It would be too costly for me to have primer sent from the US to Japan. The military bases do not sell paint or primer (hazmat issues). Benjamin Moore Japan primer is way beyond my price range and the Japanese normally don’t use primer (they use wallpaper or cloth to cover drywall). Someone told me that if I mix about 1 cup of plaster in a gallon of water base paint it will be just as good as any primer on the market. Is this true? What do you think?
I never heard of mixing plaster with paint but I have mixed drywall mud with paint without any problems, don't mix in too much. You can also just use a good flat acrylic paint for priming drywall and drywall mud. This will work as a primer for plaster after a 30 day cure time. This isn't as good as a good PVA primer but works in a pinch. Also any exterior acrylic primer will work.
After submitting the question I realized that plaster is the incorrect term. What I should have typed was drywall joint compound (mud).
I have two types of mud a base coat which is a heavier grit and a finish (top coat), which is a much finer grit. I also have a 20 kilo bag of gypsum used to mark the white lines on a baseball or football field.
Is the drywall compound you have a powder or thick 'mud'? Either way might not matter but the best to use for your purpose is regular all purpose joint compound, not the fast drying setting type. Don't use the marking powder.
I have made texture paint by adding all purpose compound to acrylic primers and don't think it will hurt a good paint. The biggest consideration is how much to add. For a regular interior flat paint I would add no more that 1/4 by volume. Sheened paints, satin, can have a little more. The problem is when the paint/mud mixture dries the mud part wants to shrink and get hard. This will cause the paint to crack if there is too much mud added. Although this could be a neat look, you need to experiment to find the right ratio.
For your purpose you don't need to add much. As stated earlier, my answer, to just prime the surface use a good flat paint. To add a little texture and get a very even finish adding the joint compound is a good idea. It will give an even seal and look to a smooth wall. This is exactly like using USG First Coat, a product used by drywallers to produce a very even smooth wall.
Another consideration is application. If rolling you need to use a good back rolling technique. Use a 3/8 roller cover, lambs wool is best but any good cover will work. Normally you would go up-down-up-down with the roller. With this mixture this will leave visible lines as the texture produced will be up-down-up-down. You need to quickly roll a narrow section, top to bottom, then go back and roll from the top down only. This will lay the roller texture in the same direction.