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Why Polymer Clay Breaks and How to Fix it

Polymer Clay is super popular in the crafting world right now, and many people are creating beautiful designs to keep, sell and wear! But what if one of your lovely polymer clay pieces breaks and why does this happen?

Why does polymer clay break?

Polymer clay breaks if the clay has not cured properly (this is due to either the temperature being too low or it wasn’t baked for long enough), if the design is uneven, or if the clay has been exposed to significant changes in temperature or humidity after baking.

Can broken polymer clay be fixed?

Broken polymer clay can be fixed with either clay dust and glue or with plumber’s putty.

Phew, that’s good news, and I’ve got the solutions for you!

Read on to learn why your clay is breaking or cracking and how to avoid it, as well as a how-to on how to fix your already cracked designs

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Why Polymer Clays breaks and How to Avoid it

Polymer clay breaks after baking because it has not cured properly. This is due to either the temperature being too low or it wasn’t baked for long enough.

It does also depend on the brand of clay you are using, as some are more brittle, some are harder. For example air drying brands are more brittle, and I believe oven baked is best, especially if you are making polymer clay jewellery like earrings!

Check out my how-to guide on making polymer clay earrings

You want your designs to be made of the sturdiest clay possible, to prevent breaking after baking, or breaking once the customer has received them – (that’s a no no!).

So, how do you properly bake your brand of clay?

Brands and their baking instructions

Here is a breakdown of how to bake each brand of clay, according to their packaging instructions:

Cernit: 30 minutes between 110 and 130°C (230-266°F)
Fimo: Maximum of 30 minutes at 110°C (230°F)
Kato Polyclay: 10-30 minutes at 150°C (300°F)
Original Sculpey: 15 minutes per quarter inch (6mm) of thickness at 130°C (275°F)
Pardo Art Clay: Min 30 minutes at 120 decrees (248 F)
Pardo Translucent Jewellery clay: Min 30 minutes at 120°C (248°F)
Premo: 30 minutes per quarter inch (6mm) of thickness. If thicker, initially bake for 15 minutes and then add another 5 minutes, another 5, and so on until done.
PVClay: 15-20 minutes at 130°C (275°F)
Sculpey III: 15 minutes per quarter inch (6mm) of thickness at 130°C (275°F)
Sculpey Souffle: 30 minutes per quarter inch (6mm) of thickness at 130°C (275°F)
Super sculpey: 15 minutes per quarter inch (6mm) of thickness at 130°C (275°F)

Top tip: you can always bake your clay again, if it’s not fully done the first time!

Check out my full guide to baking Polymer Clay

Understanding proper curing

Polymer Clay is made of polymer, stabilizers, dyes and fibres, and all of the components need to properly fuse during the baking process in order to make sturdy designs – sounds a bit like a science experiment, right? Well, it kind of is!

Understanding what makes up your clay, and how to get it to work for you is key in mastering this craft.

Side note – the clay is non-toxic so don’t worry about baking it at home, this is what it’s designed for!

Other reasons for breaking

Cracks and breaking can also be caused by variations in thickness throughout the design.

Make sure your clay slabs are rolled out properly and uniform; for example if you’re making a heart shape and one side is slightly thicker than the other, this will cause the piece to bake irregularly on either side, and one side may be more susceptible to cracks or breaks.

Alternatively, clay can also crack due to exposure to extended humidity or significant changes in temperature after baking, so make sure to store your clay somewhere safe and dry.

The test piece

Test Pieces are a sure fire way to make sure your batch of clay is fully baked.

Myself and many other polymer clay makers like to use ‘The Bend or Snap Method’ – very Elle Woods right?

The Bend or Snap Method’; your baked clay should bend but not be brittle, you should be able to leave a mark in the clay with a needle or fingernail, but not sink deep into the design.

The importance of a test piece in every batch is paramount, so you can check if your clay is done with the above method.

It’s even better to run tests before batch making, to learn about your brand of clay/oven combination, and how the clay turns out.

Top tip: Sealing the clay after baking with varnish will add an extra hardened layer to your design

How to Fix Broken or Cracked Polymer Clay

Tiny hairline cracks or breaks after baking? oh no 🙁 but wait…

If one of your master pieces is already broken – fear not! There are several ways to fix broken or cracked polymer clay.

Rule number 1.

Don’t just add new clay to your pieces and re-bake them – the clays won’t adhere to each other properly and the originally baked clay can be over baked, causing browning or burning.

Sometimes stuffing the breakages with new clay can actually make the problem worse, by growing the cracks as the clay expands very slightly when baking.

DO THIS instead

Instead adding clay shavings (like a dust) to baked pieces, can fill in the tiny hairlines.

Make the clay dust by rolling or shaving very fine pieces of clay from the same colour block you created your design from – using a grater is easiest.

Once this is done add glue to your tiny clay shavings and mix it up, creating a paste to carefully apply to your design’s cracks.

Use a super fine painting brush to do this, so you can get really precise.

The second way is to use plumbers putty on the cracks to fill them in, sand down and paint over them.

Once you’ve applied the putty, wait 10 – 30 minutes for it to harden naturally (no need to bake, just leave out to air dry), and then you can use super fine sanding paper over the cracks to smooth out any jagged edges the putty may have created.

Once this is done, apply acrylic paint in a colour match over the cracks to seal everything up.

Try out these awesome acrylic paint pens, to get really precise when doing your touch ups:

(Read this if you need help with painting polymer clay: Can You Paint Polymer Clay Earrings? A How-to Guide)

Wait for the paint to dry, and once this is done you can go ahead and varnish/glaze over your piece to prevent paint chipping, and add one final hard layer to lock everything in.

This is a great glaze to use, if you don’t already have one:

Top tip: Buy super fine painting brushes from miniature stores, craft stores or online! Always go for a good quality brush to prevent bristle shedding and rough lines over your design!


I hope my ‘Why Polymer Clay Breaks and How to Fix it’ article was helpful for you and you now feel confident to head to your craft table and have a go at fixing your polymer clay designs!

My goal is to make it as easy as possible for you to understand the world of polymer clay earring making, so you can go into your new hobby or small business venture with estimates, tips and facts under your belt for a smooth and rewarding start in this craft.

I also provide articles on: a How-to Guide for beginners, a Sales Guide for selling polymer clay earrings on Etsy, a comprehensive Cost Guide, and a bumper list of earring Design Ideas, so you’re never stumped by clay-makers block!

For more information on getting started with polymer clay earrings, check out:

How Much does it Cost to Make Polymer Clay Earrings?

Can You Paint Polymer Clay Earrings? A How-to Guide

How Long to Bake Polymer Clay Earrings – Quick Guide

How to Sell Polymer Clay Earrings on Etsy

How to Make Polymer Clay Earrings: the Basics

Design Ideas for Polymer Clay Earrings

Top Tips for Making Polymer Clay Earrings