THE BUILDING PROCESS
Now that we addressed the most important aspects which affect the planning, let’s start with the building process.
3.1 Preparation of the Dry Wood Slab
The hardness of the wood slab is not uniform throughout. The bark and outer areas are the softest and therefore the weakest. This portion of the wood has the lowest density; meaning it is porous and contains a lot of air. It is therefore required to remove all the bark and soft wood from your slab. These will prevent a proper bond between the wood slab and epoxy, leading to cracking and breaking. The table will only be as strong as the weakest part.
Start with a hammer and chisel to remove the bark. A wire brush on a baby grinder can be used to do some clean-up and remove any other soft wood from the wood slab. Use a hand wire brush to get into places where the baby grinder cannot. Do not rush this step. Poor preparation will result in a poor final product.
The second step in the process is to smooth out both sides of the slab using a CNC machine.
During these preparation steps, you may uncover natural cracks in your wood slab’s surface. These cracks develop during the drying process and are perfectly normal. Use an air hose to clean all cracks on your wood slab. This is very noisy so be sure to wear appropriate hearing protection.
Finally, wipe your workable wood slab with a clean dry cloth to remove any remaining dust particles.
During the preparation step, a portion of your table might break off and affect the final design. It is a factor you have to consider and accept.
3.2. Table Design
Now that the final workable wood slab is uncovered, it is time to decide on the final design of your table.
The design refers to the position, flow, and orientation of your wood slab within the final product. Design is often the factor that distinguishes mediocre from outstanding epoxy table builders. There are a few methods you can use to assist you in your table design and help to visualize your creative voice. Take a picture of your workpiece and load it on photoshop or any photo editing program. Play around to find the design you like most. Note that this will only give you a good idea of your intention. The final product will very likely differ slightly.
Another option is to build a wooden frame (like a picture frame) the same size as your final intended table. Place it over your workpiece and move it around to get a good idea of your design options. At DIY with Greg, we use all these methods but apply the following method most often. Take the base of the mold (discussed later in the document) and lay the slab on top of it. Move the slab around and visualize the end product. Once you decided on a design, trace or outline the shape of the slab onto the mold base with a marker. You can assess your design properly once you removed the wood slab. If satisfied, mark the cut lines on the wood slab.
3.3. The Mold
The mold or pouring box is a critical component of your building process. The mold will hold the wood slab and epoxy in the required shape and size of your table.
We build a mold using White Melamine Chipboard. It is relatively cheap and strong enough and the melamine prevents the epoxy from penetrating the chipboard. If used with care the mold can be used up to 3 times. The dimensions of the box should be slightly longer and wider, by about 10mm to 20mm, than your final intended table size. The increased size compensates for loss during surface rework and finishing, meaning there will be room for error if you make a mistake. Also, make the side walls of the mold 10mm higher than the desired thickness of your table to prevent overflow when pouring epoxy. You can either use a nail gun or screws to fasten your upright edges tightly to the bottom sheet of your mold. Use silicon to seal the connection lines of your mold to prevent any epoxy leakage. Finally, place your mold on a flat, water-level surface. This will ensure the even spread of the epoxy when pouring it into the mold. You can also use MDF super wood to build your mold but will have to seal the MDF surface with Tuck Tape, a product we don’t have locally available. I would still recommend using a melamine sheet, as it takes less time and is cheaper.
3.4. Release Agent Wax
We have tried various types of release agents and are really satisfied with the results of Ram Wax®. If this is not available in your country, ask your epoxy supplier or manufacturer which release agent they recommend. You can always try out the release agent in a small mold when you pour a sample to test the color of the epoxy. Once satisfied with the release agent, apply one coat over the entire surface of your mold, ensuring you cover all the corners as well. Allow the release agent to dry for approximately twenty (20) minutes and buff off with a dry cloth.
3.5. Setting the Wood Slab in the Mold
Ensure both the mold and the wood slab is clean and as dust free as possible. At DIY with Greg, we use an air hose to clean in between all the little cracks before wiping the slab with a clean dry cloth. Do the same with the mold. Insert the wood slab into the mold. If you have to move it, lift and move rather than sliding it over the prepared surface in order to protect the coat of the release agent. Clamp your slab onto your mold on both ends and the center to ensure it remains in place once you pour the epoxy.
3.6. The Edge Sealing Conundrum
This is a very debatable topic. There is evidence to support both views and we have found that the answer is not straightforward. It is important to understand the rationale behind both methods. The two main aspects affecting the decision are:
a) The strength of the bond between the epoxy and the wood slab, and
b) the possibility of bubbles appearing close to the edges of the wood slab.
Like all options, there are pros and cons to both methods. By not sealing our edges the quality and strength of the bond between the wood slab and epoxy is much better as the epoxy is able to penetrate deeper into the wood and all the cracks. This is an excellent method, especially when using opaque (solid color) epoxy.
The downside is the likelihood of bubbles appearing along the edges of the wood slab. There are however methods of effectively preventing and removing the bubbles from the epoxy which we will discuss below.
Preventing bubbles to form along the edges of the wood slab is therefore the primary reason for sealing the edges.
Should you decide to seal the edges of your wood slab, be sure to sand the surface once it is completely dry. You may even use a steel brush to rough up the sealed surfaces, improving the bond when you cast epoxy.
3.7. Determining the Epoxy Volume
This is the time to apply the math you thought you would never use again. It is however not too difficult. This requires a simple calculation of the volume of the void portions of your table.
Volume is calculated by multiplying the width, length, and depth (height) of the area in question. Wood does not form in perfectly straight lines. It is therefore required to divide the void area into smaller portions consisting of triangles and squares. Calculate the approximate surface area of each portion and add the values together. Multiply this total by the depth which equals the estimated volume of the void. Remember to consider the angle of the wood and how it affects the size of the surface area between the top and bottom parts of the void. If this difference is significant, you can use the average between the two or to be safe use the largest surface area of the portion.
3.8. Epoxy Pouring
As indicated earlier, environmental conditions, especially temperature can have an adverse effect on your project. Casting in very hot temperatures can cause the epoxy to overheat and boil. It is therefore critical to work in the temperature ranges recommended by the epoxy supplier or manufacturer. For best results, pour epoxy into a temperature-controlled workspace with an average temperature of 21°C (70°F).
When pouring in cold working temperatures below 14°C (57,2°F) it is advised to warm your resin and hardener to at least 27°C (80,6°F) prior to mixing. This lowers the viscosity of the epoxy and allows bubbles to rise and be removed much easier using a flame gun. The warmer epoxy also reaches into cracks and crevices much easier, binding to the whole surface of the wood slab.
Warm the resin and hardener by placing them in separate containers and into a bucket of hot water. Ensure uniform heating of the solutions by either intermittently stirring (with separate paddles) or shaking the containers (with closed lids) until the desired temperature is achieved. You can use an infrared thermometer to verify the temperature of the solutions. Once the solutions are warm enough, mix and slowly pour the epoxy into the void of the mold. This is by far the easiest step in the process. Pour slowly to minimize bubble formation in the epoxy during the pour. Remember to add calculated amounts to each void should there be multiple epoxy sections to the table. Once the epoxy is poured into the mold, allow six (6) to twenty-four (24) hours (depending on your supplier’s specifications) for the epoxy to gel and set in the mold. Areas with high volumes of epoxy may take up to thirty-six (36) hours to fully cure. Increasing the environmental temperature of your workspace twenty-four (24) hours after pouring can speed up the curing time.
Pour the epoxy to be slightly thicker than the desired thickness of the table. This will leave sufficient material to flatten and finish the table down to the desired thickness, ensuring a smooth surface.
TIP: Wipe the bottom of your buckets with a damp cloth before using them at the table. This also relates to any other equipment that is clean and dust free. We had many incidents where we put our buckets on the floor, and when it was time to cast and work over our table, dust particles would fall on our wet epoxy surface.
3.9. Dealing With Bubbles
Bubbles are removed during two phases in the building process. The first is prior to pouring each batch. You would normally have approximately 45 minutes of working time after mixing the resin and the hardener before it becomes a thick gel. During the mixing process, air enters the epoxy solution. Leave the epoxy for about 10 minutes to allow the air bubbles to rise to the surface. Sweep your flame gun over the surface of the epoxy, heating the epoxy just enough to allow the air bubbles to escape the solution. This significantly reduces the number of bubbles in the pouring mixture.
The second phase during which to remove bubbles is after the pour. Again, wait a few minutes to allow the air bubbles to rise to the surface. Most of the bubbles will form along the edges of the wood slab, especially when it is not sealed. Use your flame gun again to remove the bubbles. Repeat this step a couple of times until no air bubbles are observed.
When your epoxy is too cold or when pouring in cold conditions your air bubbles will not rise to the surface. When in doubt about the mixture temperatures, warm the solutions. Prevention is better than cure, and a lot less costly.
Lastly, air bubbles can also be removed by using a vacuum chamber, should you have access to one.
3.10. Using a Gas Flame vs Heat Gun
A gas flame is a preferred method to pop surface bubbles from the epoxy. Generally, heat guns blow with too much force and create waves or ripples in the epoxy. This may leave the epoxy surface distorted. Always use an open flame when removing bubbles. Hold the flame far enough away that your flame does not touch the surface of the epoxy. Constantly move it from side to side to prevent burning the epoxy. Never hover the flame over a single spot for too long. It is critical that the flame is always in motion to ensure only the radiant head impacts on the process.
3.11. Sanding Between Pours
This is very important when you do not have a dust-free work area, especially as the epoxy dries. Dust may settle and stick to the surface of the poured epoxy while it is still wet and sticky. These particles will display as impurities in clear or transparent epoxy. Dust will however not have any influence on the aesthetics of opaque epoxy tables. To remove these particles, you must wait for each layer to have hardened. Use an orbital sander fitted with 100 grit sandpaper to sand the surface. Yes, I have done this many times. You will not notice any sanding marks between epoxy layers afterward. Remove all dust from the surface with an air hose. Then wipe the surface of the epoxy first with a damp cloth and then a dry cloth. Use an air hose to remove any dust you may have missed. Once the surfaces of the wood and epoxy are completely dry and dusted free you may pour the next layer of epoxy. Sanding between layers will also give you a better bond between epoxy layers.
3.12. Epoxy Curing Time
Curing occurs when the epoxy passes from a liquid to a solid state. Only once this chemical reaction is fully complete, leaving a stable uniform solid, can we start working on it. Please find information on the curing times of the epoxy you use from the manufacturer or supplier. The epoxy we use requires a curing time of five (5) days before we can start working on it. Leave the epoxy in the mold during the full curing period.
3.13. Removing the Table From the Mold
When curing is complete, it is time to remove your table from the mold. In our case, the cured table is much stronger than the chipboard mold we used. The release agent will also ensure that we don’t require too much effort. Use a rubber hammer or mallet to remove the sides of the mold by gently hitting the uprights extending beyond the edges of the table. Gently drive wooden or plastic wedges in between the table and the bottom sheet of the mold, splitting the two apart. If you do this carefully enough without breaking the sections of your mold, you can reuse it multiple times. Do not use any metal objects such as chisels to remove your table from the mold as this may damage your piece or cause it to crack.
TIP: When you remove the side panels from the mold, The edges from your epoxy will be very sharp. Use a steel file to easily blunt the sharp edges, preventing any unnecessary cuts.
Comments