• This is a new system to us, how will we know it works?
• What is the self-healing ability of RAWMAT® HDB?
• Does RAWMAT® HDB dry out?
• How long can RAWMAT® HDB be left exposed prior to overlaying it with concrete?
• How heavy is RAWMAT® HDB?
• What is the size of the bentonite platelets?
• How is RAWMAT® HDB applied on an outside corner?
• How are protrusions and fins addressed during surface preparation?
• Is RAWMAT® HDB affected by molten splatter from welding?
• Is RAWMAT® HDB affected by extreme point loading?
• Can RAWMAT® HDB be tied in to old structures and with bitumen / asphalt systems?
• Bentonite systems have a poor track record in tunnels, why is RAWMAT® HDB different?
• What happens if RAWMAT® HDB cracks when bent through 90°?
• What will happen if RAWMAT® HDB is exposed to steam?
• Much of Rawell's literature indicates post-fixing to vertical surfaces; can RAWMAT® HDB be used as a pre-applied vertical membrane?
• Can RAWMAT® HDB be pre-applied / fixed directly to formwork prior to casting an RC slab or wall?
• Can formwork be struck successfully without damaging the membrane?
• What are the levels of peel adhesion achieved when pre-applied to an RC wall?
• Can RAWMAT® HDB be taken through load-bearing items; e.g. between mass concrete foundations and an RC slab?
• Does the horizontal membrane always need to be covered with a concrete blinding, or can an RC slab be poured directly on to the membrane?
• Does RAWSEAL® Waterstop swell immediately when in contact with water?

This is a new system to us, how will we know it works?

RAWMAT® HDB is not new. It has been available since the early nineties, with major projects supplied all over the world. There has never been an in-service leak with this system. Please see the Petrochemical Lining Project List, Structural Waterproofing Project List, Landscaping Solutions Project List or Environmental Protection Project List.

What is the self-healing ability of RAWMAT® HDB?

RAWMAT® HDB will self-heal punctures up to 10mm in diameter as the bentonite swell will easily accommodate this providing the hole or damage restricts the flow of water through it. If water flows through the hole faster than the speed of the swell of the bentonite, the hole will not seal as the bentonite will erode and this will prevent sufficient expansion.

Does RAWMAT® HDB dry out?

When in the ground RAWMAT® HDB will never dry out. The product is hydrophilic and will draw moisture from the surrounding concrete or ground to keep it hydrated. If left exposed in direct sunlight in dry/windy conditions, the membrane may stiffen but will not dry out or crack. Lightly spraying the membrane with water will bring back its flexibility.

How long can RAWMAT® HDB be left exposed prior to overlaying it with concrete?

This depends on the site conditions and weather conditions, Rawell recommend that you lay the membrane when you see the concrete wagon in the site gates. It can be laid that quickly. The material can be laid in rain, snow etc. as long as it is part of a continuous process. The membrane has sometimes been exposed for 4-5 days without any damage, but the longer it is left exposed, the greater the risk. Rawell have a leak-free record starting from the production of RAWMAT® HDB in the early 1990s.

How heavy is RAWMAT® HDB?

RAWMAT® HDB is supplied in 1m x 5m rolls weighing approximately 40 kg per roll, which are easily handed by two people. Larger rolls are also available - 2m x 30m - weighing approximately 500kgs - or 2m x 50m - weighing approximately 850kgs and require only simple frames to be manufactured. The product weight is 8kgs per m².

What is the size of the bentonite platelets?

Approximately 2 microns.

How is RAWMAT® HDB applied on an outside corner?

The corner should be chamfered and the membrane laid directly over the chamfer. If a chamfer is not present i.e. the corner is a straight 90° - then apply an additional 300mm (1 foot) strip of RAWMAT® HDB, held into place with Rawpaste Mastic along the corner edge and apply the membrane over this strip.

How are protrusions and fins addressed during surface preparation?

Any sharp protrusion or fins should be ground down or knocked off with a hammer. In extremely rough areas level out them out, using Rawpaste Mastic or a sand-cement mortar. RAWMAT® HDB can easily accommodate undulating surfaces such as sheet piles or secant piles without any additional surface preparation. It can also be applied direct to the rock - if the rock is very jagged then only a light shotcrete is required to smooth out the surface.

Is RAWMAT® HDB affected by molten splatter from welding?

RAWMAT® HDB is unaffected by molten splatter although the geotextile may melt. If areas of excessive splatter are anticipated, the membrane can be temporarily protected using ply or standard protections boards.

Is RAWMAT® HDB affected by extreme point loading?

A report is available from Rawell, authored by the Liverpool University Dept. of Civil Engineering. During testing, the membrane was fully loaded, samples were checked visually and tested for permeability without any resultant detrimental effect on the permeability performance. Additionally the membrane has been tested by WS Atkins at 500 Kpa and found to be unaffected. Contact Rawell for copies of laboratory reports.

Can RAWMAT® HDB be tied in to old structures and with bitumen / asphalt systems?

With regard to old bitumen / asphalt, RAWMAT® HDB Type S is one of the few materials that can easily bond to this type of waterproofing due to its ability to bond to most surfaces when further hydrated or bonded using Rawpaste mastic. The “plasticine-like” consistency of the material sticks itself to the two surfaces and prevents tracking.

Bentonite systems have a poor track record in tunnels, why is RAWMAT® HDB different?

RAWMAT® HDB is the only polymerised, vacuum-extruded, pre-hydrated, platelet-aligned, chemical- and saline-resistant bentonite on the market. The systems that have failed are dry granular bentonite systems that fail due to incorrect hydration and the ion exchange phenomenon. RAWMAT® HDB is delivered to site as an impermeable membrane and does not need to hydrate to form a barrier. Furthermore the overlaps can be seen to produce self-sealing bentonite to bentonite overlaps which allow a homogeneous seal to form between the two sheets – this cannot be said for the dry bentonite membranes.

What happens if RAWMAT® HDB cracks when bent through 90°?

The crack will self-heal, for more security just apply Rawpaste Mastic over the crack.

What will happen if RAWMAT® HDB is exposed to steam?

At 500mm away or further, the steam will be condensate by the time it is in contact with the membrane. The temperature will not affect the bentonite but will soften the outer geotextile. If the geotextile is damaged simply patch over with a second piece of membrane.

Much of Rawell's literature indicates post-fixing to vertical surfaces; can RAWMAT® HDB be used as a pre-applied vertical membrane?

RAWMAT® HDB is often used as a pre-applied membrane, fixed to either sheet piles, secant piles or diaphragm walls and exposed rock surfaces. Rawell have many photographic examples of projects carried out in this way. For examples of projects where RAWMAT® HDB has been pre-applied, refer to the Petrochemical Lining Case Histories, Structural Waterproofing Case Histories, Landscaping Solutions Case Histories and Environmental Protection Case Histories. In all such cases Type P is used, where the black woven geotextile must be the side of the membrane in direct contact with the poured concrete.

Can RAWMAT® HDB be pre-applied / fixed directly to formwork prior to casting an RC slab or wall?

This is common practice, as RAWMAT® HDB does not have the needle-punched construction that is used on the Dry Bentonite Membrane material. Rawell recommend that RAWMAT® HDB is nailed only to the top of the formwork to enable easy dismantling of the shutters - the concrete bonds to the scrim side if Type S is used or the woven (black) geotextile side if Type P is used. This has been used successfully on many projects.

Can formwork be struck successfully without damaging the membrane?

As the membrane is nailed to the top of the shutter, there is nothing to damage the membrane when the shutters are struck. If rolls of RAWMAT® HDB are installed vertically, Rawell recommend a thin bead of Rawpaste Mastic to help keep the laps together during the concrete pour. Alternatively, horizontal installation using a "roof tiling" method from the bottom up will ensure no concrete interferes with the seal at the overlaps.

What are the levels of peel adhesion achieved when pre-applied to an RC wall?

Rawell cannot record "peel adhesion", as the "bond" RAWMAT® HDB gets to the concrete is one where the clay is attached to the concrete in a grease-like manner. As such there is nothing to grip to carry out such a test. Rawell have test data which shows that Dry Bentonite membranes do not bond, because the bond between the concrete and the geotextiles actually prevent the bentonite from bonding to the concrete. This provides a route for water to track between the membrane and the concrete - Rawell has tested this and found the bentonite in Dry Bentonite membranes does not bond to the concrete - only the geotextile fibres. This may be a good marketing tool but amounts to a complete misrepresentation of what the product is supposed to be doing.

Can RAWMAT® HDB be taken through load-bearing items; e.g. between mass concrete foundations and an RC slab?

Only if the structural engineer is happy with this design: Bentonite is a lubricant and can act as a bond breaker. Rawell prefer to allow the slab/piles/foundations to be one and to wrap RAWMAT® HDB around the whole installation.

Does the horizontal membrane always need to be covered with a concrete blinding, or can an RC slab be poured directly on to the membrane?

The 50mm protective blinding is used to prevent the damage of the clay core by the steel fixers installing the rebar. If the conditions are such that the site will remain dry and the amount of foot traffic is minimal then there is no need for the protection. The reason Dry Bentonite membranes have so many leaks is because the manufacturers allow the steel fixers to walk all over their membrane even after heavy rainfall. This causes the bentonite to be displaced by footprints and means the groundwater has the whole slab to attack when even a small breach in the continuity of the bentonite is exposed. By protecting the membrane with the 50mm blinding this problem is avoided. Engineers prefer this method of working, however contractors who are looking to cut costs prefer Dry Bentonite membranes. They later pay the price in the delays and costs involved later in the contract, by having grouting crews in their basement for weeks on end - a false economy.

Does RAWSEAL® Waterstop swell immediately when in contact with water?

Two grades are available. RAWSEAL® Green, which starts to swell almost immediately in potable water and with 72 hours in saltwater, and RAWSEAL® Black which has a 7 day swell delay.