Layer-Pour an RTV Block to Beat the Heat | RUUIPON

A thick RTV block is layered so each mixed shot can vacuum-collapse in the chamber you own and so the platinum exotherm does not cook the core. It is not a way to stretch a leftover 80 g in the cup across two days. Mix 1:1 or 10:1 by weight, degas, pour a first lift, wait the grade's tack window, pour the next lift *into wet-enough rubber* so you get a chemical bite, not a peel plane. Miss the window and the dump will find the bond line. Pour all 3 kg in one cup and you overflow the pot, scorch the middle, or both.

RUUIPON layers large blocks in Bao'an, Xinhe Blvd, Shajing, 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. Platinum shrink after a full cure typically about 0.1–0.3%. Steel/LSR *parts*: wydsilicone.com. Chamber size cousin: vacuum chamber vs shot. Heat in a winter shop is the opposite problem: winter shop temperature.

Does not apply when the tool is a thin open-back tray (one shot), when you are layering *epoxy dump* in a finished mold, or when the first layer already fully cured over a weekend. We would not layer as a save for a mix-ratio mistake.

Heat, headspace, and the bond window

Platinum in a thick mass can run warmer in the core than the flask wall. That is the rubber's exotherm, not the dump. A hot core can wrinkle, yellow, or kick so fast the last bubbles never leave. Splitting the mass into lifts that fit the pot keeps each shot in a sane band.

Headspace still rules each cup: fill under about half, let foam triple, collapse. Layering is how a 5 L pot does a 2 kg block without a lid kiss.

Bond window: follow the grade. Tacky-not-wet is the usual feel; a dry shiny skin wants a mechanical key or a recast. We would not paint "silicone caulk" as a production interlayer.

The photo that would prove a layer spec: flask with lift height marked in millimetres, two cup masses on the scale, bond line on a cut witness that *does not* peel. A pretty cube on a shelf hides the plane.

flowchart TD
  A[Block mass too big for one cup or one exotherm] --> B[Split into lifts]
  B --> C[Each cup under half, vacuum collapse]
  C --> D[Pour lift 1]
  D --> E{Tack window?}
  E -->|missed, dry skin| F[Recast — do not caulk]
  E -->|in window| G[Pour lift 2 into tack]
  G --> H[Full cure, then dump]

When to stop pouring

If lift 1 already gelled to a dry film because you went to lunch, stop. A production SKU gets a recast, not a prayer layer. If the flask leaked on lift 1, fix the dam before lift 2 — you will not "make up volume" with a second mix that has nowhere honest to go.

Keys and a two-part lid: pour the first half as its own block; the second half is a separate mix against a released first half, not a "layer" in this sense. Do not confuse a two-part sequence with a heat-split in one flask.

ISO 3302-1 M2 is a rubber class on the dump. It is not a layer-height spec. CAD lock still freezes the cavity; lift heights are shop method.

Coloring one lift and not the next is a useful shop tell: a pigmented lift 1 against a natural lift 2 shows the plane on a cut witness without pretending we measured a named PO. If the dump later splits on that color line, you found a missed window. If the tear runs through both colors, the block was sound and the dump geometry is the pry. Do not pigment a *food* block as a tell — keep food rubber un-tinted unless the buyer signed a food-path colorant.

A jacket around a layered block does not glue a bad plane. Clamp the flask so lifts stay registered, but a dry skin will still peel inside a perfect FRP shell. Mother molds hold hydrostatic dump load; they do not repair a missed tack window.

Failure: peel plane at dump 6

Symptom: PU dump wedges the block open along a faint line halfway up.

Cause: missed bond window, or a dusty/talced lift 1 face.

Confirm: tear the block on the line. A clean glossy plane is a missed window. A cratered plane is contamination.

Fix: recast in window, or as one shot in a pot that fits. Do not raise Shore A to hide a delam.

Typical shop values

Caption: typical shop values, not a named PO.

Layer habits we would not recommend

We would not recommend saving a leftover cup overnight as lift 2.

We would not recommend one 3 kg cup in a 5 L pot "to avoid layers."

We would not recommend caulk as an interlayer on a production block.

We would not recommend talc between platinum lifts.

We would not recommend layering as a fix for inhibition.

Worked example: 1.8 kg cube, 5 L pot

Resin figurine block, ~1.8 kg platinum 1:1. One-cup attempt kissed the lid. We split 900 g + 900 g, collapsed each, poured lift 2 on tack. Cut witness did not peel. Prototype 3–7 business days after CAD lock of the flask. $50 CAD applied because the master was photos. Production MOQ 20 of that design.

Mix-up: layers to save rubber

You still mix the grams the flask needs. You only split *when* you mix them. A 1.8 kg cavity still consumes about 1.8 kg plus heel in the cup; layers do not discount platinum. Weigh every lift 1:1 or 10:1; a starved second cup is a short fill, not a savings. Related: how much silicone, contact.

What to ask when you're buying a layered block

• Estimated platinum mass, and chamber ID you or we will use?
• Grade's tack window you can actually staff?
• Two-part split vs heat-lifts in one flask — which job is this?
• Dump that will pry at a bond line (PU)?
• After lock, 3–7 business days, then MOQ 20 / design?

RFQ copy-pack — layer pour

Paste into [email protected]:

Object: RTV block, layer-pour if mass demands, not an LSR/HCR part Master L×W×H mm, flask clearance Dump chemistry Chamber constraint if you degas File: STEP / STL / photos with a millimetre scale CAD: mold-ready OR USD $50 3D if that scope applies Prototype 3–7 business days after CAD lock, then MOQ 20 per design Who keeps the master

Send mass and pot size, not "pour it in layers to save money." We split heat and headspace — not a blank quote request. Phone +86 135 3006 2969. Xinhe Blvd, Shajing, Bao'an. Shop since 2018.

FAQ

Should I pour a thick silicone mold in layers? When the shot will not fit the pot or the mass would run too hot, yes. When you just have leftovers, no.

How long between layers? The grade's tack window, not a lunch break. A dry skin is a recast.

Will the dump find the bond line? If you missed the window or dusted the lift, yes. A good bite should not be the weak plane.

Can I layer tin the same way? Tin has its own moisture/air story. Do not copy a platinum lift SOP onto tin without naming that chemistry. Food stays platinum.

Does layering change lead time? CAD lock still starts the 3–7 business day window. A block that needs two lifts is scheduled as one prototype, not two SKUs. MOQ 20 per design.