If you are dealing with moss, mold, or mildew stains on outdoor surfaces, Wet & Forget is one of the more popular options for tackling it without scrubbing or pressure washing. It is heavily marketed as a “set it and forget it” solution, but there is a lot of confusion about how it works and whether it is safe.
Our Top Pick
Wet & Forget Outdoor Concentrate covers the most ground per dollar since you dilute it yourself (mix 1 part concentrate to 5 parts water per label directions).
What It Actually Does
Wet & Forget’s active ingredient is alkyl dimethyl benzyl ammonium chloride (a quaternary ammonium compound). This is not bleach and it is not an acid. It works by penetrating moss, mold, mildew, and algae growth. Rain gradually washes the dead growth away over the following weeks, meaning there is genuinely no scrubbing or rinsing required after application.
It is registered with the EPA (registration number 84115-1) as a pesticide product for this specific use. This means it has been evaluated for the specific uses and application methods on its label. However, it is not a blanket “safe for anything” endorsement.
Where to Use It
It works on a surprisingly wide range of surfaces: pavements, roofs, painted surfaces, decking, siding, concrete, brick, aluminum, fiberglass, vinyl, teak, PVC, steel, asphalt, and ceramic. It is ideal for walkways, driveways, roofs, fences, outdoor furniture, playsets, and pool liners.
How to Apply It
Weather matters: Avoid applying on very hot days; heat can evaporate the solution before it has time to work. Aim for a day above freezing, with no rain expected for several hours after application, since rain too soon can wash it off before it penetrates.
Timing: Moss stains typically clear within a couple of weeks to a month. Darker mold and mildew stains can take longer (sometimes a few months) depending on how established the growth is. For lichen specifically, let the solution sit about 15 minutes to soften the outer layer before it can fully penetrate.
Safety: Read This Before You Apply
This is not a mild, casual-use product, despite what marketing language might suggest. The concentrate’s own safety data sheet lists it as capable of causing serious skin burns and eye damage, and it is classified as harmful if swallowed.
When applying it:
- Wear gloves, eye protection, and avoid breathing the spray mist.
- Don’t apply on windy days. Overspray drifting onto skin or into eyes is a real risk given the corrosivity.
- Keep people and pets off treated surfaces for 4–6 hours, or until fully dry.
- If a pet does walk on a wet, treated surface, rinse their paws before they have a chance to lick them.
- Cover or pre-wet nearby plants before applying, since overspray can cause temporary browning (plants typically recover, but it is avoidable with prep).
None of this means the product is dangerous when used correctly. It is a legitimate, EPA-registered product that thousands of people use safely every year. But “safe” here means “safe when you follow the label directions and basic precautions,” not “harmless to touch or breathe.”
Pros and Cons
Pros: Long shelf life; biodegradable once diluted and applied; works on a wide range of outdoor materials; one-step application with no scrubbing or rinsing required; effectively removes moss, mold, mildew, and algae.
Cons: May need a second application for heavier staining; the concentrate itself requires real care and protective equipment during handling and application.
Frequently Asked Questions
Is Wet & Forget toxic to humans?
In its liquid concentrate form, it can cause skin burns and eye damage. However, once it is sprayed on a surface and fully dries, it is generally safe for humans to walk on. Always wear protective gear while handling the liquid.
Does Wet & Forget kill plants?
It can burn the leaves of sensitive plants if it drifts onto them. It is best to cover nearby landscaping with a tarp or pre-wet the plants with water before spraying your roof or driveway.
Does it really work without scrubbing?
Yes, but it takes time. The chemical kills the moss and mold, and the rain slowly washes it away over the following weeks. It is not an instant fix.
Bottom Line
Wet & Forget is a genuinely effective, low-effort way to clear moss, mold, and algae stains from outdoor surfaces without scrubbing or pressure washing. Just treat it with the same respect you would give any EPA-registered pesticide product: gloves, eye protection, and keep pets and people clear until it is dry. Don’t assume that “biodegradable” means “harmless to handle.”