Render question

[paulb33]

With your kind help, I've established that the brickwork mortar contains lime. So, I'm now checking out the 1900 roughcast render.

One big lump has fallen off. See below. It shows a couple of coats of render on (corroded) metal mesh with outer roughcast layer. This has been lime washed and then painted with modern exterior paint.

I'd long assumed the render was cement-based. But, I've dropped a few lumps into vinegar and they're fizzing, reducing in size. Question: will the lumps disappear if its pure lime? If its a lime/cement mix, will cement residue be left behind?

Perhaps this test is too crude to draw definitive conclusions? Its pretty critical because it determines how I approach re-rendering and painting the gables. If its non-breathable cement render, then I'll re-render in cement and cover with non-breathing paint. If its a breathable lime or lime-mix then I'll have to go the breathable lime/lime-wash route.

Thanks for all your continued help.

Paul

 

[Zebra]

No, the lumps won't disappear if it's lime with no cement. Left will be the aggregate - the sand in the mix. I don't know whether a lime mortar which contains no cement would disintegrate in acid, as the lime dissolves. I don't know, in fact, whether lime does dissolve completely in acid. I can find out if you like. I have here some lumps of old lime mortar with no cement; I have some pure lime putty, and, wait, do I have some vinegar? Ah, only a tiny bit. Well here goes.....

I didn't used to do this kind of thing on a Saturday evening......

 

[Zebra]

Well, that was unhelpful I'm afraid. A lump of 300-year old lime mortar fizzed a bit, but didn't change shape at all. A lump of dried up putty didn't fizz at all. I wonder why.
In any case, I don't think this will help you. As you say, perhaps the test is too crude. In any case, the vinegar test will only tell you whether there is lime present in the mix, not whether there is cement present in the mix. You could have a combination of the two, which is quite common, in which the lime is added to a cement mortar only to improve workability, and in every other way it behaves exactly as a cement mortar.
It is possible to send a sample away for analysis to find out exactly what it in it. I know Ty-Mawr in Wales (www.lime.org) offer this service and others probably do as well. (Googling "lime mortar analysis" seems to come up with a few.) There is a charge, but I don't think it's much, if in your case the question is really important.

 

[paulb33]

Thanks a million for your input, Zebra. Funnily enough, my samples are still fizzing several hours later. I'm minded to speculate because there's trace lime within a mainly cement substrate. as you say, I should send it away. Which I will.

Regardless, I think we can conclude two things: 1. we need more sophisticated analysis. 2. we should get out more on a Saturday night.

:roll:

 

[LadyArowana]

I didn't used to do this kind of thing on a Saturday evening......

I know, isn't it amazing how much more fun we all have since joining PPUK :lol:

 

[paulb33]

I just read that cement itself might yield a mild fizzing in acid…..

http://www.linkedin.com/groups/Lime-cement-render-how-do-2740091.S.165026640

 

[LadyArowana]

I just read that cement itself might yield a mild fizzing in acid…..

http://www.linkedin.com/groups/Lime-cement-render-how-do-2740091.S.165026640

I thought that was only if you used something like a higher concentration of hydrochloric acid, not vinegar. Time to send Ms Zebra back to the laboratory.............

 

[paulb33]

that makes sense m'lady