Sbs &App;Membranes For Flat Roof Waterproofing:10 Major Mistakes

 

We use SBS and APP membranes in Greece for many decades. I will describe hereunder the most important mistakes Greek installers make during their application:

 

 1) Use of improper, inadequate quality and weight. The main products used are APP products protected with granules, 4kg/m2 , cold bending point 0oC. We urge them to use at least 4,5kg/m2 products with a minimum cold-bending point of -5oC.

 

We try to use more SBS than APP at least in north Greece where the weather is quite colder than the southern part.

 

 2) Flashings are not worked properly. We recommend only aluminium covered membranes with exceptional adhesion and high in solids primers. We recommend stripes of 25cm×1m, never longer. We choose SBS membranes of at least 4,5kg/m2 weight and a cold bending temperature of at least -15oC.

 

 3) The use of thixotropic bitumen emulsions loaded with fillers as primers is extensive. This is not a proper adhesion layer!

 

 4) The use of aerators without a proper diffusion layer. This renders them totally ineffective!

 

5) Total bonding of APP – SBS membranes even on surfaces of 1000m2 or more! This induces undue stresses at the overlaps. A method of semi-independence – from the many available – should be adopted.

 

 6) The erroneous use of alumimium covered SBS or oxidized – bitumen membranes. These products need a minimum slope of 3%. Stagnant water could induce severe corrosion problems particularly at the seaside front.What’s more the reflective insulation properties of these products have been severely misinterpreted and overvalued.

 

 7) There are many unnecessary elevations at the overlaps.The reason is that head-to-tail overlaps are not finished properly(there are cuttings to be made at the edges). These hinder the proper water drainage and contribute to the formation of stagnant water and hydrostatic pressure.

 

 8) Rigorous use of spatulas or trowels can severely harm the membrane and especially its reinforcement.This must be avoided.

 

 9) Head – to – tail overlaps are poorly executed due to the existing granules. This procedure demands careful but persistent torching to make granules sink in the asphaltic mass.

 

 10) Overheating the APP – SBS membranes is common practice. But this weakens membranes and sometimes induces irreversible damage.

 

 Chris Strogilis

 

 Civ. Eng. – MBA – DipM

 

 http://maconwaterproofing.blogspot.com