FlexsoTar - Epoxy-Bitumen Sealer Kit


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Product Overview


FlexsoTar ™ is a high build dense black epoxy/bitumen co-polymer based two pack product. The product sets to render a tough, durable and UV stable gloss black, flexible rubbery finish. This product is non-toxic and can safely be used in applications where it comes into contact with drinkable water.

FlexsoTar ™ is a versatile sealer that can be used in a wide range of applications. Such as:

  • Concrete tile and metal roof repairs: - FlexsoTar™ can be used in conjunction with fibreglass membrane or hemp cloth to form a laminate or on its own for long lasting repairs of leaks, etc.
  • Animal drinking troughs: - FlexsoTar™ can be used on concrete drinking troughs to render a high quality water proof liner. The liner will also protect against moss and will make cleaning effortless.
  • Vehicle undercarriage protection: - FlexsoTar™ will give a long lasting, durable coating on vehicle undercarriages and will prevent rusting.
  • Trailer bins and frames: - renew your trailer with a tough and hard wearing bin coating by applying FlexsoTar™.
  • Steel and metal structures
  • Seal and water proof timber and plywood structures
  • Water proof brick and block work
  • Water proof concrete floors: - FlexsoTar™ can be used under carpets.



  • FlexsoTar ™ is a versatile water proof and surface protection sealer.
  • FlexsoTar ™ is ideally suited for major roof repairs and is compatible with our GilsoFlex ™ roof paint and sealer
  • FlexsoTar ™ is non-corrosive to metals
  • Easy to mix as our kit contains the correct quantities of PART-A (co-polymer) and PART-B (hardener)
  • The pot life is 30 minutes and the product will be fully set after 6 hours, depending on the temperature.
  • FlexsoTar ™ can be left as the final finish and does not require further painting.
  • If it is used to repair leaky roofs we recommend a top coat with GilsoFlex ™ Roof sealer and paint.
  • If it is used as a paint, you can expect to get 3 to 4 m2 per liter coverage, depending on how thick it is applied.
  • FlexsoTar ™ can be used to fill small cracks up to 3mm in depth.



For more detailed information please see our documents below.

Application Instructions:

Surface preparation:
Ensure the surface to be coated/sealed is dry and clean; remove any old, loose or flaked paint or rust, moss, lichen, old silicone sealer, etc. before application. Rust does not need to be pre-treated and FlexsoTar™ can be applied directly onto rusty surfaces although for best results it is recommended to use our, RUST MECHANIC™, rust converter before application of FlexsoTar™.

Mixing Instructions:
FlexsoTar™ is available in one (1) litre kits only. The product is supplied as a two pack system consisting of PART A (Epoxy/Bitumen co-polymer) and PART B (Hardener). Add PART B (entire content) to the can containing PART A (This can is big enough to hold the entire content of PART A and PART B). We however do recommend that you only mix the correct quantity required for your project. Multiple small batch mixes are easier to manage that one big mixed batch.

Final Finish:
FlexsoTar™ can be left as the final finish and does not require further painting. If it is used to repair leaky roofs or gutters we recommend a top coat with GilsoFlex™ Roof sealer and paint.

Clean up:
Clean hands with plenty of soap and water to remove any FlexsoTar™ before gelling occurs. It is recommended to use disposable gloves during application.



These documents contain important information about:

  • Material Safety Data
  • General Information
  • Application
  • Storage
  • Safe use
  • First Aid
  • Clean Up
  • Warranty
  • Available Packing Sizes
  • and more information

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Material Safety Data Sheet (MSDS)

Product Data Sheet (PDS)



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  • 4

    Posted by Wayne Eyles on 10th Mar 2024

    Used this product as a coating on a boat trailer. First attempt didn't go to plan as it is very thick (like thicker than treacle and then some) emailed Biosymph and found it can be thinned with isopropyl alcohol. Game changer there, excellent product. I have just ordered some more.

  • 5
    Great Product

    Posted by Joel on 2nd Jan 2023

    I used Flexotar to repair cracks in cement fibre board flooring on a balcony. It has worked really well and lasted well making the surface completely watertight.

  • 3

    Posted by Rowland Stanley on 17th Aug 2022

    My first impression is that it is too brittle. I expected a very flexible coal tar like material. My guess for corrosion protection, where vibration or cyclic deflection is present it would not be ideal. Or maybe even thermal expansion contraction.

  • 5

    Posted by John on 11th Apr 2022

    Excellent product - does exactly what it claims to do. Really great customer service. !!!!

  • 5
    Great for repairs & excellent customer service

    Posted by Lucia on 8th Mar 2022

    I came across BioSymph products when researching how to fix my flat roof extension. I had some rust issues and the flashing was failing allowing water in. During my first repair attempt, I ran out of usable product before I'd finished because the product set more quickly than expected. Pierre responded very promptly with great advice, revised instructions and a free replacement. I've now completed the repairs and no more leaks! Always happy to support NZ made products, and when it comes with excellent customer service it's even better.