Adhesive and sealant troubleshooting tips from Dr. Dave Dunn.

Question:What are your recommendations for threadlocking adhesives for titanium, preferably without an activator? What types and curing times are available?

Answer:You can use all types of anaerobic threadlockers on titanium: low strength, medium strength or high strength. Bear in mind, however, that the cure time of anaerobic adhesives is very much affected by the type of metal being used.

Some metals, such as copper and iron, are called “active” metals because they actually promote the curing reaction, while other metals, such as aluminum and, unfortunately, titanium, are an inactive surface for anaerobic adhesives. Therefore, cure times will be longer with these metals compared to a steel or iron surface. Full cure may take several days, but the joints should cure fully. Surface activators will, of course, speed up the curing, but since you prefer not to use them, try heating the assembled parts to 100°C for two hours to get full cure.

Question:We want to attach thin sheets of PVC to canvas fabric. Can you guide us regarding which kind of adhesive to use?

Answer:Flexible PVC can sometimes cause problems with adhesive bonding because of the different types of plasticizers used. (PVC plastic is basically a hard, brittle polymer and plasticizers are used to soften it.) Adhesives sometimes give an initially strong bond that breaks down with time because of migration of the plasticizer into the bond line.

I would recommend trying a PVC solvent cement for your PVC-to-canvas application. Neoprene contact adhesives can also be used and are available in spray versions. You may have to try adhesives from more than one supplier to ensure compatibility with your particular flexible PVC.