Demilec Crawl Space Encapsulation: The San Antonio Owner’s Guide
We stock and install Demilec-compatible crawl space encapsulation materials across San Antonio, with most full encapsulations running $4,200 to $7,800 depending on square footage, access clearance, and whether your existing liner failed at the seams or is simply missing in sections. We carry Heatlok HFO and the Demilec sealant line on our trucks, so a seam repair or a full re-liner can usually happen same week, not next month. Most San Antonio homeowners discover the failure the same way: a musty smell that drifts up through the floorboards, or the electric bill climbing in July as humid crawl space air forces the AC to work overtime. You notice the symptom before you ever see the torn poly lining sagging off the foundation wall.
If you already know your Demilec liner is compromised, call (903) 437-9164 and we’ll confirm the liner type, measure the affected area, and put a written price in front of you before anyone crawls under the house.
Which Demilec Models This Applies To
The Demilec name covers a specific spray foam and sealant lineup that regularly shows up in San Antonio crawl spaces, and the compatibility question depends on which layer failed. Heatlok HFO is the closed-cell spray foam many local builders specified for rim joists and band boards in crawl space encapsulations from roughly 2016 onward; it is an open-cell-density product that, when installed at 2 inches, delivers both air seal and moisture control. If your encapsulation uses Demilec’s 6-mil reinforced poly liner, the failure is usually at the seam tape or the termination points where the liner meets the foundation wall, not the foam itself.
Read the can label or the liner stamp before calling. Demilec products carry a manufacturing code near the lot number that tells you the exact formulation, and that matters because Sealed Cell and Heatlok HFO do not interchange cleanly on an existing encapsulation without redoing the adhesion surface. We match OEM Demilec foam for extensions and repairs; for liner replacement we stock a reinforced 12-mil poly that outlasts the original 6-mil in San Antonio clay-shift conditions, and we’ll show you the difference before you choose. Thistledown Insulation San Antonio is an independent installer; we are not affiliated with Demilec, but we install their product line alongside seven other insulation brands because the right material depends on the crawl space, not the other way around.
Signs Your Demilec Crawl Space Encapsulation Is Failing
- A persistent musty odor in the main floor rooms. When the liner tears away from the wall, soil moisture migrates into the crawl space air and rises through the floor assembly. In San Antonio’s summer humidity, that smell shows up within two weeks of a seam failure, not two seasons later.
- Condensation on ductwork or copper lines under the house. The Demilec foam and liner are supposed to prevent warm humid air from hitting cold surfaces. Visible sweating on ducts means the air seal is broken somewhere, usually at a rim joist the original installer skipped.
- Standing water after a storm that did not used to pool there. The poly liner channels water toward a sump or drain. Once it tears, water finds the low spots in the native soil and sits against your piers. Look for liner edges curling away from the foundation.
- Rising indoor humidity on your thermostat. San Antonio homes with an intact encapsulation typically hold 45 to 55 percent indoor RH with the AC running. A creeping reading above 60 percent usually points to a liner breach or a failed seam tape, not the HVAC system.
- Increased pest activity under the house. Rodents and roaches follow moisture. A torn liner creates the damp, dark path they travel along. We have pulled back failed encapsulations in older Terrell Heights homes and found the same thing every time: the tear, the moisture trail, and the droppings right behind it.
Replacement Cost & What’s Included
In San Antonio, a full Demilec-compatible crawl space encapsulation runs $4,200 to $7,800 installed for a typical 1,200 to 1,800 square foot crawl, including all materials and labor. The range depends on three things: access clearance (crawl spaces under 30 inches slow the work and add labor), the condition of your existing vapor barrier (salvageable or full tear-out), and whether the rim joists need re-foaming with Heatlok HFO or just seam repairs. A partial liner repair with new seam tape and re-termination runs $600 to $1,400 depending on how much liner has to be cut back.
Every quote from us is a written number before any work starts. That price covers the liner or foam, all seam tape and adhesive, a photo of the finished crawl space, and our sweep of the workspace before we pack up. If the job is not done right, our 365-Day Done Right Promise means we come back and make it right. No debate, no fine print.
DIY or Call Us?
A homeowner can safely check the liner edges where they meet the foundation wall, the condition of the seam tape, and whether any poly is sagging off the piers. That inspection costs nothing and tells us a lot before we visit. What a homeowner should not do is crawl into a tight San Antonio crawl space with a staple gun and a roll of replacement poly. The soil gases, the heat, the sharp pier edges, and the weight of doing it wrong mean most DIY repairs fail within a month. Spray foam rim joist work is not a weekend project; the two-component Demilec product requires proper mixing and a respirator. We are happy to do the inspection with you, show you what we see, and if it is a simple seam tape refresh, the fix is often under $700 and done in an afternoon. Call (903) 437-9164 and we will walk you through what to look for before we ever schedule the truck.
FAQs
The closed-cell Demilec foam itself can function for 20+ years, but the plastic liner and seam tape are the weak points, and in San Antonio’s heat and humidity cycles they typically fail within 7 to 10 years. We see the most common failure at the seam overlaps where summer expansion pulls the tape apart. Replacing the liner while keeping the existing foam is often the smartest repair path. Call (903) 437-9164 for an honest assessment of your liner’s remaining life.
Yes, a tear under three feet with intact surrounding material can usually be repaired with new reinforced poly and seam tape for a few hundred dollars. The catch is that San Antonio clay soil shifts seasonally, and a liner that tore once in a stress point will often tear there again unless we re-terminate it with mechanical fasteners instead of tape alone. We will tell you which approach fits your crawl space before quoting anything.
Most full encapsulation replacements in a standard San Antonio crawl space take one to two days with our crew. Smaller seam repairs and liner patches are a half-day job. You will have a written price and a scheduled day before we start, and we work quietly; if a baby is napping upstairs, we adjust the schedule.
We keep Heatlok HFO, Demilec sealant, reinforced 12-mil poly, and seam tape on our trucks and in our San Antonio inventory, so we do not wait on a distributor order for typical repairs. For full replacements or large foam additions, we confirm material availability before scheduling. We also stock Reflectix radiant barrier for related crawl space applications. Call (903) 437-9164 and we will confirm what is on the truck today.
Written by Neil Barron, Owner, Thistledown Insulation San Antonio at Thistledown Insulation San Antonio, serving San Antonio and nearby areas.