct contact. Without resorting to some sort of sustained pressure system holding everything in place, it wouldn't be possible to have the joint any narrower.

but jointed flags
Butt jointed patio flags
butt joint
Typical butt joint cross-section
Where it's used
  • Cheap jobs such as shed bases
  • Low traffic driveways
  • Patios
Advantages
  • No jointing medium required
  • No additional labour required to carry out jointing
  • No risk of staining from jointing medium
Disadvantages
  • No 'cushion' between adjacent pavers
  • High risk of spalling
  • No vertical or horizontal interlock
  • No opportunity to disguise variations in manufacturing tolerances
Comments
  • Very popular with cowboys who have no real understanding of pavement construction and eager to minimise the amount of effort they have to put in.
  • May be justified on low-priority, low-traffic, low-budget jobs such as, for example, shed bases, bin stores and greenhouse paths.
  • If it must be used, best used with chamfered units.
Gallery
butt jointed pcc flags
Butt jointed pcc flags
butt jointed patio flags
Butt jointed decorative patio flags
sandstone setts
Butt jointed sandstone setts - accuracy required
granite setts
Butt jointed granite setts with inevitable spalling
HB2 butt jointed
Butt jointed half-battered concrete road kerb
mitred granite kerb
Mitred and butt jointed granite kerb - very neat work

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Close Jointing:

This is a narrow joint, usually 1-5mm in width. The adjacent paving units are close to each other but not actually touching at any point.

This arrangement allows a fine-grained jointing medium to fill the joint and create an essential cushion between the paving units and to generate a huge amount of both horizontal and vertical interlock which helps ensure the units remain firmly where they are meant to be.

close jointed block pavers
Close jointed block pavers
close joint cross section
Typical close joint cross section
Where it's used
Advantages
  • Relatively cheap
  • Usually low-skill level required to install
  • Helps prevent spalling
  • Generates phenomenal horizontal and vertical interlock
  • Enables easy maintenance and repair of pavements
  • Usually clean to install with little risk of staining
  • Useful at disguising minor dimensional variations of paving units
Disadvantages
  • Unbound, loose jointing material prone to loss by scour from wind or water
  • May be colonised by weeds
  • Usually requires intermittent minor maintenance
Comments
  • Should not be underestimated. Deceptively simple, but this is how pavements have been jointed for over five thousand years, right from the earliest mud brick roads of ancient Babylonia
  • The key is to use the right sort of jointing medium: hard, angular grains are always the best option
  • The few disadvantages are easily countered by using stabilisers, sealants and basic regular maintenance
Gallery
close jointed shaped cbp
Close jointed W-Blocks
close jointed clay pavers
Unsanded close jointed clay pavers
close jointed decorative cbps
Close jointed decorative block pavers
close jointed permeable block paving
Close jointed permeable block paving
close jointed yorkstone setts
Close joints on yorkstone setts laid circa 1880.
Bloody good work!
close joints with granite setts
Sawn and tumbled red granite setts with close joints.
Circa 2010 - is that progress?
close jointed small element flags
Close jointed small element flags
close jointed patio flags
Close jointed patio flags
close jointed sawn yorkstone
Close jointed sawn yorkstone flags
close jointed caithness flags
Close jointed caithness flags
close jointed quadrant kerb
Close jointed quadrant kerb
close jointed kerb-drain units
Close jointed kerb-drain units

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Open Joints:

Open joints are just what the name suggests: they are wide, gaping maws between the paving units and need to be filled with something substantial, usually a bound jointing medium such as a cement or resin mortar.

There has always been some debate over just what width is the boundary between close and open joints. It used to be a quarter inch (6mm) but some said three-eighths (9mm) which I always thought of as being too wide to be considered a close joint. Modern thinking seems to be settling at the 5mm mark, but there will always be some who want to see it pushed to 8mm or so.

open jointed textured flags
Mortar-filled (pointed) open joints
For projects where a regular, consistent joint width is required, the use of paving spacers is often the best option.
open joint typical cross section
Typical open joint cross section
Where it's used
  • Traditionally with natural stone setts and cubes, as well as natural stone flags.
  • With the advent of dimensionally accurate concrete flags in the interwar period, the tradition of open joints persisted (I spent most of my 1960s childhood filling the damned things!) and it's only with the emergence of small element paving in the late 1970s that its use with flags has reduced.
Advantages
  • Holds paving firmly in position
  • Almost no risk of spalling
  • Can provide an attractive contrast to the paving units
Disadvantages
  • Needs a bound material for best results
  • High skill level required to keep it neat and tidy
  • Rigid mortars (both cement and resin) can be prone to cracking
  • Huge risk of staining with cement mortars
  • Can impede access for maintenance and repair
Comments
  • Highly traditional but cement mortars nearly always crack
  • New generation of proprietary cement mortars and resin mortars reduce incidence of cracking and allow high-pressure washing
  • Slurries and gun-injected mortars are increasing in popularity
Gallery:
mortar pointed setts
Cement mortar-pointed setts
pitch jointed setts
Pitch jointed setts
gold granite cubes
Golden granite cubes with open joints
cobbles
Open jointed cobble paving
purbeck limestone flags
Open jointed Purbeck limestone flags
indian sandstone flags
Indian sandstone flags pointed with light-coloured mortar
patio flags
Mortar pointed reproduction patio flags
crazy paving
Open jointed crazy paving using Donegal Quartzite

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Other definitions:

spacer

Jointing Medium:

 
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Spalling:

  • Chipping or other damage to the edge or arris of a paving unit, often caused by the unit being in direct contact with an adjacent unit.
  • Spalling can occur during installation, which we call "bad workmanship", or it can occur post installation due to there being no 'cushion' of jointing material between paving units, allowing them to exert pressure on neighbouring units
spalled kerb
Spalling of limestone kerb due to butt-jointing and subsequent minor settlement of kerb
spalling
Spalling of concrete kerb that can only have happened during installation as there is no direct contact with adjacent kerb
spalled block pavers
Spalling of block pavers resulting from oversize cut pieces being forced into place
spalled pavers
Spalling of block pavers resulting from direct contact during compaction process
spalled setts
Spalling of granite setts due to direct contact
spalling
Spalling of wet cast concrete flags

 


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Horizontal interlock:

The friction generated by the jointing medium which helps the paving units resist forces which try to shift it in the horizontal plane, ie backwards, forwards, side-to-side, or rotationally.

spacer

Vertical interlock:

The friction generated by the jointing medium which helps the paving units resist forces which try to shift it in the vertical plane, ie, up or down.
spacer interlock explained

 


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Chamfered Units:

Paving units where the arris, the edge where the vertical sides face meets the horizontal base or top surface, has been modified to an angle of around 45°

This helps relieve pressure on the most vulnerable point of contact, and so reduce the risk of spalling.

Commonly found on clay and concrete block pavers, high quality decorative concrete flagstones and small element paving flags.

spalling

 

chamfered units

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Other pointing and jointing pages...

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