If there is latent water behind the crack, I suppose a latex or maybe even a siliconized-latex could taking a while to set up. For silicon, the only time I've heard of it not setting was when it was an old tube, a bit past its prime. Even if the crack wasn't cleaned well, the silicon might lose it's grip, but it should still cure. Sorry I don't have better info for you, fortunately it's not something I've had to deal with. Mongo

Hi Oakrun, Yes, it is a daunting process. In fairness to all the homeowners here, (and respect to the pro deck builders who give so much help), we homeowners have pretty much one shot at the deck. In other words, we are not builders, and we are not Martha Stewart types, so we have to live with our decisions, warts and all. But on the other hand, we can afford to take a chance on something new. It will not wreck our livelyhood. I have nearly finished my 5/4" Ipe deck, 12' X 30'. After much thought, I went with the hidden fasteners - Tiger Claw TC-G http://www.deckfastener.com/products_tcg.asp They look great! Time will tell if they work. One difference between these clips and many of the old ones is that these are solid stainless, not fiberglass. To get these fasteners to bend would take quite a bit of force. I put one in a bench vise and hit it with a hammer. It didn't bend. One definite advantage of this system (assuming the boards don't lift) over face screwing, is the whole deck is "floating" on the pressure treated frame. The ipe boards are free to expand and contract slightly. In the long term, this may minimize end checking. Also, your air circulation under the deck seems optimal. (I have the same situation). I suspect that many installs of hidden fasteners don't have good air circulation. That may contribute to failure. Installation notes: 1) I used a biscuit joiner to slot the boards where the fasterers attach. It takes time, but I think it's a better job that having the boards slotted along the full length. 2) For butt joints, definitely ease the edges with an 1/8" radius. I think that's a John Hyatt trick. Looks great!! 3) I had to ease the backs of the ipe boards with a 1/4" radius router bit where the fastener attached. (the ipe comes with a 1/8" radius edge, not enough for correct installation) 4) most of the SS screws for this are # 8. If you are screwing into another hardwood (Ipe, Garapa, etc) I think the correct drill size is 9/64" . I broke a screw very early using the recommended 8/64" Here is a pic of a few weeks ago (I am doing most of this myself):

I have an ipe deck and handrail around a guard which had been down for over 10 years. I pressure wash it every couple of years as pollen and dust collect on it and being in the Pacific NW, the rain we get promotes a thin mossy growth which is slippery when wet. However the pressure washing does create a slightly rougher texture, different from when it was new and dry. And ipe being what it is, a tough as nails hardwood, the slivers created from pressure washing can be really sharp and painful. So yes, I am looking for an easy way to 'calm down' the surface of the ipe, but it sounds like it will be something that reoccurs when pressure washing. I too have heard of the orbital sander route as a cure and will give it shot soon.

its a misleading term self leveling :), you must use a spike roller to get results, did you scarify and prime the slab ? encapsulate mastic properly? ambient temps and improperly prepped slab, abnormal moisture readings etc..