Stone sill bedding

[mcd700]

Ive just repointed the exterior of my 1880's school project. The window sills are cut sandstone and are bedded in a very weak sand slaked lime mix and are loose. Ive intentionally not sealed them in when pointing as im intending to lift them out completely and rebed them in lime. The inside walls will be paneled as original and the top line of the panel will be level to the internal window sill therefore I need my external sills to be leveled through. Question is do I simply bed my stone sill in lime as it was done originally or would you try to fit any form of damp proof under it?

Tia Mark

 

[Cubist]

My preference in similar circumstances would always be to use a plastic DPC membrane between the timber and any stone/masonry. That may be overkill depending on any other damp management approaches employed in the wall but I would be playing better safe than sorry particularly with the hidden faces and edges of the paneling.

 

[mcd700]

And turn the plastic dpc out under the exterior sill as you would with a concrete sill on a modern house?

 

[Cubist]

I can't think of any reason why not to. Unless anyone can point to good reasons not to?

 

[malcolm]

It's important to make sure there is a fall to the outside of the sills when you bed them back in. Also a good idea to clean out any drip edge with an angle grinder while they are out. I've done a few and just use lime mortar.

I'm not a fan of using any kind of plastic membrane and didn't use one on mine. The wood and the lime mortar are both breathable, and the lime mortar will dry to the outside. It would be a shame to deny the wood one opportunity to dry should some water get in.