Get fixing those potholes!

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No matter what type of surface is used to create a path potholes may well develop when the surface is worn through use or becomes damaged by the winter weather.

pothole

In the case of bound surfaces like bitmac or asphalt, with repeated travel by path users over a weak or worn out surface, small hairline cracks can develop. These cracks can then eventually develop into larger cracks which can separate, allowing water to drain into the path's sub base. The water builds up in the sub base stone, freezes and expands, like a bottle of frizzy drink lifting the surface apart and creating a void. When the sub base stone thaws, a space is left between the sub base and surface course layers. Forces imposed by path users as they travel across the void, cause the surface course to sink into the void, with parts of it breaking away and a pothole starts to form.

With unbound or semi bound path surfaces - such as granite dust or Toptrec - where water scours down a sloping path, or, where insufficient camber or cross fall has not been provided to shed surface water off the path, small irregularities in the surface can hold water and form small puddles. When path users pass through these puddles, water is displaced quickly, washing out the fine particles of material and eroding the edges to increase their size.  This process can start to form potholes. As the surface is washed away the path's sub base stone becomes exposed and breaks up. The loose stone is eventually displaced by more water and path users. Progressively the potholes develop into larger and deeper holes.

In both cases, a pothole will get deeper and deeper as subsequent feet, wheels and hooves continue to pass over it, progressively causing more damage to the path. It can be easy to just fill the pothole in with some new materials in its existing condition, compact it down and walk away expecting it to last for a long time. Unfortunately, what happens in most cases is the pothole reappears.

It is important that potholes are repaired when they first appear. Do not wait for them to get large and difficult to fix. Knowing how to repair potholes efficiently will make them less of a nuisance and more cost effective. It also keeps your path in better condition.

The key principles to successful pothole repair are, whether it is an unbound, semi bound or bound path surface:

  • Undertake full depth repairs only, part depth repairs do not work - excavate the pothole to the full depth of the sub base layer, creating vertical sidewalls and straight edges inside the pothole repair area.

  • The excavated pothole repair area should be dry before backfilling - repairs should only be undertaken in dry weather conditions, if possible.

  • Backfill with new, dry granular sub base and surfacing materials only using the layer-on-layer technique.

  • Compact all new granular sub base and surfacing materials until firm. Non-compacted loose materials will soon get washed out by the first rainfall or will be displaced by path users.

Repairing potholes in an unbound or semi bound surface:

1. Mark out the repair area around the pothole, including all surrounding damaged areas, to allow ample working space.

2. With a hand-held power cut off saw, cut the marked repair area to form vertical sidewalls and straight edges ready for chiseling out and excavation.

3. With a pick (small repairs) or hydraulic breaker (large repairs), chisel out and excavate the cut repair area to the full depth of the sub base layer. Take care not to damage the geotextile sheet, if one is installed. Remove excavated and old materials from the cut repair area, to expose clean, vertical sidewalls and straight edges and level bottom ready for backfilling. Dispose of all excavated and old materials off site.

4. Backfill and level out new Type 1 material, up to about half the depth of the excavated repair area.

5. Compact the Type 1 with heavy tamper (small repairs) or wacker plate (large repairs) until it is solid and no further movement of materials. Backfill the remaining half of the excavated repair area with more Type 1 to just below the existing path surface levels. Again, compact to refusal. If necessary repeat the process until the Type 1 is finished at original sub base levels.

6. Backfill the remaining excavated repair area with new surfacing material that matches the existing unbound or semi bound path surface. Compact the surfacing material with heavy tamper (small repairs), vibrating plate or walk-behind vibrating roller (large repairs) until it is solid and no further movement of materials. Repeat the process until surfacing material is compacted and finished at original path surface levels. The pothole is now repaired!

Repairing potholes in a bound surface:

1. Complete steps 1 to 5 above for repairing potholes in an unbound or semi bound path surface.

2. Prior to laying the new bound surface course layer, the vertical cut edges of the existing surface course layer can be coated with a cold bitumen emulsion or hot cutback bitumen as a 'tack coat'. This will soften the existing surface course layer, encouraging it to bind together with the new hot bitumen bound material, helping to keep out water, and preventing it getting under the surface, where frost heave could cause the repair to fail.

3.Backfill the excavated repair area with the first layer of new, hot bitumen bound material, level out and them compact, using a heavy tamper (small repairs), vibrating plate or walk-behind vibrating roller (large repairs) until it is solid and no further movement of materials.

4. Apply a final layer of new, hot bitumen bound material, compact to refusal, and finish the new surface course layer just above the level of the original path surface.

5. Next apply a cold pour bitumen sealant to the seams of the repair to seal them. This sealant will prevent the ingress of water. Although this makes the pothole repair more noticeable, it will reduce the chance of the repair failing because of water penetration into the joints.

6. If possible, corner off the new repaired area to allow the newly laid surface course to cool down before being walked or ridden on, otherwise, the repair could be damaged, and you area back to square one again!

Remember, potholes will not fix themselves and if they are large enough, they will be hazardous to users; trip hazards for pedestrians and horse riders, and a hazard to cyclists, who have to swerve to avoid them, which can result in damage to the bike, and, more seriously, injury. It is best to deal with the problem as soon as it is discovered, not just from the user's point of view, but also for appearance. A path with many potholes looks unpleasant and gives the impression of general neglect, not good path management!

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