Demilec Crawl Space Encapsulation Nationwide | Walt’s Insulation

Demilec Crawl Space Encapsulation: The San Antonio Owner’s Guide

If your Demilec crawl space encapsulation is failing, we stock what you need and install it fast – most jobs run $2,800 to $5,200 depending on square footage and how much of the liner and sealing needs to go. We can usually be on site within 24 to 48 hours in San Antonio, and we carry Demilec-compatible liner, tape, mastic, and fasteners on the trucks so we’re not making you wait on a parts order. Most homeowners figure out something’s wrong when they walk into a house that smells musty, or they open the crawl space door in July and feel damp air that should have been sealed out months ago.

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We’ve been doing crawl space work in Bexar County since 2000, and Demilec’s closed-cell and open-cell spray foam systems are a brand we know well. A quick note: we’re an independent installer and service provider, not a Demilec dealer or affiliate. That means we can be honest about what needs replacing versus what’s still got life in it, and we don’t have a manufacturer’s quota hanging over our heads.

Which Demilec Models This Applies To

Demilec makes a few different product lines that show up in San Antonio crawl spaces, and the encapsulation part usually involves their spray foam paired with a reinforced liner. The two you’ll see most often here are Heatlok HFO Pro, a closed-cell foam used on crawl space walls and rim joists, and Sealection 500, an open-cell foam more common on interior applications. If your crawl space was sealed with Heatlok, the liner typically runs 12-mil or 20-mil reinforced polyethylene. Sealection jobs sometimes use a vapor barrier without the same level of reinforcement, which matters in our clay-heavy soil.

The compatibility gotcha: Demilec’s foam doesn’t play well with just any tape or mastic. The liner seams need a butyl or acrylic tape rated for polyethylene-to-polyethylene bonding, and the foam-to-liner transition at the wall uses a polyurethane mastic. We stock both on the truck. If your liner says “Demilec” on it, or you have a spec sheet from the original install, snap a photo of the label before calling – it saves a trip. If you don’t have the paperwork, measure the wall height and check whether the foam at the rim joist is dense and hard (closed-cell) or soft and spongy (open-cell). That tells us which system we’re working with. We also stock parts for Reflectix insulation, and the skills transfer, but the Demilec jobs have their own spec sheet for a reason.

Signs Your Demilec Crawl Space Encapsulation Is Failing

• Musty, earthy smell rising through the floor. A failed liner seam or a gap at the foam-to-liner transition lets soil moisture into the crawl space air. That moisture rises through the subfloor and starts showing up as a smell in the living space. In San Antonio’s summer, the temperature differential makes this worse because the damp air under the house gets warm and mobile.
• Condensation on ductwork or floor joists. When the encapsulation is intact, the crawl space stays dry below the liner. Once a seam fails, humid air enters and condenses on anything cooler than the dew point. That’s usually your AC ducts first. It looks like sweating, and it’s the first step toward rust and mold.
• Liner pulling away from the foam at the walls. Open-cell Demilec foam moves slightly with temperature swings. Over 10 to 15 Texas summers, the bond between foam and liner adhesive can fail, and the liner starts to droop or peel. This is the most common failure point we see in San Antonio; not foam breakdown, but the transition points.
• Visible tears, holes, or pooled water on the liner surface. Rodents, a plumber doing work under the house, or an overzealous home inspector can puncture the liner. Clay soil in San Antonio also expands and contracts with rainfall, which can stress the liner at the perimeter. Once you see standing water, the encapsulation is no longer doing its job.
• Rising indoor humidity or higher cooling bills. A compromised crawl space means your AC is conditioning damp air. Homeowners notice the thermostat set at 74 but the house feels sticky, or the July electric bill is $80 higher than last year. That’s your house telling you the building envelope has a leak in it, and the crawl space is usually where it’s hiding.

Replacement Cost & What’s Included

Here’s what a Demilec crawl space encapsulation repair or replacement runs in San Antonio. These are installed prices, including parts, labor, and haul-away of the old material:

• Full liner replacement (up to 1,200 sq ft): $2,800 – $4,200
• Full liner replacement (1,200 – 2,500 sq ft): $4,200 – $5,800
• Foam patch + liner seam repair (isolated damage): $450 – $900
• Tape and mastic re-seal along wall transition: $350 – $750
• Dehumidifier add-on (if humidity stays high after repair): $1,800 – $2,600

What drives the range is access, ceiling height, and how much of the old liner has to come out. A crawl space with 30 inches of clearance is a different job than one where a technician is on his back for four hours. The foam itself rarely needs full removal; Demilec closed-cell foam holds up well underground unless there’s been repeated water intrusion. We give you a line-item quote before we start, and that quote is what you pay. Every job is covered by our lifetime Done Right Promise. If it’s not done right, we make it right, no runaround.

DIY or Call Us?

You can safely do a visual inspection: crawl under the house with a flashlight, look for pooled water, check the liner seams, and take note of any tears or gaps at the wall. That information helps you have an informed conversation with whoever you call. What you shouldn’t do is try to re-foam the rim joists yourself. Spray foam is applied under pressure, it off-gasses, and closed-cell Demilec gets hot during application. A bad foam job creates more problems than it solves, and you’ll pay more to fix it than if you’d called someone in the first place. Same goes for working under a house with low clearance and questionable ventilation. If you’ve got a tear you can see, give us a call at (866) 751-4428. We’ll come look, tell you what actually needs doing, and hand you a written quote. No trip charge inside the county, and we answer the phone with a live person. We answer the phone live – talk to a real person, get a straight answer.

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