Sealer on Porous Masters Before RTV Pour | RUUIPON

A sealer on a porous master is a barrier coat that stops the master from drinking A/B and from poisoning platinum. It is not mold release, and it is not a polish. Wood, plaster, foam, and some 3D prints all leak air, moisture, sulfur, or uncured resin into the face. You seal first, let that film dry the way its TDS says, patch-test a coin of 1:1 or 10:1 platinum, then pour. Spraying release on raw plaster and calling it sealed is how you get a tacky cavity and a master that never leaves the flask clean.

RUUIPON seals masters in Bao'an / Shajing since 2018. Prototype 3–7 business days after CAD lock. Production MOQ 20 pieces per design. Simple 3D is USD $50 when that CAD scope applies. Platinum shrink after full cure typically about 0.1–0.3%. Food-contact is the *cavity article*, not the sealer on the pattern. Steel/LSR *parts* — wydsilicone.com.

Does not apply when the master is already a sealed CNC metal or a fully post-cured, barrier-coated SLA that passed a patch. It also does not apply to sealing a *finished food tray* with wood varnish — that is the wrong chemistry on the wrong object.

Seal is a barrier coat, not a polish

Wood grain drinks platinum and then sheds fibres into the face. Plaster dust inhibits and soaks. Open-cell foam fills with rubber and will not demold. SLA/DLP prints that skipped wash and UV post-cure are a classic platinum poison — sibling protocol on 3D-printed masters and inhibition. Air-dry clay is its own master page.

What we actually do:

1. Dry the master. Damp plaster is not "ready."
2. Barrier coat the TDS allows against addition-cure (often an acrylic or a dedicated mold sealer — we pick from what we have qualified, not from a kitchen can).
3. Let it dry. Tacky sealer is a new inhibitor.
4. Optional: a thin release *after* the sealer is dry, if the geometry will lock.
5. Coin patch of the same 1:1 or 10:1 shot you will pour.

Release without sealer on plaster: the oil sits on dust, platinum still drinks, inhibition still happens. Sealer without drying: you laminated a wet film into the cavity.

flowchart TD
  A[Porous or printed master] --> B[Dry]
  B --> C[Barrier sealer]
  C --> D[Sealer dry]
  D --> E[Optional release]
  E --> F[Coin patch of weighed platinum]
  F --> G{Patch cures on the face?}
  G -->|no| H[Change sealer or recast the master]
  G -->|yes| I[Box, vacuum, pour]

The photo that would prove a sealer call: master with a masked raw stripe and a sealed field, patches on both, only the sealed field dry. We are not attaching a staged lot.

Foam is the nasty case. Open cell becomes a rubber brick around a foam skeleton. Prime or film-coat until the surface is closed, or print/CNC a real master. We would not bury raw floral foam in 1:1 platinum and hope.

A glossy sealer can hide texture you wanted. If the dump needs the wood grain, seal with something that fills pores without building a plastic skin, or accept that you are molding the sealer, not the oak. Say that on the RFQ.

Coin-patch after the sealer film is dry

Coin patch on a hidden land after the film is dry. Lid patty of the same mix as a control. Face tacky + lid dry = still inhibiting (sealer wrong, still wet, or print undercured). Both tacky = ratio, cold drum, or expired B — mix mistakes. Both dry = pour.

Plaster masters used as *art* and plaster used as a *jacket* are easy to mix on a packing list. If the gypsum is the pattern, seal it and pour the cavity. If the gypsum is the mother mold, it goes around a already-cured skin and should not see A/B on the show face. Write "master" or "jacket" on the crate. We have opened boxes where both were loose plaster and the wrong one got coated.

Prints with leftover alcohol in the lattice outgas for days. A sealer film over wet IPA is a blister factory. Dry the print, UV it, then coat. Rushing that stack to hit a same-week ship date is how the face comes back tacky and the calendar still slips — because we recast. ISO 3302-1 M2 does not replace a patch.

Shop numbers for sealed masters

Caption: typical shop values, not a named PO.

Sealers we would not run

We would not recommend kitchen oil as a sealer on plaster.

We would not recommend pouring platinum on a still-damp wood prototype "to save a day."

We would not recommend a food-contact claim because the sealer can was labeled non-toxic. Name 21 CFR 177.2600 on the finished rubber article.

We would not recommend sealing, then sanding the master for the recast. You moved the library.

A tooling charge is not unrestricted ownership of the sealed pattern. Write whether we may coat it.

Worked example: foam tile that locked into open cells

CNC foam master, 300 mm architectural tile, unsealed. First 1:1 pour locked into cells. We film-coated, patched, poured a 15A skin plus plaster jacket. Prototype 3–7 business days after CAD lock of the jacket split. USD $50 3D did not apply (they had a millimetre STEP). Production MOQ 20 skins of that design. Related: sculptures.

Mix-up: spraying mold release and calling it sealed

Release is a slip film. Sealer is a pore closer and a chemistry barrier. You often need both, in that order after dry. The other mix-up is using a tin-cure leftover as a "primer" under platinum. Tin residue inhibits.

Questions that put sealer on the traveler

• Master: wood / plaster / foam / SLA / clay / metal?
• May we coat it, and does texture have to survive?
• Food or craft dump?
• Who keeps the sealed master for recast?
• CAD: STEP, or USD $50 3D if we must rebuild after a failed pour?

Related: mold box, contact.

RFQ copy-pack — sealer before A/B

Paste into [email protected]:

Object: RTV mold I pour into, not an LSR/HCR part Master material and whether it is already sealed / UV-post-cured Permission to apply barrier coat: yes/no Dump material and peak °C File: STEP / STL / photos with a millimetre scale CAD: mold-ready STEP OR USD $50 3D if that scope applies Prototype 3–7 business days after CAD lock, then MOQ 20 per design Coin patch required before a full pour on porous or printed masters

Send master material and permission to coat. We patch-test — not a blank "free quote." Phone +86 135 3006 2969. Licheng Technology Industry Park, Xinhe Blvd, Shajing, Bao'an. Shop since 2018.

FAQ

Is PVA glue a sealer? Some shops use thin PVA on plaster. We still patch-test against the platinum grade on the floor. Do not assume a school glue is a barrier.

Do I seal CNC aluminum? Usually no. Clean metal is a different conversation (release for lock, not porosity).

Can sealer make an SLA print safe for platinum? Sealer is one step after wash and UV post-cure. Sealer alone on a wet print still inhibits.

Will sealer change my millimetres? A heavy film adds thickness. If size is a CTQ, say so; we keep coats thin or we recut the master.

If you seal my wood original, do I still own it? A tooling charge is not unrestricted ownership. Write custody, and whether the coat is allowed.