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Old 11-24-2009, 04:29 PM   #1
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painting old cob walls

I've recently bought a17c cob cottage. took off all the 1920's wall paper found the plaster to be in reasonable condition. the plaster is a grey blue colour. cleaned it with sugar soap, then painted the room with farrow and ball emulsion. however after the first coat dried i noticed some areas had very slight craking and they were still apparent even after a second coat. the cracks are a sort of marbled effect. any ideas how to get rid of them.

can i paint further walls with pva, to stop this from happening again. can i use pva on cab walls



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Old 11-24-2009, 05:22 PM   #2
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I think you are going to have to explain you're terminology,I have no idea what you are talking about. Are you in England?

cob cottage?
sugar soap?
emulsion ? oil?
cab walls?


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Old 11-25-2009, 03:25 PM   #3
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Wow. If the cottage is really that old it has held up well. Cob construction I know about is primarily sand, earth and straw? I guess the equivalent I know better in the US would be adobe but nothing I have ever worked on goes as far back as what you have. Hope you can find some experts. Just curious, how old do you think the plaster is and how has it managed to stick this long?

I would just be guessing as to what to use to fix the surface and prime this situation so will leave it alone. Do post pictures at some point.

And to mirror Chris' question? Where are you? The terminology is not US. And we only have a few sections of the country with 17th Century structures and most of them are not occupied or privately owned.

Last edited by user1007; 11-25-2009 at 03:29 PM.
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Old 11-25-2009, 03:54 PM   #4
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Sugar soap from Wikipedia: a cleaning material, commonly composed of sodium carbonate, sodium phosphate, and sometimes sodium silicate as an abrasive; other chemicals might be added to modify the performance or preserve the product. The dry powder looks like table sugar, which gives it its name. The term is used mainly in Commonwealth countries. The solution is alkaline and its uses include cleaning paintwork in preparation for repainting.
The similar compound trisodium phosphate is sometimes described as sugar soap in the USA..
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Old 11-25-2009, 04:43 PM   #5
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There are quite a few Cob cottages in the West of England
where I live. In recent years they have become very sought after, especially from wealthy Londoners as second homes.
Emulsion is a water based paint used for walls and ceilings, but Lime wash should really be used on old lime plastered buildings to allow them to breathe.
Sugar soap is used by most pro painters to clean up the walls and woodwork before painting.
Here is an example of a Cob cottage.
painting old cob walls-1127726_8153017c.jpg
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Old 11-26-2009, 07:22 AM   #6
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Originally Posted by bob22 View Post
trisodium phosphate is sometimes described as sugar soap in the USA..
Think I have it now as far as what people use to clean these delicate houses. Same as we use here. I love calling it sugar soap and will see if I can get a few more bucks in my next bid demanding it be used---when the idiot competing against me demands to use something potentially caustic like TSP?

Given the age, you should ask for a core sample that goes all the way through one of your cottage walls to get an honest read on the Ph levels. Scraping a tiny area of both the exterior and interior surface would be a good idea to see what chemistry you have.

As suggested, it is probably a limed surface. How do you feel about replacing it with one to match but minus the wallpaper? I've worked on only one interior limed surface, and it was not in the US, so ask for additional advice.


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