Is cold-lay tar any good? This is an often-debated question in the industry, with varying answers depending on the intended user. Their experience with such a material and what they plan to use it for.
Before we answer this, though, let's get one thing straight; 'cold-lay tar' or 'cold lay asphalt' is a historic terminology used in the surfacing industry for most types of cold mix bitumen based surfacing materials, often used for pothole repair, which are generally supplied in 25kg bags or buckets and sometimes even loose bulk loads.
In recent years, these materials have been more commonly known as either Delayed Set Macadams or Permanent Cold-lay Surfacing Materials... this is where the answers to the original question begin to vary.
A short answer would be that cold mix bitumen-based surfacing material does what they say on the tin (or the bag) if the installer does what it says on the tin!
Now let's look at the two main types of cold mix bitumen based surfacing materials in more detail to highlight their intended uses, unique benefits and known limits.
Delayed Set Macadam (DSM)
Probably the oldest and most commonly used cold lay material is Delayed Set Macadam, which is typically produced using minerals, graded aggregates and a modified bitumen binder, which delays the curing process, keeping the material workable for longer periods.
DSMs are commonly used as a short term repair by local authorities and their contractors for defects and potholes, minimising public claims whilst they wait for a permanent hot repair to be carried out. Utility contractors also use it as a temporary reinstatement for road openings whilst they wait for effective mobilisation of plant and equipment to carry out the permanent hot repair.
In some cases, if adequately compacted, DSMs can result in a permanent repair if the location is not subject to heavy traffic. In such situations, the installer would be required to cut back the edges of the patch to defect-free surrounding surface and properly seal the edges before laying the DSM.
Permanent Cold-Lay Surfacing Materials
Another option for repairing defects, potholes and reinstatements are Permanent Cold-lay Surfacing Materials (PCSMs) which have become more popular in recent years, as they are designed for permanent repair and are approved by the Highways Authority Product Approval Scheme, known as HAPAS in the industry.
Generally, permanent cold-lay surfacing materials (PCSMs) are made using higher quality bitumen binders containing solvents that evaporate after compaction, causing the material to harden. However, some permanent cold-lay surfacing materials (PCSMs) contain reactive binders, which cure when activated with water. These hardening and curing characteristics mean that the repair can be trafficked immediately, which is one of the main reasons permanent cold-lay surfacing materials (PCSMs) are very popular with reactive maintenance crews.
PCSMs tend to have a poor reputation for early failure, mainly due to incorrect installation and sometimes due to user expectations beyond the realistic limits of the material.
Most permanent cold-lay materials are designed to provide higher placement adhesion than traditional materials and, in some cases, will last a reasonable length of time if well compacted into wet potholes without edge cutback and sealing, or even in shallow defects with minimal preparation. The key for these repairs is to apply almost excessive mechanical compaction, avoiding migration of the binder to the surface or crushing the aggregate.
Obviously, there are limits to how these types of materials can be used, and it is not to be assumed that by following the correct application method, a complete road would be able to be resurfaced with a PCSM; the material cost alone would disqualify such a proposal apart from the fact that they are not intended for such situations.
In summary, when correct application methods are not followed, such as being thrown into a defect or pothole with little or no compaction, no matter how permanent it is designed to be, it will more often than not be destined to fail. When used beyond their limits, such as for large surface reinstatements, cold lay surfacing materials will be costly.
If you want to know more about cold-lay tar check out our Asphalt & Pothole Repair Materials, or get in touch today to discuss your project in more detail on 02392 200 606 or mail@meonuk.com.
