Hard-Shelling can be problematic as far as (secondary bond) adhesion is concerned. If we look microscopically at the top of the hard-shelled part, we will see peaks and valleys. These valleys would not be easily sanded without great effort and the possibility exists of sanding into the foam part in many areas. There's no way to adequately remove blush and impurities in these valleys without removing the thin layer of micro applied. The problem with hard-shelling exists at the surface level of the micro applied.
Questions to ponder: Even if one were to vacuum bag the micro slurried part, to create a uniformed hard-shelled part, how would one sand the part adequately to get adhesion across the surface? Could you actually use peel ply to prepare the surface properly for the secondary bonding? Does a problem exist with "secondary bonding" to the hard-shelled part, in which adhesion is not taking place uniformly across the part? If I hard-shell, will the microscopic imperfections of the bond effect me down the road, after years of use and differing temperatures and altitudes my plane will be subjected to? Best regards, Larry A. Capps Naperville, IL "The quickest way to double your money is to fold it in half and put it back in your pocket." -----Original Message----- The term Hard-Shelling (circa 1980) - is the practice of covering foam with micro slurry, letting it cure, sanding it and then applying a fiberglass layup over the top. (not recommended) ..................................................... can you say a bit more here. This is precisely the mistake I would make (working alone). Is this not similar to a second lay-up (over a cured lay-up) with whatever precautions would apply, like peel ply or sanding? In this particular case I would have thought that the adhesion of the subsequent cloth /resin to the layer of cured micro, however low, would be substantially better that then mechanic strength of the core material. i.e. - no matter how it was done, the bond (and shallow penetration zone) between micro and foam would always be the weakest link.
