when to sand

Hey guys. Sorry to post another thread with a question but I have one last question.

I noticed that sometimes when I paint a model (after primer), that there are little spots of dust or whatever the makes a itty bitty bump in the paint.

My question is, can I just sand the area of the bump and not the whole car. I noticed that it will be less dull then the rest of the model. Will there be a problem when I clear it after this? The dust particles usually end up on the hood, the roof, and the trunk.

As a rule I sand the whole primed surface, simply because the primer usually can't be laid down as a very smooth surface, and if you want to have a smooth paint surface you have to start with a smooth primed surface first of all.

Sand off the dust particles with as high a grade of paper as possible. It will naturally be dull compared to the rest of the painted surface unless you take further steps and start to polish out those spots. Clear coat only when the final paint layer is without blemish and smooth. Clear coat can and will cover any dull spots to a degree. One way I check is to place the model under running water. It gives a good example of how the clear coat will look on the paint. There is no need to sand the whole car, unless there are defects on the entire body. Like jano mentioned, make sure your primer layer is as smooth as possible too.

I somewhat understand what you are saying. I sand the primer when I feel bumps. Its when I lay down coats of paint is when I notice new dust particles in the paint. Should I sand in between coats to cut down on the amount of dust particles?

I somewhat understand what you are saying. I sand the primer when I feel bumps. Its when I lay down coats of paint is when I notice new dust particles in the paint. Should I sand in between coats to cut down on the amount of dust particles?

Yes you should, otherwise they do not go away.

Should I sand in between coats to cut down on the amount of dust particles?

Definitely. I gently sand most/all of the body between every coat. It eliminates flaws from dust/debris, and it eliminates texture.

You need to leave enough time after a coat of paint to allow it to harden enough to sand it safely- typically an hour or so if your coats aren't heavy.

You can sand between coats to remove imperfections. I usually use well worn 2000 grit wet and dry, used wet for this purpose. How soon you can sand depends on the type of paint you are using. Zero base coats for example, take minutes to dry before they can be sanded, some other paints take hours..... Depends on the paint type..??? What paint are you using..???
You can also make sure your spraying area is as clean as possible. Wipe it down with a damp cloth before you spray to minimize surface dust. Also strain and filter the paint before use to remove any foreign particles that may be in it, another cause of bits in the finish. You can also use a tack rag on the surface of the model before you spray and in between coats to remove any foreign particles that may or may not be there. Leaving the model in a dust free place whilst it dries will also minimize particles falling into the surface of your fresh paint. If you have no where that you consider dust free, hang the model upside down whilst it dries, then nothing can fall onto the painted surface. In general cleanliness whilst you spray will pay dividends in the long term. Sure you can sand out the particles, but cleanliness may prevent them in the first place.

I see. I am using tamiya spray paints for models. So, in between each coat I will try to sand down the particles with some 2000 grit then. Sounds good. OH and for the guy who recommended the sharpie inside the window trims, thanks. That does work. thanks alot guys, I really appreciate it.