Preparing Broken Terracotta Pots

What product repairs a broken outdoor terracotta pot or garden planter?

Use a neutral cure silicone. Selleys nominates two for this job — Selleys Roof & Gutter Silicone and Selleys Brick & Concrete Silicone — and either will give a weatherproof, long-term repair.

The reason a silicone suits a cracked planter better than a rigid glue is movement. A terracotta pot sitting outdoors goes through a full temperature swing every day, gets loaded and unloaded as the soil wets and dries, and the pot itself is porous and brittle. A rigid bond concentrates that stress on a thin line of adhesive and the pot cracks again beside the repair. A silicone joint stretches instead. Brick & Concrete Silicone is rated at plus or minus 50% joint movement capability (ISO 9047), Roof & Gutter at plus or minus 25%.

Which of the two to choose

Both are neutral cure and both cure at 2mm per 24 hours, so the substrate and the position decide it.

Brick & Concrete Silicone is the closer match for terracotta. Its data sheet lists bricks and mortar, fibre cement, metal, ceramics, porcelain, concrete, marble and stone, wood and most plastics among its materials — fired clay sits squarely in that group. It is the more flexible of the two, and it carries a 25-year guarantee against cracking, crumbling or peeling away. It comes in a 415 g cartridge in grey.

Roof & Gutter Silicone is the one to pick if the pot lives in full sun all day. Its data sheet makes UV and weather resistance a headline feature, it is available in a range of colours so you can get closer to the terracotta tone, and its listed porous substrates include bricks, concrete, masonry, timber and fibre reinforced cement. It also has a wider service temperature range, from -60°C to +150°C.

What the figures mean for the repair

Property	Brick & Concrete Silicone	Roof & Gutter Silicone
Technology	Neutral cure (oxime)	Neutral cure, 100% silicone, moisture curing
Cure rate	2mm / 24 hr	2mm / 24 hr
Tooling time	35 minutes	5 minutes
Skin time	70 minutes	5–10 minutes
Tack-free time	90 minutes	30 minutes
Joint movement	±50% (ISO 9047)	±25%
Elongation at break	960%	330% (ASTM D412)
Shore A hardness	16	32
Application temperature	—	+5°C to +30°C
Paintable	No	No

Figures are indicative data only and are not intended for the preparation of specifications.

The number that governs your working day is the 2mm per 24 hours cure rate. It describes depth, not surface. A hairline crack in a pot wall skins over quickly and is effectively done in a day, but if you have packed silicone into a chip several millimetres deep, the middle of that plug is still soft after 24 hours. Brick & Concrete Silicone's own directions say the sealant will cure in 72 hours, at which point excess can be trimmed off with a sharp blade — take that as your realistic figure before repotting.

The difference in tooling time is the other practical split. Roof & Gutter skins in 5 to 10 minutes and gives you about five minutes to shape the joint; Brick & Concrete gives you 35. On a fiddly curved break with several pieces to line up, that extra half hour is worth having.

How to do the repair

1. Clean both broken faces thoroughly and get them dry. Remove oil, dirt and grease with mineral turps — Brick & Concrete Silicone's data sheet names turps specifically for surface preparation. Old potting mix in the break is the usual cause of a failed repair.
2. Cut the cartridge tip, cut the nozzle at a 45° angle, fit the nozzle and load the cartridge into a caulking gun.
3. Hold the gun at 45° and gun the sealant ahead of the nozzle, pushing product into the joint rather than laying it on the surface. A bead sitting on top has no depth of bond.
4. Bring the pieces together and support them — tape, a strap, or the weight of the pot itself — while the silicone sets.
5. Tool the joint smooth with a spatula dipped in soapy water, or in mineral turps, before the sealant skins.
6. Clean up excess with a cloth dampened in mineral turps before it skins. Once cured, silicone has to be cut or scraped off, or removed with Selleys Sealant Remover.
7. Leave it 72 hours before putting the pot back into service.

If you are working with Roof & Gutter Silicone, note its joint design guidance: minimum joint width and depth is 5mm, and for widths up to 12mm use a width-to-depth ratio of 1:1. A very fine crack may be worth opening out slightly so there is enough material in the joint to flex.

Limitations — where these silicones should not be used

• Neither is paintable. If you want to paint the pot, paint it first and allow at least seven days before applying the sealant on top.
• Not for continuous submersion or below-waterline use. A repaired pot that drains is fine; a pot converted into a pond or water feature is not a suitable application for either product.
• Brick & Concrete Silicone is not for below-ground applications. Do not use it on a pot or edging that will be buried.
• Not for polyethylene, polypropylene or Teflon. Pre-test any plastic before use. This matters if the "terracotta" pot is actually a moulded plastic lookalike.
• Roof & Gutter Silicone must not be applied if the ambient or substrate temperature is below +5°C or above +40°C, and it needs atmospheric moisture to cure — in low humidity, curing slows.

Safety: what these products need

The two silicones nominated for this repair are mild. The remover mentioned in the clean-up step is not.

Product	Classification
Roof & Gutter Silicone	Warning — H319 serious eye irritation, H317 may cause an allergic skin reaction
Brick & Concrete Silicone	Warning — H227 combustible liquid, H315 skin irritation, H317 allergic skin reaction. No eye classification
Selleys Sealant Remover	Danger, Poison Schedule S5 — H304 may be fatal if swallowed and enters airways, H226 flammable liquid and vapour, H336 drowsiness or dizziness, H315 skin irritation

What follows for a pot repair

H304 is the one to take seriously, and the setting is why. Aspiration hazard Category 1 means that if the material is swallowed and any reaches the airways it can cause a chemical pneumonitis that is potentially fatal — which is why the first aid is to never induce vomiting. More than 60% of the tub is petroleum naphtha, but it presents as a beige paste in a screw-top tub that looks no more threatening than filler, and garden work is done where children and dogs are. Lid on between applications, and it goes back on a high shelf, not the potting bench.

H226 and the garden shed. Sealant Remover is a Class 3 flammable liquid, Packing Group II. Sheds are where the mower fuel, the whipper snipper and often a fridge compressor live. Brick & Concrete Silicone is separately a C1 combustible liquid for storage purposes under AS 1940 — academic for one cartridge, not for a carton. Store both away from fuel and away from anything that sparks.

H317 belongs to the method above. Holding several curved pieces of a broken pot together while a bead sets is a job done with fingers, and tooling with a turps-dampened cloth puts uncured silicone against skin repeatedly. Sensitisation is permanent once acquired and is built from exactly this kind of small, repeated contact. Gloves, and tool with a spatula rather than a finger.

The choice between the two silicones has a safety dimension as well as a technical one. If you are leaning over an upturned pot, gunning sealant into a crack with your face above the work, Brick & Concrete Silicone carries no eye classification at all, where Roof & Gutter carries H319. Its longer 35-minute tooling time also means less rushing. Safety glasses either way.

The lower-hazard clean-up is already on this page: let squeeze-out cure and trim it with a sharp blade. Poisons Information Centre — 131 126 in Australia, 0800 764 766 in New Zealand.

Common questions about repairing terracotta pots

Why neutral cure rather than an ordinary silicone?

Neutral cure is what Selleys specifies for this repair. Both nominated products cure by reaction with atmospheric moisture without releasing an acid as they do it.

How long until I can replant the pot?

Allow 72 hours. Both products cure at 2mm per 24 hours, and Brick & Concrete Silicone's directions give 72 hours as the point at which the sealant is cured and excess can be trimmed.

Can I paint over the repair to hide it?

No. Neither silicone is paintable. Roof & Gutter Silicone is available in a range of colours, which is the better way to make the repair less obvious.

Will the repair survive a frost or a heatwave?

Brick & Concrete Silicone has a stated temperature resistance of approximately -40°C to 140°C. Roof & Gutter Silicone has a service temperature range of -60°C to +150°C.

Will it hold if the pot is full of wet soil?

Damp soil against the inside of the pot is within normal service. Continuous submersion is not — neither product is recommended for below-waterline use.

How do I get rid of the silicone that squeezed out?

Wipe it with a cloth dampened in mineral turps before it skins. Cured silicone has to be trimmed with a sharp blade, scraped off, or softened with Selleys Sealant Remover. When trimming, avoid under-cutting the seal.

What if the pot is glazed rather than bare terracotta?

Brick & Concrete Silicone lists ceramics and porcelain among its substrates, so a glazed pot is covered. Clean the glaze with mineral turps first — a glazed surface holds oils that a porous one absorbs.

Can I use these silicones on other outdoor stone and masonry repairs?

Yes. Brick & Concrete Silicone is made for joints in walls, patios, floors, fencing, windows and expansion joints in concrete. See also gluing sandstone to sandstone and fixing a cement paver to a concrete surface.