Patchy chimney render

[Zebra]

Needing a job to do during this enforced seclusion, I suddenly remembered the patchy render on the side of the chimney.
About five or six years ago I hacked off the cement render applied in the 60s, repaired and repointed, then rerendered. Here I used NHL2, finished off with a salad-cream-colour limewash.
It's patchy. Always has been. I think the top coat is too thin, and some of the scratch marks from the scratch coat are showing through. It's also stained, in parts it's gone orange.
Will coat after coat of limewash fix it? Bit loath to buy a bag of NHL2 just for this but I have plenty of putty, could I do another coat in that?

 

[malcolm]

My gable went a bit like that. I started putting limewash on quite soon after applying the render as it was the last job and the scaffolding was costing me money! I kept getting really bright green patches appearing in the limewash, and I guess that came from colouring in the render that hadn't fully set being pulled out with the water as it evaporated. Over a week and a few coats of limewash the problem stopped.

For the colouring I would just try limewashing again now everything has properly carbonated and water isn't racing out any more. I can't see any problem with the finish in the photos so I'm sure nobody else will once it's the same colour.

 

[Zebra]

You had green patches? Was the render supposed to be green? So it was the pigment in the limewash?
I did wonder if it could be soot staining. The chimney is probably 18th century, soft red bricks, was the main chimney used (unlined obvs) for cooking in the house, and was very sooty - I cleaned some of it off when I repointed but not all, and the chimney is now lined.
But soot staining wouldn't be orange.

 

[Feltwell]

I can't see the harm in putting more limewash on, to see if that does the trick

 

[malcolm]

You had green patches? Was the render supposed to be green? So it was the pigment in the limewash?
I did wonder if it could be soot staining. The chimney is probably 18th century, soft red bricks, was the main chimney used (unlined obvs) for cooking in the house, and was very sooty - I cleaned some of it off when I repointed but not all, and the chimney is now lined.
But soot staining wouldn't be orange.

Mine wasn't as bad as yours and I think it was caused by pigment from my home made rendering sand blend coming through. It stopped coming through after the render had a chance to dry for a few days. Photo here: http://www.the-salutation.co.uk/photos/stain-detail.jpg

I would try limewash on top and see what happens. I ended up using a slightly thicker limewash mix from putty than I had been recommended as I was covering dark sand render and it was November.

 

[Zebra]

I dunno. Looking more closely the top coat of plaster is quite cracked.
I have a tub of plaster mixed in June 2015 - still looks good - and a bit of an itchy trowel hand. Question is whether putty based render will stick to limewashed NHL2. Should do?

 

[tobydog]

Hi Zebra. Just a thought but is it worth considering a silicate masonry paint? Tougher and more resilient but still breathable. Several options including Earthborn. Might cover up a multitude of sins.

 

[Flyfisher]

I would try limewash on top and see what happens. I ended up using a slightly thicker limewash mix from putty than I had been recommended as I was covering dark sand render and it was November.

I would do the same, as a first step anyway. I’ve also mixed up varying thicknesses of limewash depending on the wall. We have some flint/chalk/rubble walls that had some fairly large cracks but a thickish limewash filled them in nicely. Might be worth a try, even if it doesn’t work I can’t see it doing any harm, unlike other possible solutions.

 

[steveb]

Silicate paint, although I adore it, is not a universal cure if the wall is still bleeding through. We did the front of the house in kiem royalan which is their premier silicate paint and if has still blown in a couple of places - which were, admittedly, salt stained from the damp still not being completely dried out. I guess the salt prevented the silicate from penetrating the lime and it just formed a skin on top, to be pushed off as the damp and salt continued it's journey out of the wall.

If I had lime and safe access, I'd be giving that a go first

 

[Zebra]

I'm afraid I've decided to go against everyone's advice, and have hacked off that top coat, used a devil float to key it, and will have a go at another top coat when the weather is warm enough to work in lime. Soon!!



But I'm interested in this idea of thick limewash. I had thought the mix ratio was fairly critical, and that it had to be thinly applied, in order for the lime to bond to the layers underneath and not just sit dusty on the top when dried. I hadn't realised you could simply mix it thicker to achieve greater coverage. What sort of mix ratios are we talking?

 

[malcolm]

Good plan! It's nice weather now to be outside rendering. Hopefully everything underneath wiill have dried and carbonated nicely and the stain won't come through again.

For my limewash I originally made it up from putty to instructions probably from here. The render was quite dark and I had stain coming through, and after 3 coats I started to feel that I would need 10, so added a bit more putty to the mix and finished it with another 2 coats. It was only 1.5 times or maybe 2 times from memory. That improved coverage a lot and it worked out OK and didn't dust, but the render was fresh and it was November so temperatures had dropped.

Of course when the scaffolders took the scaffold down they helpfully lent it against my fresh lime, so bits aren't perfect.

 

[a twig]

I went on texture, double creamish worked well for filling in cracks etc for me

 

[Zebra]

Well, I redid the top coat of the patchy render on the chimney. Four coats of limewash, all good.



Course, jobs beget jobs...next to the new bit, the rest of the house - the through-coloured render which supposedly never needs painting or limewashing (far right in the picture) - looks to me like it could do with a coat of limewash.........

 

[malcolm]

That looks beautiful!

The render next to the limewash looks like it is going a little green. Is that stuff coming through or your actual green stuff growing? Never had anything green trying to grow on my limewash and it'll look lovely.

 

[jsmac]

Excellent work. That looks fantastic. We're dealing with cement render so we'll never get anything like as nice a finish on our chimney, but this is something to aspire to on the parts of the house where we'll be patching and repairing the lime render.

 

[Zebra]

That looks beautiful!

The render next to the limewash looks like it is going a little green. Is that stuff coming through or your actual green stuff growing? Never had anything green trying to grow on my limewash and it'll look lovely.

Thanks malcolm The render on the upstairs is not stain coming through, it's definitely something on the surface, so unless it's just dirt.. but the downstairs, done in the same stuff is not like that. Why would the upstairs be worse? Dirt blowing on the wind....tried rubbing a bit and it's not coming off. You're right, you don't get mould on limewash, do you? I think I will then. Can't hurt, can it. My friend Giraffe has a tower (you'd think he wouldn't need one...) - one of the gable ends above a smaller pitched roof is a bit tricky to get to but I'll give it a go.

 

[TheForge]

You do get mould on limewash, especially once it’s carbonated and the pH drops.

 

[Zebra]

You do get mould on limewash, especially once it’s carbonated and the pH drops.

Aha! And when that happens, the solution is.........?

 

[malcolm]

My limewash has stayed bright for 5 years. Some other things have turned green but only in poorly ventilated areas. I'm at the bottom of a hill near a river and moss is common around here. I guess the solution is to limewash again if it goes green.

The new build next door has a pretend chimney made from plastic with brick facings. That's gone green even on the south side. My limewashed wall on the north side is still perfect (apart from shrinkage in the green oak frame and where the scaffolders rested their poles against the new lime). Green doesn't grow on a dry surface.

 

[Zebra]

Well, having decided to limewash the entire upper storey, now that it looks ropey next to the newly limewashed chimney, I made a start, then made up a big batch of limewash using my last decent bit of putty and........ I mixed in the wrong pigment! It's the wrong colour! :roll: Not flamingo pink or anything, just a paler yellow.
Questions are a) if I use it up as a base coat will it show through in time? b) I have some really old lumpy putty that went off a little bit in the bag, I think, before making it into putty, and I only kept it thinking it might be alright for limewash, will it? c) if I have to buy a new bag, will it have to mature for three months before I can finish the job?