How to Get Smooth Tops on Molded Candles: Fixing Sinkholes & Shrinkage

There is nothing more heartbreaking in candle making than the "Demold Reveal." You’ve spent hours melting, mixing, and pouring. The sides of your candle look smooth and perfect. But when you look at the pour site (which is often the base of your candle), you see it: a crater. A dip. A jagged void near the wick.

This is called a sinkhole.

If you are using silicone molds, sinkholes are not a sign of failure—they are a sign of physics. Almost every professional candle maker deals with them. The difference between a hobbyist and a pro is knowing how to fix them efficiently.

In this guide, we will move beyond basic advice and dive into the technical "how" and "why" of achieving a perfectly flat, smooth surface on your molded candles.

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Table of Contents

• Why Do Sinkholes Happen? (The Science of Wax Shrinkage)
• Pricking Relief Holes: The Secret Pro Tip
• The "Second Pour" Method: Step-by-Step
• Using a Heat Gun for Minor Imperfections
• Best Waxes to Minimize Shrinkage in Molds

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1. Why Do Sinkholes Happen? (The Science of Wax Shrinkage)

To fix the problem, you must understand the material science. Wax is not a static material; it changes density based on temperature.

When wax is hot (liquid), it is expanded and takes up more volume. As it cools (solidifies), it contracts and takes up less volume.

Here is the mechanics of a sinkhole:

1. Cooling from the Outside-In: When you pour wax into a silicone mold, the wax touching the cooler silicone walls hardens first.
2. The Molten Core: The center of the candle (near the wick) stays hot and liquid the longest.
3. The Pull: As the wax cools and shrinks, the hardened outer walls hold their shape. The only place the wax can "pull" from is the molten center and the top surface (where it meets the air).
4. Gravity: As the liquid level drops due to shrinkage, gravity pulls the center down, creating a crater or "sinkhole" around the wick.
   

Note on Orientation: Most 3D silicone molds (like our Bubble or Body molds) are poured upside down. This means the "sinkhole" actually forms on the bottom of your finished candle. If you don't fix this, your candle won't stand up straight!

2. Pricking Relief Holes: The Secret Pro Tip

We are putting this step before the "Second Pour" because you must do this while the candle is cooling, before you attempt to fill the hole.

Many beginners see a sinkhole forming and immediately pour more wax on top. Do not do this yet.

If you pour fresh wax over a semi-cooled candle without venting it, you will trap air pockets inside. The sinkhole isn't just on the surface; it often extends deep into the candle near the wick.

The Relief Hole Technique:

1. Wait until the candle has formed a thick "skin" on top (usually 45–60 minutes after pouring, depending on size).
2. Take a skewer, chopstick, or knitting needle.
3. Poke 3–4 holes around the wick, aiming deep into the candle (but not touching the mold walls).
4. Why? This releases trapped air pressure and creates a channel for the liquid wax in the center to shrink down without collapsing the outer walls. It also creates a pathway for your "Second Pour" to bond with the core.

3. The "Second Pour" Method: Step-by-Step

This is the industry-standard method for professional pillars. When you calculate how much wax you need for a mold, always calculate 10-15% extra for the second pour.

The Process:

• Save Your Leftovers: Keep the remaining wax from your initial batch in your melting pitcher. Do not clean it out yet!
• Wait for the Dip: Allow the first pour to cool completely. You will see a significant dip or crater around the wick.
• Reheat the Wax: Reheat your leftover wax.
  Pro Tip: Heat this second batch to 10°F - 15°F (5°C - 8°C) hotter than your initial pouring temperature. This extra heat helps the new wax melt the top layer of the cold wax, ensuring they bond together seamlessly so the bottom doesn't crack off later.
• The Fill: Carefully pour the wax into the sinkhole.
  Do not fill past the original "fill line" of the candle. If you overpour, the wax will run down the sides (between the candle and the mold), creating ugly streaks on your finished design.
• Cooling: Let this layer cool completely before demolding.

4. Using a Heat Gun for Minor Imperfections

Sometimes, you don't have a massive crater—just a slightly uneven surface or a small dimple. In this case, a second pour is overkill.

When to use a Heat Gun:

• To smooth out rough texture on the base.
• To fix "white spots" or jump lines.
• To level out a base that is slightly wobbly.

The Technique:
Use a heat gun on the low setting. Hold it about 4-6 inches away from the wax. Move it in a circular motion constantly. Do not hold it in one spot, or you will burn the fragrance oil (creating a brown spot) or deform the silicone mold.

Warning: Never use a hair dryer. The airflow from a hair dryer is too strong and will blow hot wax all over your workspace.

5. Best Waxes to Minimize Shrinkage in Molds

If you are constantly fighting massive sinkholes, your wax choice might be the culprit. Not all waxes are designed for pillars and molds.

Paraffin Wax (High Shrinkage)

Paraffin is notorious for shrinking. It provides great detail, but you will always need a second pour. It is rigid and brittle.

Soy Wax (Low Shrinkage, Prone to Frosting)

100% Soy wax shrinks very little, often leaving a flat top without much effort. However, it is too soft for detailed silicone molds and often breaks upon demolding.

The Winner: Pillar Blends (Soy/Paraffin or Beeswax Blends)

For the best results with Silicone Molds, we recommend a "Pillar Blend."

• Soy + Paraffin: Gives you the creaminess of soy with the stability of paraffin.
• Beeswax: Shrinks significantly (like paraffin) but produces a very hard, durable detail.

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Looking for the perfect mold to test your new skills?
Check out our collection of High-Durability Silicone Molds designed to withstand high-temperature second pours without warping.

Ready to start pouring? Shop our latest New Arrivals and create your masterpiece today.

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Frequently Asked Questions About Candle Sinkholes