Clapboard - painting not required

Not impregnated, no. There is prefinished product (as well as primed) but afaik it's only a factory-applied finish. Even then, of course, have to finish cut ends, etc.

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If the paint only lasted two years there was something wrong with the installation...or the house is on Venus. Hardie takes and holds paint beautifully if done correctly.

Who painted the house and what steps were taken?

While conditions in some areas are harsher than others, two years is a might short time for a properly applied appropriate quality paint on a properly prepared surface.

Is Hardie a strong non flexible, minimaly expanding siding with a cement base? With proper prep, knowing how and when to apply, using the right product, I could paint it not to peel for 20 years, or more. All colors fade, discolor and age, you would eventualy need a repaint. If it failed in 2 you need to strip and read up on painting procedures.