Akfix P635 PU Construction Sealant Grey 600ml – Polyurethane Joint Sealant for Concrete & Expansion Joints

Key Features & Benefits

• Excellent adhesion without primer on most substrates — grips concrete, screed, plaster, brick, blockwork, natural and cast stone, ceramic, glass, aluminium, galvanised and painted steel, timber, and most rigid plastics.
• Permanently flexible — accommodates ±25% of the original joint width in movement, so seasonal and structural movement is absorbed instead of splitting the seal.
• No shrinkage — 100% solids chemistry means the bead you tool is the bead you keep. There is no solvent to evaporate and no hollowing or sinking as it cures.
• Fully paintable — accepts most water-based and alkyd paint systems once skinned over, so beads can be finished flush with the wall colour. (Always test-patch first; see the painting notes below.)
• Weather, UV and ageing resistant — holds up to direct tropical sun, driving rain and repeated wet/dry cycling without becoming brittle or chalky.
• Non-sag / thixotropic — stays put in vertical and overhead joints without slumping.
• High mechanical strength — resists abrasion, tearing and light foot traffic once fully cured, which makes it suitable for floor joints as well as wall joints.
• Isocyanate-cured, solvent-free formulation — low odour, and no shrink-back from solvent loss.
• Sandable and over-coatable after full cure.
• Meets recognised international standards — formulated to the elastic-sealant class ISO 11600 F 25 HM and to ASTM C-920 performance criteria.

Where to Use Akfix P635 Grey PU Sealant

Concrete and civil works

• Expansion joints, control joints and construction joints in concrete slabs, screeds and pavements
• Precast concrete panel joints and connection joints
• Kerb, culvert, manhole and drainage channel joints
• Sealing concrete cracks after routing out to a sound V or square profile
• Warehouse, workshop and parking-deck floor joints

Buildings and finishes

• Perimeter joints around window and door frames in masonry openings
• Joints between dissimilar materials — concrete to metal, blockwork to timber, plaster to aluminium
• Façade, cladding and curtain-wall movement joints
• Parapet, coping, flashing and roof-detail sealing (as a roof sealant on non-bituminous details)
• Skirting, threshold and stair-nosing perimeter sealing

Metal, timber and industrial

• Gutter, downpipe, box-profile and IBR roof-sheet lap sealing
• Steel structure joints, ducting seams and prefabricated panel joints
• Container, truck body, trailer, bus and caravan body sealing
• Marine and boat-building applications above the waterline
• Timber joinery, staircases and general carpentry gap-filling

 HOW TO USE PU CONSTRUCTION SEALANT (STEP-BY-STEP)

Step 1 — Surface Preparation

1. The joint must be clean, dry, sound and structurally stable. Remove all dust, laitance, loose particles, old sealant, curing compounds, form-release oil, grease, rust and flaking paint.
2. Mechanically clean concrete and masonry — wire brush, grinder, or route out the joint to a fresh square profile.
3. Degrease non-porous surfaces (metal, glass, glazed tile, plastics) with isopropyl alcohol or Akfix cleaner and allow to flash off completely.
4. New concrete must be at least 28 days old and fully cured before sealing.
5. Protect joint edges with masking tape for a razor-sharp line on visible work.

Step 2 — Priming (only where needed)

• No primer is required on most common substrates.
• Use a PU primer on: highly porous or friable concrete, joints under permanent water contact, joints subject to continuous heavy traffic, and marginal substrates.
• If in doubt, run an adhesion test: apply a 100 mm bead, allow 7 days to cure, then attempt to peel it. Cohesive failure (the sealant tears within itself) = good bond. Adhesive failure (it peels clean off) = prime, or the surface is unsuitable.

Step 3 — Insert Backer Rod

• Press a closed-cell polyethylene backer rod into the joint to the depth given in the joint design table. Choose a rod roughly 25% wider than the joint so it holds itself in place by compression.
• Do not puncture the rod — a punctured closed-cell rod releases gas and creates bubbles in the bead.
• Where the joint is too shallow for a rod, lay bond-breaker tape along the joint base instead.

Step 4 — Load and Apply

1. Cut the 600ml foil sausage open at one end, drop it into a sausage gun (a 600ml skeleton/barrel gun — a standard 310ml cartridge gun will not take it), fit the nozzle and screw the cap on.
2. Cut the nozzle at a 45° angle to a width slightly smaller than the joint.
3. Hold the gun at 45° to the joint and apply with steady, continuous pressure, pushing the bead ahead of the nozzle rather than dragging it behind. Pushing forces sealant into the joint and eliminates voids.
4. Fill the joint completely, in one continuous pass. Stopping and restarting introduces air pockets and cold joints.

Step 5 — Tool the Bead

• Tool within 10–15 minutes, well before skin formation.
• Use a spatula, joint tool or soap-and-water-wetted finger to press the sealant firmly against both joint faces and form a slightly concave profile.
• Do not use silicone smoothing agents or detergent-heavy solutions on PU — plain soapy water lightly applied is enough.
• Remove masking tape immediately after tooling, while the sealant is still wet, pulling it away from the bead at an angle.

Step 6 — Cleaning

• Clean uncured sealant and tools immediately with white spirit, acetone or Akfix PU cleaner.
• Wipe skin contact off with a dry cloth first, then soap and water. Do not use solvent directly on skin.
• Cured sealant can only be removed mechanically — by cutting or abrading. There is no practical solvent for it once cured, so work clean.

Step 7 — Curing, Painting & Overcoating

• Cures at roughly 3 mm per 24 hours; a 12 mm-deep joint therefore needs about 5–7 days for a full through-cure.
• Curing is faster in warm, humid conditions and slower in cool, dry ones. Do not force-cure with heat.
• Do not disturb, wash down or expose the bead to standing water for the first 24 hours.
• Painting: wait until the surface has skinned fully (ideally 24 hours or more), then apply water-based or alkyd paint. Because the bead stays elastic, hard, brittle paint films may hairline-crack over a moving joint — that is a property of the paint, not a sealant failure. Always test-patch your paint system first.

Common Mistakes to Avoid

1. Sealing over dusty, damp or oily concrete — the number-one cause of adhesion failure.
2. Omitting the backer rod, producing three-sided adhesion.
3. Applying below +5 °C or onto frosted / wet substrates.
4. Over-deep beads in narrow joints — the bead cannot stretch and tears.
5. Sealing green concrete less than 28 days old.
6. Leaving masking tape on until after skinning — it lifts the bead edge when pulled.
7. Storing opened sausages — once opened, moisture starts the cure. Use the sausage in one session.

FAQ BLOCK 

Q: What is PU construction sealant used for? A: Polyurethane construction sealant is used to seal movement, expansion and construction joints in concrete, masonry, metal and timber — anywhere two building elements meet and move relative to each other. Akfix P635 grey 600ml is typical of the class: it stays flexible for the life of the joint, resists weather and traffic, and can be painted over.

Q: How long does Akfix P635 take to cure? A: It skins over in 60–90 minutes and cures at about 3 mm per 24 hours. A 12 mm-deep joint reaches full cure in roughly 5–7 days at 23 °C and 50% relative humidity.

Q: Can you paint over polyurethane sealant? A: Yes. Akfix P635 is paintable with most water-based and alkyd systems once it has skinned over — allow at least 24 hours. Test-patch first, and expect that a hard, brittle paint film may hairline-crack across a joint that moves.

Q: Is PU sealant waterproof? A: Once cured it forms a watertight, weatherproof elastic seal and resists rain, seawater and wet/dry cycling. It is not intended for permanent immersion — do not use it in swimming pools, water tanks or aquariums.

Q: What is the difference between silicone and polyurethane sealant? A: Polyurethane is paintable, tougher, abrasion-resistant, bonds to concrete without primer and can take floor traffic. Silicone is not paintable but is better for glass, sanitaryware and high-temperature work. For structural and construction joints, PU is the correct choice.

Q: How many metres will one 600ml sausage seal? A: About 6 metres of a standard 10 × 10 mm joint, or roughly 16 metres of a 6 × 6 mm joint. See the coverage chart above.

Q: Do I need a special gun for the 600ml sausage? A: Yes — a 600ml sausage gun (skeleton or barrel type). A standard 310ml cartridge gun will not take it. We stock sausage guns at both Shabbiri Hardware branches.

Q: Does Akfix P635 need a primer? A: Not on most substrates — concrete, masonry, metal, timber and most plastics. Prime only on highly porous or friable concrete, joints in permanent water contact, or heavy-traffic floor joints.

Q: Where can I buy PU construction sealant in Nairobi? A: Shabbiri Hardware stocks Akfix P635 PU Construction Sealant Grey 600ml at our Magadi Road, Ongata Rongai branch and our Tuala branch past Nazarene University. Call 0741 042484 or 0745 554008, or email info@shabbirihardware.com

Buy PU Construction Sealant Grey 600ml in Nairobi — Shabbiri Hardware

Shabbiri Hardware supplies Akfix P635 PU Construction Sealant and the full range of construction chemicals, sealants and adhesives to contractors, fundis, developers and homeowners across Ongata Rongai, Rongai, Tuala, Kiserian, Ngong, Karen, Langata and Greater Nairobi. Trade pricing and bulk carton rates are available — call us for a quote on your joint-metre requirement.

Shabbiri Hardware — Rongai Branch Magadi Road, Ongata Rongai, Kajiado County, Kenya

Shabbiri Hardware — Tuala Branch Tuala, past Africa Nazarene University, Magadi Road, Kenya

Phone / WhatsApp: 0741 042484 · 0745 554008

Email: info@shabbirihardware.com

Website: www.shabbirihardware.com

Call to action to use: Need PU Construction Sealant Grey 600ml today? Call 0741 042484 for stock and trade pricing, or collect from Magadi Road, Ongata Rongai and Tuala.