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How to use epoxy resin moulds

Updated: 23 October 2026

The usual failure is not a mysterious mould. It is a wet cavity, a resin that was never meant for that depth, or a pull while the back is still soft. You then get a cloudy cast, a torn letter, or a piece that stays tacky. This is how to use epoxy resin moulds so the silicone flexes off a finished cast. The products themselves are ranked on the [epoxy resin mould comparison](/hub/fillers-adhesives-and-sprays/epoxy-resin-mould). Products Compared did not run a lab pour. A qualifying purchase can earn a commission. Health and Safety Executive guidance treats epoxy resins as skin sensitisers, so gloves go on before the first drip.

The usual failure is not a mysterious mould. It is a wet cavity, a resin that was never meant for that depth, or a pull while the back is still soft.

Our top picks

ZMD ZMD 6-cavity deep round mould

Best overall

ZMD ZMD 6-cavity deep round mould
8.0/10about £7.59
View offer
LET'S RESIN LET'S RESIN 18-piece coaster moulds

Rank 2

LET'S RESIN LET'S RESIN 18-piece coaster moulds
8.8/10about £17.99
View offer
ZEROMX ZEROMX geometric kit with LED base

Rank 3

ZEROMX ZEROMX geometric kit with LED base
7.4/10about £23.79
View offer
On this page
  1. 1.Set the mould up before you mix
  2. 2.Mix and pour to the bottle, not to a blog clock
  3. 3.Demould only when the surface is firm
  4. 4.Wash, dry, and store flat

Set the mould up before you mix

Wash the cavity with soap and water if it is dusty, then dry it fully. Resin Pro warns that a damp mould clouds the cast, and that a hairdryer can push dust and leave the surface warm and still wet. A lint-free cloth, then time on a level bench, is the safer finish. Pouring water in to see the volume is useful on a deep round such as the ZMD cavities at about 165 ml, but only if you tip it out and dry the mould before resin goes in. A bead left in a corner becomes a white patch you cannot sand away. Set the mould on a board that is level in both directions. EPODA reviewers saw a square mould that was not flat from the packet, so the cast rocked. Check that before you mix. Gloves and an open window belong in this step. The bottle comes out only when the cavity is clean, dry and sitting still.

Mix and pour to the bottle, not to a blog clock

Read the ratio on your bottle and measure it the way that bottle says, by weight or by volume. Under-mixing leaves tacky patches even when the amounts were right. LET'S RESIN's 500 ml kit reviewers often found the leaflet limited to safety and the cup marks hard to read. Do not invent a 1:1 because another brand uses 1:1. ZEROMX states 1:1 on its own listing only. The ZMD listing says casting resin, not coating resin, for cavities about 0.8 inch deep. Coating resin in a mass like that can overheat, and Apex Resin warns a deep pour can fuse resin to the mould. If your resin's maximum depth is thinner than the mould, pour in layers the bottle allows. A heat gun kept moving can raise bubbles in an open tray. LET'S RESIN's coaster listing says a torch or heat gun is not recommended. The clock on the bottle is the one that counts.
ZMD ZMD 6-cavity deep round mould

Testsieger

ZMD ZMD 6-cavity deep round mould
8.0/10about £7.59
View offer

Demould only when the surface is firm

Press a clean glove on a spare edge or the back. If it prints or feels tacky, it is not ready, however many hours have passed. Resin Pro cites 24 to 48 hours and, on another page, 8 to 12 hours. Do not average those into one rule. Cold rooms and deep pours take longer. When the surface is firm, flex from the edges. Do not hook a fingernail under a thin letter. Opopark reviewers tore letter strokes that way, and one EPODA buyer ripped circles on three of four pieces. If the resin is still liquid after the bottle's window, do not pour that batch into a second cavity. One ZEROMX reviewer had a resin that would not set and spoiled other moulds.

Wash, dry, and store flat

Wash again, dry fully, then store the mould flat. Apex Resin suggests cardboard between stacked moulds so faces do not imprint each other. Do not bake the mould, and do not use the heat gun as a dryer. This stays a home method until uncured resin is on your skin, in an eye, or on your breath. HSE lists epoxy resins as skin sensitisers. A rash, eye contact or breathing symptoms need urgent care. Selling pieces as toys for under-14s, or as food-contact ware, is a different set of rules, and a clean demould does not prove either. A river table is a different specification. If the pour is that large, you are past this mould and this method.

Common questions

How long do I wait before I flex the mould?
Wait until a touch test shows no tack, inside the window on your bottle. Resin Pro cites 24 to 48 hours and, on another page, 8 to 12 hours. Those are not one rule. Cold rooms and deep cavities take longer. If the surface still marks, leave it.
What if the back is still soft?
Leave it in the mould. A soft back means the cure has not finished, or the ratio was off. Pulling now is how Opopark letters snapped and how EPODA circles tore. If it stays soft past the bottle's window, do not spread that batch into other moulds.
Can I use a heat gun on the silicone?
Not as a parked flame, and not on the LET'S RESIN coaster moulds, whose listing says a torch or heat gun is not recommended. If you use a gun at all, keep it moving above the resin, not on the rubber. The gun does not replace a correct mix.
Why did the piece come out cloudy?
Moisture is the common cause. A mould that was not fully dry, including after a water-volume check, clouds the resin. Dust and a heavy release spray do it too. Dry the cavity until it is free of droplets. Sanding does not clear a cloud through the whole thickness.
What if the resin never hardens?
Stop pouring. Check the ratio on that bottle, and that you did not use coating resin in a deep cavity such as the ZMD rounds. A kit resin that stays liquid, as one ZEROMX reviewer reported, can spoil the next mould. Discard that mix as the bottle's waste instructions say.
When do I stop and get medical help?
When uncured resin is in an eye, you are short of breath, or a rash is spreading. Epoxy is a skin sensitiser in HSE's list. Wash off a small skin splash as the label says. A stuck coaster can wait. Your eyes and breathing cannot.

Related pages

How to choose an epoxy resin mould

Resin coaster moulds

Resin mould kit vs moulds only

Epoxy resin mould

Best epoxy resin moulds: a top pick and best value

Sources

Public UK sources used for this comparison. amazon.co.uk prices, stars and review counts were taken from the listings on 19 October 2026.

  1. HSE skin sensitisers (retrieved 19 October 2026)
  2. HSE COSHH and skin exposure (retrieved 19 October 2026)
  3. HSE GB CLP (retrieved 19 October 2026)
  4. Regulation (EC) No 1935/2004 Article 3 (retrieved 19 October 2026)
  5. Toys (Safety) Regulations 2011 Schedule 5 (retrieved 19 October 2026)
  6. FSA food contact materials (retrieved 19 October 2026)
  7. Go Bespoke resin mould guide (retrieved 19 October 2026)
  8. Apex Resin silicone mould care (retrieved 19 October 2026)
  9. East Coast Fibreglass resin moulds (retrieved 19 October 2026)
  10. amazon.co.uk listings for the ten ASINs in this set (retrieved 19 October 2026)