Akemi Hyperclear 2-Part Clear Urethane Adhesive: A Spotlight

Pale stone is unforgiving. A seam or a repair on a white marble vanity top, a light quartzite waterfall panel or a translucent crystalline slab shows every flaw in the adhesive line, and a glue that carries even a faint tint or slowly warms toward yellow turns a sound bond into a visible defect. Fabricators who work with light material know the routine: pick the adhesive for what it will look like in five years, not only for what it does in the first hour. Clear two-component chemistry exists for exactly this reason, and the Akemi Hyperclear system is one of the products built around that job.

This spotlight looks at the Akemi Hyperclear 1 kg two-component clear urethane adhesive the way a fabrication lead would read it: what the product is, how the published timing and mix data translate into a bench routine, where its limits sit, and how it compares with the epoxy habit many shops default to. Every product figure below comes from the Dynamic Stone Tools product listing for the item or from the manufacturer figures reproduced in it. Where a number is not published, this article says so instead of guessing, and general chemistry statements are limited to points that independent technical sources agree on.

What a clear polyurethane gel actually is

Hyperclear is described by the manufacturer, AKEMI GmbH of Nuremberg, Germany, as a gel-like, solvent-free, two-component polyurethane reaction-resin adhesive made for the stone and slab industry. Two words in that sentence do most of the work. Two-component means the adhesive is supplied as Part A and Part B, and the bond forms only when the two are mixed and a chemical reaction starts. Polyurethane, often shortened to PUR, names the chemistry of that reaction. It is a different family from the epoxies that dominate stone workshops, and the difference shows up in how the cured line behaves.

Independent technical references describe the general split fairly consistently. Epoxies are known for high-strength bonds, high modulus and good chemical and moisture resistance, and they tend toward a hard, rigid cured state. Polyurethanes are typically described as tougher and more flexible, with greater elongation, though usually at lower absolute strength and with more sensitivity to moisture and heat. These are family tendencies, not guarantees for any single product, so treat them as a starting frame for reading a data sheet rather than a substitute for it.

The listing states that Hyperclear delivers a transparent, colourless bond with good stability against yellowing, which is why it is recommended for very light-colored and white stone and even crystalline-transparent natural stone without discoloring the contact area. Note the careful wording: good stability to yellowing, not immunity. The same listing later explains one way the stability can be lost, through an off-ratio mix, and that detail matters more in daily use than the headline claim. A clear adhesive is only as clear as the discipline of the person mixing it.

Consistency is the second design goal. Hyperclear is a gel, described as knife-grade, which gives good hold on vertical surfaces while still allowing thin, precise bonding joints. Anyone who has tried to set a vertical return or a backsplash cap with a runny adhesive understands the value: the material stays where the knife puts it. The listing adds that the solvent-free formulation gives low shrinkage, keeping tension in the bond line to a minimum, which is relevant on thin joints in pale stone where stress and visibility both punish a heavy hand.

Using Hyperclear in the shop

The published applications list is broad. The listing names natural stone such as marble, granite and quartzite, including very light-colored and white stone, porcelain and ceramics such as Dekton and Neolith, artificial stone, terrazzo and concrete, and mentions other materials including plastics, paper, wood and glass, with a test bond recommended for those. A broad list is convenient, but the fabrication logic is unchanged: match the adhesive to the substrate on a scrap piece first, and never assume that a materials list replaces a test bond on the actual slab from the actual lot.

Surface preparation

The directions are short and strict. Surfaces to be bonded must be thoroughly cleaned, free of dust, dirt and grease, and smooth surfaces should be slightly roughened. They must also be dry: the listing states that humidity causes bubbles and loss of stability. This is the single most common way a clear line goes wrong in practice, because slab edges cut wet can hold water below the visible surface. Allow real drying time after wet cutting or washing, and never bond over a film left by a cleaner or sealer.

Mixing and colouring

Mixing is 1:1 by the published ratio, Part A to Part B, blended until homogeneous. The listing is emphatic that the ratio be observed strictly, because a surplus of Part A acts as a plasticizer and can slowly cause yellowing, while a low surplus of Part B, at most 5%, does not harm the product. If the bond line needs a tint, up to 2% polyester colouring paste can be added; the coloring pastes collection carries products of that type. Measure by weight or by matched dispensing rather than by eye, especially on the small batches used for seam work.

Timing at 68°F (20°C)

All manufacturer timing figures are given at 68°F (20°C). The mixture stays workable for approximately 5–8 minutes, so small batches and a staged sequence are the sensible approach. Bonded parts may be moved after approximately 1 hour, further processed after approximately 4 hours, and reach maximum strength after approximately 24 hours. The listing adds that warmth accelerates hardening and cold delays it, and that the product will not harden sufficiently below 41°F (5°C). Those two facts set the temperature window of a job before any slab is touched.

Read the hardness row as a picture of the cure curve rather than a specification to design around. Shore D hardness of 40 at one hour, 60 at two hours, 65 at three hours, 70 at four hours and 78 at 24 hours shows the bond gaining most of its hardness in the first couple of hours and finishing slowly afterwards. That matches the practical milestones: handle carefully at one hour, machine at four, and treat the 24-hour mark as the point at which the line has reached its published maximum strength for loaded or transported work.

Where it does not belong

The listing is direct about exclusions. Hyperclear is not suitable for polyolefins such as polyethylene and polypropylene, for Teflon or PTFE, for silicone, or for other materials containing plasticisers such as soft PVC. It is also only conditionally suitable in areas of permanent moisture or direct contact with water. That last point deserves attention in wet-area planning: sink surrounds, shower benches and exterior installations call for a deliberate decision, ideally checked against the manufacturer data sheet, not an assumption that a clear adhesive can be used everywhere the stone goes.

Advanced tips for light stone and vertical work

Because the pot life is approximately 5–8 minutes at 68°F, sequence the job before mixing. Dry-fit every piece, mask the stone beside the joint, set clamps or tape within reach, and have the cleaning solvent open. The manufacturer names AKEMI Universal Dilution for cleaning tools while the adhesive is uncured. Once hardened, the adhesive can only be removed mechanically, which on polished pale stone means grinding or scraping close to a finished surface. Careful masking is far cheaper than repair.

Thin joints are where a gel earns its place. The listing points to low shrinkage and the ability to bond in thin, precise joints, so the goal is a tight, well-fitted line with just enough adhesive to wet both faces, not a thick bead squeezed out as insurance. A thick line in translucent stone shows more of everything, including bubbles. Pressure and fit do more for appearance than extra material, and a clean, dry joint face does more than either, since humidity is the documented cause of bubbles.

Vertical and overhead moments, such as returns, laminated edges before they are clamped, and backsplash caps, suit a knife-grade gel. The listing says the gel gives good stability on vertical surfaces. That does not remove the need for support: use tape, props or clamps to hold the piece during the 5–8 minute working window and through the first hour, after which the parts may be moved. Warmth accelerates cure, so a warm shop shortens the working window, and a cold slab lengthens it while also delaying strength.

Temperature deserves a jobsite check, not a guess. Below 41°F (5°C) the adhesive will not harden sufficiently, so cold garages, unheated exterior work and slabs that spent the night on a truck are all risks. Equally, the cured bond is rated for continuous exposure to 140°F (60°C) with short-term exposure up to 212°F (100°C), so consider sun-heated exterior faces and areas beside heat sources before choosing it. When conditions fall outside those numbers, choose a different adhesive rather than stretching the data.

It also helps to be honest about the alternatives. Epoxies remain the workhorse for structural stone bonding, and independent references describe them as rigid, high-modulus and heat-tolerant. A clear polyurethane is a specialist choice for light and translucent stone. Many shops therefore keep both: a clear gel for visible pale seams and returns, and an epoxy from the epoxy adhesives collection for darker material and general structural work. Choosing per job, using the data for each, is more reliable than choosing one product for everything.

Finally, remember what the strength figures are and are not. The listing gives bending strength of 7,250–8,700 psi and tensile strength of 2,900–4,350 psi, measured under the DIN EN ISO 178 and ISO 527 methods respectively, and states that technical values are manufacturer figures that may vary with jobsite conditions. They are useful for comparing products on paper. They do not certify a particular installation, and structural or load-bearing designs should be reviewed against the current technical data sheet and the applicable building requirements.

Storage, handling and long-term considerations

Store the kit cool and sealed. The listing gives a shelf life of approximately 12 months in the sealed original container, kept below 77°F (25°C). A tool crib that sits in a hot metal shop in summer is a poor home for it. Date the boxes on receipt, rotate stock so the oldest goes first, and keep the two components together in their original packaging so that the labeling and batch information stay with the kit.

The product is an industrial chemical, and the listing instructs users to work only in well-ventilated areas and to wear chemical-resistant gloves and eye protection. It also directs users to read the AKEMI Safety Data Sheet before use, available from the manufacturer through its stone care product portal. Keep the current SDS and technical data sheet in the shop file, and check the revision date occasionally, because formulations and documents can be updated after a product has been on the shelf for a while.

Long-term performance depends on the environment the bond lives in. The listing says Hyperclear is only conditionally suitable where moisture is permanent or where the joint contacts water directly, and it names sustained heat above 140°F (60°C) as a limit. For interior dry-area work on light stone these are rarely a problem. For kitchens, baths and exterior faces they are real design questions, so document the decision and, where doubt remains, ask the manufacturer before committing a finished slab.

Good records are the last piece. Note the batch, the temperature, the mix ratio method and the time of mixing on the job ticket for any visible seam in pale stone. If a line ever needs investigating, those four details answer most of the questions quickly. They also make it easy to repeat a good result, which is the real point of a repeatable adhesive routine: predictable timing, predictable color, and predictable handling across every kitchen and vanity that leaves the shop.

To compare the wider range, browse the adhesives collection, look at the epoxy adhesives for structural and darker-stone work, check the adhesive cartridges for dispensed formats, and see the coloring pastes if you plan to tint a bond line. You can also review the Akemi Hyperclear product page for current sizes and documentation before ordering.