How to Repair Broken Terracotta Pots and Garden Features

Terracotta is a hard, fired clay that’s reddish-orange in colour, and is commonly used for making pots and garden features. This material has been used by human civilisations for centuries, dating back to the times of ancient China, Greece and Egypt, a testament to its usefulness.

Unlike plastic pots which degrade over time with exposure to sun’s UV rays, terracotta pots can last for decades, and are a natural material, making them far more sustainable to use.

The disadvantage of terracotta is that it is brittle, and can crack if dropped or exposed to freezing temperatures. That shouldn’t deter sustainable gardeners though, because terracotta can also be repaired, extending its serviceable life considerably.

In this article we’ll explain the various ways that cracked or broken terracotta can be repaired.

Can Terracotta Be Glued Back Together?

Most terracotta pots and garden features can be repaired fairly easily using modern adhesives, as they produce very structurally sound glue joins in this material.

Two different types of adhesives are be used for repairing terracotta, and each has its advantages and disadvantages.

1. Two-part epoxy adhesive – products such as Selleys Araldite Super Strength Epoxy (Australia), Loctite Epoxy Adhesive, J-B WELD Epoxy Adhesive, 3M Scotch-Weld Epoxy Adhesive (US)
   
2. Landscaping-grade exterior construction adhesive, also known as landscape block adhesive – products such as Selleys Liquid Nails Landscape (Australia), Loctite PL 500 Landscape Block Adhesive (US).

So, the question is, which to use?

Two-part Epoxy Adhesive for Terracotta Repairs

The two-part epoxy adhesives are better for smaller jobs, as it typically comes in a 24mL syringe, or 35mL (2×17.5mL) tubes. It is also better for cracked items, as it can be forced into a crack more easily than landscape construction adhesive. For cracked terracotta, use epoxy!

When using two-part epoxy, choose the super-strength formulations that take 24 hours to cure, they create a far stronger bond than the faster curing 5-minute varieties. The longer curing varieties give you more working time to glue everything together and align all the pieces together if they’re not fitting perfectly. In contrast, with the fast setting epoxy adhesives, once you’ve mixed the glue, there isn’t much working time before it hardens! It’s best to work without having to rush when carrying out these repairs!

Listed below are the features of two-part epoxy adhesives:

• Dry Clear
• Form a very strong, rigid, durable bond
• Very high water resistance, but not for use below the water line
• Can be used for gap filling, the surfaces don’t need to fit closely
• Good chemical resistance
• Heat resistant
• Clamping is recommended to achieve a stronger bond

Landscape Construction Adhesive for Terracotta Repairs

For larger jobs, exterior landscape construction adhesives are a better choice as they comes in large tubes for use in a caulking gun, which hold around 400g. Weight for weight, this adhesive is much cheaper than two-part epoxy. It’s typically used for installation of cement paving stones, securing block walls and capstones, stabilising and strengthening interlocking masonry walls, and for bonding brick, stone, timbers, concrete, metal and wood.

Using a large tube of adhesive for a small job is not very efficient, though the tubes can be capped to be used at a later time, but they don’t keep forever once opened.

Additionally, a caulking gun is required to use tubes of construction adhesive, but they’re quite inexpensive, only a few dollars, and a good quality one will last forever.

Listed below are the features of exterior landscape construction adhesives:

• High flexibility for coping with seasonal weather extremes which result in movement.
• Weather resistant bond, but not recommended for permanent water immersion applications.
• High temperature resistance, so the bond won’t crack.
• Can bridge minor gaps when bonding irregular surfaces
• Non corrosive.

One important disadvantage of exterior landscape construction adhesive is that it can’t be painted over.

How to Repair Cracked or Broken Terracotta in 5 Easy Steps

In this example, we’ll be repairing an unglazed terracotta bird bath pedestal, which is quite large, thick and heavy.

It’s important to note that neither two-part epoxy adhesive nor landscape construction adhesive can be used in applications where the joint will be under water permanently or for prolonged periods of time, and both are not suitable for use in aquariums or potable (drinking) water systems.

If a bird bath bowl for example was cracked, since it holds water and birds drink from it, these adhesives would not be suitable. In such applications, aquarium grade silicone sealer would need to be used, it’s what is used to glue the glass panels of fish tanks together. In such applications, it must be aquarium grade silicone sealant, as the bathroom and roofing grade silicone sealants contain toxic chemicals added to kill mold, fungi and bacteria.

Step 1 – Clean and Dry the Surfaces to Be Joined

If the joining surfaces of the broken pieces are dirty, they need to be cleaned for the adhesive to form a good bond:

How to clean materials being glued with two-part epoxy adhesives:

• Clean and dry surfaces to be glued.
• If necessary, wash with water, then allow to dry.

Note:

If dirt remains on the surfaces to be glued together and can’t be removed by washing, scrub them with a soft nylon brush while washing. Don’t use a wire brush, as terracotta is soft, and the wire brush will remove material, destroying the tight fit between parts.

Leave the pieces to dry thoroughly in the sun, it’s best to wait for as long as that takes, because moisture may affect the performance of adhesives.

How to clean materials being glued with landscape construction adhesives:

• Clean and ensure surfaces to be glued are sound, dry and free from oil, grease and loose powdery material.
  
• If necessary, use mineral turps (turpentine) to clean the surface, then allow to dry.

With either adhesive when repairing cracked terracotta that has not come apart:

• Clean the crack and the surrounding area on the outside and inside surfaces, removing any loose dirt or debris, so it doesn’t contaminate the glue join and weaken it.

Step 2 – Pre-fit Parts to Be Joined and Mark Them for Easy Alignment

Depending on the nature of the repair task, sometimes pieces will obviously fit back together only one way, but if there are multiple pieces, or if a symmetrical item is broken in two, alignment may not be so straightforward.

Before any glue is applied:

1. Test fit the pieces together.
   
2. Draw an alignment mark using a pencil. A simple line that crosses both pieces will suffice. Don’t press too hard, as you’ll want to erase the line afterwards!

If in doubt, make a test mark on the item in a discrete, non-visible location such as the underside, then try to erase it with a pencil eraser.

Step 3 – Prepare the Adhesive

Follow the steps outlined below to prepare whichever adhesive will be used.

How to prepare two-part epoxy adhesives:

1. Syringes – snap out cap from plunger and carefully cut the sealed tips at the end of the syringe tip.
   Tubes – pierce each tube with spike found in top of its own cap.
   
2. Dispense equal parts of both liquids onto a clean disposable surface. A piece of cardboard works well, or a small sheet of glass works for a non-disposable option that can be scraped clean and re-used indefinitely.
   
3. Mix both parts together thoroughly.
   
4. Depending on the formulation, the instructions on the label may recommend leaving the mixed glue for 5-10 minutes, then mixing it again before applying.
   
   Check the instructions for the product being used, as faster drying epoxy glues set faster also, with less working time. The glue used here is a 24-hour epoxy and the mixed glue remains usable for 1 hour at 20°C.

How to prepare exterior landscape construction adhesives:

1. Cut the tip of the cartridge and fit the nozzle
   
2. Cut the end of the nozzle to a suitable size opening (approximately 5mm)
   
3. Insert the adhesive tube into caulking gun.

Step 4 – Apply Glue to Broken Edges or Crack

Glue is applied to the broken pieces, which are then fit together using the alignment marks drawn in pencil earlier to line them up precisely.

With cracks, they can be opened with gentle pressure to create a gap to force adhesive in.

When the pieces are fitted together, glue will squeeze out of the join, that is inevitable. Both glues have their specific clean up directions listed below.

Using two-part epoxy adhesives:

1. Apply mixed glue to both surfaces of job, then bring together.
   
2. Hold join in place using tapes or weights if necessary. Do not apply undue strain to bond for 6-8 hours as this will squeeze out to much of the glue and weaken the joint. Maximum strength reached after 24-72 hours when using a 24 hour epoxy adhesive.
   
3. clean up any excess glue runoff with a cloth soaked in acetone (or nail polish remover), or carefully scrape off running glue to minimise smearing.

Handy tips for using two-part epoxy adhesives:

• For maximum working time, mix in small quantities. Large quantities accelerate the curing process and reduce working time.
  
• To extend product life replace caps immediately after use. Ensure you wipe excess from nozzle with a tissue (dipped in acetone or nail polish remover if necessary) before replacing cap.
  
• When using the tube variant, ensure you replace the correct cap on the correct tube. Placing the wrong cap on the wrong tube will cause the tube to harden. Caps and tubes are colour coded to help.
  
• To remove product after it has cured (hardened), mechanical action (scraping or sanding) is recommended. Since the product is chemically resistant, solvent will NOT dissolve this product.
  
• Allow for longer bonding times in colder weather.
  
• Clamping recommended for a stronger bond. Don’t use too much force as this will squeeze too much glue out, weakening the join.
  
• Bond strength will soften above 80°C but strength is retained when temperature returns to normal.
  
• To reposition the bond once cured, check that the item is heat resistant. If safe, heat the item slowly, e.g. in an oven, to at least 150°C. The product will soften and liquify slightly. Scrape off any excess then reposition the joint carefully using appropriate safety equipment. Allow the item to cool down in the correct position. The product will reharden once returned to room temperature.

Using landscape construction adhesives:

1. Using the caulking gun, apply ‘dobs’ or ‘beads; of adhesive of appropriate thickness to ensure sufficient contact and spread between both surfaces. To minimise ‘squeeze out’ apply at least 12mm in from edges.
   
2. Immediately bring surfaces together before product forms a skin (within 5 minutes) and apply sufficient pressure to spread adhesive between both surfaces.
   
3. Do not wipe excess ‘squeeze out’. Wait until product cures and them remove excess by trimming with a sharp blade, but avoid cutting into the bond. Any adhesive that has dripped onto other surfaces can be cleaned with a cloth soaked with mineral turpentine, but don’t clean the surface of the glue join with it.
   
4. Leave undisturbed until adhesive cures sufficiently. Do not place any load or stress on the join for 24 hours.

Handy tips for using landscape construction adhesives:

• If repositioning materials, fresh adhesive must be applied to achieve bonding.
  
• Working time is 10 minutes. Ensure surfaces are brought together before this time.
  
• Spilt or smeared adhesive is best left to cure and then remove by abrasion.

Step 5 – Clean Up Dry Glue

Once the glue had dried, any drips and runoff need to be cleaned up and removed , otherwise they can look unsightly.

Clean Up for two-part epoxy adhesives:

• Uncured (unhardened) product may be removed with acetone.
  
• Cured (hardened) product can be scraped, and can softened with heat to make scraping easier.
  
• Cured (hardened) product can be sanded using sandpaper and a sanding block.

Clean Up for landscape construction adhesives:

• Uncured product may be removed with mineral turpentine.
  
• Cured (hardened) product can be removed by mechanical action such as cutting or scraping. Remove excess by trimming with a sharp blade, but avoid cutting into the bond.
  
• Cured (hardened) product can be removed with a silicone remover (such as Selleys Silicone Remover)

In the example below, I used a coarse 80-grit sandpaper to sand away the dried epoxy adhesive. The material had a rather coarse finish, so I was able to use a fairly coarse grit sandpaper. For terracotta with a finer finish, something like a 220-grit may be more appropriate.

Use an aluminium oxide sandpaper, it’s are suitable for all materials and is long-lasting, garnet-based sandpapers are only suitable for woodworking.

The terracotta dust from sanding shown below can be gathered, and mixed with epoxy glue to fill in any large gaps still visible in the glue join. Mix epoxy as described previously, add enough terracotta dust to make a paste, apply to any gaps, allow to dry, then sand once again. This step is optional, and I just left the glue join as it was after sanding it smooth.

Here is the repaired birdbath, ready to be set up in the garden.

The assembled bird bath looks great, and easily bears the weight of the bowl on top,

Birdbath repaired and in place, test filled with some water, which is why the bowl appears darker, and ready to be filled with water.

Cutting Corners…

No matter how much a technical writer lays out instructions on what to use and how to perform a certain task, some people want to cut corners or try to do things on the cheap, resulting in disappointment and wasted money.

To explain the ‘whys’ with some science to dissuade any recklessness, I’ve included this section.

What Is the Difference Between Interior and Exterior Construction Adhesive?

Landscape construction adhesive is not the same as interior construction adhesive, they are completely unrelated adhesives with completely different properties.

Here are two extracts from the materials safety data sheets for two such products.

The first is an interior construction adhesive, it’s a polyurethane-based adhesive, and the ingredients are listed for comparison.

SELLEYS LIQUID NAILS RAPID CURE

3. COMPOSITION INFORMATION
CHEMICAL ENTITY CAS NO PROPORTION
4, 4′ – diphenylmethane diisocyanate (MDI) 101-68-8 10 – 30 % (w/w)
2,4 – diphenylmethane diisocyanate (MDI) 5873-54-1 10 – 30 % (w/w)
Morpholine, 4,4′-(oxydi-2,1-ethanediyl)bis- 6425-39-4 1 – 10 % (w/w)
Benzene, 1,1′-methylenebis[2-isocyanato- 2536-05-2 <1 % (w/w)
Ingredients determined to be non-hazardous or below reporting limits Balance
____________
100%

The second is a landscape construction adhesive, for outdoor use. It is NOT a polyurethane adhesive, and as such, the ingredients are completely different.

SELLEYS LIQUID NAILS LANDSCAPE

3. COMPOSITION INFORMATION
CHEMICAL ENTITY CAS NO PROPORTION
2-Butanone, O,O’,O”-(methylsilylidyne)trioxime 22984-54-9 1 – 10 % (w/w)
Distillates, petroleum, hydrotreated middle 64742-46-7 1 – 10 % (w/w)
2-Butanone, O,O’,O”-(ethenylsilylidyne)trioxime 2224-33-1 <1 % (w/w)
1,2-Ethanediamine, N-[3-(trimethoxysilyl)propyl]- 1760-24-3 <1 % (w/w)
Ingredients determined to be non-hazardous or below reporting limits Balance
____________
100%

The only similarity is in the name of the product, but that’s where the similarity ends, they are not interchangeable.

Do use interior construction adhesive to repair terracotta.

Why Can’t Epoxy Adhesives Be Used in Potable Water Applications?

Two-part epoxy should never be used in applications where drinking water will be in contact with the glue, either for humans, other animals or fish swimming in it. Firstly, the glue will fail if immersed for prolonged periods of time or permanently underwater, but the hardened glue is a form of plastic now banned form use in drinking vessels.

Everyone remembers the heath concerns and news headlines that hit worldwide in 2008 over food containers made with BPA plastics and metal drink bottles and cans lined with BPA, and how this chemical leached into food and beverages, poisoning people. Bisphenol A (BPA) and is known endocrine-disruptor, it’s a synthetic estrogen (xenoestrogen), so it mimics the hormone estrogen causes hormonal imbalances. In animal studies, researchers have linked developmental exposure to various serious health concerns, such as reproductive harm, increased cancer susceptibility, and abnormalities in brain development and fat metabolism.

Now, guess what one half of two-part epoxy resin conttains? Looking at the ingredients list below, it’s Bisphenol-A (BPA), so, wear gloves when using it, and don’t use it for potable water applications.

SELLEYS ARALDITE SUPER STRENGTH EPOXY
ADHESIVE – PART A

3. COMPOSITION INFORMATION
CHEMICAL ENTITY CAS NO PROPORTION
Bisphenol-A epoxy resin 25068-38-6 >60 % (w/w)
Bisphenol F epoxy resin 9003-36-5 10-30 % (w/w)
Ingredients determined to be Non-Hazardous Balance
____________
100%

SELLEYS ARALDITE SUPER STRENGTH EPOXY
ADHESIVE – PART B

1,2-Ethanediamine, N,N’-bis(2-aminoethyl)- 112-24-3 <10 % (w/w)
1,3-Propanediamine, N’-(3-aminopropyl)-N,N-dimethyl- 10563-29-8 <10 % (w/w)
Ingredients determined to be Non-Hazardous Balance
____________
100%

Is Glue Alone Sufficient to Repair Terracotta?

Most terracotta pots and garden features can be repaired fairly easily using appropriate modern adhesives, which can create very structurally sound glue joins in this material.

It’s only when fastening very large pieces of broken terracotta that bear very heavy loads that additional support is required. This is usually done by drilling and wiring the pieces together to brace them, and gluing them, but this is a tedious process and the final result looks unsightly.

To drill and wire terracotta together, a series of holes are drilled in both pieces of terracotta using a narrow diamond drill (glass and tile drill bit) around 3 – 5mm (1/8” – 3/16”) thick. They are used for drilling holes in bathroom tiles and can be purchased from a hardware store.

When using an electric drill, if it’s a hammer drill, don’t use the hammer drill setting which is used for drilling masonry such as concrete and brick, just set it to the regular drilling setting otherwise it will smash the terracotta, it’s a soft material.

For most terracotta items in the garden, glue alone is sufficient, as long as the right one is used for the job.