How To Adhere Concrete Mailbox to Exposed Aggregate Driveway
Which adhesive fixes a reinforced concrete mailbox to an exposed aggregate driveway?
Check the Liquid Nails Landscape specification
Selleys' product page and its dated technical sheet disagree on Landscape's chemistry, colour, paintability and pack size. Landscape figures below from the November 2020 technical sheet describe that document, not a confirmed specification for every current cartridge. Confirm the matching instructions before painting, choosing a colour, or relying on cure and loading times. See the source comparison and dated documents.
Liquid Nails Landscape is ideal for this job. It is a premium grade, high strength construction adhesive that delivers a weather resistant, high strength, flexible and shock proof bond, and it is made for exactly this class of work — stone, concrete, capstones, terracotta and timber outdoors.
You will need to support or protect the mailbox from being moved or bumped for the first 2 to 3 days. You can also use Selleys 650FC adhesive sealant, which is available in grey, white or black.
What exposed aggregate does to the job
This is the part worth thinking about, because an exposed aggregate driveway is not a flat surface and that changes how you apply the adhesive.
The contact area is much smaller than it looks. Exposed aggregate is a field of stone tips standing proud of the matrix. A flat concrete base set onto it touches only the high points. If you apply a thin, even bed of adhesive the way you would on a smooth slab, most of it never touches anything.
The answer is in the directions themselves: apply dobs or beads of adhesive of appropriate thickness to ensure sufficient contact and spread between both surfaces. On exposed aggregate, "appropriate thickness" means generous — thick enough that when you press the mailbox down, the adhesive is squashed into the valleys between the stones as well as onto their tips. That gives you both a larger bonded area and a mechanical key into the surface texture.
Cure runs at 2 mm per 24 hours, from the outside in. A thick bed takes correspondingly longer to cure through than a thin one, which is precisely why the advice is 2 to 3 days of protection rather than the 24 hours the data sheet gives as a minimum before traffic. On a mailbox that will be knocked by a wheelie bin or leaned on by a delivery driver, take the longer figure.
The numbers
| Property | Liquid Nails Landscape | Selleys 650 FC |
|---|---|---|
| Technology | Neutral cure silicone | Silane modified polymer |
| Colour | Grey | Grey, black, white |
| Packaging | 300 g cartridge | 300 mL cartridge or 600 mL sausage |
| Skin time | 10–15 minutes | 20 minutes |
| Tack free time | 35 ± 5 minutes | — |
| Cure rate | 2 mm / 24 hrs | 2.5 mm / 24 hrs |
| Shore A hardness | ~30 | 40 ± 5 |
| Elongation at break | >300% | >500% (ASTM D412) |
| Joint movement | — | ±20% |
| Tensile strength | — | 2 MPa |
| Application temperature | — | 5–35°C |
| Service temperature | — | −40°C to +70°C, brief points at 100°C |
Indicative data only, not intended for the preparation of specifications.
Which one to choose. Landscape is grey, which disappears against concrete, and it is the product specifically built for landscaping work. 650FC is the stronger of the two on published figures, is available in three colours, and is rated to −40°C — worth having if you are in a frost area. Landscape's flexibility and shock-proof bond are the more relevant properties for something that gets bumped. For Landscape, confirm the specification for your cartridge: the manufacturer sources disagree.
How to fix it down
- Ensure the driveway surface is sound, dry and free from oil, grease and loose powdery material. If necessary, clean with mineral turpentine and allow it to dry. Sweep out the valleys between the aggregate — that is where the dust sits.
- Check the base of the mailbox too. New precast concrete often carries a film of release agent, which will stop any adhesive bonding. Wash it, or abrade it, and let it dry.
- Position the mailbox and mark around it so you know exactly where it goes.
- Cut the cartridge tip, fit the nozzle and cut it to a suitable size opening — approximately 5 mm. Apply with a caulking gun.
- Apply dobs or beads of adhesive of appropriate thickness to ensure sufficient contact and spread between both surfaces. Keep them at least 12 mm in from the edges to minimise squeeze-out.
- Immediately bring the surfaces together before the product skins — within 5 minutes — and apply sufficient pressure to spread the adhesive between both surfaces. On a heavy mailbox, its own weight does most of this; rock it slightly to seat it.
- Do not wipe excess squeeze-out. Wait until the product cures, then remove it by trimming with a sharp blade, taking care not to cut into the bond.
- Leave it undisturbed. Do not allow traffic or loading for at least 24 hours, and protect the mailbox from being moved or bumped for 2 to 3 days.
Limitations
- Not for soft or crumbly materials. If the driveway surface is flaking or the aggregate is loose, the adhesive will hold the loose material rather than the slab. Deal with that first.
- Do not use as the sole bonding agent for structural bonding. A mailbox is not structural, but this is why a large or top-heavy pier should be dowelled or pinned as well as glued.
- If repositioning, fresh adhesive must be applied to achieve bonding. You cannot lift the mailbox to check and put it back down on the same adhesive.
- Not for permanent water immersion. Rain and puddles are fine; a base sitting in standing water is not.
- For 650FC: do not apply below 5°C; not recommended for continuous submersion; do not apply in the presence of curing silicone or polyurethane sealants; avoid solvent cleaners during cure.
- Consider whether your council or the property has requirements about where a mailbox may be fixed, particularly on a shared driveway.
Clean up
Uncured product removes with mineral turpentine. Cured product can be removed with Selleys Sealant Remover or by mechanical action. Spilt or smeared adhesive is best left to cure and then removed by abrasion — which on exposed aggregate is genuinely difficult, so mask around the base before you start.
Safety: adhesive and clean-up hazards
Check each adhesive and any clean-up product separately; their hazard classifications differ.
Selleys 650 FC is classified Warning — H319 (causes serious eye irritation) and H317 (may cause an allergic skin reaction). Liquid Nails Landscape's Australian SDS version 7.0, 16 November 2023, lists Danger: H227, H317 and H318 — combustibility, allergic skin reaction and serious eye damage. Follow the matching pack and SDS for protection, handling and first aid.
Selleys Sealant Remover, named in the clean-up section above, also presents serious hazards. It is classified Danger, Poison Schedule S5, and carries H304 (may be fatal if swallowed and enters airways), H226 (flammable liquid and vapour), H336 (drowsiness or dizziness) and H315 (skin irritation). More than 60% of the tub is petroleum naphtha.
What follows for this job
H304 is not a swallowing warning in the ordinary sense. It means that if the material goes down and any of it reaches the airways, it can cause a chemical pneumonitis that can kill. Light hydrocarbons flow rather than being coughed back, which is why the first aid instruction is to never induce vomiting — vomiting is the mechanism that gets swallowed solvent into the lungs. The reason this matters on a mailbox job is the setting: the tub is a beige paste that looks like ordinary filler, and it gets left open on a front driveway where children and dogs go past. Lid on between applications, and put it up high, not on the step.
The flammable and narcotic classifications are the one place this job is genuinely easier than most. H226 and H336 are both about the air around you, and a driveway is open air. The exposure that gets people is the same product used in a closed bathroom. Keep it outdoors, keep the turps you clean up with away from anything hot, and do not smoke over it.
H317 on 650 FC belongs to the method above. You are told to seat a heavy mailbox by rocking it, which forces squeeze-out, and then to leave the squeeze-out to cure rather than wipe it. Both of those are hand-contact moments. Sensitisation is permanent once acquired and is built from repeated casual contact, not one incident — so gloves, on a job where you would not normally bother.
The lower-hazard route for the clean-up is already on this page: mechanical action. Trimming cured adhesive with a sharp blade carries no chemical hazard at all, and on a mailbox base there is not much of it. Poisons Information Centre — 131 126 in Australia, 0800 764 766 in New Zealand.
Common questions about fixing a mailbox to a driveway
How long before it is safe to bump?
Support or protect the mailbox from being moved or bumped for the first 2 to 3 days. The data sheet's minimum is no traffic or loading for at least 24 hours.
Will it stick to exposed aggregate?
Yes, provided the surface is sound. Liquid Nails Landscape is intended for stone and concrete. Apply dobs thick enough to fill between the aggregate rather than a thin even bed.
How much adhesive do I need?
Landscape comes in a 300 g cartridge. An exposed aggregate surface consumes more than a smooth slab because of the thicker dobs required. For Landscape, confirm the specification for your cartridge: the manufacturer sources disagree.
Do I need to prepare the mailbox base?
Yes. New precast concrete often carries release agent, which prevents bonding. Wash or abrade it and let it dry.
Can I lift it to check the coverage?
No. If you reposition it, fresh adhesive must be applied to achieve bonding.
What if the driveway surface is crumbly?
Landscape is not for soft or crumbly materials. Clean back to a sound surface first.
What about wind and knocks in the long term?
Landscape gives a weather resistant, flexible, shock proof bond. For a tall or top-heavy pier, do not rely on adhesive alone — it must not be used as the sole bonding agent for structural bonding.
Which colour do I want?
Landscape is grey only. 650FC comes in grey, white and black. For Landscape, confirm the specification for your cartridge: the manufacturer sources disagree.
How do I deal with squeeze-out?
Do not wipe it. Let it cure and trim it with a sharp blade, avoiding cutting into the bond.
Can I use this for pavers too?
What adhesive should be used to fix a reinforced concrete mailbox to an exposed aggregate driveway?
Liquid Nails Exterior is the recommended adhesive for adhering a reinforced concrete mailbox to an exposed aggregate driveway. It is a high-performance construction adhesive designed for outdoor use and delivers 3 tonnes per m² adhesion strength after just 4 hours on porous surfaces, and it resists heat, water, and UV radiation without cracking or becoming brittle.
Are there alternative adhesives to Liquid Nails Exterior for bonding concrete to concrete?
Yes, Liquid Nails Heavy Duty or Liquid Nails Original could also be used for bonding concrete to concrete, though these are better suited for covered applications rather than fully exposed outdoor surfaces like a driveway.
How should the driveway and mailbox surfaces be prepared before applying the adhesive?
Both the concrete mailbox base and the exposed aggregate driveway surface should be clean, dry, and free from dust, oil, grease, and loose particles. Any pooled water should be removed from the driveway surface, and the bonding surfaces should be cleaned thoroughly to maximize contact between the adhesive and both substrates.
What is the step-by-step process for applying Liquid Nails Exterior to install the mailbox?
First, cut the cartridge tip and fit the nozzle to the caulking gun. Then apply a 5mm bead of Liquid Nails Exterior to the base of the mailbox in a pattern that ensures sufficient contact spread. Press the mailbox firmly onto the driveway surface before the adhesive skins, which happens within about 20 minutes depending on weather. If necessary, use temporary bracing or support to hold the mailbox in position while the adhesive cures.
How long does Liquid Nails Exterior take to reach its bonding strength on porous surfaces?
Liquid Nails Exterior delivers 3 tonnes per m² adhesion strength after just 4 hours on porous surfaces.
Why is Liquid Nails Exterior suitable for an exposed aggregate driveway specifically?
Liquid Nails Exterior is engineered to resist heat, water, and UV radiation without cracking or becoming brittle over time, which is critical for exposed aggregate surfaces that face constant weathering and outdoor exposure.