paint testing

Excel Building Surveying Ltd have recently been commissioned to complete paint adhesion testing to external window frames at a listed building in Surrey. The testing was requested following the cyclical re-decoration using Farrow and Ball water-based paint over a Zinser (solvent based) primer. Several defects had been noted by the residents and confirmation of adhesion was requested as one measure of suitability. Pull-off testing was completed using Elcometer 510 Model T automatic adhesion test equipment with 20mm diameter sacrificial steel dollies adhered using common superglue (cyanoacrylate based). The pull rate was selected as 1mPa/s. The surface of the dolly and paint were very lightly abraded prior to adhesion to provide a key. The dollies were held in position for a few minutes (until adhesion occurred) then left to cure for approximately 90 minutes during which time the other dollies were being set. The surveyor elected not to cut around the dollies in order to gain the maximum strength result. Cross-hatch testing was completed at each pull test position in order to provide an instant idea of the quality class and thereby degree of consistency. The cross-hatch test comprises cutting through the paint using an 8 bladed cutter in 2 directions resulting in 49no 1mm squares. An adhesive tape with specific adhesion capacity is then fixed down over the squares, left for 1 or 2 minutes before being peeled off in a controlled manner (i.e. not ripped off). Results were variable ranging from 0.2 to 5.53N/mm² by pull off test. The number of paint layers was not consistent however we did not determine the layers by microscopy and therefore we did not accurately determine the adhesive/ cohesive failure code. Results varied from ISO class 1 (ASTM class 4B) to ISO class 5 (ASTM class 0B) by cross hatch test and it was therefore reported that inconsistencies with preparation were probably the major fault. We have also completed lead paint sampling and surveys at numerous sites and have expertise in the analysis of paint build-up and lead content which is completed at our partner laboratory. It is of course a legal requirement to confirm the presence of lead (The Control of Lead at Work Regulations 2002) prior to undertaking refurbishment or demolition work.