Why the Mold Box Leaks While Pouring RTV | RUUIPON

Platinum RTV finds the open corner of a mold box the way water does, only you notice after 800 grams are on the bench. A leak during the pour is a dam problem, not a "thicker silicone" problem. You water-test or dry-fit the box *before* A meets B, then you pick the seal that matches the joint: a clay coil at the master-to-board interface, hot glue on plywood seams that will never be food-contact, tape on a disposable foam dam, or a gasketed reusable box. Mixing the rubber stiffer, raising Shore A, or pouring faster will not close a 1 mm gap. The wasted cup is also a short cavity and a foam face where the level dropped.

RUUIPON builds and pours in boxes in Bao'an since 2018. Prototype is 3–7 business days after CAD lock. Production is MOQ 20 pieces per design. Simple 3D is USD $50 when that CAD scope applies. LSR *parts* do not use a plywood dam — wydsilicone.com. Box construction companion: how we think about the envelope lives with the quote pack at RFQ checklist.

Does not apply when the "leak" is rubber creeping into an intentional vent or key slot, when you pressure-potted an unrated box and blew a seam, or when the master itself is porous and drinking RTV (that is a sealer job). Food cavities still get a clean dam — we would not leave glue crumbs on a chocolate face. Jewelry and concrete boxes leak the same way; those dumps are not food.

Where the leak actually starts

Master sitting on a board, no clay coil. RTV wicks under the pattern. You get a flash skirt and a starved pour height. Confirm: cured rubber under the master footprint. Fix: oil-based clay coil, pressed, no gaps at corners. Sulfur clay can inhibit platinum — use a clay the grade will cure against, or a sealed barrier.

Plywood or foam-core seams. Factory edges look closed and are not. Confirm: a puddle on the outside during a water test. Fix: hot glue on the inside corner, or tape on a disposable dam. Glue on the *outside* only hides the seam until hydrostatic head finds it.

Sprue / pour hole cut after the box was sealed. The new cut is the leak. Confirm: drip at the hole you just made. Fix: reseal, then pour.

Keys and registration bosses that pierce the wall. A CNC key through a foam wall is a straw. Confirm: rubber on the bench under that boss. Fix: clay around the pierce, or a designed boss that does not through-hole the dam.

Reusable gasket box with a crumb or a hair. Confirm: one corner weep. Fix: clean the gasket; do not glob glue on a tooled box and call it a process.

Water-test: fill the empty box to pour height with water (master sealed or bagged if it cannot get wet), wait, look. Dry, then mix. A water test after A/B is already in the cup is theater.

The photo that would prove a sealed box is the water-test at height with a dry bench, plus a clay coil at the master footprint with no daylight at corners. A glue gun on the outside of a wet seam is the failure photo.

Typical shop values

Caption: Typical shop values.

Common mix-up: pour thicker rubber to plug the gap

Buyers raise viscosity or add a filler "so it won't leak," then trap bubbles and starve serifs. RTV should be the grade you spec for tear and Shore, not a caulk. The cousin mix-up is vacuuming the whole leaky box so the chamber "helps" — you pull air in through the same gap. Dam first. Another: leaving hot-glue strings on a food master. Glue on the box, not on the chocolate face.

Worked example (anonymized)

A 250 × 180 mm resin block, 70 mm pour height. First pour used a foam-core box taped on the outside. About 200 g of 1:1 platinum left through a corner; cavity shorted; foam at the drop line. Remake: interior fillet, clay coil at the master, water test to height, cup vacuum to collapse, same CAD (no extra $50). Proto still inside 3–7 business days. Production MOQ 20 used a reusable keyed box with a gasket, not twenty disposable foam dams. Craft resin, not food.

We would not recommend

We would not recommend thickening platinum to act as caulk.

We would not recommend sulfur clay against a food-contact platinum pour.

We would not recommend vacuuming a leaking box as the seal method.

We would not recommend leaving glue crumbs on a food master and keeping the 177.2600 story.

flowchart TD
  A[Box built around master] --> B[Water test to pour height]
  B -->|Dry bench| C[Clay coil + interior seam seal]
  B -->|Weep| D[Find joint: footprint / seam / pierce]
  D --> C
  C --> E[Mix, vacuum cup, pour]
  E --> F{Leak during pour?}
  F -->|yes| G[Stop if you can catch it; remake — do not thicken]
  F -->|no| H[Cure, demold]

What to ask when you're buying production skins poured in a box

• Do you water-test reusable boxes, or only look at them?
• Clay type against platinum — will it inhibit?
• Is the production box reusable and keyed, or a one-off foam dam each time?
• Food face: how do you keep dam materials off the cavity?
• After CAD lock, 3–7 business days, then MOQ 20?

Related: mold design service, contact.

RFQ copy-pack — box integrity

Email [email protected]:

Envelope L x W x pour height Structure: open-back / block / split Duty: food / resin / jewelry / concrete (jewelry and concrete are not food) Box: you build reusable / disposable dam Dam materials must be platinum-safe Vacuum the cup, not a leaking box CAD: locked / USD $50 if you model Prototype 3–7 business days after CAD lock, then MOQ 20 / design

Send the envelope and whether the box is reusable. We seal the dam before A meets B. Phone +86 135 3006 2969. Quote desk: custom mold quote.

FAQ

The box leaked — can I just pour more RTV to top it up? Only if the rubber is still wet and you can find the gap. A gelled short pour is a knit line. Safer to remake. Do not thicken the second cup as caulk.

Is hot glue safe against platinum? On the *box*, as a seam fillet, shops use it. Keep it off the food master face. Test if a new glue smells of something that inhibits. When in doubt, clay coil + tape.

Can I seal leaks with more clay after the pour starts? You can sometimes catch a weep. You also smear clay onto the cavity. Stop, decide remake vs rescue, and do not push clay into a food logo well.

Does a mother-mold jacket stop box leaks? No. The jacket comes after the skin exists. Leaks happen at pour #1 of the RTV.

If the proto box leaked, do I still pay MOQ 20? A shop leak on our box is our remake inside the same CAD lock. A box you built and shipped that weeps is a dam conversation, not a free redesign of the cavity.

Reusable production boxes versus proto dams

A proto can live in foam-core and tape if you water-test it. MOQ 20 of a locked design should not. Twenty pours in twenty leaky dams is how grams drift and how keys wander. Move to a reusable box or a jacketed open-back once CAD is locked. Keys that pierce a wall need a designed boss, not a drill-and-hope. ISO 3302-1 M2 on the rubber drawing will not close a plywood corner.

Concrete countertop forms and jewelry plaque boxes fail the same joints. Call the dump by name. Do not paste a food extraction PDF onto a leaking craft dam and call the rubber safer.

Licheng Technology Industry Park, Xinhe Blvd, Shajing, Bao'an, since 2018. Mix 1:1 or 10:1, vacuum the cup, pour a dry-tested box.