One of the most common issues installers run into is rust coming through a floor coating. What looks like a perfect installation at first can end up with ugly orange-brown stains if the source of the problem isn’t addressed.
The root cause? Moisture vapor movement in the slab. Without a proper Moisture Vapor Barrier (MVB), rust can migrate upward from rebar, mesh, or other embedded metal and bleed right through your chip or epoxy system.
At Allsource Supply Inc., we’ve seen this issue time and time again—and we know how to stop it. The solution combines proper prep with the right products, like Armidex, or our Moisture Vapour Barrier epoxy primer for moisture control.
1. Identify and Treat the Source
Rust originates from iron in the concrete or embedded metal such as rebar, mesh, or old fasteners. When moisture migrates upward, it carries iron oxides (rust) into your coating system.
The fix starts with proper surface prep:
- Grind down and expose the stained or suspect areas.
- Clean thoroughly with a phosphoric acid–based rust remover or concrete rust treatment.
- This chemical process converts iron oxide into a more stable compound and prevents further migration.
Tip: Skipping this step and just coating over rust guarantees the problem will come back.
2. Moisture Control
Rust migration is almost always linked to moisture vapor movement. Without moisture, rust has no pathway to travel.
- Conduct moisture testing (Calcium Cloride, Relative Humidity probe, or Trimax Moisture Meter).
- If high values are detected, a Moisture Vapor Barrier coat is critical before applying your chip or epoxy system.
- A moisture-mitigating epoxy primer—typically 100% solids and high-build—is recommended, especially for slabs with strong vapor drive.
3. Barrier Primers and Basecoats
After treating the rust, you need to seal off the substrate from oxygen and water.
- Apply a direct-to-concrete epoxy or urethane primer with strong adhesion and low permeability.
- For severe cases, use a two-coat system:
- First coat: Moisture Vapor Barrier epoxy
- Second coat: High-build pigmented epoxy to create a dense base layer before the chip broadcast
This starves the rust source of oxygen and moisture, stopping future migration.
4. Coating Build
Film thickness is critical. Thin systems (5–8 mils) are more likely to allow stains to transmit.
- Build up to 15–20 mils of thickness before broadcasting chips.
- A thicker base ensures a long-lasting system and blocks rust bleed effectively.
How Armidex Solves the Problem
This is where Armidex makes all the difference. It’s more than a primer—it’s engineered to:
- Block moisture vapor transmission before it carries rust to the surface
- Absorbed moisture barrier that withhold’s moisture vapor transformation.
- Provide a reliable base for chip and epoxy floor systems
- Extend the life of coatings by keeping rust stains locked out
By incorporating Armidex as part of your system, you stop the problem before it starts and deliver a finish that looks good—and stays that way.
Here’s the proven formula for preventing rust bleed-through:
- Grind and chemically treat rust at the source
- Control vapor with a Moisture Vapor Barrier epoxy
- Seal the slab with a dense primer/basecoat
- Build enough film thickness for durability
- Protect the floor long-term with Armidex
At Allsource Supply Inc., we provide the products and expertise to help you get it right the first time.
To learn more and how we can improve efficiency in your projects, contact our team at (833)-663-4255.