So you want to make a River Tray?
I’d like to offer up a few lessons learned that I think will be of value for people setting out to make a river tray or table. Some are practical (Don’t touch the hot stove!”) and some are just my personal taste (Well, there’s just too much/too little epoxy in that tray!). I’ll leave it to the reader to pick and choose which ones to apply.
You will need wood, epoxy and hardener, epoxy dyes, a tray mold, measuring cups, mixing cups, stirring sticks, a thermometer, a timer, and a temperature-controlled place to work with epoxy. Once the epoxy sets, you will need tooling and materials to thickness plane, sand and finish the tray; and to attach the handles to the tray.
Some Lessons Learned:
Use Tray Molds
Epoxy is sneaky stuff, it will take advantage of the slightest pinhole opening to escape from confinement and run out across your floor. A properly sealed tray mold is the only way to prevent these break-outs.
Epoxy will bond to porous or even semi-porous surfaces with great tenacity, making release of your tray from a mold quite “challenging” if the mold is made from plywood or even low-pressure laminate material. It’s best to use molds made of silicon rubber or high density polyethylene (HDPE). A light spray of mold-release lubricant is not strictly necessary with these materials, but it certainly won’t hurt. You can use low-pressure laminate materials to make molds, but you must cover them with strapping tape and then spray the end result with mold-release or you are never getting that tray out of the mold. Molds made this way have a limited life – you will get at least 10x the number of trays from a silicon or HDPE mold than you can with a low-pressure laminate mold.
Store-bought molds work very well, if you can find one in the proportions you like. The golden ratio preferred by many designers is approximately 3:5, which translates to a mold that is 9”x15” (which is really a bit small) or 12”x20” (which is a bit large). I make my own molds out of HDPE in either 9”18” or 12”x24” sizes, and use store-bought silicon molds in the “12×18” size.
2. Use dry wood
Epoxy doesn’t bond very well to wet wood, as water interferes with the chemical reaction that occurs when epoxy sets up and becomes hard. Make sure the wood you use has been dried down to 8-12% moisture content – typical of kiln-dried or well aged air-dried wood. This will also help prevent your trays from warping and cupping as they acclimatize to in-home air moisture.
3. Choose interesting wood
Color variation – walnut sapwood (next to the bark) is light cream-colored, walnut heartwood is dark chocolate-colored. This contrast makes for an interesting tray. Cherry does not have as extreme a contrast between sapwood and heartwood, maple has almost none.
Natural edge with lots of character – Look for wood slabs that have a lot of character in the bark edge – curvature, coves and bays, indentations, and protrusions … they will add lots of visual interest to your tray.
Spalting – wood that has been invaded by fungus (spalted wood) may streaks of color, dark and light lines, and random variations of color that will add lots of visual interest to your tray.
Figure – figure refers to the pattern wood grain shows in a sawn piece of wood. Figure can be straight, arched, curly, flaked, burly, or fiddleback. Look for wood with lots of figure!
Splits, checks, knotholes – these are sometimes considered defects, but not in a river tray! You will need to pick out, chisel out, or dremel out loose wood before you pour epoxy, but epoxy will fill in cavities and stabilize the wood, turning what was a defect into a feature.
4. Remove Bark
Epoxy will stick very well to bark, but bark will not stick very well to wood. If you don’t remove the bark before casting, you can expect the tray to fall apart eventually. Peel the bark off with a draw knife, and then use a belt sander to scuff up the sapwood to ensure good adhesion between the sapwood and the epoxy.
5. Cut wood to the proper width
I prefer the epoxy river to be between 2” to 3” wide, depending upon the width of the tray. A 9” wide tray should have 3.5” wide wood panels to either side of a 2” wide river; a 12” wide tray should have 4.5” wide wood panels to either side of a 3” wide river. Obviously with a natural edge slab the width will vary a bit across the length, so these width values are approximate. Flat-sawn slabs usually have two natural edges with heartwood in between. I cut a straight line (or lines) down the center of the heartwood to create two natural edge pieces. The cuts are done to place the river where I want it – either in the center, offset from the center, or diagonally across the tray.
6. Joint and thickness wood before putting in mold
Wood is never perfectly straight or flat, and should always be edge and face jointed before use. This will ensure that the wood will fit in the mold without gaps at the sides or bottom that will fill in with epoxy and have to be cut away. This will allow you to cut the edges squarely to length.
Once jointed and cut to length, you may wish to thickness plane them. I prefer to plane them down to about 1” thick. I usually like to have a layer of epoxy that is 3/4” to 7/8” thick when it sets up, which allows me to make a tray that is 5/8” thick when finished. If I pour to the top of a 1” thick board, it will soak into the wood and seep around the sides and the level will drop eventually to between 3/4” to 7/8” thick.
7. Use Clamps or Weights
You need to clamp or weight the wood in the mold to prevent it from floating to the top of the mold when you add epoxy. Clamp if you need to move the mold before the epoxy sets up, otherwise weights are fine. Don’t try to flatten a warped board by clamping or weighting it down firmly, as it will result in stresses in the wood that may cause cupping or twisting after the tray is finished. Clamp or weight just enough to prevent the wood from floating upward when the epoxy is poured. I always flatten wood pieces on the jointer before placing in the mold, to minimize wastage.
8. Put wood in mold upside down (unless you are doing a mica or a multi-color pour)
If I am going to do a single-color pour with translucent dye, I always put the good side face-down in the mold. The good side is what will be the top of the tray when finished.
If I am doing a multi-color pour or a mica-dye pour, I put the good side face-up in the mold. This allows me to control (somewhat) the patterns formed by the mica or the colored dyes on the top of the tray.
9. Use the right epoxy and follow the manufacturer’s guidelines for use
In general (gross oversimplification) Epoxy manufacturers have 4 woodworking formulations, as follows:
Structural – used to laminate and glue solid wood
Penetrating – used to penetrate and seal soft and rotten wood
Table Top – used to seal and clear-coat table tops, signs, coasters, ...
Deep Pour – used for river tray and table fabrication, comes in deep pour (max 1” thick) and extra deep pour (max. 3” thick) formulations
I use MAS Deep Pour epoxy for river trays and tables. It uses a 3:1 ratio by volume of epoxy to hardener. It cures in 36 hours, clears bubbles very well, remains transparent (unless you use dyes), and is very forgiving. And it’s less expensive than the other vendors’ deep pour epoxies. This could change.
Don’t get creative with ratios of epoxy to hardener. – always follow manufacturer’s recommendations.
10. Let the epoxy get HOT before you pour when doing a multi-color pour or a single-color mica pour
There’s a bit of a trick to doing a multi-color or a single-color mica pour. Simply stated, you have to let the epoxy get quite hot before you do the pour. If you don’t the colors will all blend together and you will lose the separation between colors that you might have been hoping for. Or the pattern you create in the mica pour by stirring will disappear and it will create its own pattern as it cures.
If the epoxy is too cold, it will mix together in the mold in a way that you can’t control. If it’s too hot, it could set up in the mixing jar and not be pourable. I mix the epoxy in a large bucket, measure the temperature of the mixed epoxy periodically, and pour it into smaller containers (for dyeing) when it hits 125 degrees. You have maybe 5 to 10 minutes at that point to mix dye into the smaller containers, do your pours, and swirl the epoxy to create the patterns you want. If it gets up to 135 degrees it will set up very fast and you may not have enough time to dye and pour.
If you pour the epoxy into smaller containers immediately after its mixed, it will take a very long time to get to the right temperature. I’ve had it take 4-5 hours. It gets hot more quickly if you leave it in the large bucket – I usually have to wait no more than 1 to 1.5 hours before it’s ready to dye and pour.
So … mix in a large bucket, set a timer, measure temperature constantly after the first hour, and have your smaller containers and dyes ready for use before it gets hot.
11. Only swirl the epoxy once
The more you swirl the epoxy, the more the colors and patterns will mix together and become muddy. I get the best results by swirling patterns and colors one time and then letting it do what it wants – you have to accept that you can influence but not really control the results.
12. Choose the right sized handles
For a 9” wide tray I prefer to use handles that are 3.75” (96mm) from screw hole to screw hole, and are 1” high from handle to tray, set about .75” from the edge of the tray. For a 12” wide tray, I prefer to use handles that are 6” from screw hole to screw hole, and are 1” high from tray to handle, set about 1” from the edge of the tray.
13. Use rubber or plastic bumpers to protect your counters from the handle screws
I attach the handles to the tray using screws threaded through holes that I drill in the tray. I don’t counter-sink the underside of the tray to accept the head of the screw, as the tray is usually too thin to do so. Instead, I attach rubber/plastic bumpers to the bottom of the tray. This prevents the screw heads from rubbing against counters or tabletops.
The tray may warp, so your tray may not sit flat on counter over time. To fix this, identify the bumpers that are the long poles in the tent, and light sand one of them down until the tray sits flat again.
14. Use a food-safe finish that can be re-applied by the eventual user/owner of the tray
I use Odies Dark, which is a mixture of oils, waxes, and stains. There are lots of other options – Walrus Oil, Butcher Block conditioner, or mineral oil finishes all work well. Whatever you do, don’t lacquer or polyurethane the trays. Not only does this look tacky (IMHO) but if it ever gets chipped, scored or waterstained it will be very difficult to refinish. The beauty of Odies (or the others that I have mentioned) is that they can easily be reapplied when the original finish gets worn or washed away.
