Exterior limewash?

[Keithj]

I'm back again, looking for advice as usual!

It's been a hectic time, with major repairs to a Grade 1 listed church to watch. It's coming on well, but I've hit an "interesting" question.

When we did the major repairs on our Grade II listed Tudor-era Ag Lab Dwelling a couple of years ago, I was told very firmly that I should plan on a coat of limewash a year, best delivered as three coats at once, at three-yearly intervals. This we are still planning to do.

So I asked how many coats of limewash will go on the new lime where the repairs have been done to the outside of the church, and to the older lime that hasn't been disturbed (and is a mix of light buff, dark grey, and algae green). The answer given was "Limewash? Why on earth would you do that?"

The church's lime render is over the top of ragstone, or timber, or brick (and probably more) but NOT over laths. Does that make a difference, and does it need limewashing? (There are areas, especially on the tower, which are not lime rendered).

Does my house, which is lime on chestnut laths, need limewashing?

 

[Nigel Watts]

Lime wash is chemically pretty much the same as lime render. Its purpose is principally aesthetic rather than protective. I believe limewash can help consolidate the surface of stone or render which is a little flaky, but if the substrate is sound and looks OK I don't see why one would need to apply anything.

 

[Keithj]

The way it was explained to me was that external limewash is "sacrificial" - rainwater being slightly acidic during thunderstorms (nitrous acid formed by the lightning). I was told that the acid slowly dissolves away the lime, which is replaced by the fresh limewash. That was from the techie person in the team that did our house repairs, and came with the "one coat a year" recommendation. That may have been designed to assure them of ongoing work limewashing our house, I suppose.

This excellent article from Cornish Lime talks about the process of painting, and about why the likes of Beeck paint or another silica-based one may be preferable for durability reasons - but it doesn't say why or if regular painting is necessary.

The Diocesan Advisory Committee seems to be slightly geared towards NOT limewashing the church, because that removes the patina of age from 12th Century buildings. It is rather more against using anything other than limewash, for historical reasons. The cost of limewashing the building is high (mostly to do with scaffolding and the like), so if we do it at all we want it to be a more durable paint such as Beeck or Keim. If we don't need to do it, we'll brush off the algae and leave it at that.

I was surprised at the DAC's view that limewashing the outside is not necessary. We're spending a lot of money repairing timbers, roof tiles, stonework, and lime render properly (they've been bodged a couple of times in living memory). We want to make this set of repairs last for a very long time.

 

[Moo]

I can't remember if anyone on the forum has used one of these silica-based paints.
The article from Cornish Lime is interesting, but I trust PPUKers' experiences much more than information on a commercial website.