To Strip or not to Strip?

[bobbyaitken]

I recon that the render on my house is a mix of lime in some areas and concrete in others.
On reflection I think the major areas are concrete.
It's hard to know how to paint it!
One again I have to thank you for your time and interest in my problems.

 

[MdB]

I'm not sure about the fizzing test. Cement (I believe) is also alkaline, so I don't know how differently the two materials would behave in acid.

Well I gave it a go to see.

Old lime mortar + vinegar fizzes
New lime mortar + vinegar fizzes
New dry cement mixture + vinegar does not fizz
Old cement + vinegar fizzes.

So its not a useful test.

 

[Penners]

I think the major areas are concrete.

If that's the case, and the current exterior paint isn't beathable, and you haven't got any damp problems, then I shouldn't lose any sleep about what you paint it with. Even if you use a modern alkyd resin paint, I don't think you'll be making the situation any worse.

The alternative is to hack off all the exterior rendering and start again with lime.

 

[Penners]

its not a useful test.

It may not be immediately useful in this case, MdB, but it's very interesting nonetheless.

Can any passing chemist tell me why old cement would appear to be alkaline, while new is not?

 

[Jill]

As a passing chemist, the fizz is caused by the carbon dioxide being given off from the substance. The difference in the cements "fizzing" may be due to the different types of cement. Some cements are hydrated and have undergone a chemical process to drive off the carbon dioxide. Also over time old cement may absorb Carbon dioxide from the atmosphere where the new stuff might not have not had long enough to do so or possibly because of the process it has been through in manufacture may not have the capability of absorbing it. Lime mortar hardens by absorbing carbon dioxide, so will give it off when put into the acid (in your case the vinegar). Hope this helps a bit.

 

[Becka]

back to F&B again briefly.. when I first moved in here (about 3 1/2 years back) F&B was advised as being breathable, so I sloshed their estate emulsion liberally over my various types of plaster.. now this seems less certain I'm starting to get concerned, especially seeing as in the more naturally damp rooms (bathroom and kitchen) it's now to got a crackle glaze effect and look annoyingly plasticy.. more so on gypsum plaster than the lime admittedly.. I've been wondering what to do about this, another coat of the same would not seem sensible, but I can't see it being removable, is it likely to be doing any harm? and any suggestions as to what might work better (over the top?) when i come to redecorate?

 

[jocelyn plummer]

Phone up Rose of jericho. Their technical advice and products are second to none.

It is a pity about F & B, they ain't what they used to be.

 

[bobbyaitken]

I have made an appointment to see a surveyor who specializes in ancient buildings.
He is going to start by taking render samples from various parts of the walls for analysis.
I will keep you all posted!
Once again I would like to thank all of you for your help with our problem. Annie (my wife) and I are very mindful that this lovely building has been standing for 400 years and will be for another 400.
We are keen to look after it to the best of our ability during our brief watch.