Pressure casting is a technique that uses controlled pressure to compress air bubbles in curing resin to microscopic size, resulting in clear, professional-grade castings. This guide will walk you through:
- Equipment selection and setup
- Safety considerations and best practices
- Step-by-step casting procedures
- Troubleshooting common issues
- EU-specific sourcing guidance
Whether you're casting dice, decorative pieces, or professional props, understanding the equipment and proper pressure casting technique is crucial for consistent, high-quality results. Safety considerations are integrated throughout, as proper handling of both equipment and materials directly impacts your success rate (and more importantly, your health.)
⚠️ SAFETY NOTICEResin casting involves hazardous materials and pressurized equipment. Proper safety equipment and procedures are essential. Please review the complete safety disclaimer before proceeding.
⚠️ RESIN TOXICITY FACTSEpoxy and polyurethane resins present significant health risks that require proper safety precautions:
- Respiratory Exposure: Resin vapors can cause both immediate irritation and long-term sensitization1
- Skin Contact: Direct contact can lead to chemical burns and permanent sensitization2
- Eye Exposure: Vapors and splashes can cause severe eye damage3
Sensitization is particularly concerning because it:
- Safety Notice & Disclaimer
- Overview
- Safety Requirements
- Equipment Recognition
- Required Equipment
- Step-by-Step Process
- Applications
- Troubleshooting
- Common Myths
- Essential Features
- EU-Specific Resources
- Safety Notes
- Additional Information
- Footnotes
Ben Rossi (u/Mtinie) is a visual artist and maker with over six years of resin experience-—mostly learned the hard way—-with a focus on artwork encapsulation and casting techniques.
This guide combines hands-on experience with technical research, aiming to provide other makers with clear, actionable information about pressure casting fundamentals. It emphasizes practical problem-solving and addresses common failure points that are often overlooked in the sea of information.
Last Updated: January 2025 Version: 1.0
⚠️ PLEASE READ CAREFULLYThe information in this guide is accurate to the best of my knowledge, but it is the reader's responsibility to:
Ensure personal safety – Always verify the information provided against your specific equipment and materials before pressure casting resin.
Understand material differences – There are many resin formulations, each with unique characteristics. This guide provides general best practices, but users must refer to their resin manufacturer's guidelines for precise handling.
Respect high-pressure safety – Working with pressurized equipment carries inherent risks. The condition and safe operation of pressure pots, compressors, and related tools are the sole responsibility of the user. Always inspect your equipment before use.
By using this guide, you acknowledge that you assume all risks associated with resin casting under pressure.
Stay safe and happy casting!
A pressure pot transforms ordinary resin casting into professional-grade results through controlled gas compression. The sealed container maintains pressure above atmospheric levels (typically 40-60 PSI), using Boyle's Law (P₁V₁ = P₂V₂) to compress air bubbles to microscopic size.
In practical terms: bubbles that would normally ruin optical clarity become invisible in your final piece. While it sounds like magic, it's just basic physics working in your favor. The higher pressure physically compresses any trapped air to roughly 1/5 of its original size at 60 PSI, small enough that even clustered bubbles become imperceptible to the naked eye.
Pro tip: Those PSI numbers aren't arbitrary but represent practical limits. Below 40 PSI, bubble compression is often insufficient for professional results. Above 60 PSI, you're adding risk without meaningful improvement.
For those new to pressure casting, understanding the following concepts can enhance your experience and results:
-
Boyle's Law in Practice:
- Boyle's Law states that at constant temperature, the pressure and volume of a gas are inversely related. In the context of resin casting, as pressure increases, the volume of trapped air bubbles decreases.
- At 60 PSI gauge pressure (approximately 74.7 PSI absolute), the volume of air bubbles can be reduced to about 20% of their original size. This compression is crucial for achieving clear, bubble-free castings.
-
Pressure Range Considerations:
- 40 PSI Minimum: This is generally the lowest pressure recommended for effective bubble compression. Below this threshold, you may still see visible bubbles in your final product.
- 60 PSI Maximum: While some may be tempted to exceed this pressure for better results, it often leads to diminishing returns and increased risks, such as equipment failure or resin foaming.
-
Resin Viscosity and Cure Time:
- The viscosity of your resin affects how bubbles behave under pressure. Thicker resins may require higher pressures or longer cure times to achieve optimal results.
- Always refer to the manufacturer's guidelines for specific recommendations regarding pressure settings and cure times.
-
Mold Design and Venting:
- The complexity of your mold can influence bubble formation. Molds with tight corners or intricate details may trap air more easily, necessitating the use of a pressure pot.
- Proper venting in your mold design can help minimize trapped air, making the pressure pot's job easier.
-
Safety Precautions:
- Always inspect your pressure pot and equipment before use. Ensure that seals and gaskets are in good condition to prevent leaks.
- Familiarize yourself with emergency pressure release procedures to ensure safe operation.
By understanding these principles, you can make informed decisions about your pressure casting setup and achieve better results in your projects.
You'll encounter two main pressure pot designs in the market. Understanding their differences is crucial for both purchasing and operation:
CA Air Tools style pressure pot: Note the integrated casters, handle system, and multiple point clamping mechanism. This design typically offers better stability and more even pressure distribution.
C-clamp style pressure pot: More basic design requiring careful attention to even clamp tightening. While functional, these demand more attention during setup to ensure proper sealing.
Critical Safety Note: The following is a vacuum chamber, NOT a pressure pot. They serve different purposes and are NOT interchangeable:
This is a vacuum chamber - used for silicone degassing only. Never attempt to use this for pressure casting.
While both pressure pots and vacuum chambers address air bubbles in resin work, they operate on fundamentally different principles:
Standard open pour: Note typical bubble formation and clarity issues
Pressure casting: Bubbles compressed to microscopic size, achieving optical clarity
Vacuum degassing: Bubbles expand and rise for removal before cure
Images courtesy of Polytek Development Corp.
Pressure Pot Operation:
- Compresses existing bubbles to microscopic size
- Bubbles remain in the resin but become effectively invisible
- Maintains pressure throughout cure process
- Ideal for: Professional castings, optical clarity requirements
Vacuum Chamber Operation:
- Removes bubbles by reducing ambient pressure
- Bubbles expand and rise to surface for removal
- Process completed before pour/cure
- Ideal for: Silicone mold making, degassing specific materials
Key Distinction: Pressure pots affect bubbles throughout the entire cure cycle by compressing them to microscopic size, while vacuum chambers can only remove bubbles during the liquid phase. Since some resins may trap air or generate gas as they cure, pressure pots are the preferred method for resin casting when achieving a completely bubble-free result is critical.
| Tier | Price Range | Models | Key Features | Notes |
|---|---|---|---|---|
| Entry Level | €100-150 | VEVOR 5L Basic, California Air Tools Mini | Basic gauges, Manual bleed valves | May need gasket upgrades |
| Mid-Range | €150-250 | BACOENG 10L Standard, VEVOR 10L Pro, Stark Pro Series | Dual gauges, Better clamping | Standard warranty |
| Professional | €250-400 | California Air Tools Premium, BACOENG Pro Series | Digital monitoring, Quick-release valves | Full warranty coverage |
Example of appropriate compressor setup: Note dual gauges for monitoring both tank and output pressure.
| Requirement | Specification | Price Range | Recommended Brands | Notes |
|---|---|---|---|---|
| Entry Level | 1.5 HP, 20L | €120-180 | Einhell, Parkside | Sufficient for pots up to 5L |
| Mid-Range | 2.0 HP, 30L | €180-300 | Michelin, Metabo | Faster pressurization time |
| Professional | 2.5+ HP, 50L | €300-500 | Metabo, DeWalt | Multiple pot capacity |
Note: Any compressor capable of reaching 60 PSI will work - the main difference is how quickly it reaches target pressure.
Proper air handling is crucial for successful pressure casting. Here are the key components and setup options:
Basic air regulator: Single gauge setup sufficient for most casting operations
- Single regulator sufficient for casting-only setups
- Must be rated for your maximum working pressure (minimum 60 PSI)
All-in-one regulator/filter unit: Space-saving option if workspace is limited
- Combines regulation and filtering in one unit
- Often more compact than separate components
- Ensure the filter element matches your needs
- Usually more expensive than separate components
Quality air line with proper fittings: Note the robust construction and secure connections
- Minimum 15m (50ft) primary line recommended between compressor and filter
- This length allows air to cool and moisture to condense
- Coiled hoses work fine but measure their actual extended length
- Secondary line (filter to pot) can be shorter
- Use quality air lines rated for at least 100 PSI
- Check fittings for compatibility with your pot and filter setup
Standard moisture/oil separator: Note the transparent bowl for monitoring water collection
- Essential for preventing contaminant transfer to your casting
- Position after the cooling line but before the pressure pot
- Choose a filter with:
- Moisture separation capability
- Minimum 50 micron particulate filtering
- Easy drain access for regular maintenance
Pro tip: The seemingly excessive primary line length isn't about distance - it's physics. Compressed air needs time to cool and drop its moisture content. Shorter lines mean more water in your system, regardless of filter quality.
Resin casting requires proper personal protective equipment (PPE). Each component serves a specific purpose and all are essential for safe operation.
Resin vapors are invisible but hazardous. Proper respiratory protection is your primary defense against both immediate and long-term health effects. Two main options exist:
Full face respirator: Offers combined respiratory and eye protection. Essential when working with highly volatile resins.
Half-mask respirator: Popular choice when using separate eye protection. Ensure proper cartridge selection (OV rated).
Important Safety Note: Standard particulate respirators (FFP2/N95/N99) do NOT provide protection against resin vapors. Resin casting requires specific organic vapor protection - this is non-negotiable.
Recommended Setup:
- 3M Half Face Respirator (6000 or 7500 series)
- 3M 6001 (Organic Vapor) or 6003 (Organic Vapor/Acid Gas) cartridges
- Optional: Full face respirator for combined eye/respiratory protection
Respirator Selection:
- 3M is one of several major manufacturers serving the EU market, alongside European brands like Draeger and Scott Safety
- While 3M products are generally available in the EU, specific cartridge availability can vary significantly by country
- Consider local industrial safety suppliers rather than relying on general retailers
- When selecting a respirator system, verify local cartridge availability before committing to a specific brand or model
Practical Tip: Once you find a reliable local source for your preferred cartridges, buy an extra set. Supply chain hiccups happen more often than you'd think.
Cartridge Maintenance and Storage:
Replace cartridges under any of these conditions:
- After 40-50 hours of cumulative exposure (~20-25 casting sessions)
- Every 6 months from first use, regardless of usage
- Immediately if you detect any resin odor through the respirator
- If cartridges have been exposed to high humidity for extended periods
Proper Storage Protocol:
- After each use, remove cartridges from respirator
- Clean respirator body with mild soap and water, dry thoroughly
- Place cartridges in a sealed zip-lock freezer bag (better barrier properties than standard bags)
- Press out as much air as possible before sealing
- Store in a clean, dry area away from:
- Direct sunlight
- High humidity
- Chemical storage areas
- Temperature extremes
Pro tip: Write the date of first use on each cartridge with a permanent marker. Activated carbon continues to absorb contaminants even when not in use, so tracking time from first exposure is crucial.
Think of cartridge life like a parking meter - it's running whether you're casting or not, just at different rates. Proper storage merely slows the timer; it doesn't stop it entirely.
For glasses wearers: Half-mask respirators with separate eye protection often prove more comfortable than full-face options. If splash protection is needed, a separate face shield works well with this setup.
Source: FFP2 Respirator Standards and Selection Guide
Note on Cost Effectiveness: While the initial investment in a quality respirator system may seem high compared to disposable masks, the superior protection and relative comfort during extended use make it a worthwhile investment. Moreover, the ability to immediately detect when cartridges need replacement (via odor breakthrough) provides better safety assurance than disposable alternatives.
Consumables Budget (Hobby Level):
- Respirator cartridges (2 pairs/year): €50-60
- Nitrile gloves (200 count): €20-30
- Miscellaneous replacements: €20-30
- Total annual safety budget: €90-120
Note on Usage Patterns: These estimates assume weekend hobby work averaging 2-3 casting sessions per month. Scale up proportionally for more frequent use. Proper storage of consumables (especially cartridges) helps maximize lifespan without compromising safety.
Resin splashes are uncommon but potentially serious. Eye protection must form a complete seal - standard safety glasses are insufficient for resin work:
Chemical-resistant safety goggles: Note the complete seal around eyes and side protection.
Choose one of these options:
- Chemical-resistant safety goggles with complete seal
- Full face respirator with integrated eye protection
- Half-mask respirator plus separate chemical-splash goggles
Your hands are most likely to contact resin during normal operations:
Chemical-resistant nitrile gloves: Single use only. Never reuse gloves exposed to resin.
- Chemical-resistant nitrile gloves (EN ISO 374-1 rated)
- Single use only - never reuse gloves exposed to resin
- Keep multiple sizes available for proper fit
| Item | Specification | Price Range | Durability | Notes |
|---|---|---|---|---|
| Respirator System | 3M Half Mask + OV cartridges | €35-50 + €25-30/pair | Replace cartridges per schedule | Must be OV rated |
| Eye Protection | Chemical-resistant goggles | €15-40 | 6-12 months | Get backup pair |
| Hand Protection | EN ISO 374-1 nitrile, 100ct | €12-25/box | Single use | Buy in bulk |
| Full Face Shield | CE marked, chemical rated | €30-60 | 12+ months | Optional but recommended |
Annual Safety Budget (Hobby Level):
- Respirator cartridges (2 pairs/year): €50-60
- Nitrile gloves (200 count): €20-30
- Miscellaneous replacements: €20-30
- Total annual safety budget: €90-120
Note: Budget assumes weekend hobby work (2-3 sessions/month). Scale up for more frequent use.
- Verify equipment condition:
- Inspect pot for damage (chips or cracks in the body of the pot)
- Check gaskets and seals
- Test pressure holding capability with air only
- Set up in well-ventilated area
- Organize materials and safety equipment
-
Mix resin according to manufacturer specifications:
- Use proper measuring method (weight or volume as specified)
- Follow exact ratio requirements
- Mix thoroughly but carefully to minimize bubble introduction
-
Pour into prepared mold:
- Complete pour within resin's pot life
- Use appropriate techniques for mold type
- Consider using a clean pour container
-
Pressure pot procedure:
- Place in pressure pot within 5 minutes of pour
- Secure lid following manufacturer's torque pattern
- Pressurize to 40-45 PSI initially
- Monitor pressure for first 15 minutes
- Maintain pressure for full cure time
- After full cure time:
- Verify cure completion if possible
- Release pressure slowly
- Remove from pot
- Clean equipment immediately
- Document results and settings
Best suited for:
- Complex molds with tight corners or intricate details
- Deep pours exceeding 2cm thickness
- Professional-grade clear castings
- Items requiring optical clarity (dice, display pieces)
- Verify your resin's mixing requirements:
- By Weight: Use a scale (more precise, preferred for craft work)
- By Volume: Use graduated containers (acceptable for some 1:1 resins)
- Confirm mixing ratio (common variants):
- 1:1 (typical for faster-cure resins)
- 2:1 (common in deep-pour formulations)
- Other ratios exist - always verify your specific product
- Mix according to verified ratio and methodology using proper tools:
- Use wide, synthetic mixing paddles (minimum 25mm width)
- Avoid wooden stir sticks (they're porous and can introduce air bubbles)
- Mix with deliberate, broad strokes rather than whipping motions
- Pour into mold within stated pot life
Pro tip: "Close enough" isn't. If your resin specifies mix by weight, using volume measurements will likely result in cure issues - especially with 2:1 ratios where the components have different densities.
-
Surface Tackiness
- Primary causes:
- Unmixed resin from container sides contaminating the pour
- Incorrect mix ratio
- Secondary causes:
- Temperature too low during cure
- Humidity contamination
The Container Edge Problem: Even perfectly measured resin can cure tacky if you don't manage your mixing container properly. When you pour your mixed resin, any unmixed components stuck to the container sides will run down and contaminate the top of your pour. This is particularly insidious because:
- It often affects only the last bit poured
- The contamination tends to concentrate at the top surface
- It can occur even with correctly measured and mixed resin
Prevention:
- Scrape container sides thoroughly during mixing
- Transfer mixed resin to a clean pouring container (often called "double potting")
- Never scrape the last bits out when pouring - they're more likely to contain unmixed material
Pro tip: If you consistently get tacky tops on otherwise perfect casts, this is almost certainly your culprit. The physics of fluid flow means those unmixed components will always end up concentrated at your pour surface. Double potting adds an extra step but eliminates an entire category of potential failures.
- Primary causes:
-
Soft Spots or Uncured Pockets
- Usually indicates inadequate mixing
- Can also result from:
- Volume measurement of weight-ratio resins
- Temperature variations during cure
- Prevention: Use proper measuring method, mix thoroughly but carefully
-
Excessive Exotherm (Too Hot)
- Typically caused by:
- Mass too large for resin type
- Wrong resin for pour depth
- Incorrect ratio (often too much hardener)
- Solution: Match resin to project requirements, verify measurements
- Typically caused by:
-
Cloudy or Opaque Results
- Common causes:
- Moisture contamination
- Inadequate pressure
- Wrong mixing tool introducing excess air
- Prevention: Use synthetic tools, maintain proper pressure throughout cure
- Common causes:
-
Cure Too Fast/Slow
- Usually temperature-related
- Can indicate wrong resin choice for project
- Solution: Match resin specifications to project needs
Note on Mixing Tools: The width and material of your mixing implement aren't just pedantic details - they directly impact your results. A wider paddle creates more efficient mixing with fewer strokes, which means less introduced air. But material choice is equally crucial:
Wood Issues:
- Porous nature means it can trap and release air bubbles
- Often contains moisture that can react with resin
- Tendency to break down over time when reused between pours, potentially contaminating mixes and introducing inconsistency
- Popsicle sticks compound these issues by being both narrow and porous
Better Choices:
- Plastic putty knives or broad mixing paddles
- Silicone spatulas (bonus: cured resin pops right off)
- Acrylic or polypropylene stir sticks
If you must use wood:
- Opt for tongue depressors or paint stir sticks over popsicle sticks - at least you'll have the advantage of width
- Consider sealing wooden implements with nitrocellulose lacquer:
- Apply thin coat, allow 24 hours minimum dry time
- Inspect for complete coverage
- Replace if coating shows signs of wear
- Note: While generally compatible, test your specific lacquer with a small resin sample first
- For tiny batches (think 10ml or less), even a sealed wooden stick can work, but synthetic alternatives eliminate variables
Remember: Your mixing tool is the first thing that touches your combined resin components. It's a odd place to try saving a few cents, particularly when that savings might compromise your results.
-
"Vacuum chambers work better than pressure pots"
- FALSE: Vacuum chambers are effective for removing air bubbles during mold making by expanding and extracting trapped air. However, in resin casting, while a vacuum can remove some air, it may cause resin to foam. Pressure pots compress air bubbles to microscopic sizes, making them invisible in the finished product
- Source: Resin Obsession, Resin Casting Fundamentals6
-
"Higher pressure = better results"
- FALSE: Exceeding 60 PSI offers no measurable benefit and increases risk
- Most resins achieve optimal results at 40-50 PSI
- Excessive pressure can damage equipment or molds
- Source: Alumilite, Pressure Casting Guidelines7
-
"Paint pressure pots work the same"
- FALSE: Paint pots typically lack proper sealing for sustained pressure
- May not meet EU pressure equipment directive requirements
- Require extensive modifications for safe resin casting use
- Source: European Union, Pressure Equipment Safety Standards8
-
"You don't need a pressure pot if you pour resin slowly"
- FALSE: While slow pouring helps minimize bubble introduction:
- Resin viscosity variations
- Mold complexity
- Chemical curing reactions All can still trap air, requiring pressure casting for optimal clarity
- Source: Smooth-On, Advanced Resin Casting Techniques9
- FALSE: While slow pouring helps minimize bubble introduction:
-
"A pressure pot will remove all bubbles"
- FALSE: Pressure pots compress bubbles rather than removing them
- Proper mixing and mold design remain essential
- Prevention is still better than compression
- Source: Professional Casting Association, Professional Casting Methods10
-
"You can use any resin in a pressure pot"
- FALSE: Not all resins are formulated for pressure casting
- Specific formulations may have incompatible:
- Curing characteristics
- Viscosity profiles
- Pressure tolerances
- Always verify manufacturer recommendations
- Source: Polytek Development Corp., Resin Selection Guide11
-
"Pressure pots speed up curing time"
- FALSE: Pressure compression has no significant effect on cure time
- Curing is determined by:
- Resin chemical formulation
- Environmental conditions
- Pour volume
- Source: Innovative Polymers, Resin Curing Dynamics12
-
"You can open the pressure pot as soon as the resin looks solid"
- FALSE: Surface solidity doesn't indicate complete cure
- Premature pressure release allows bubble re-expansion
- Maintain pressure for manufacturer's full recommended cure time
- Source: Resin Obsession, Pressure Casting Best Practices13
Every pressure pot should have:
- CE marking (mandatory for EU use)
- Minimum 2.5mm wall thickness
- Safety release valve rated for 60-80 PSI
- Clamp-style lid (not twist-on)
Supply Sources:
- Resin Pro France (www.resinpro.fr)
- Bricomarché (compressors/equipment)
- ManoMano.fr (pressure pots/safety equipment)
Required Certifications:
- CE marking (mandatory)
- TÜV certification (recommended)
- EN 286-1 compliance
- Always verify equipment meets EU pressure equipment directive (2014/68/EU) requirements
- Never exceed manufacturer pressure ratings
- Learn emergency pressure release procedures before first use
- Maintain regular inspection schedule for gaskets and seals
Note: While this guide compiles information from manufacturer documentation and industry standards, always refer to your specific equipment manufacturer's guidelines and local safety regulations.
Footnotes
-
European Chemicals Agency (2023). "Epoxy Resin (reaction product bisphenol-A-(epichlorhydrin)) Substance Information." ↩
-
European Chemicals Agency (2022). "Guidance on Safe Use of Epoxy Resin Systems." ↩
-
National Institute for Occupational Safety and Health (NIOSH). "Epoxy and Polyurethane Safety Guidelines." CDC.gov, 2022. ↩
-
Occupational Safety and Health Administration (OSHA). "Health Effects of Diisocyanates." OSHA.gov, 2021. ↩
-
Aalto-Korte, K., Pesonen, M., & Suuronen, K. "Occupational allergic contact dermatitis caused by epoxy chemicals: occupations, sensitizing products, and diagnosis." Contact Dermatitis, 75(3), 172-182, 2015. ↩
-
Resin Obsession. "Understanding Pressure vs. Vacuum in Resin Casting." Technical Guides, 2023. ↩
-
Alumilite. "Pressure Settings and Safety Guidelines." Technical Documentation, 2023. ↩
-
European Union. "Equipment Safety Standards for Pressure Vessels." Official Standards, 2023. ↩
-
Smooth-On. "Advanced Casting Techniques Guide." Technical Resources, 2023. ↩
-
Professional Casting Association. "Bubble Prevention and Management." Industry Guidelines, 2023. ↩
-
Polytek Development Corp. "Resin Selection for Pressure Casting." Technical Guide, 2023. ↩
-
Innovative Polymers. "Understanding Resin Cure Dynamics." Technical Documentation, 2023. ↩
-
Resin Obsession. "Pressure Casting Best Practices." Technical Resources, 2023. ↩
