Sealant + Caulk Selection Quick Reference
Why this matters
Wrong sealant for the application fails - silicone where painted-over needed (paint won't stick), latex where flexibility needed (cracks), wrong sealant for fuel/oil exposure. Tech grabs whatever's in the truck + the customer's repair fails 6 months later. The right sealant for the right job lasts 10 - 25 years; the wrong one fails by next season. This is the field card.
Sealant categories
- Acrylic latex: cheapest + paintable, 10 - 25% flex, interior trim/baseboards/small gaps, NOT wet areas/exterior, water cleanup.
- Siliconized acrylic: paintable + more flexible than latex, interior + light exterior, tub caulking (paint-grade), water cleanup.
- Pure silicone: 25 - 50% flex, waterproof, NOT paintable, bath/shower/sink + glass-to-tile + exterior, mineral spirits cleanup.
- Polyurethane: 35 - 50% flex, paintable after cure, excellent UV + weather, exterior siding/gutters/masonry, mineral spirits cleanup.
- Hybrid polymer (MS / SMP): flexible + paintable + UV-resistant, interior + exterior gold standard.
- Butyl rubber: highly flexible, NOT paintable, HVAC/roof flashing/automotive, stays tacky.
- Roof flashing cement: asphalt-based, exterior flashings/roof penetrations, black, long-term durable.
Selection by application
Bath / shower
Pure 100% silicone (kitchen + bath rated):
- GE Silicone II Kitchen + Bath
- DAP Kwik Seal Ultra
- Loctite Polyseamseal Tub + Tile
Don't use latex - fails in months.
Kitchen counter / sink
Pure silicone OR siliconized acrylic:
- Around sink + faucet
- Behind sink at backsplash
- Stove + counter joint
Exterior siding
Polyurethane OR hybrid polymer:
- Trim joints
- Window + door frames (around perimeter)
- Siding joints (specific to siding type)
- Vent + electrical penetrations
NOT acrylic latex (cracks in sun).
Roofing + flashing
Roof flashing cement OR butyl rubber:
- Around chimneys, vents, skylights
- Flashing seams
- Granule-coated for shingle bond
Concrete / masonry joints
Polyurethane self-leveling (for horizontal cracks):
- Concrete control joints
- Expansion joints
- Garage floor cracks
- Pool deck
Polyurethane non-sag for vertical: walls, foundation cracks.
HVAC ductwork
UL 181 listed mastic OR sealant:
- Duct seams + joints
- Hard-cast mastic (preferred per IECC)
- Aluminum tape secondary
NOT duct tape (despite the name; fails).
Plumbing
Threaded fittings: PTFE thread sealant (yellow for gas, white for water) OR pipe dope.
NOT silicone sealant (won't hold pressure).
Sink mounting: 100% silicone OR plumber's putty (under sink rim).
Gas piping
Black pipe / iron: pipe dope rated for gas, OR yellow PTFE tape (gas-rated).
CSST: no thread sealant needed at fittings; per manufacturer.
Electrical penetrations
Fire-stop sealant: red 3M Fire Block, AmeriCaulk, etc. Required by code for penetrations through fire-rated walls.
Outdoor electrical: silicone OR polyurethane around boxes + conduit entry.
Windows + doors
Exterior perimeter: polyurethane OR hybrid polymer.
Interior caulk (paintable): acrylic latex OR siliconized acrylic.
Glazing (between glass + frame): polyisobutylene (PIB) - manufacturer factory-applied.
Color matching
- Most sealants: white, clear, gray, beige, black, almond
- Custom colors available (premium)
- Match to substrate OR trim
Don't use white silicone behind dark stone counter - looks like a line.
Surface preparation
Critical for adhesion:
- Clean (no dust, grease, old sealant)
- Dry (most sealants don't bond to wet)
- Solvent wipe (denatured alcohol, mineral spirits)
- Primer (some products require)
Common adhesion failures:
- Old caulk under new (peels off old)
- Wet substrate (silicone won't bond)
- Dust + dirt
- Silicone residue (silicone bonds POORLY to silicone)
Application technique
Cut nozzle properly:
- Match opening to joint width
- 45° angle for joint contact
- Cut farther back for wider joint, closer for narrow
Tooling:
- Smooth bead with finger (silicone) or tool (acrylic)
- Tape edges first for clean line
- Remove tape before sealant fully cures
Apply temperature:
- 40°F - 100°F most products
- Some specific for cold weather
- Some products designed for high-heat application
Cure time:
- Skin: 15 - 30 minutes
- Tack-free: 1 - 6 hours
- Full cure: 7 - 21 days (depends on humidity + product)
- Don't paint over until manufacturer's cure complete
Sealant joint design
Joint depth + width:
- Depth ~ half of joint width
- Backer rod for joints > 1/4" wide
- Backer rod also prevents 3-side adhesion (allows joint movement)
Bond breaker tape:
- Behind sealant for movement joints
- Prevents bottom adhesion to deep joint
Removing old sealant
Tools:
- Plastic putty knife (avoid scratching)
- Caulk-removing tool (specific)
- Razor blade (caution)
- Mineral spirits + acetone (loosens residue)
Process:
- Cut bead from substrate at both edges
- Pull / peel out
- Solvent-wipe residue (mineral spirits, acetone)
- Sand if needed
- Clean + dry before new sealant
Common sealant mistakes
Latex caulk in bathroom: fails in 6 - 12 months.
Silicone where paint needed: paint beads off; have to remove silicone + redo.
Wrong color: white sealant on stained wood; redo.
Skipping prep: residue prevents adhesion.
Over-tooling: pressing sealant out of joint.
Wrong sealant for movement: rigid sealant on expansion joint cracks.
Old sealant under new: separation + leak.
Painting before cure: paint cracks + peels.
Specialty sealants
Anaerobic threadlocker (Loctite): bolts + fasteners.
Marine sealant (3M 5200, 3M 4200): boats, exterior, salt-water.
Fire-rated sealant: code-required at fire wall penetrations.
Acoustic sealant: drywall + framing joints in soundproofing.
Concrete repair: epoxy + polyurethane for cracks.
References
- ASTM C920 (sealant performance standards)
- Sealant Waterproofing + Restoration Institute (SWRI)
- Manufacturer technical data sheets
- Manuall internal: Building Envelope Fundamentals, Moisture Control Construction