When Can Resin Be Laid Over an Existing Surface?
For an overlay installation to be suitable, the existing surface must meet all of the following criteria:
- Structurally sound — no significant cracking, subsidence, or areas of failure
- Stable — no movement, heaving, or areas that flex under load
- Adequate drainage — the existing drainage arrangement must still work effectively. For a resin bound overlay to remain permeable, the sub-base beneath must also be permeable (open-graded stone or similar)
- Free from contamination — oil, chemical, or fuel contamination can prevent proper adhesion of the resin primer
- Level and even — significant undulations or lips will telegraph through the overlay
- Sufficient depth clearance — the overlay adds approximately 15–18mm of depth, which must be accommodated at thresholds, garage entrances, and drainage channels
Resin Over Tarmac
Tarmac (asphalt) is one of the most common existing surfaces under resin overlays, and it works well when in sound condition. Key considerations:
- Tarmac must be structurally intact with no soft spots, potholes, or major cracking
- Surface must be thoroughly cleaned and degreased before priming
- Any cracks wider than approximately 2mm should be filled and sealed prior to overlay
- Tarmac less than 12 months old should be avoided — fresh tarmac may still be off-gassing compounds that can affect resin adhesion
- Old or oxidised tarmac surfaces may need a specialist primer to ensure adhesion
Resin Over Concrete
Concrete bases are excellent substrates for resin overlays when in good condition. Points to check:
- Concrete must be crack-free — concrete's tendency to crack with ground movement means any existing cracks are likely to reflect through the overlay over time
- Surface must be clean and free from laitance (the weak surface layer that forms on concrete when it cures)
- Expansion joints in the concrete must be replicated in the resin overlay to prevent cracking
- Damp concrete can prevent proper resin adhesion — the surface should be dry before installation
When an Overlay Is NOT Suitable
An overlay should not be attempted in the following situations:
- The existing surface has widespread cracking, subsidence, or is breaking up
- There are areas of standing water indicating drainage problems
- The existing base is block paving, gravel, or soil — these cannot support a resin overlay
- There is significant oil contamination that cannot be fully removed
- The existing surface is at a level that would cause problems at thresholds or drainage points if raised further
- Tree roots are causing movement in the existing surface
In these cases, full excavation and installation of a new sub-base is the correct approach. While more expensive upfront, it avoids the risk of premature failure that an unsuitable overlay would carry.
⚠️ The Risk of Skipping a Survey
Some homeowners ask for an overlay installation to keep costs down, even when the existing surface may not be suitable. A reputable installer will always carry out a proper site survey and advise honestly on suitability. Be cautious of any contractor who agrees to overlay without a survey — if the installation fails prematurely, the cost of full removal and replacement can exceed the original saving.
Cost Saving of Overlay vs Full Installation
When an overlay is suitable, the cost saving is meaningful:
| Installation Type | Typical Cost Per m² | Notes |
|---|
| Overlay (existing base suitable) | £55 – £85/m² | No excavation or sub-base required |
| Full installation (new sub-base) | £80 – £120/m² | Includes excavation, sub-base, and surfacing |
For a typical 50m² driveway, a suitable overlay could save between £1,250 and £1,750 compared to full excavation and installation.
The Installation Process for an Overlay
- Site survey — installer assesses the existing surface condition, drainage, levels, and thresholds
- Surface preparation — thorough pressure washing, crack filling, and degreasing as required
- Priming — specialist primer applied to ensure adhesion between existing surface and new resin layer
- Edging installation — aluminium or steel edging strips installed around the perimeter to contain the overlay
- Resin mixing and laying — aggregate and resin mixed in a forced action mixer and laid to the correct depth (typically 15–18mm)
- Curing — surface cures within a few hours in good conditions; typically walkable within 4–6 hours and driveable within 24–48 hours
How to Arrange a Survey
The best way to find out if an overlay is suitable for your driveway is to request a free site survey from a professional installer. They will assess your existing surface and advise on the most appropriate and cost-effective installation approach for your specific situation.