LBS Screed WT
Waterproof cementitious screed, C25 F5 to EN 13813. Carries the LBS waterproof render system across the floor, laid over a two-coat spritz to form a non-absorbent base for floor coverings.
A pre-bagged semi-dry screed with WT waterproofing additives and a 3mm grain. Laid at 20 to 50mm as a bonded screed over fresh LBS Spritz and Bonding Mortar, or as a floating screed over a separating sheet, it gives a level, non-absorbent floor for basements, cellars and ground-bearing slabs exposed to water. Adhesion holds under reverse water pressure.
What the screed does for the system
Tanking a basement stops at the wall-floor junction unless the floor is dealt with too. LBS Screed WT continues the waterproofing across the slab and gives a level, non-absorbent base that floor coverings can be laid on.
Waterproof floor refurbishment
WT additives make the screed itself resist water. Capillary absorption is below 0.2 kg/m²·h½, and the open, coarse structure of the cured screed limits capillary rise from the substrate.
C25 F5 A4 to EN 13813
Compressive strength above 25 MPa, flexural strength above 5 MPa and Böhme abrasion class A4. A screed suitable for tiles, stone, timber and resin floors in commercial and residential use.
Bonds under reverse water pressure
Adhesion to concrete above 1.5 MPa, stable when water is acting from below. As a bonded screed over a two-coat LBS spritz it stays part of the tanking system rather than a separate layer on top of it.
Controlled shrinkage
Restrained shrinkage is held at or below 0.3 percent, protecting the screed from through-cracking. Additives also moderate the rate of evaporation, which reduces curling and surface crazing in fast or slow drying conditions.
Bonded or floating
Laid at 20 to 40mm bonded to fresh LBS Spritz and Bonding Mortar, or above 30mm as a floating screed on a separating sheet. Semi-dry consistency at 7 to 8 percent water, placed by hand or by screed pump.
Breathable, fast to cover
Water vapour resistance Sd of 10m ±5 lets the screed dry through. Hardens in 1.5 to 2 hours. Tiles and stone can follow after 4 days, timber and resin after 7 days once surface moisture is 2 percent or below.
The floor of the tanking system
LBS Screed WT is a grey, pre-bagged cementitious screed with WT waterproofing additives and a maximum grain size of 3mm, mixed to a semi-dry consistency at 7 to 8 percent water. It is the floor component of the LBS three-coat waterproof render system.
On floors the system is two coats of LBS Spritz and Bonding Mortar as the waterproofing layer, with Screed WT laid onto the second coat while it is still fresh to form a bonded screed of 20 to 40mm. Where a floating screed is needed, Screed WT is laid at 30mm or more over a separating sheet.
The result is a level, non-absorbent, C25 F5 screed that takes tiles, stone, timber, carpet and resin floor finishes. It is also used to restore existing floors exposed to ground moisture and water erosion.
Where it is used
- Non-absorbent, level screed beneath floor coverings, C25 F5 to EN 13813
- Floor component of the LBS waterproof render system in basements and cellars
- Restoration of floor substrates exposed to ground moisture and water erosion
- Fresh LBS Spritz and Bonding Mortar, two coats, for bonded screeds
- Separating sheet, for floating screeds
- Concrete and aerated concrete
- Brick, stone and terracotta
- Existing floor substrates and cementitious mortars
Cementitious substrates must have moderate water absorption: neither excessive nor absent. For other substrate types, contact Licata technical support.
Product information
| Characteristic | LBS performance | Standard requirement |
|---|---|---|
| Compressive strength, EN 13813 | >25 MPa (C25) | Classes C1 to C30+ |
| Flexural strength, EN 13813 | >5 MPa (F5) | Classes F1 to F10+ |
| Abrasion resistance, Böhme, EN 13813 | A4 | Classes A1 to A50 |
| Restrained expansion and shrinkage | ≤0.3% | Not declared |
| Adhesive strength on concrete | >1.5 MPa | Not declared |
| Capillary absorption | <0.2 kg/m²·h½ | Not declared |
| Water vapour permeability, Sd | 10m ±5 | Not declared |
Values from the LBS Screed WT technical data sheet, determined at 21°C and 65% RH. Rows marked "Not declared" are standalone tests with no class requirement in the standard. Higher temperatures shorten working and curing times; below 5°C hydration stops.
Before laying
- Clean the substrateRemove anything loose or poorly bonded: old friable layers, dust, rubble. Remove oils, waxes, fats and detergents by thorough cleaning or light abrasion.
- Fix perimeter isolation stripFix a compressible strip at least 5mm thick (foam band, cork or EPS) around the perimeter and against columns and upstands.
- Bonded screed, 20 to 40mmApply LBS Spritz and Bonding Mortar as a rough key coat. The screed is laid onto it while fresh.
- Floating screed, 30mm and overLay a polymer separating sheet (PVC, PE or similar) with joints overlapped by at least 200mm.
- MixAdd three quarters of the mixing water (2.1 to 2.4 litres per 28kg bag) to a clean container, add the powder and mix for 3 minutes with a low-speed mixer. Add the remaining water gradually to a semi-dry, earth-moist consistency. Mix whole bags only. The screed can also be placed by pump.
Laying the screed
- Place and compactSpread the mixed screed directly onto the fresh spritz or the separating sheet. Compact it thoroughly and work it level with a trowel and straight edge.
- Keep 20mm minimumMaintain at least 20mm of screed at every point, including over pipes, ducts and any raised feature in the floor.
- Reinforce over servicesWhere the screed crosses ducts, channels or cables, reinforce with hexagonal mesh.
- Day jointsWhere laying stops and restarts, set steel bars 300mm long and 4 to 8mm diameter into the fresh edge at 200 to 300mm centres, half their length embedded, to tie the next pour.
- Cure and coverHardens in 1.5 to 2 hours. Shield from wind, direct sun and rain for 48 to 72 hours. Tiles, stone and carpet after 4 days. Timber, parquet, resin and PVC after 7 days and once surface moisture is 2 percent or below. Wash tools with water while the mortar is fresh.
Complete the system
Specifying LBS on a waterproofing project?
Licata technical support can advise on build-up, detailing and BS 8102 design. Stock is held at all six UK branches.