Originally Posted by hellosailor
Minerat, what do you mean by a guide coat here?
I'm used to a guide coat being an undercoat, i.e. applied before the rest of coatings, so that when or if you see the guide coat showing through you know you've gone down too far. But if you're just polishing, not painting...you can't be applying a guide coat under the polish, can you? I'm obviously missing something from this picture.
Guide coat is a standard method used by painters everywhere for paint
prep. It is essentially day glow orange chalk in a solvent base that comes in a spray can. You lightly spray the whole surface you are going to sand with it, just dusting it so it looks like it has overspray all over it. It dries instantly and sands right off with no gumming. It is a "guide"coat because it shows very clearly where you have sanded and where you have not. This keeps you from missing any little hand sanding
spots around the edges, it prevents "holidays", and it will show up every little crack, divot, chip, or needed repair that may have been missed. It also prevents over sanding
, because you can see exactly when enough material has been removed. It's difficult to explain and often looks unnecessary to the uninitiated, but it only takes minutes with a few dollars worth of materials and it really does save time and effort while increasing quality of finish. The first time you use it you will never go back. I am religious about guide coat at many stages of sanding, it really can simplify fairing as well. No masking is needed, it wipes right off with a damp alchohol rag. If you are going to dry sand a hull
with DA film discs I feel it is really necessary to prevent over sanding. I usually sart with 800 film discs, I feel anything coarser leaves swirly scratches that are hard to get out, especially if done by hand. 800 on a DA sands much faster than 600 by hand, and leaves a much nicer finish. This helps you get to the desired level of perfection much faster and with much less sweat.