Exterior Stucco: Natural Cement vs Natural Hydraulic Lime
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daveT



Joined: 11 Jan 2014
Posts: 5
Location: Westchester, NY

PostPosted: Sat Jan 11, 2014 9:56 pm    Post subject: Exterior Stucco: Natural Cement vs Natural Hydraulic Lime Reply with quote

Hoping to get some advice on what to do with the exterior of a 100 year old house in Westchester County, NY.

House is constructed of Natco hollow clay tiles (blocks) covered with a few coats of either natural cement or Portland cement (or something else)-- ending in an exterior stucco finish.

Over the last 50 years many local contractors have come through patching and replacing entire areas with mixes of Portland cement. During my 20 year ownership, I've seen that Portland mixes look fine initially, but always crack after a few years. Then water gets behind them, and the Portland layer falls off.

As an experiment, I had an experienced contractor try one wall with Virginia Lime Works 150 (natural hydraulic lime). Maybe it was too late in the season (cold), but it became sandy and disintegrated.

Contacted Edison Coatings in Connecticut, they recommended Rosendale Natural Cement (14S plus RL-4 latex high permeability additive). This held up well (2 years so far) no cracks. Appears to be more flexible than Portland mixes. But this Rosendale Natural Cement discolors and becomes blotchy after rain or humid weather. The blotches fade when it dries out, but not completely.

I was going to try Everkote (a potassium silicate, low viscosity tinted coating sold by Edison) to darken the stucco to hide the moisture blotching.

Anyone know the details of Natural Cement vs Natural Hydraulic Lime (vs Portland) and what works for exterior stucco in the NorthEast? I have many exterior walls to reconstruct. What should I be using?
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Don Wagstaff



Joined: 09 Sep 2010
Posts: 102

PostPosted: Sun Feb 02, 2014 8:55 am    Post subject: Reply with quote

I guess the lime you used was either to old or yes, it froze while there was still water in there. Neither inherent problems that cannon be simply dealt with.

Greetings,

Don Wagstaff
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daveT



Joined: 11 Jan 2014
Posts: 5
Location: Westchester, NY

PostPosted: Mon Feb 03, 2014 9:55 am    Post subject: exterior stucco in Westchester, NY Reply with quote

What would your first choice be--
natural cement or hydraulic lime. Would you agree that the original was probably natural cement in this area year 1911? Any advantage of hydraulic lime?
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Don Wagstaff



Joined: 09 Sep 2010
Posts: 102

PostPosted: Mon Feb 03, 2014 2:20 pm    Post subject: Reply with quote

Hello,

So, when I could work out what went wrong the first time with the lime or otherwise get a satisfactory test section, that is what I would use. That said I'm not familiar with the materials or context as you have described, these clay blocks for example, and that could alter things. If there was a reason for natural cement to be on there, beyond average rain exposure or something like that, I would still use lime and just add in some puzzolan. You would essentially have then natural cement.

One thing that comes to mind is it might be the case that these clay blocks tend to draw water from the lime to rapidly. This could certainly cause it to fail as you describe. I have used alum as a coating on extra absorbent surfaces to slow this moisture exchange. But then you will also have to keep the surface of the lime moist and above all protected from the wind for about 4 days. The puzzolan in there will shorten this initial setting-up period.

Regards,

Don Wagstaff
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daveT



Joined: 11 Jan 2014
Posts: 5
Location: Westchester, NY

PostPosted: Mon Feb 03, 2014 4:16 pm    Post subject: Reply with quote

OK.

Thank you.
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Don Wagstaff



Joined: 09 Sep 2010
Posts: 102

PostPosted: Fri Feb 07, 2014 3:17 am    Post subject: Reply with quote

Pleasure
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