Sika

Sika is the name on the tube when a driveway, patio, slab or foundation wall cracks and the fix has to last more than one winter. Its Sikaflex polyurethane sealants go in from a standard caulk gun, cure to an elastic rubber, and move with the concrete as it opens in the cold and closes in the heat, so they stay bonded in the crack where a stiff filler lets go. Sika also makes the rest of what a concrete job needs: a mortar-joint sealant, an all-purpose construction sealant in house colors, a self-leveling floor underlayment, a ready-mix concrete patch, anchoring adhesives, a construction adhesive and bonding agents.

Sika AG is a Swiss specialty chemical company headquartered in Baar, Switzerland, supplying the building and motor vehicle industries. Kaspar Winkler founded it in Zurich in 1910, and its breakthrough came in 1918, when the Swiss Federal Railways used its waterproofing agent in the Gotthard tunnels. The company is publicly traded on the Swiss stock exchange and makes products for bonding, sealing, damping, reinforcing and protecting. Sikaflex is one of more than 900 product brands it sells, alongside Sikadur, SikaBond and Sika ViscoCrete.

Three Sikaflex sealants for three kinds of crack

Pick by the surface and by whether it’s a crack or a joint. Crack Flex is the one for a random crack wandering across a flat driveway or patio: it’s self-leveling, and it cures with a texture that blends into the concrete around it instead of leaving a gray stripe. The Sikaflex Self-Leveling Sealant is for joints, the sawcuts and expansion joints between slabs, and it cures to a smooth finish. Concrete Fix is non-sag, so it stays where you put it in a foundation wall, a step face or any vertical crack, and it works on flat work too. Crack Flex and the Self-Leveling Sealant both flow, so keep them on level surfaces; on a wall or a slope, reach for Concrete Fix.

All three resist dirt and can sit underwater once cured without losing their properties. Concrete Fix takes more movement than Crack Flex, ±35% against ±25%, and it stays permanently elastic, which makes it the tube to buy for a crack that is still working.

Getting the crack ready

Most failed crack repairs start with a crack that was too thin. Crack Flex and Concrete Fix both need a crack at least 1/4 in. wide and 1/4 in. deep, so open a hairline crack with a cold chisel and hammer until it reaches that size. Sealant smeared over a hairline skins across the top with nothing to grab and peels.

The crack has to be sound, clean, dry and frost-free, with oil, grease and curing-compound residue removed. A wire brush and a shop vacuum handle most of it.

For a deep joint, push closed-cell backer rod in first. It fills the depth so a cartridge goes further, and it keeps the sealant bonded to the two sides only, so it can stretch when the joint opens.

Bring Crack Flex to 65 to 75 °F before you gun it, and seal when the joint is at the midpoint of its expected movement: a mild day, away from the hottest afternoon or the coldest morning. Keep the nozzle down in the sealant as you move so you’re pushing it into the crack. Self-leveling sealant runs when it first comes out, so fill a little shy of the top and let it settle; overfilling is the usual mess. Crack Flex is tack-free in 1 to 2 hours, but keep tires off a driveway repair until it has fully cured. Sika rates both Crack Flex and Concrete Fix for new concrete 24 hours after cure, and for wet concrete an hour after the water stops.

Painting over Sikaflex to match the house

Paint is the question that stops most people, since a gray line across a tinted patio or a painted foundation can look worse than the crack did. Crack Flex takes water-based, oil-based and rubber-based paints. Keep silicone-based paints and paints high in solvent off it. Concrete Fix is paintable once cured, so let it reach its full cure of 5 to 7 days before the brush comes out.

Concrete Fix on basement slabs and foundation walls

Concrete Fix is the Sikaflex for basement slab cracks and foundation walls. It’s a moisture-cured, non-sag urethane that goes on vertical or horizontal, bonds to most construction materials without a primer, and resists water, diluted acids and diluted alkalines. It also works between materials that expand at different rates, so it handles joints in walls, floors and balconies and around window and door frames. It doesn’t stain the concrete beside the joint, and it cures tough enough to shrug off cuts and tears where boots and shovels cross it.

Sika describes Concrete Fix as urethane-based and suggested by the EPA for radon reduction. The Flathead Valley is radon Zone 1, which makes Concrete Fix the tube for sealing basement slab cracks and the joint where the slab meets the foundation wall.

For contractors writing a spec, it meets ASTM C-920, Type S, Grade NS, Class 25, and Federal specification TT-S-00230C, Type II, Class A. One thing to handle first: where groundwater is pushing through a wall or slab under strong hydrostatic pressure, no sealant holds against it, so stop the water, then seal the crack with Concrete Fix.

Mortar Fix, Construction Sealant and the rest of the Sika shelf

For cracked brick and block joints, use Sikaflex Mortar Fix, a textured one-component polyurethane made for cracks and joints in mortar, so the repair reads as mortar rather than a caulk line.

Sikaflex Construction Sealant is the all-purpose, non-sag polyurethane for the gaps around trim, siding and the rest of the house, and it comes in white, limestone, capitol tan and dark bronze, so the bead can match the trim or the siding instead of standing out against it. Being polyurethane, it takes paint like the rest of the Sikaflex family when the color still needs to change.

SikaLevel and the ready-mix patch

Don’t confuse the self-leveling sealant with SikaLevel. The sealant goes in a joint; SikaLevel is a high-strength, high-flow cementitious underlayment in a 50 lb. bag that flattens an interior concrete floor before the finish floor goes down, whether that’s a new slab or an old one being renovated. It pours from 1/8 to 2 inches thick, takes foot traffic in 2 to 3 hours, and takes tile or stone in the same 2 to 3 hours, vinyl, carpet or rubber after a day, and hardwood after three days. Prime the slab with SikaLevel Primer first, so the concrete underneath doesn’t pull the water out of the pour.

For a spalled step, a chipped sidewalk edge or a crack too wide for a tube, Sikacryl Ready-Mix Concrete Patch comes ready to use in a quart tub: stir it and trowel it on. It’s an acrylic patch with a textured finish, it works on vertical and horizontal surfaces, and it cures tough in about a day at 1/4 inch. Build it up 1/4 inch at a time, to 1/2 inch in all.

AnchorFix for rebar, rod and bolts

When a ledger, a post base, a railing or a dowel has to hold in concrete that’s already poured, Sika AnchorFix-1 is the adhesive for it. It’s a high-strength, two-component anchoring adhesive for rebar, threaded rod and bolts in uncracked concrete, solid masonry, hard natural stone and solid rock, and it comes in a 10.1 fl. oz. cartridge that runs in a standard gun. Drill the hole, clean it out, fill it and set the steel. At 68 to 77 °F you have about 6 minutes to work and a full cure in about 50 minutes, so the anchor is ready to load the same hour instead of the next day. Keep it to 41 °F and warmer; on a cold morning, warm the cartridge and wait for the afternoon. For the heaviest loads, Sika also makes a high-strength epoxy AnchorFix.

Rounding out the concrete job, Sika’s high-performance construction adhesive handles general building bonds from a standard gun, and its concrete bonding agents, Acryl 60 among them, help new patch and concrete grab old.

Sikaflex concrete sealant specs

Spec	Crack Flex	Self-Leveling Sealant	Concrete Fix
Type	Textured, self-leveling polyurethane	Smooth, self-leveling polyurethane	Non-sag polyurethane
Made for	Horizontal cracks	Horizontal expansion joints	Vertical and horizontal cracks and joints
Size	1/4 in. by 1/4 in. up to 1 in. wide	1/4 in. up to 1-1/2 in. wide	1/4 in. by 1/4 in. up to 1 in. wide
Movement	±25%	±25%	±35%
Application temperature	40 to 100 °F	40 to 100 °F	Placeable at 40 °F
Full cure	3 to 5 days	3 to 5 days	5 to 7 days
Cartridge	10.1 fl. oz.	10.1 or 29 fl. oz.	10.1 fl. oz.

Frequently Asked Questions

What is Sika self-leveling sealant used for?

Sika self-leveling sealant is a one-part polyurethane made for horizontal joints, like the sawcuts and expansion gaps between driveway and sidewalk slabs. You gun it in, it levels itself and it cures smooth. For a random crack across the same slab, Crack Flex is the self-leveling Sikaflex made for cracks, with a textured finish that blends in.

Is Sika self-leveling sealant paintable?

Yes. Sikaflex sealants are paintable, and that includes the smooth self-leveling sealant used in slab joints. Wait for a full cure before you paint, because paint over sealant that’s still curing underneath can crack as the sealant firms up.

How do you apply Sika self-leveling sealant in a Montana winter?

Wait for a day above 40 °F. Sika calls for 40 to 100 °F at application and storage between 40 and 95 °F, so keep the cartridges in the house or a heated shop, not the truck, and seal the joint on a mild spring or fall day when it’s at the middle of its movement. Once it’s cured, the Self-Leveling Sealant handles service temperatures from -40 to 170 °F, so neither a January cold snap nor a hot August slab will hurt the repair.

What is the best Sika caulk for concrete cracks?

For a flat crack in a driveway or patio, Crack Flex. For a foundation wall, a step or any crack that’s still moving, Concrete Fix, which stretches ±35%, goes on vertical surfaces and bonds without a primer. For the joints between slabs, the Self-Leveling Sealant, and for brick and block, Mortar Fix.

Is Sika Crack Fix the same thing as Crack Flex?

No. Sikadur Crack Fix is an epoxy crack-repair product, and Crack Flex is a flexible polyurethane sealant. Epoxy cures hard and suits a crack that has stopped moving. A slab crack that opens in January and closes in July needs a sealant that stretches with it, and that’s Crack Flex or Concrete Fix.

What is Sika AnchorFix-1 used for?

Setting rebar, threaded rod and bolts in uncracked concrete, solid masonry and solid rock. It’s a two-component adhesive that dispenses from a standard gun and cures in about 50 minutes at room temperature, so a post base or ledger can go on the same day.