I'm new to this group, and totally fascinated by the posts I've read. I am a professional plasterer with a strong background in earthen materials and I have recently absolutely fallen in love with lime. I am a tech geek with a good understanding of different types of limes, pozzolans and pigments.

But recently I felt very much in over my head. I am doing an interior application of a polished lime finish on a two coat application. First coat 1 : 2.5 lime to plaster sand, second coat 1 : 1 lime to marbledust. I get wonderful color saturations and a readily sealed polished surface. I won't call it tadelakt because it's not made with Morrocan lime, but that is the type of finish for which I am aiming.

Here's the problem: the base coat is spalling off the walls. I was advised by the lime manufacturer (NHL product) to install cement board (Durarock), wet it back to saturation, and apply the base coat directly over it. It adhered well for over a month, but now it is slowly detaching. My best guess is a poor chemical bond to begin with, now exacerbated by daily temperature fluctuations between 90-50 degrees F along the exterior walls. Also, the Durarock is hung 16" OC but not blocked, and still has slight movement.

So now what? I'm looking at demolishing the first installation and starting over. One contractor has suggested expanded metal mesh over the Durarock for a mechanical bond. Another recommends Plaster Weld. I am reluctantly considering adding some portland cement to the base coat, going on the like bonding to like theory. Temperature stress will continue to be an issue in the space; in addition to the two exterior walls, two walls are adjacent to a sauna.

Are there any other lime plaster contractors out there? What experiences have you had with lime renders over Duraroack? Some phots of ILia and other fresco artists show a sort of freestanding "canvas"; I wonder if this is a cement board product?

Thanks for any advice you can offer.
Cheers,
Kirsten