fitting new slate windowsills

[JanJonWestWales]

hi, I am just about to fit new Welsh slate windowsills(custom made to 2.5 inch thickness !!!...beautiful)...anyway, I have been told to fit a "weather bar" along the back of the Sill, for the new wooden sash windows to sit onto.
Does anyone have any instructions on how to do this, what depth-width, should it be sealed?, what with? etc, and where to get weather bar??
I have assumed that Galvanised steel strip would do, but am seeking advice.
Ta!
J&J

 

[chuckey]

If you sit your nice new wooden window frame directly on the slate window cill, water will be drawn backwards under the wood by means of capillary action. If there is not enough slope on the cill or there is driving rain, there could be quite a little puddle trying to get under the frame. So what you want to do is to space the frame off the cill by, say ~1/2", and set this spacer back by say 1/2" and have a drip groove under the front of the frame. So now a sizeable puddle can exist on the cill without getting under the frame and water running down the front of the frame will drip off at the groove leaving the frame/spacer joint nice and dry.
You could use mortar, slate, horror of horrors- plastic, or some patent system for this spacer. It must have a 100% water tight seal against the cill or the water will find its way in.
Frank