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Sikalastic 621 TC UV Stable Polyurethane Membrane:

Sikalastic-621 TC High performance, one-component, liquid applied polyurethane top coat for SikaRoof MTC roof waterproofing systems  


Sikalastic-621 TC is a cold-applied, one-component, seamless, highly elastic and UV-stable moisture triggered polyurethane Top Coat (TC) designed to provide easy application and a durable solution as part of the SikaRoof MTC systems, as well as for detailing on single ply membranes.  


  • Sikalastic-621 TC may only be used by experienced professionals. Top Coat for SikaRoof MTC 12, 15, 18, 22 in both new construction and refurbishment projects
  • For roofs displaying complex detail areas and geometry, even when accessibility is limited
  • For cost efficient life cycle extension of failing roofs Highly reflective top coat Sikalastic-621 TC - SR (traffic white RAL 9016) as part of the Sika SolaRoof MTC systems for excellent cool roof characteristics and bi-facial photovoltaic panels.
  • For detailing on singly ply membranes 


  • Proven technology - over 25 year track record
  • One component - no mixing, easy and ready to use UV resistant - Highly reflective (RAL9016) and resistant to yellowing
  • Cold applied - requires no heat or flame
  • Seamless roof waterproofing membrane Compatible with Sika Reemat Premium - easy to detail
  • Fast curing - free from resin damage almost immediately on application
  • High elastic and crack-bridging - retains flexibility even at low temperatures
  • High root resistance
  • Easily re-coated when needed - no stripping required
  • Good adhesion to most substrates- see primer chart
  • Vapour permeable - allows substrate to breathe
  • Strong resistance to common atmospheric chemicals 


  • As part of SikaRoof MTC Systems Liquid applied roof waterproofing kit according to ETAG 005, ETA-09/0139 issued by technical assessment body British Board of Agreement (BBA), provided with the CE marking. Declaration of Performance:
  • SikaRoof MTC 12: 44125185
  • SikaRoof MTC 15: 27265077
  • SikaRoof MTC 18: 15813688
  • SikaRoof MTC 22: 75346978
  • Root resistance approval according FLL (Institute of Horticulture)
  • Reaction to fire according to EN 13501-1: Euroclass E
  • External fire performance according to EN 13501-5: BRoof (t1) - BRoof (t4) (SikaRoof MTC 15, non-combustible substrates)
  • BRoof (t1)- BRoof (t4) (SikaRoof MTC 18, build up roofs)
  • BRoof (t1) (SikaRoof MTC 22, Build up roofs) 


  • Composition: One-component, moisture-triggered aliphatic polyurethane
  • Packaging: 15 l (21.6 kg approx.) metal pail
  • Colour: Slate grey (RAL 7015), other colours available upon request
  • Shelf life: 9 months from date of production
  • Storage conditions: The product must be stored properly in original, unopened and undamaged sealed packaging in dry conditions at temperatures between 0oC and +25oC. Higher storage temperatures may reduce shelf life of product.
  • Reference shall also be made to the storage recommendations within the safety data sheet.
  • Density: ~1.44 kg/l (23oC) (EN ISO 2811-1)
  • Solid content by weight: ~87.4 % ( +23oC/ 50 % r.h.)
  • Solid content by volume: ~81.3 % ( +23oC/ 50 % r.h.) 


  • Chemical resistance:
  • Salt spray: 1000 hours continuous exposure, (ASTM B117)
  • Prohesion testing:  1000 hours cyclic exposure, (ASTM G85-94: Annex A5)
  • Strong resistance to a wide range of reagents including paraffin, petrol, fuel oil, white spirit, acid rain, detergents and moderate solutions of acids and alkalis. Some low molecular weight alcohols can soften the material.
  • Solar reflectance index: >= 109* (ASTM 1980)
  • *All values refer to the initial (properly cured, non-weathered) status of Sikalastic-621 TC white (RAL 9016).
  • Service temperature: -30oCmin. / +80oCmax. 


  • System structure: Please refer to System Data Sheets of SikaRoof MTC Systems
  • System performance: Please refer to System Data Sheet of SikaRoof MTC Systems. 


Ambient air temperature: +5oC min. / +35oC max.

  • Relative air humidity: 5 % r.h. min. / 85 % r.h. max.
  • Substrate temperature: +5oCmin. / +60oCmax. ≥3oCabove dew point
  • Substrate moisture content: <= 4 % pbw moisture content. Test method: Sika-Tramex meter. No rising moisture according to ASTM (Polyethylene-sheet).
  • Substrate pre-treatment: Please refer to System Data Sheets of SikaRoof MTC Systems
  • Pot Life: Sikalastic-621 TC is designed for fast curing. High temperatures combined with high air humidity will increase the curing process. Thus, material in opened containers should be applied immediately. In opened containers, the material will form a film after 1-2 hours approx. (+20oC/ 50 % r.h.)

Waiting time to overcoating

Ambient conditions

Minimum waiting time

+5oC/ 50 % r.h.

18 hours

+10oC/ 50 % r.h.

8 hours

+20oC/ 50 % r.h.

6 hours

*After four days the surface must be cleaned and primed with Sika Reactivation Primer before continuing. Note: Times are approximate and will be affected by changing ambient conditions particularly temperature and relative humidity.  

Applied product ready for use:

Ambient conditions

Rain resistance

Touch dry

Full cure

+5oC/ 50 % r.h.

10 min

8-12 hours

16-24 hours

+10oC/ 50 % r.h.

10 min

4 hours

8-12 hours

+20oC/ 50 % r.h.

10 ,om

3 hours

6-8 hours

* Be aware that impact of heavy rain or rain showers can physically damage the still liquid membrane. Note: Times are approximate and will be affected by changing ambient conditions particularly temperature and relative humidity.  


The surface must be sound, of sufficient strength, clean, dry and free of dirt, oil, grease and other contamination. Depending on the material the substrate must be primed or mechanically cleaned. Grinding may be necessary to level the surface. Suitable substrates are such as: concrete, bituminous felts and coatings, metal, brickwork, asbestos cement, ceramic tiles, wooden substrates. For detailed information regarding substrate preparation and primer chart please refer to Method Statement No. 850 94 01.  


Mixing is not required, however if the product is settled or separated on opening, stir Sikalastic-621 TC gently but thoroughly in order to achieve a uniform colour. Stirring gently will minimise air entrainment.  


Prior the application of Sikalastic-621 TC the priming coat if used must have cured tack-free. For the Waiting Time / Overcoating please refer to the PDS of the appropriate primer. Damageable areas (handrails etc.) have to be protected with tape or plastic wrapping. Please note, always begin with details prior to the installation of the horizontal surface.

1. Apply first coat of Sikalastic-601 BC. Work only so far in advance that the material stays liquid*.

2. Roll in the Sikalastic Reemat. Overlap the Reemat a minimum 5 cm and ensure overlaps are sufficiently wet to bond both layers.

3. The roller may require only a little extra material to keep wetted but no further significant material needs to be added at this stage.

4. After the coat is dry enough to walk on, seal the roof area with second coat of Sikalastic-621 TC.

5. For SikaRoof MTC 22 apply a third coat of Sikalastic- 621 TC.    


Clean all tools and application equipment with Thinner S immediately after use. Hardened and/or cured material can only be removed mechanically.  


For detailed information regarding substrate preparation, primer chart and application method please refer to Method Statement of SikaRoof MTC Systems No. 850 94 01.  


  • Do not apply Sikalastic-621 TC on substrates with rising moisture.
  • Sikalastic-621 TC is not suitable for permanent water immersion.
  • On substrates likely to exhibit outgassing, apply during falling ambient and substrate temperature. If applied during rising temperatures pin holing may occur from rising air.
  • Do not dilute Sikalastic-621 TC with any solvent.
  • Do not use Sikalastic-621 TC for indoor applications. Do not apply close to the air intake vent of a running air conditioning unit.
  • Do not apply Sikalastic-621 TC directly on Sikalastic Insulation boards. Instead use Sikalastic Carrier between Sikalastic Insulation board and Sikalastic- 621 TC.
  • Volatile bituminous materials may stain and or soften below the coating.
  • Areas with high movement, irregular substrates, or timber based roof decks require a complete layer of Sikalastic Carrier.
  • Do not apply cementitious products (e.g. tile mortar) directly onto Sikalastic-621 TC. 

BASIS OF PRODUCT DATA All technical data stated in this Product Data Sheet are based on laboratory tests. Actual measured data may vary due to circumstances beyond our control.  


Please note that as a result of specific local regulations the declared data for this product may vary from country to country. Please consult the local Product Data Sheet for the exact product data. 


For information and advice on the safe handling, storage and disposal of chemical products, users shall refer to the most recent Safety Data Sheet (SDS) containing physical, ecological, toxicological and other safety-related data    


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