Smooth-On Thixotropic Agent Silicone Thickener, Pint Bottle — Brushable, Prevents Sagging

THI-VEX is Smooth-On’s thixotropic thickening agent designed to turn pourable silicone into a brushable, vertical-surface silicone for making durable brush-on moulds.

When you need silicone that will cling to walls, undercuts, or vertical sculpted surfaces, THI-VEX lets you control the body of Smooth-On silicones so they stay in place during brush application. It’s formulated to be mixed into Part A of two-component silicone systems, then blended with Part B; by adjusting the amount you add, you can achieve a range of viscosities from slightly body-enhanced to paste-like. Note that THI-VEX is not compatible with Mould Max 40 or Mould Max 60.

How does THI-VEX change silicone behavior for brush-on moulds?

THI-VEX increases the thixotropy of Smooth-On silicones so the mixture resists sagging yet flows under shear during brushing. This gives a stable, buildable layer that captures detail without running off vertical surfaces.

• Adds body to liquid silicone for layer-by-layer brush application.
• Prevents sagging or dripping on undercuts and edges.
• Preserves surface detail while allowing workable open time.

How much THI-VEX should I add to get the right thickness?

Viscosity depends on the amount of THI-VEX relative to Part A; small increments create slightly thicker fluid, larger percentages produce paste-like consistency. Start with a low percentage and test on a sample to dial in the ideal feel for your particular silicone and project.

• Begin with a conservative percentage of THI-VEX to Part A and increase as needed.
• Mix thoroughly into Part A before combining Parts A and B for even texture.
• Test a sample coat to verify brushability and cure before full application.

Which silicones and processes are compatible with THI-VEX?

THI-VEX is formulated for use with most Smooth-On silicone systems that require thixotropic modification for brush-on moldmaking. It must be mixed into Part A and then combined with Part B for proper cure. Do not use it with Mould Max 40 or Mould Max 60, as it will not function with those formulations.

• Works with many Smooth-On two-part silicone rubbers when added to Part A.
• Not compatible with Mould Max 40 or Mould Max 60 — avoid mixing with those products.
• Requires thorough mixing of Parts A and B after THI-VEX addition for uniform cure.

What practical tips improve results when using THI-VEX?

Good results come from measured additions, thorough mixing, and testing. Use a clean container and tools, mix THI-VEX into Part A until homogeneous, then combine with Part B and apply in thin, consistent layers to build thickness without entrapped air.

• Measure THI-VEX by weight or volume for reproducible viscosity control.
• Mix Part A and THI-VEX thoroughly before adding Part B to avoid streaks.
• Apply multiple thin coats, allowing recommended cure time between layers.

Who is this for? THI-VEX is aimed at moldmakers, prop fabricators, sculptors, and restoration professionals who need a brushable silicone that holds on vertical and complex surfaces. If your workflow requires building up rubber over a form, capturing fine surface detail on undercuts, or converting pourable silicone into a paste or butter-like consistency for hand application, THI-VEX provides a controlled, studio-friendly way to get there — provided you avoid incompatible Mould Max 40/60 silicones and follow proper mixing practice.