Finishing Greyfoam

Putty Priming It is advisable to rub a thin layer of putty on the prototype part before sanding  Fill up the microscopic cells on the greyfoam surface  Fill up the unevenness, holes, cracks and other surface defects which are difficult to spot  Act as a marker so that in subsequent sanding, it is easy to visualise which areas had been sanded Blow the model clean and dry before rubbing putty

Sanding Sandpaper is a form of paper where an abrasive material has been fixed to its surface; it is part of the "coated abrasives" family of abrasive products Used to remove small amounts of material from surfaces, either to make them smoother (painting and wood finishing), to remove a layer of material (e.g. old paint), or sometimes to make the surface rougher (e.g. as a preparation to gluing) Waterproof or wet/dry sandpapers use a resin bond and a waterproof backing Adapted from:

Grit Size Grit size refers to the size of the particles of abrading materials embedded in the sandpaper ISO 6344 is an international standard covering the materials sizes and tests regarding sandpaper and other similar coated abrasives. It has three parts:  ISO :1998: Coated abrasives, sizes and tests  ISO :1998: Macrogrit, P12 to P220  ISO :1998: Microgrit, P240 to P2500

Grit Designation ISO/FEPA Grit designationAverage particle diameter Material removal P mm P mm Sanding finishes P mm P mm Final sanding before painting P mm P mm P mm Sanding finishes between paint coats P µm P µm P40035 µm P µm P µm Finishes before buffing P µm P µm P µm Final sanding before buffing P µm P µm

Material removal Use #60 to #100 for material removal Use a rigid sanding block whenever possible Wrap the paper around half-round or round sanding-block to shape concave surfaces Dry or wet sand Use the hand to feel the surfaces Change sand-paper frequently

General Sanding Rules Face by face From large face to small From flat face to pronounce Keep small protrusion and fillets untouched

Putty Priming After the first putty priming and sanding, there are usually over-sand areas that reveal the greyfoam surface The area must be covered, otherwise it is not possible to achieve a even, glossy spray painting finish Lightly sand down the over-sand areas, rub putty on them and sand them Repeat the process until the entire greyfoam model is covered by putty

Spray Priming It is advisable to spray a thin base-coat on the foam model before sanding finishes  Give the part an even colour, reveal the unevenness, holes, cracks and other surface defects which are difficult to spot  Act as a marker so that in subsequent sanding, it is easy to visualise which areas had been sanded  Reveal contaminations such as uncured putty or ink on the part

Sanding finishes Change to #200 - #400 paper The base-coat will be removed gradually to reveal body material The target is to ‘replace’ previous coarse sandpaper strokes with finer strokes The progress will be fast at the beginning and will slow down when the contact surface area increase

Progressive Sanding A: Thoroughly sanded away all previous strokes B: Leave a trace of previous strokes C: Change sandpaper pre-maturely D: Use finish sanding to ratify unevenness of C A B C D