Termite spray for wood falls into two main categories: borate-based treatments that protect wood from future infestations and chemical sprays (liquid or foam) that kill active colonies. Which one you need depends on whether you’re preventing damage or fighting an existing problem, and in some cases you’ll want both.
Borate Treatments for Long-Term Protection
Borate-based wood preservers are the go-to option for preventive treatment. They protect against termites, carpenter ants, wood-boring beetles, and wood decay fungi all at once. Borates work by disrupting the digestive system of wood-destroying insects. Because they’re mineral-based and low in toxicity to mammals, they’re one of the safest options for indoor use on exposed framing, joists, and other structural wood.
Most borate products come as ready-to-use sprays or concentrates you mix with water and apply directly to bare, unfinished wood. The key limitation is penetration depth. Research from the USDA Forest Products Laboratory found that boron from topical spray applications typically penetrates less than 5 mm into the wood, regardless of the specific borate solution used. That outer shell of protection is enough to deter termites from feeding, but penetration depends heavily on moisture and drying conditions.
In humid environments where wood stays damp longer, boron diffuses much deeper. The same USDA research showed that after 26 weeks of diffusion in high-humidity conditions, penetration exceeded 11 mm, covering over 70 percent of the wood’s cross section. In dry conditions, the wood dries too quickly for the boron to migrate inward. This means borate sprays work best when applied to wood in enclosed, humid spaces like crawlspaces or wall cavities, rather than in well-ventilated areas where the solution evaporates before it can soak in.
Borate treatments are strictly preventive. They won’t reach deep into wood that’s already riddled with termite galleries. If you’re building, renovating, or treating accessible framing before closing up walls, a borate spray is one of the most practical steps you can take.
Fipronil-Based Sprays and Foams
For active termite infestations, fipronil is one of the most widely used active ingredients in professional termite control. It’s a non-repellent chemical, meaning termites can’t detect it and will walk through treated areas without avoiding them. They then carry the chemical back to the colony, spreading it to other termites through contact. This transfer effect is what makes fipronil so effective at eliminating entire colonies rather than just killing individual insects at the surface.
Fipronil is available in both liquid concentrate (for trench treatments around foundations) and expanding foam formulations for direct wood treatment. The foam versions are especially useful for targeting termites inside the wood itself. When injected through termite kick holes or small drilled openings, the foam expands up to 30 times its original volume, filling galleries and voids that a liquid spray would never reach. This makes foam the better choice for spot-treating walls, crawlspaces, and any area where termites have already hollowed out the wood.
One important distinction: foam treatments kill active infestations but do not prevent future ones. Once the product breaks down, the treated area has no residual barrier. If you’re dealing with an active colony in your walls, foam gets the job done now, but you’ll still need a perimeter treatment or borate application to keep termites from coming back.
Liquid Spray vs. Foam: When to Use Each
Liquid termite sprays work well for surface application on exposed wood. You can brush or spray them onto joists, sill plates, and framing to create a treated layer. They’re the practical choice for large surface areas and preventive work, especially with borate-based products.
Foam is the better tool when you need to reach inside enclosed spaces. Wall voids, behind siding, inside hollow block foundations, and within termite galleries are all situations where liquid would simply run off or pool at the bottom. The rapid expansion of foam lets it coat surfaces inside cavities evenly. Pressurized foam cans (similar to a shaving cream canister) are available for homeowners, while professionals typically use liquid concentrates fed through specialized foaming equipment that produces denser, more consistent foam.
For many infestations, professionals use both: foam to treat active colonies in specific locations and liquid barriers around the foundation to prevent re-entry.
Safety Around Pets and Family
Most liquid termiticides contain chemicals that are toxic while wet but safe once fully dried. The drying period is the critical window. Keep children and pets away from treated wood until the product has dried completely, which typically takes a few hours depending on ventilation and humidity.
Borate treatments carry the lowest risk profile for indoor use. They’re toxic to insects but pose minimal danger to mammals at the concentrations used for wood treatment. Fipronil-based products require more caution during application but are considered safe after drying. Top-performing professional termiticides are now odorless and water-based, reducing both indoor air quality concerns and risk to landscaping around treated areas.
If you’re treating wood inside living spaces, ventilate the area during and after application. Wear gloves and a respirator while spraying, especially with chemical termiticides. Borate sprays are more forgiving, but standard protective equipment is still a good practice any time you’re spraying a pesticide indoors.
Choosing the Right Product
- Bare wood you want to protect before an infestation: A borate-based wood preserver applied by spray or brush. Best for new construction, renovations, or accessible framing in crawlspaces and attics.
- Active termites inside walls or wood: A fipronil-based expanding foam injected directly into galleries and voids. Kills the colony but won’t prevent future problems on its own.
- Perimeter defense around a structure: A liquid non-repellent termiticide (fipronil or similar) applied as a trench treatment around the foundation. These barriers can last for years when applied correctly.
- Small, localized infestations in accessible wood: A liquid termiticide spray applied directly to the affected area. Works when you can see and reach the damage.
For anything beyond surface-level preventive treatment on exposed wood, a professional inspection is worth the cost. Termite damage is often far more extensive than what’s visible, and the difference between a spray that reaches the colony and one that only touches the surface can mean thousands of dollars in structural repair down the road.