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For small, detailed shapes or objects with undercuts, make a flexible silicone mold. For straight-sided pieces such as borders and panels, build a rigid melamine form. In either case, seal the mold, follow the specific product directions for mixing and curing, and plan how the casting will come out before you pour.
Choose the right mold for your project
The shape and removal method matter more than choosing a mold material by habit. Silicone flexes around a casting; a rigid form is a practical choice for larger, straight-sided work that can be released by taking the form apart.
| Consideration | Flexible silicone mold | Rigid melamine form |
|---|---|---|
| Good fit | Small objects and shapes that benefit from a flexible mold | Straight-sided castings, borders and panels |
| Removal | Flex or carefully cut the silicone to free the casting | Unscrew and disassemble the form where needed |
| Surface | Depends on the master and silicone mold surface | Melamine provides a smooth form surface |
| Release considerations | Follow the selected silicone and concrete product instructions | QUIKRETE says melamine does not need release oil; other form surfaces may need a suitable release agent |
These are approaches demonstrated in separate QUIKRETE projects, not the results of a head-to-head performance test. See QUIKRETE’s silicone mold and concrete casting project and its cast concrete borders guide.
Make a small silicone mold
- Choose a master. Check that it fits inside a container that can surround it and rise above its highest point.
- Build the housing. Cut a plastic bottle or container into a tube, and cut a support band from the remaining plastic. Hot-glue the master to a plastic base, then glue the tube to the base around it.
- Check for leaks and estimate volume. Fill the housing with water until the master is covered. If water escapes, seal the assembly before proceeding. Measure the water to estimate how much silicone the mold will need.
- Mix and pour the silicone. Follow the instructions for the silicone you selected. QUIKRETE’s project names Mold Star 30, but silicone mixing and cure directions depend on the specific product.
- Remove the housing and master. Once the silicone has cured as directed, remove the plastic. Carefully work out the master; a cut in the silicone can help, and placing it somewhere less visible can reduce its impact on the mold.
- Support the mold for casting. Use the plastic support band if needed, and follow the rubber manufacturer’s directions. The mold should be supported well enough to resist bulging or distortion when filled.
- Fill with concrete. Mix the concrete according to its package directions, pour it into the mold and gently tap or vibrate the mold to help air bubbles escape. QUIKRETE suggests a slightly more fluid mix for easier pouring in its small-mold project; treat that as project-specific advice, not a general change to the water proportions.
- Cure and release the casting. Follow the concrete mix directions for curing, then carefully flex or cut the silicone as needed to remove the piece.
Build a rigid melamine form
- Plan the dimensions. Cut melamine-faced panels and any blocking to the size of the casting you want.
- Assemble it for removal. Screw the blocking and panels together, keeping the edges aligned and flush. Arrange the form so you can unscrew and disassemble it if the casting cannot be lifted out intact.
- Seal and prepare the inside. Seal screw heads with silicone caulk and flatten the caulk to keep the surface smooth. QUIKRETE says melamine itself does not require release oil; apply a thin layer of clean vegetable oil or another suitable release agent to non-melamine surfaces, following the product label. Its guide describes melamine this way: “The melamine creates an exceptionally smooth finish and doesn’t need oil or a release agent to prevent the concrete from sticking.”
- Place and level the concrete. Mix according to the product directions, fill the form, then tap the work surface or form to settle the mix. Screed the top level.
- Cover and remove the form carefully. For its cast-border project, QUIKRETE recommends covering the casting with plastic and leaving it undisturbed for 48 hours before carefully unscrewing and disassembling the form. That is guidance for that project, not a universal demolding time.
- Continue curing as directed. For the same project, QUIKRETE recommends keeping the casting damp under plastic in a shaded area for three to five days for maximum strength. Follow the instructions for your chosen mix and account for the specific casting and conditions.
Prevent leaks, sticking and trapped air
- Seal before you cast. A sealed mold preserves the intended shape and prevents material escaping. Water-test small silicone housings before pouring the rubber; caulk seams or screw heads on rigid forms where needed.
- Plan release and removal together. A rigid form should come apart if the casting cannot be lifted free. Use release agent only where appropriate for the form material and follow its label. A master object and a mold-making material can have separate release requirements; a specialized Polytek GFRC panel tutorial, for example, describes sealing wood and applying release agent to a pattern before making a mold.
- Settle the pour. Gentle tapping or vibration helps air escape and can reduce bubbles in the finished surface.
Mix and cure according to the products you use
There is no single water ratio or demolding schedule established for every concrete mix, casting thickness and environment. Use the concrete package directions for water, mixing and curing, and the silicone manufacturer’s directions for rubber mixing and cure. The Formlabs silicone mold guide also emphasizes following the chosen silicone product’s instructions.
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#1 Best Overall
Silicone Mold Making Kit 66 oz SHORE RESIN, 15A Platinum Silicone Rubber
- 1️⃣ 66 OZ FOR LARGER MOLDS & MULTIPLE PROJECTS — Includes 33 oz Part A + 33 oz Part B for larger molds, multiple small molds and repeat making. Suitable for resin casting, candle and wax, soap, plaster, clay, concrete and craft mold projects.
- EASY 1:1 TWO-PART SILICONE MIX — Mix equal parts A and B by weight or volume and stir thoroughly for 3–5 minutes. About 30 minutes of working time at 77°F/25°C gives more time to pour, position originals and fill detailed shapes.
- LOW-VISCOSITY LIQUID SILICONE FOR MOLDS — Smooth-flowing platinum-cure silicone reaches narrow details and intricate textures while helping trapped air rise naturally. Slow mixing and thin-stream pouring can help create cleaner molds.
- FLEXIBLE 15A SILICONE RUBBER FOR MOLD MAKING — Shore A 15 provides a practical balance of softness, flexibility and tear resistance. Cured molds bend around undercuts for easier demolding while preserving fine detail through repeat casting projects.
- 4-HOUR INITIAL ROOM-TEMPERATURE CURE — At about 77°F/25°C, initial cure is around 4 hours and full cure typically takes 4–6 hours. Larger molds, thicker pours or cooler rooms may require more time before demolding.
Protect yourself from cement
Cement dust can irritate the eyes and respiratory tract, while wet concrete can damage skin and cause serious chemical burns; pain may not immediately indicate the injury. Wear eye protection and suitable waterproof or alkali-resistant gloves, keep dust and wet mix off your skin and out of your eyes, and rinse or wash promptly after contact. Follow the safety data sheet for your concrete product. OSHA advises: “Prevent burns and skin and eye irritation by avoiding skin contact and eye contact with cement dust or wet cement.” See OSHA’s Concrete Manufacturing guidance and Concrete and Concrete Products: Controlling Hazards.
Quick Recap
Best Value
BBDINO Silicone Mold Making Kit 30A Platinum Liquid 2 Gallons Sapphire Blue
- 【MIX RATIO 1A:1B BY VOLUME】no weighing scale necessary, this silicone mold making kit comes with 2 bottles, 2 gallon /17.6 lbs kit, part A 8.8 lbs, part B 8.8 lbs, very easy to use, also the bottle come with tinfoil sealed inside the cap, double guarantee for no leaking, a set of very helpful tools kiot will be included in the package: 20 pairs of disposable gloves, 10 mixing sticks, and 1 premium edge trim and 1 detailed user manual;
- 【SELF-DEGASSING & LOW VISCOSITY & EASY MIXING & POURING】this BBDINO 30A mold making silicone rubber has low viscosity so that you can easily mix and pour the silicone material, no degassing vaccum chamber needed, the molds finished with this liquid silicone for mold making has great flexibility & Strength. very easy to demold, Great silicone for mold making for simple one- or two-piece block molds making;
- 【WORKING TIME: 30 MINS, CURE TIME: 3~4 HRS AT ROOM TEMPERTUARE 25℃(73.4℉)】This pourable silicone for mold making cures at room temperature with negligible shrinkage, heat cure will shorten the cure time.
- 【LARGE VOLUME: 2 GALLON = 17.6 Lbs】PERFECT FOR ART AND INDUSTRIAL APPLICATION: BBDINO 30A mold making silicone rubber is a platinum grade additional silicone rubber mold making kit, which is widely used for mold making of arts crafts, like casting Resins, Wax, Gypsum, Concrete, Soap, Candle, and during making the silicone molds, no worries for contacting and touching, there will be no odor, no toxic, and no worry, the residues are very easy to clean by wiping off or peeling off after cured.
- 【LONG SHELF LIFE & VIVID COLOR】our BBDINO silicone rubber for mold making has a very long shelf life of over 1 year, you can easy save the rest materials for next time using by cover the cap back, no waste at all, and this mold making silicone 30A designed with a stunning Sapphire Blue Color, you can easily see whether part A and B mixed evenly enough and also you will make your arts and molds in a unique and beautiful Color!
Rank #4
BBDINO Silicone Mold Making Kit 30A Platinum Liquid 1 Gallon Sapphire Blue
- 【MIX RATIO 1A:1B BY VOLUME】no weighing scale necessary, this silicone mold making kit comes with 2 bottles, 1 gallon /10 lbs kit, part A 5 lb, part B 5 lb, very easy to use, also the bottle come with tinfoil sealed inside the cap, double guarantee for no leaking;
- 【SELF-DEGASSING & LOW VISCOSITY & EASY MIXING & POURING】this BBDINO 30A mold making silicone rubber has low viscosity so that you can easily mix and pour the silicone material, no degassing vaccum chamber needed, the molds finished with this liquid silicone for mold making has great flexibility & Strength. very easy to demold, Great silicone for mold making for simple one- or two-piece block molds making;
- 【WORKING TIME: 30 MINS, CURE TIME: 3~4 HRS AT ROOM TEMPERTUARE 25℃(73.4℉)】This pourable silicone for mold making cures at room temperature with negligible shrinkage, heat cure will shorten the cure time.
- 【LARGE VOLUME: 1 GALLON = 10 Lbs】PERFECT FOR ART AND INDUSTRIAL APPLICATION: BBDINO 30A mold making silicone rubber is a platinum grade additional silicone rubber mold making kit, which is widely used for mold making of arts crafts, like casting Resins, Wax, Gypsum, Concrete, Soap, Candle, and during making the silicone molds, no worries for contacting and touching, there will be no odor, no toxic, and no worry, the residues are very easy to clean by wiping off or peeling off after cured. ATTN: the silicone can be not removable if stick to any kind of fabric materails;
- 【LONG SHELF LIFE & VIVID COLOR】our BBDINO silicone rubber for mold making has a very long shelf life of over 1 year, you can easy save the rest materials for next time using by cover the cap back, no waste at all, and this mold making silicone 30A designed with a stunning Sapphire Blue Color, you can easily see whether part A and B mixed evenly enough and also you will make your arts and molds in a unique and beautiful Color!
Rank #3
BBDINO Silicone Mold Making Kit Liquid Platinum 30A 2.42 Lbs Sapphire Blue
- 【MIX RATIO 1A:1B BY VOLUME】no scale necessary, this silicone mold making kit comes with 2 bottles, net weight 38.8 Oz kit, part A 19.4 Oz, part B 19.4 Oz, very easy to use, also the bottle come with tinfoil sealed inside the cap, double guarantee for no leaking;
- 【LOW VISCOSITY FOR EASY MIXING & POURING】this BBDINO 30A liquid silicone for mold making has low viscosity so that you can easily mix and pour the silicone material, no degassing equipment needed, the molds finished with this silicone for mold making has great flexibility & Strength. very easy to demold, a Great pourable silicone mold making kit for making simple one piece or two-parts block molds;
- 【WORKING TIME: 30-40 MINS, CURE TIME: 3-5 HRS AT ROOM TEMPERTUARE 23℃(73℉)】This mold making silicone rubber cures at room temperature with negligible shrinkage, heat cure will shorten the cure time. High temperature will fasten the working time and the cure time, lower temperature will make he working time and cure time longer. Heat to cure is available, but please follow up our very detailed user manual guideness!
- 【PERFECT FOR ART AND INDUSTRIAL APPLICATION】BBDINO silicone rubber mold making kit is a platinum grade additional silicone rubber for mold making, which is widely used for mold making of arts crafts, like casting Resins Molds, Wax Molds, Gypsum Molds, Concrete Molds, Soap Molds, Candle Molds etc.
- 【LONG SHELF LIFE & VIVID COLOR】Our BBDINO silicone for mold making has a very long shelf life of over 1 year, you can easy save the rest materials for next time using by cover the cap back, no waste at all, and our silicone rubber mold making kit is designed with a stunning Sapphire Blue Color, you can easily see whether part A and B mixed evenly enough and also you will make your arts and molds in a unique and beautiful Color!
Rank #2
BBDINO Silicone Mold Making Kit, Liquid Silicone for Molds Making 30A Sapphire Blue, High Strength Silicon Rubber 4.4 lbs, 1:1 by Volume Ideal for Mold Casting of Resin/Jewelry/Candle/Concrete/Plaster
- Mix Ratio: Silicone Molds Kit Can Be Mixed 1A:1B By Volume Or Weight
- Self Degassing: Liquid Silicone For Mold Making Has Low Viscosity So It Mixes Easily And Cures Without Need For Vacuum Chamber
- Long Working Time: Silicone Molds Kit Provides At Least 30 Minutes Of Working Time And Cures In 5 Hours
- Super Durable: Platinum Grade Silicone Rubber Makes Most Durable And Supportive Molds That Can Be Used Hundreds Of Times
- Wide Application: Silicone Molds Kit Can Be Used To Cast With Almost All Kinds Of Materials Like Resin, Plaster, Cement, Concrete, And Low Temperature Metal
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