lime or not ?

[dandrew]

At the risk of being dragged over hot coals I'll post the following question:

1850-ish sandstone villa, frontage faces south
Persistent leaking from portico roof, this has been re-leaded in last 3 years (apparently capably done, but do not have the expertise to tell)
Internal paint finishes either side of the front door show water damage at cornice level. Hasten to add that they are modern emulsions on gypsum plaster - lime plaster hacked off by a 'developer' 5 or so years ago. Exterior stone above door was painted with Sandtex or some other masonary paint. This had deteriorated so I finished it off by hand stripping. Now the paint is off the exposed stone seems dry, though the pointing is defective in places. Will repoint the gaps but wonder whether lime is best in this situation. Whole house has been repointed at least twice with cement mortar (probably 1960's and then again by developer), and all the lime plaster stripped off and replaced with gypsum. In this situation I have no inclination to re-do all of the pointing and then re-plaster the whole of the house, therefore will it really make any difference if I do this small bit of re-pointing with lime when the house has since stopped breathing ? I want to cure the leaking portico and the re-pointing is just one job that may help, though I have my doubts.
What do you folks think ?

David

 

[FamilyWiggs]

The purists will say that even a couple of feet of lime pointing is better than none... and will save someone after you the trouble!

It may also be that the cement pointing has damaged the stonework or trapped water ingressing elsewhere and channelled it to your problem area. I would suggest trying to identify the source of your leak, and fixing that. If you repoint in cement, you may find that you haven't solved the problem.

However if you really are talking a very few small gaps compared to a whole building coated in cement, then I can't see it being a hanging offence.... except for your "developer".

 

[DaveBrigg]

Sorry if this sounds like a silly question, but are you sure that the portico roof still leaks? If the only evidence is the water mark on the paint, could this be showing through from the earlier incident? Alternatively, if the stone and brickwork was heavily waterlogged three years ago, with Sandtex providing a waterproof barrier on the outside, and the gypsum and modern emulsion doing a similar job on the inside, it may be that the wall still cannot dry out. Removing the sandtex sounds like a good idea, and this may help to cure the problem. If the roof is no longer leaking, and you don't want to replaster inside, a tin of stain blocking paint might be the answer.
As for repointing with lime, aside from any breathability issues, this will be much kinder to the stonework.

 

[dandrew]

DaveBrigg raises a valid point, however there is still water getting in (or maybe it never really went away) as the internal paint has deteriorated since the roof was re-leaded. Had a roofer look at the leadwork this morning and he says it is fine. He did point out some stonework whose face has become badly eroded, which has the effect of allowing rainwater to pool at the base of a line of carved architectural stone moulding, and the height of the moulding seems to correspond with the high point of the paint damage internally. Amusingly he suggested some waterproof silicone spray to seal the stone, which I shall give a wide berth to. However the erosion of the stone is such that something needs to be done, does anyone know if it possible to repair stone by facing up the eroded surface and then fixing some replacment stone over the front of it - almost like a tile ?
[Even while I'm writing this it seems cock-eyed, but the alternative is removing the whole stone and replacing it which seems like taking a sledge hammer to crack at nut.]