Resin coasters, trays and small casts
The first project most people finish, and the family where the method is the same every time — only the mold changes.
A standard 100 mm coaster cavity holds about 79 ml, so a set of four takes roughly 346 ml of mixed resin including wastage. Use a casting resin rather than a coating one: at 10 mm a coaster is well past what table top epoxy takes in a single pour. Pour slowly, torch the bubbles within the first twenty minutes, cover it against dust, and leave it alone until full cure.
Coasters, trays, keychains and tumblers are one project wearing four hats. The method does not change — mix, colour, pour, release the bubbles, cover, wait — and what changes is the mold and how much goes in it. That is why this is a single page: the technique that gets you a clean coaster is the same one that gets you a clean tray, and the only thing worth looking up separately is the volume.
The one decision that catches beginners is the resin. A coaster is 10 mm deep, and 10 mm is a casting rather than a coating: 4 separate coats of table top / coating epoxy over as many days, or one pour of deep pour / casting epoxy. Most beginner kits contain the coating kind and ship it with molds at a casting depth, which is where a great many disappointing first batches come from.
The second is bubbles, which is the commonest complaint at this scale and mostly a matter of the first twenty minutes. The troubleshooting guide covers the ones that are not, and the calculator sizes any mold you own — including the ones whose listing does not state a capacity. The beginner's guide covers the mixing and the pour itself.
What each project takes
Cavity volumes are derived from each mold's dimensions rather than taken from a listing. "To mix" includes 10% for what stays in the cup, which at this scale is a real share — a 30 ml pour leaves a genuinely awkward amount behind. Costs are materials only, at $90 a gallon for casting resin.
The three that behave differently
Poured to the top of the cavity and left. The mold decides the finish entirely: a glossy mold gives a piece that needs nothing, a matt one gives a frosted piece that has to be sanded and polished back. A tray is the same job at 480 ml, and is the pour where running short mid-way leaves a line you cannot remove.
Shallow enough that UV resin cures them in about a minute each, so a tray of ten is finished in an evening rather than over three days. Anything past about 10 mm goes back to a two-part casting resin, because light stops reaching the bottom. The UV resin guide covers where the line falls.
The one genuine method difference in this family. A tumbler is coated rather than filled, and it has to rotate while it sets or the resin sags to the bottom and cures as a drip line. About 31 ml of table top / coating epoxy covers a 20 oz cup — a fraction of what people expect, because the resin is a skin rather than a volume.
What decides whether it comes out clean
Almost every bubble complaint at this scale is air folded in during mixing, and it is dealt with before the resin thickens. Stir slowly rather than whipping, let the mixed cup stand for a minute so the big ones rise, pour in a thin stream from a height rather than dumping it, and pass a torch a few inches above the surface in a sweeping motion. After about twenty minutes the resin is too thick for anything to rise through it.
Silicone casts whatever it has. A polished mold gives a clear glossy piece straight out; a matt one gives a frosted piece that needs sanding through several grits and polishing. This is the single biggest difference between molds and it is almost never in the listing — the mold guide covers what else to look for.
44 ml for a tray of keychains is at the edge of what a kitchen scale resolves, and at that size a gram either way is several per cent of the hardener — enough to leave the piece tacky. Weigh on something that reads to 0.01 g, or mix enough for several pieces at once, which is more accurate as well as less wasteful.
A coaster stays open and sticky for hours, so anything that lands on it in that time is part of the piece. Cover each mold with a box or an upturned tub the moment the bubbles are out. Do not pour in a room you have just been sanding in, and do not put a fan on it.
Dried flowers float, glitter sinks, and both do it slowly over the hours a casting resin gives them. Pour a shallow layer, let it thicken to honey, place the inclusion, then pour the rest — or accept where it ends up. Anything organic also needs sealing first, or it browns and outgasses into the pour.
A mug on a coaster is incidental contact rather than a food surface, and it still needs to be fully cured. The food safe guide covers what a manufacturer's claim actually means, and why hot pans and dishwashers are outside all of them.
Making a set
Four coasters in one pour is more repeatable than four separate pours and wastes less — 691 ml for 8 of them against 86 ml for one, which is not a quarter of it because the wastage does not scale down.
A silicone mold on an uneven shelf casts wedge-shaped coasters, and you find out the next day. Put it on something flat and check with a small level. Once poured, a gentle look along the surface shows a tilt immediately, and it can still be shimmed for the first few minutes.
The geode and ocean effects everyone is after come from pouring colours separately and letting them meet, not from mixing them together. Split the batch into cups, colour each, and pour them into the cavity in turn. The pigment guide covers the loads — well under a per cent is usually enough.
Rotating slowly for the whole set time is the entire technique — a cup left standing cures with a fat drip line along the bottom. A cheap rotisserie motor does it; so does turning it by hand every few minutes for an hour, badly.
48 hours before a casting resin will come out cleanly, and full hardness at 7 days. A piece pulled early flexes, keeps a fingerprint, and can never be made flat again. If it is stuck, twenty minutes in the freezer releases it.
If a piece comes out matt or has a lip, wet-sand from 400 through 800, 1500 and 2000, then polish. Dry sanding cured resin makes a dust you do not want to breathe, and it clogs the paper immediately. Wet sanding is faster, cleaner and gives a better result.
Size your own molds
Enter the cavity capacity and how many you are filling — or the dimensions if the listing does not state one — and the calculator gives what to mix, the split, and whether the depth needs more than one pour.
Open the epoxy calculator →Print the pour-depth card
Maximum pour depth and cure windows by resin type — the number that cracks a casting. Free.
Estimates, not advice. Every figure on this page is computed from published reference values and standard measures, so your own inputs, equipment and conditions will move it. Nothing here is professional advice — talk to a qualified professional before acting on it.