Is Polymer Clay Waterproof? And What Happens When It Gets Wet?


Cute polymer clay miniatures would be a fabulous addition to any fairy garden, but what happens if they get wet outside? I didn’t want my daughter’s fairy garden accessories to be a washout, so I wanted to find out if polymer clay models are waterproof.

So, is polymer clay waterproof? As polymer clay is a type of plastic, once your model has been baked and cooled it will be waterproof, you don’t have to seal it. However, there are some exceptions to this, what you embellish or seal your clay with may not be waterproof. Air-dry clay, a popular alternative to polymer clay, is not waterproof at all.

Below I dive deep into everything related to waterproofing and polymer clay.

How Waterproof Is Polymer Clay?

Very, is the short answer! As polymer clay is made out of plastic (polyvinyl chloride (PVC) to be exact), once it’s baked and cured properly, it’s completely waterproof and pretty indestructible. It doesn’t soak up water like unglazed ceramic pottery or air dry cay can.

Polymer clay is oil-based, so it’s actually waterproof before it’s been baked as well – remember, oil and water don’t mix!

It’s a remarkable material that you can even reheat after being cured, without it melting. As it’s a thermosetting plastic, once it’s cured, you can’t melt it with heat or dissolve it with water.

As polymer clay is waterproof, it’s often used for outdoor decorations, such as animal figurines, mobiles, wind chimes or even embellishments for bird houses, making it perfect for fairy garden accessories.

What Happens When Polymer Clay Gets Wet?

Nothing! Polymer clay can easily withstand being submerged in water for long periods of time.

I did an experiment and left a miniature piece of pink polymer clay in a tub of water for a week and… nothing happened. The miniature ball was just as sturdy as when I put it in. Below you can see the very uneventful before and after photos! It was a very different story for the air dry clay, but more on that later!

In fact, you would have to leave it submerged for many months, if not years, before you noticed a difference.

Cured polymer clay does have a slightly porous surface, so after a very long time, you might find some surface discolouration, such as a whitening or chalky effect on the darker colours.

TOP TIP: Polymer clay can be used to create for models for snow-globes as it can remain submerged in water and glycerine for many years without changing appearance!

Although polymer clay is waterproof, if you choose to seal the clay, then the sealant you use is unlikely be able to handle being exposed to water long-term.

Does Sealing Polymer Clay Protect It For Outdoor Use?

Sealing polymer clay doesn’t actually add any protection to the clay itself, as polymer clay is already strong and waterproof due to being plastic. People usually seal polymer clay to make clay models shinier and give a glossy finish.

However, if you want to add embellishments to a polymer clay model that you plan to put outside, then sealing polymer does help to protect decorations such as glitter or paint from the elements.

Most sealants are just water-resistant, rather than being waterproof, so it won’t take long before they start peeling or cracking on any models you put outside. This means your model will outlast whatever you sealed it with!

What this means is that any delicate designs you’ve done on your model could be ruined if you put them outside long-term. The best option is to not add any embellishments, such as glitter, mica powders or paint, to any models you want to display outside. Leave any embellishments for your inside models!

If you just can’t resist a glittered covered or painted fairy door, then seal the clay with a couple of coats of strong sealer (try Ronseal Interior Varnish Gloss or a yacht varnish) before putting it outside.

It’s important to note that different sealers react differently to different brands of polymer clay. What creates a flawless finish on one brand of clay may create a sticky surface on another.

Therefore, always test out a sealer with your clay before covering an entire project with it.

TOP TIP: Avoid using metal embellishments with any polymer clay you’re going to put outside. When exposed to the elements, any metal used in your model will rust and ruin the overall look.

Is Air Dry Clay Waterproof?

Air dry clay is not waterproof. Air dry clay is water-based, so as the water in it dries out, the clay hardens. Whereas polymer clay hardens when it’s baked. Even when air dry clay is fully dried, it can still feel slightly soft, when compared to polymer clay.

The only way to make air dry cay waterproof is to thoroughly seal it. The reason why it needs to be sealed thoroughly, is that even if a tiny bit of the clay is left unsealed, water can penetrate the clay and slowly dissolve it.

The best sealer to use on air dry clay is a couple of coats of yacht varnish, but again, every millimetre of your model will need to be covered, including the base, to avoid a dissolving disaster!

Even if you seal air dry clay, the sealant will eventually crack and peel if it’s left outside, which will mean your model could be significantly damaged by water. It’s best to use unsealed polymer clay for any outside models.

Conclusion

Polymer clay is fully waterproof. For best results when using polymer clay outside, don’t add embellishments or any finish with sealants and you’ll have a long lasting addition to your fairy garden!

Further Questions

Can Polymer Clay Be Damaged By UV Rays?

This could happen but it’s highly unlikely, unless your model is in direct prolonged sunlight (not a problem here in the UK!). Over time, excessive exposure to UV rays may make the polymer clay brittle or cause some brighter colours to fade.

Cured polymer clay is an extremely sturdy plastic, but if it’s left in extreme heat for a long time it may soften slightly, which could cause thin or protruding designs on the clay to droop.

For example, if you have a model of a character in the front of your car in excessive heat, you may notice the arms bend or droop slightly. But this is an extreme case as most environments are unlikely to get as hot, as quickly as a car (except maybe for greenhouses!).

You can seal your model with a sealant that contains UV protection, such as yacht varnish. But you’ll probably find the sealant will crack and peel well before the polymer clay model is significantly damaged by the sun.

Can Humidity Damage Polymer Clay?

This is unlikely as polymer clay is waterproof, so no matter how much humidity there is in the air, it’s not going to damage the clay.

If you’re putting the clay in a humid location, either because it’s humid where you live or if you want to add it to a terrarium, make sure you don’t add any sealants or embellishments to the clay. As with water, humidity will crack and peel any sealants well before it does any damage to the clay.

Can Polymer Clay Be Used In Snow Globes?

Yes! Polymer clay models can last for years in snow globes. The only issue you might find is that as polymer clay has a very slightly porous surface, over time the surface may take on some white discolouring, which will be more noticeable on darker coloured clay.

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