lime/limewash on waterproofer

[MrT]

I'm about to add either a limewash or lime plaster to a stone wall which has previously been painted with a black waterproofer
and white emulsion, I can't get all of the black stuff off. I'm looking at using either hydraulic lime NHL 3.5, limewash or Stuart Furby's Lime Earth Paint from the green shop. Any advise on how to get any of these products to stick would be welcome. The only
suggestion so far is PVA which I want to avoid if possible.

 

[middi]

If you cannot get all the impermeable previously applied paints etc.. from the walls there is little point in applying limewashes, lime renders or other breatheable products on top of it.

It may look nice but they will not function as intended. Any additional "sealing" barrier such as PVA or similar which you may use as a bonding agent will make matters worse, eventually.

The objective with breatheable materials is to have an uninterrupted flow of "trickling air" so it can gradually evaporate any excess moisture from all direction.

 

[MdB]

Would I be correct in saying that if say 50% of the black tar stuff has been removed then breathability would be significantly better so still worth doing?

 

[middi]

In theory yes, but due to the uneven impermeable undersurfaces itwould be in order to assume that any breatheable top coats will eventually react differently in the different sections where the breathing mechanism is impaired.

 

[Ian Bond]

Just wondering if the wall in question has been treated in the past due to penetrating damp - perhaps a cellar area, or a external wall with earth banked against it? Or even a gable subject to driving rain?

If you did get all the gunk off and lime plaster / limewash you'd have to accept an uneven appearance as damp patches appeared and dried in various places.

But perhaps the earlier problem has been cured/reduced by removing earth from against walls, french drains, gutter repairs, repointing etc etc?

 

[middi]

The conundrum with " damp" is :

1) The damp has always been there from original costruction. ( bad choise of site or constuction perhaps)

2) If a perfectly good building to start with, "something" has happened in the interim period for it to show signs of damp.
Finding that "something" is the million dollar question. This usually leads to extensive knowledge as to how old buildings were built and how they behave.

 

[MrT]

Thanks for all the replies.

The tar black stuff is only on the bottom few course of brick and stones. The wall is now internal as an extension is now installed.
The reason for opting lime is based on its green credentials in comparison to cement, I could use a gypsum plaster I suppose.
breathable is less of and issue as both sides of the wall are internal. No damp I'm aware of, often common to paint the bottom of
old stone wall with a tar paint locally so I assume it was just tradition.

Prefer to use lime if possible but can use a 1:1:6 lime/cement/sand on PVA if the lime will not work.

 

[Ian Bond]

We did have a discussion a while back on the old forum, about a similar project MrT...

http://periodproperty.co.uk/forum/viewtopic.php?f=1&t=8506&p=94490&hilit=thoroseal#p94490

Inwood was attempting to lime render and decorate over a tanked wall. The product was Thoroseal, which is sold by Mike Wye - they may be able to offer some further advice...

http://www.mikewye.co.uk/mikeprices.htm#vandex

It's down under lime products, waterproof slurry. Of course, this is not something they recommend using other than in exceptional circumstances, but it may be similar to what someone put on your wall in the past.

There just may be a way of getting lime render to stick for aesthetic, if not breathability purposes given the right preparation.