Sided my own house in 2007-2008 with Hardi and Miatec trim. My house is a modern cape, so I went with a very traditional 5/4 x 4 trim detail with window sills and a kicker at the top. The sills were made from laminated azek and the kicker is azek as well, mounted at a 15 degree angle at the top. There are kerf cuts in the kicker and under the sill as well to drop water. Instead of cutting the frame at a 15 degree angle, I left it square and make a 15 deg dado into the kicker so it actual sat over the 5/4. I then placed aluminum flashing over the kicker and wrapped the tips down the side, and caulked it in. Also should mention that the frames were pre made in the shop, painted on all sides, and glued and pocket screwed together. I figured that using azek on the surfaces that are more horizontal would be better than going all Miratec.
Anyhow, I was washing the siding over the weekend, and that's holding up great, but while if was working, I saw a strange shadow and took a second look. The top corners of the frame are swelling up, somewhere between and 1/8 and 3/16 of an inch. They are swelling starting at the outside corners and traveled in about 8-10 inches from each side. I had to investigate, so out came the moisture meter first. Stab it into the trim at the outside corner, boom 46%. move in a few inches, mid 20's, move in a little more, 8-9%. So obviously the water is getting in at the ends and traveling inward. I'm reasonably confident that everything is flashed and the water isn't coming from above, but at the same time its really bugging me to thing that the small joint between the kicker and the head trim allowed enough water in for it to have this affect, especially considering the fact that the kicker was actually glued/adhered to the head with dynaflex. Had the aluminum flange been just a little bit larger it would have covered this completely.
So out comes the scraper and putty knife. Once I got a corner up on the paint, it basically peeled back in one large piece, taking the factory primer with it, and some material. The surface was noticeable wet and was very soft. Gentle scraping was just peeling layers of miratec off, and sanding it just made the surface fuzz like crazy. So I'm basically looking at an area about 2" x 8" on each side of the window casing that is basically significantly damaged and I'm sure as it dries will form a noticeable rut.
I guess the lesson and most concerning part is that without a rain screen and air behind the miratec, any small gap could eventually result in the trim just dissolving. I think the issue is that the water gets in, and because their is paint on the face, the material can't dry, and it can't dry in due to the tyvek, tar paper, etc behind it. The swelling starts small and just turns the material more and more into a sponge.
So now I'm faced with repair or replace. To remedy the joint, its pretty easy to slip an additional piece of trim coil under the existing flashing to cover the seam, but not sure how to treat the damaged area. First thing is I'm gonna leave it to dry out in the sun and keep it covered in the rain. Thinking about treating it like rotted wood and just using abatron epoxy, first drill it a bunch with a small bit and inject the liquid hardner to make it more solid, and then top it with the epoxy. Its either than or take it off and replace it with PVC. Part of me just wants to replace it because I feel like repair could mean just revisiting it in another few years. The good news is I used screws to hold it on and it should come out without too much of a fight.
Not very happy with Miratec right now, not sure I would use it in situations where air can't get behind it now. I certainly took a lot of care in manufacturing and painting these very carefully to give the product the best chance it could have. Of 22 windows on the house, its only the south side of the house that shows signs of this, probably due to no overhangs, and almost all day sun.
I'll get some pics posted as well.