Adhesive bonding of insulation boards
Through this column we have talked a lot about the requirements for inverted roofs, so, Dear Reader, you would be forgiven for thinking that QI only supply insulation board for inverted roof applications: an understandable misconception. Our focus on inverted roof applications has been, and will continue to be, a regular feature of this column clarifying the correct design, function and assembly of an inverted roof; but we don’t want you all thinking we are a one trick pony, so we thought we would take a look at warm roof construction.
BS 8217:2005 Reinforced bitumen membranes for roofing. Code of practice covers various bond strengths depending upon substrate type and whether controlled partial bond or full bond. Since this British Standard was published there have been some significant changes in the adhesive market, and we certainly find most of our warm roof insulation customers using Moisture Curing Polyurethanes (MCP). The benefits of MCP technology are many and include low weight, minimal equipment, no hot works, no significant odours and bond strengths of up to 10 kN/m² compared to 3.6 kN/m² for bitumen. However, there are factors that the contractor needs to be aware of.
MCP’s generally come in 2 types, ‘free pour’ and ‘controlled rise’
Free Pour: typically, a rectangular 6.5 kg tin covering up to 60m2. To use remove the lid and puncture a hole in the bottom. The liquid adhesive is applied a continuous 10mm to 20mm bead in an ‘S’ pattern at 150m or 300mm centres. The bead diameter increases as the MCP liquid reacts with the moisture in the air. A simple process but there are some considerations:
1. The insulation board should not be larger than 2.88m².
2. Insulation should be applied within 5 minutes. Full cure takes up to 6 hours.
3. Consistent application is key; a thicker bead risks the adhesive not fully curing in the centre and outgassing CO2 over time, lifting the insulation boards.
4. If applying a carrier layer over the insulation on small roof areas/balconies, bead thickness is critical and applying extra adhesive is to be avoided, see 3 above.
5. Disposal requires the can to be empty except for a skin of adhesive, or to be left for the contents to fully cure.
Controlled Rise: a pressured containers that contain the adhesive already foamed. A hose and ‘wand’ are attached to the container. The tap on the container is opened, adhesive comes out in a 19mm to 25mm bead applied in an ‘S’ pattern at 300mm centres. Coverage is up to 100m². One advantage of Controlled Rise MCP’s is they can also be used on vertical substrates. Application is again simple but also with its considerations:
1. The insulation board should not be larger than 2.88m²
2. Insulation should be applied within 5 mins. Full cure takes 20 to 40 mins.
3. Wands and hoses need cleaning or replacing.
4. Any residual material at end of use should be sprayed into a cardboard box and left 24 hours to cure, it is then non-hazardous waste.
5. Cylinders need to be de-pressurised for disposal, which is simply done by following the instructions. After 1 week the cylinder is metal waste.
Next month’s QI by QI – Compliance & Accreditation, do they matter?