If there hasn't been a sufficient effort to accommodate expansion joints in a building or landscaping project, there may significant aesthetic or structural problems at a later date, whereby substantial and expensive remedial action may be needed to rectify any damage.
Expansion of materials such as wood, concrete and metal is common during periods of extreme temperature, as the materials expand and contract, pulling and pushing forces and all directions: damage is cause in areas of weakness and vulnerability when these materials can no longer move within their normal tolerance.
Making good use of old surfaces
It is often the case where new projects - such as pathways, patios or features - are built directly on to the top of an existing concrete base: examples of this may be a site of an old building, farm yard or roadway - where it may be financially prohibitive or impractical to remove the base.
Using old surfaces as a new base makes sense because there is normally a great deal of expense and preparation that goes into creating a sub-base where the visible part of the project is set.
Historical stress fractures
Old bases are notorious for fractures and fissures as they've settled and moved over the years - often as a result of the lack of a suitable expansion joint or because of poor sub-base compaction.
Chances are, although the base might show significant signs of movement or surface damage, further settlement is unlikely. However, lateral (expansion/contraction) movement caused by heat and cold, could cause any minor movement as forces transmit through any new structures that might be built on top.
If it's intended to build on an old surface, there's one simple but effective and relatively inexpensive technique that can be applied as a safety net and insurance against damage.
Plastic and geotextile membrane.
The following makes the assumption that any new construction has been planned to fit within the existing space and there is sufficient height to be able to build up and there is to be a further concrete or sharp sand and cement mix sub-base to be laid on top before the final surface.
Clean off the old base. It's not necessary to scrub clean but all loose material, including soil and stone, must be brushed away.
If it's a patio or pathway that is to be laid, all that will be needed is two separate sheets of Damp Proof Course (DPC) grade plastic sheeting.
Lay the first sheet out fully over the old surface (if it's an odd shape then don't cut because the surplus can be trimmed with a Stanley knife or scissors afterwards) making sure there are no folds, wrinkles or bubbles.
After this, lay the second sheet on top of the first - again making sure there are no folds, wrinkles or bubbles.
Be warned: at this stage, walking on the surface, especially if footwear is damp or there has been some rain, will be hazardous due to the slippery surface.
A geotextile membrane may be utilised directly on top of the plastic sheeting to protect the plastic.
Now continue to construct the new project in your normal way.
The above method stops the two surfaces bonding and at the same time, allows movement of the two surface independently and ensure that stress fractures are not transmitted up through the new surface.
Experience: here's an example of a project I rectified after another firm had built a stone pond on top of an exiting base.