You can get rid of the mildew by mixing bleach and water in a sprayer. Spray the mildew, let it sit for 20 minutes, then pressure was it off (but keep the pressure low enough not to damage your siding). Regarding the siding damage, the important thing for hardboard siding is to keep it sealed. So unless all the cut ends were primed when the siding was built (which is quite uncommon) you need to keep gaps caulked. As long as you can't poke your finger through the siding, you can cut any loose chips off, seal it with an oil base primer, and then at least two topcoats to match your house. You definitely don't want to leave the siding unsealed or it will rot on you. Hardboard siding is pretty much junk, but I have it on my house so have learned to deal with it.

The slight deformations on the edges could be from moister causing the wood to swell.

On using bleach to clean the mildew you have a choice of two types.

Oxidizing - Chlorine . The draw back is they can kill plants and grass. If using it. Cover flowers or other plants along the side of the house that it may come in contact with.

Oxidizing - Peroxide. Safer to use around plants and does not require you to cover them.
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Our cabin (rear view).. Ceder LP siding on sides and rear. Ceder shingles on the front.

Protection. Hydraulic oil applied with a Graco Paint sprayer. If you find a better wood protection product than hydraulic oil let me know. For I haven't in the past 40 years. This cabin was built and allowed to weather a full year before the oil was applied. And I will spray it again next year and add some RIT cloth dye to the oil to make it darker. $27 dollars for 5 gallon and still had some left over. Once the second coat is applied it will never had to be touched again,

The darker bloch is caused by the shadow of roof on the porch and is not in the wood.

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This post was edited by millworkman on Tue, Jul 15, 14 at 15:47