Hi,
We cast a resin river table using Glass Cast 50 after watching the video on EasyComposites website, it all looked very easy but then the fun started when we tried to polish the resin. No matter what grit and polish we have used there is always marks on the resin. We have used up to 2500 wet and dry followed by NW1 recommended by Easy Composites and finally tried 3M 3 stage ultra polish. Even using a random orbital polisher the finish looks great from a distance but up close you can still see the swirls and small sanding marks. If we wipe over the resin with a piece of kitchen paper you can see the very fine scratches where it has been? If this is to be a table for someone it will be marked in days, does this sound right? I expected GC50 to be much harder than this and able to sustain a bit more than kitchen paper without marking? How do we get it as close to the original glossy cast with sanding and polishing? Should it be harder to scratch than this or do we need a tougher top coat?
Many thanks,Vix
P.S we used 2litres of resin to 1 litre hardner and its been 15days since we cast. 

Polishing is a bit of an art, it actually takes a lot of experience combined with the right tools and products to be able to compound scratches out completely.

Random orbital polishers are not excellent for this, they are too gentle to get rid of scratches completely. They do an ok job to about 95%, and they will take a long time to get there. Much quicker if you compound from 4000 grit.

Rotary polishers are better. More powerful to get the surface you want much quicker, and can easily polish from 1200 grit with the right combination of pads and compounds.

As for final hardness, resins can scratch much easier than you might expect, they aren't as hard as glass. In all likelihood, your scratches are probably coming from tiny bits of dust on the surface or the kitchen paper rather than the actual kitchen paper itself. It is quite difficult to avoid this, and realistically surfaces that see a lot of use will require compounding after awhile.

Hanaldo is right about it being a bit of an art.

However, being systematic and careful and you should be able to get good results.

If scratches are there still then there is something going wrong with your sanding or polishing.  If you can feel them, then chances are you are working through the grits too quickly (ie not removing all the scratches before you move up a grit), skipping a vital grit, or not being careful enough about cleanliness - ie you've caught a bit of coarse grit in the paper and its putting scratches into the resin.

Finer scratches can usually be solved with polishing technique.  NW1 is a modern diminishing abrasive, so the bits of grit start off coarse then break down finer the more you work it.  If you aren't too careful then using too much or getting bits on the edge of the pad can cause problems if they later on end up on the main part of the pad. This is because by that stage, the rest of the polish will be fine and you will be fine cutting the now shiny plastic.  Introducing the unused polish will scratch up the plastic as it is still coarse and not yet broken down.   So make sure you aren't using too much polish and use all the polish on the pad before moving on.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant