How to Make Concrete Molds from Wood

Introduction

Concrete molds made from wood are a great way to create custom concrete projects. With some basic tools and materials, you can make wooden molds for concrete planters, retaining walls, stepping stones, pavers, furniture and more. Wood is an ideal material for concrete molds because it is inexpensive, easy to work with and durable enough to be reused multiple times.

Learning how to make concrete molds from wood only requires a few steps. You’ll need to construct a watertight wooden frame, seal and reinforce it, prepare the mold for pouring, and unmold the concrete after it has cured. With a bit of practice and patience, you’ll be able to create beautiful concrete creations from homemade wooden molds.

How to Make Concrete Molds from Wood

Choose the Right Type of Wood

When making wooden concrete molds, using the correct type of wood is important. The best options include:

Plywood – Multiple layers make it very rigid and durable. It also resists warping better than solid wood. Use at least 3/4″ thick exterior grade.
MDF – Dense composition resists swelling and delivers smooth concrete finishes. Seal edges to prevent water damage.
Melamine – Waterproof coating creates ultra-smooth concrete finishes. Edges must be sealed.
OSB – Cheaper than plywood but not as smooth. The strands can telegraph through the concrete.

Stay away from solid woods like pine which tend to warp and leak over time. Also avoid particleboard, which disintegrates when saturated with water.

Construct the Mold Frame

Once you’ve selected the right wood, it’s time to construct the mold frame. Follow these tips:

Cut wood pieces to the desired dimensions using a circular saw or handsaw.
Assemble into a watertight frame using wood glue and nails, screws or biscuit joints.
Seal all seams with silicone caulk to prevent leaks.
Attach a bottom panel in the same watertight fashion if making an enclosed mold.
Make sure corners are square using an adjustable square or measuring diagonally.

For more complex molds with irregular shapes, make a template first out of rigid foam or cardboard. Trace the outline onto the wood.

Add Reinforcement and Structural Support

Fresh concrete exerts significant pressure on mold walls, so the frame needs extra reinforcement:

Apply wood brace pieces to the exterior at corners and vulnerable areas.
Drive screws through the mold sides into the bracing for added strength.
Use 2x4s or plywood gussets in larger molds to prevent bulging.
For heavy molds, attach a 2×4 base frame to prevent spreading and cracking.
Drill holes for rebar or dowels to reinforce the cured concrete product later.

Waterproof and Prepare the Mold Surface

Sealing and prepping the interior surface is crucial to clean concrete removal:

Apply 2-3 coats of paste wax letting it dry between applications.
Form release agents also prevent sticking and create smooth finishes.
Fiberglass resin works as a durable sealer for many reuses.
Lightly sand melamine and other slick surfaces for better concrete bonding.
Coat wood surfaces with heavy plastic sheeting secured with staples.
Wrap edges with foam tape to prevent leaks and hide imperfections.

Pour and Cure the Concrete

With a fully prepped mold, you’re ready to pour the concrete:

Layer release agent or plastic onto the mold right before pouring concrete.
Funnel premixed concrete or make your own mixture without aggregates.
Tap the sides as you pour to prevent air pockets and settle the concrete.
Insert any rebar or dowels at this stage per your design plans.
Cover the open top with plastic sheeting to retain moisture while curing.
Wait at least 24-48 hours before removing the concrete from the mold.

Remove the Concrete and Clean the Mold

Once cured, removing the concrete requires patience and care:

Run a utility knife around edges to break the seal.
Pry the concrete out bit-by-bit starting at corners and edges.
Avoid hammering which can damage the mold and concrete surface.
Rinse the mold with water and scrub off residual concrete with a brush.
Let the wood dry fully before applying more release agent and reusing.
Make any repairs before the next use to prevent leaks.

Following these steps will allow you to reuse your wooden concrete molds many times. With practice, you’ll be able to create amazing custom concrete projects!

Tips for Making Wooden Concrete Molds

Here are some additional tips to help you make the best concrete molds from wood:

Use screws instead of nails to assemble the mold frame. This allows easier disassembly for concrete removal and mold reuse.
Elevate enclosed molds on blocks or bricks to make removing the cured concrete easier.
Make drain holes fitted with plugs to drain excess water from fresh concrete as needed.
Craft chamfer strips from wood to create smooth beveled edges on concrete products.
Line the mold interior with foam shelf liner for quick, clean releases.
Apply paste wax to the mold surface with a disposable chip brush for an even coat.
Construct your mold at least 1/8” larger in dimensions to account for concrete swelling as it cures.
Use a plastic concrete trowel or wood float to smooth and level freshly poured concrete.
Spray form release agents onto the mold right before pouring for best results.
Store wood molds flat and covered to prevent warping between uses.

Frequently Asked Questions About Making Concrete Molds from Wood

What kind of wood works best for concrete molds?

The best woods for concrete molds are exterior plywood, MDF, and melamine. These materials resist swelling and deterioration from moisture contact. Plywood is one of the most common and affordable options.

How thick should the wood be for a concrete mold?

Aim for at least 3/4″ thickness for plywood molds and 1/2″ for MDF or melamine. Any thinner and the wood risks warping or bowing under the weight and pressure of the concrete.

What is the easiest way to waterproof a wooden mold?

Coating the wood in layers of paste wax effectively waterproofs the surface while acting as a release agent. Fiberglass resin also seals and protects wood molds for multiple reuses. Plastic sheeting and garbage bags also prevent leaks on a budget.

How many times can you reuse a wooden concrete mold?

With proper care, a wooden concrete mold can be reused 10-20 times. Maintaining the structural integrity and release coatings allows extended reuse. Eventually the wood will show signs of wear requiring repairs or replacement.

Should you nail or screw together a wooden concrete mold?

Screws are better than nails when assembling a wooden mold frame. The screws allow you to disassemble the form more easily for removing the cured concrete. Nails tend to hold the wood too tightly.

How long does concrete take to cure in a wooden mold?

Most concrete should cure in a wooden mold for 24-48 hours before attempting removal. This ensures the concrete has hardened sufficiently to withstand demolding without damage. Cooler curing temperatures extend the curing time.

Should you apply release agent to an already sealed mold surface?

Yes, it’s advisable to reapply release agent even on a sealed wooden mold before each use. The agent prevents minute bonding between the concrete and wood sealant, allowing easier release.

How can you avoid concrete sticking to a wooden mold?

Start with very smooth mold surfaces free of defects. Applying multiple coats of paste wax or form release agents ensures the concrete won’t stick. Avoid overworking the concrete during pouring which can cause it to cling.

What are some beginner wooden mold projects to try?

Great starter projects include concrete planters, bricks, garden stepping stones and tiles. These smaller items allow practice working with wooden molds before tackling large projects. Make molds using simple squares or rectangles.

Conclusion

Creating your own wooden concrete molds opens up amazing potential for DIY concrete projects. The fundamental techniques involve constructing sturdy molds, properly sealing and preparing the wood surfaces, then pouring and releasing the concrete. With some practice and experimentation, you can refine your skills and make molds for elaborate concrete furnishings, sculpture, and architectural elements. Wooden mold making is also a cost-effective method that allows reusing materials compared to commercial single-use plastic molds. Let your creativity run free, and make homemade molds the launchpad for designing unique concrete pieces that showcase your style.