Painting - Rule of thumb for primer?

What is the rule of thumb for when to use primer? We are beginning a major painting project this weekend, but I'm not really sure when primer is necessary.

what is the project?

I use primer anytime indoors.

I never prime unless it is called for. why would you prime if you are repainting a bedroom flat paint]the same color?

We prime in these cases:
Fairly different color change
Adhesion issues
System change (oil to latex, latex to oil)
There are other reasons, but these are the most common.

1. In the living room, drywall will be painted a flat bungalow gold (tan color). Is primer necessary here?

2. In the kitchen, we are using a flat cabin red to paint the drywall (been advised to use grey tinted primer here).

3. The rest of the house is a beige semi-gloss (I think) that will be painted the bungalow gold. Primer?

4. One bedroom, beige again, will be painted flat navy blue. Primer?

THANKS!

If the drywall is new [unpainted] by all means prime. Otherwise I would not. You were told correctly to prime with grey tint on the kitch, it will cut down on the number of coats to get a good finish.

I would recommend sanding the walls with a sanding pole and 100 grit paper then wash the walls with a sponge and mild cleaner to remove the dust and dirt.Also strain your paint and mix all gallons into a bigger bucket to get even color mix.Prep is more than half the work but results will be better in the end.Excellence is its own reward.

We are painting our kitchen red and were given a slightly lighter shade of red for the tint on our primer, but I am reading here that it should be gray - would I run into problems - like having to paint innumerable coats?

Thanks!

Gray would be better. You might have to do an extra coat with the primer you have unless it is real close and even then you might have to depending on the quality of paint. You should have started a new thread maybe the moderator will do it for you. What brand of paint do you have.

You also want to prime when you have done a lot of repairs. Otherwise spot prime the repairs.
TroupB - I'd also prime the br that is to be painted navy blue. Navy blue is a deep color and has a lot of pigment. Use the gray primer.
Covering the semi-gloss depends on how much sheen is left. Do use the sanding pole. You don't need to rub hard. Just a quick pass should suffice.

The reason for a gray primer isn't to help with the final color. White doesn't work as well. It all has to do with light and how the paint interacts with the light. Gray just seems to do a better job. I've had success with a deep beige (as opposed to a pastel beige).

Stormdog and TroupB - a couple key items to help with the dark colors: Buy good paint. This is definitely a time where $30/gallon paint is cheaper than $12/gallon paint. Buy quality roller sleeves and brushes.