1. Preparation is the key to a successful repair when using body fillers. Use a P80 – P180 grit sanding disc to remove paint in areas to be filled when repairing damage on metal surfaces and make completely sure surfaces are properly cleaned and degreased prior to filler application. Make sure all areas are clean and dry before applying filler. 
2. Body filler requires maximum adhesion to surfaces to give you a stronger and longer lasting repair.
3. Do not use paint thinners to clean panels and parts before the application of body fillers. The main problem with typical acrylic thinners is that they dry too fast. A good degreaser or silicone remover needs to stay wet on the surface long enough for floating contaminants to be picked up by a clean wipe. Acrylic thinners can melt dirt down. Even dirt that does not necessarily show signs of melting may remain and be softened enough to penetrate the surface of your filler repair.
4. Do not add more than the recommended percentage of BPO body filler hardener paste to filler. Adding more or extra hardener will not improve body filler performance, but simply decrease the working time before hardening occurs and make it more likely to bleach or discolour topcoat paint because of the increased levels of hardener in the mix. All TechniQ body fillers use a 2% hardener to 100% filler ratio, meaning that the size of a pea to a golf ball is where you need to be.
5. Do not over load or over apply body filler and attempt to fill very deep holes or dents in one single application. Body fillers have specific recommended thickness levels that should be followed for best results.
6. Allow body filler to fully harden before attempting to sand it. All TechniQ body fillers have a recommended hardening time, Do not try and sand body filler before it is properly hardened and cured, it may drag and ball up, potentially pulling it back from the surface. A better surface result will be achieved when sanding fully cured filler with the correct P grade of abrasive.

Are body fillers with aluminium particles only suitable for repairing aluminium parts?

No, aluminium filler can also be used on a number of materials, including iron, bare steel, galvanized steel and even fibreglass (GRP).

Can standard body fillers be used to repair alloy wheels?

No, do not use standard polyester body fillers to repair alloy wheels. These are not suitable and do not possess the same level of strength as fillers which contain aluminium particles which in turn create a high strength repair.

If a tin of filler has resin on the top surface when I open it, does it mean it is off or not useable?

No, if a tin of body filler has been standing, if could have liquid resin on top of the polyester filler, this is quite normal. Better that the product is wetter than dry, which means there is probably a lack of resin. Simply stir the product thoroughly with a mixing stick before mixing with BPO hardener and using as normal.

Can I use any type of body filler to get a fine surface finish before paint application? 

No, unfortunately most body fillers will require one or two applications before you can sand them to a fine enough level to paint over and be confident that there are minimal surface imperfections. TechniQ 31445 Super fine filler stopper or TechniQ 31500 Premium Glaze can be used as a second application layer of filler over any other TechniQ Filler and can be suitably sanded using finer abrasives such as a P400 or P500 to obtain a fine enough finish for paint application. For very small or minor damage such as stone chips or minor scratches, Premium Glaze is the perfect single stage filler for these applications.