Overview

Waterproofing does not usually fail because the product was poor. It fails at a joint, a lap, or a hairline crack that opened six months later when the slab moved.

Liquid Lastic PU-991 is liquid applied, so there are no joints to fail. You roll, brush or squeegee it on, it cures into one continuous elastic skin, and it stretches with the substrate instead of splitting when the substrate moves. Chemstuk measures that at 110 percent elongation at break. It goes on balconies, terraces, flat and low pitch roofs, planter boxes, plant rooms and below grade concrete, which is to say anywhere water has to stay on one side of a surface that will not sit perfectly still.

Key Features

• Two pack polyurethane, liquid applied and seamless
• Highly elastic, with crack bridging from its low modulus
• Bonds to concrete, screed, metal, ceramic tile and asphalt
• Good chemical and abrasion resistance
• Can also be used as a joint sealant
• Chemstuk lists compliance with ASTM C836-95

Specifications

• Pack: 10 litre kit, Part A 6 L and Part B 4 L
• Mix ratio: 3 to 2 by volume, 10 to 4 by weight
• Pot life: 30 minutes at 25 degrees Celsius
• Touch dry: 8 hours. Recoat window: 8 to 48 hours. Full cure: 7 days
• Solids by volume: 68 plus or minus 5 percent
• Build: 200 microns dry film per coat
• Coverage: 6 square metres per litre at 200 microns, so about 30 square metres per 10 litre kit at two coats
• Elongation at break: 110 percent
• Service temperature: 0 to 60 degrees Celsius
• VOC: maximum 90 g per litre. Flash point: 28 degrees Celsius

Applications

• Balconies, terraces and verandas
• Flat and low pitch roofs, including inverted roof build ups
• Planter boxes and green roofs
• Basements, foundations and below grade concrete
• Bathrooms and wet areas, usually with a flake finish

It Needs A UV Topcoat

Left bare in full sun, this membrane will yellow and chalk the way every aromatic polyurethane does, and Chemstuk lists UV exposed applications as a limitation. If it is going to stay exposed, overcoat it with an aliphatic polyurethane so the topcoat takes the UV instead.

What You Need to Complete the Job

Preparation is most of this job. Grind or abrade back to an open profile, remove every bit of laitance and any old coating, then prime with Primit E6-111. Bridge any crack wider than 1 mm locally before the main coat, and make good damaged areas with Quick Build CP-114. Where the membrane stays exposed, finish with Polyurit PU-232. The rest of the range sits in Concrete Coatings.

Frequently Asked Questions

How much does a 10 litre kit cover?

About 30 square metres at two coats over smooth, primed concrete. Rough or porous surfaces take more, so allow 15 to 20 percent on top.

Does it need a primer?

Chemstuk recommends one, and specifies an epoxy primer for concrete. The substrate should be at least 25 MPa, below 10 percent moisture, between 5 and 35 degrees Celsius, and under 85 percent relative humidity.

What is the working time?

Thirty minutes at 25 degrees Celsius, and closer to 15 on a hot roof in February. Mix what you can lay in that window rather than the whole kit.

Can I use it in a bathroom?

Chemstuk lists bathrooms, verandas and balconies among the recommended uses, usually finished with flake. It also lists non potable water tanks, and specifically not potable ones.