Limewash on Cement

[MD]

Now that I have the lime/chalk plastering cracked (er, I mean without cracks), I'm moving on to limewashing!

I want to limewash the outside of the house. Half of the infill panels are new lime render, but the other half are still old cement covered with a horrible plastic type paint which refuses to budge. I'm told that I may have trouble getting the limewash to stick to the cement panels.

Do you think PVA or some such product would enable the limewash to stick? I know PVA is not breathable, but it would only be going on the cement panels. I'm not even sure if you can use PVA externally.

Any ideas?

 

[biffvernon]

I would guess the limewash might stick so I would give it a go. I've just been cleaning some splashed limewash off some ceramic and glass. It was stuck on jolly firmly.

 

[Nemesis]

Try linseed oil as an additive - Gervase reckons it helps it stick.

 

[MD]

Thanks for the suggestions. I spoke to the lime plasterer and he felt that linseed oil seemed to stop subsequent coats sticking to each other, as it makes it slightly waterproof.

 

[NT]

As suggested, try it and see first, a plastic paint doesnt sound a prime candidate but I've had limewash stick to things its often said it wont before.

PVA turns to mush in water.


NT

 

[Penners]

PVA turns to mush in water.

Eh? PVA is water soluble. It just gets thinner the more water you add.

 

[MD]

Yes, I can see the problem with PVA - don't really have my thinking cap on there!

I've done a bit of a test section today on the cement to see how it goes.
Someone suggested using something called Beeck Fixative as a primer.
I found some sites that sell it and it seems very expensive so I'm hoping the limewash will stick on its own.

 

[Moo]

Waterproof wood glue seems, to my uneducated eye, very similar to PVA. If it is, you could use it diluted..... (?)

 

[Nemesis]

It's the same stuff, and dilutes in water.

 

[Moo]

But once it's set it isn't water soluble, or so I've been led to believe.

 

[worms]

I've been limewashing the outside of the house this summer and it has covered a range of different surfaces with no problem. All I did was mix up some old home-made lime putty with water and add a splash of linseed oil. The batches varied (some thicker than others) but all have gone on fine. The only problem areas I have are a couple of damp stones that always seem to remain as damp patches on the wall and these were early parts where I had carefully removed all the old plastic paint and cement! The walls that received less preparation actually look better!

 

[nickc]

I have the same problem as MD with infill panels being a mix of cement and lime and mostly covered in "weathershield" type paint. I don't want to add yet more of this paint but stripping is out of the question so I'll be interested to know how you get on applying limewash over it.

A further point regarding the external timber beams. These are covered in a mix of tar and black paint (?some gloss). Can I simply limewash over these as well or should I try to scrape off the worst of the tar (which is almost like a burnt covering)? Again, stripping wuld be a huge undertaking. I'm keen to get some lime on them as water finds its way in through some of the oak framing.

Nick

 

[NT]

PVA turns to mush in water.

Eh? PVA is water soluble. It just gets thinner the more water you add.

Once set it resists wetting for a short while, so PVA paints are washable, but outdoors it will be wet long enough to turn to mush.


NT

 

[Penners]

Ah - clarification!

Yes, if set PVA is exposed to water for long enough it becomes a rather sludgy mess.

 

[DaveBrigg]

The limewash I splashed on the pvc kitchen wastepipe is still there, despite several periods of heavy rain.

 

[MD]

Just thought I'd post a qucik update. The limewash I made from a tub of Anglia Lime's putty seems to be sticking to the cement reasonably well - first coat looked a lot lighter on cement than on lime, but after two coats the difference is very small.

I have been wondering if I should add something to the final coat to help to shed water. Linseed oil had been suggested to me, but my lime plaster recommeded not to. He said that it was very difficult to mix in well and you could end up with shiny patches if it is not well mixed. He says he doesn't add anything and has never had any problems.

I've also seen tallow and casein suggested. My understanding of tallow is that it is just animal fat, so maybe the mixing problem you get with linseed oil would apply here too?

Does anyone have any experience of mixing their own limewash? Would you add anything or just do as my lime plasterer suggests and leave well alone? Comments and opinions would be grately apreciated.

 

[Gervase]

I use linseed oil regularly - half a cup in a plastic bin-full of limewash should do it, and mix it up with one of those basket-on-a-stick mixers you can buy for an electric drill,
Tallow limewash is more weather resistant still, but is trickier to make. Ideally you make it when the lime is slaked so the heat melts the tallow, but you can make it by mixing boiling water with lime putty and grating the tallow into it.

 

[electricianid]

There is a product called pozi-lime which is limewash mixed with, I think PVA and linseed oil (possibly more) which is suitable for colouring cement etc, it is made by a company in Sudbury 5 mins from Anglia lime. The proprieter of the company also manafactures a range of paints/limewashes for a variety of substrates including uPVC. I don't use anyone else.

 

[MD]

Gervase, so you haven't experienced any mixing problems? Does it alter the appearance at all? How big a "bin" are we talking about for half a cup of linseed oil?

Electrianid, Can you remember the name of the company? I must admit though, the price of these ready-made limwashes seem so expensive for what is just lime putty and water.

 

[Gervase]

I use a household plastic dustbin into which I put one 20-litre tub of lime putty and about 30 litres of water. The linseed oil doesn't alter the appearance in any way, but does impart rather a nice smell.