Bottom Line
The Mold Armor FG516 is the same product as the FG502, in a larger container at better value per ounce. It’s the right buy for homeowners treating multiple bathrooms, doing exterior mold treatment, or maintaining regular mold prevention on high-humidity surfaces. No spray nozzle included — plan for a separate applicator.
Our rating: 4/5 — Same effective formula, better value for larger or recurring jobs.
What Is the Mold Armor FG516?
The FG516 is a 1-gallon (128 oz) container of Mold Armor mold and mildew stain remover. The formula is identical to the smaller FG502: sodium hypochlorite (bleach) plus surfactants and wetting agents.
The key practical difference: it’s sold as a jug with no included spray nozzle. You need to decant into a spray bottle for application.
Who Should Buy the Gallon vs the 32 oz
Buy the FG516 (gallon) if:
- You’re treating two or more bathrooms
- You do seasonal exterior treatment (vinyl siding, concrete, deck boards)
- You want to keep a supply on hand for maintenance without frequent repurchasing
- You’re treating a larger area like a basement wall or laundry room
Buy the FG502 (32 oz) if:
- You have a single spot or surface to treat
- You prefer a ready-to-use trigger sprayer
- You don’t want to handle and store a gallon jug
Performance
We tested the FG516 (decanted into a standard trigger sprayer) on the same surfaces as the FG502 — ceramic tile grout, fiberglass tub surround, and vinyl siding. Results were identical, as expected from the same formula.
Indoor tile/grout: Effective with 5–10 minutes dwell time. Heavy staining improved 80–95% with light scrubbing.
Vinyl siding (exterior): Good performance on light to moderate mold and algae staining. Heavy organic growth may need multiple passes.
Concrete: Moderate improvement; bleach-based products have limited penetration on porous masonry. For basement walls with recurring mold, an antifungal primer after cleaning provides better long-term protection.
Dispenser Setup
The FG516 has no built-in applicator. Recommended setup:
- Purchase a 32 oz trigger sprayer ($3–$5 at hardware stores)
- Fill as needed — don’t mix with anything else in the bottle
- Label the bottle clearly (bleach content)
- Rinse the sprayer after use to extend its life
This adds minor inconvenience over the FG502’s ready-to-use bottle, but the cost savings justify it for larger jobs.
Safety
Same safety notes as FG502 apply:
- Bleach fumes — ventilate all interior work areas
- Protect colored grout, natural stone, and metal fixtures from contact
- Never mix with ammonia or acidic cleaners
- Gloves and eye protection recommended
- Store sealed, away from heat and sunlight
Cost Comparison
| Product | Size | Typical Price | Cost per oz |
|---|---|---|---|
| FG502 | 32 oz | $7–$10 | ~$0.28/oz |
| FG516 | 128 oz | $15–$20 | ~$0.14/oz |
The gallon saves approximately 50% per ounce. For recurring mold maintenance — which is the right approach for chronically humid spaces — the gallon pays off quickly.
Long-Term Mold Prevention
Like all mold removers, FG516 treats visible surface mold. The underlying driver is moisture. After cleaning:
- Improve bathroom ventilation (longer exhaust fan runtime or upgraded fan)
- Fix any leaking fixtures or seals
- In high-humidity climates, consider a dehumidifier for bathrooms and basements
- Reseal grout annually to reduce porosity
Without addressing moisture, mold regrows regardless of which product you use to clean it.