How do I make minor repairs to stucco?

[michael]

Following my earlier posting on Roman cement, can anybody suggest the best material for repairing minor cracks in 19th century Stucco? I can only guess from its age (I think mine is about 1880) that it comprises of artificial cement (post 1860) rather than natural cement (pre 1860). I’m pretty sure that lime products wouldn’t be appropriate for repairs here as I think these facades were designed not only to be decorative with sharp lines i.e. imitation block work etc but also to be water tight.

 

[Moo]

Oh, come on PPukers - someone must have some useful advice.

 

[Flyfisher]

Didn't Nigel have some stucco to patch up?

Edit: just found this, though haven't read it all: http://www.periodproperty.co.uk/forum/viewtopic.php?p=129689

 

[c r]

Hi

I do remember somewhere a good page about stucco methods, possibly it was through one of Nemesis' old links, if you were to do a search...BUt i can't quite remember/find it, sorry

I sympathise as last year worked on a house of similar age with stucco and external window architrave/moulding features that needed repairing, both of which seemed to be formed of thick coarse lime mix (to build the basic profile) and then a thin hard finishing screed of fine cement- a cement that I gathered was different in nature to that available today. Think it will be very hard to source a similar 'Roman' type cement as was likely used originally- at least I should say I couldnt find it anywhere last year

Stucco was formed in three ways as I understand:

1. Lime& sand- hydraulic mix (generally think used on older houses than yours, before the cements you've described were developed)
2. Lime& sand as above with a thin 'natural/Roman' cement finishing coat
3. Lime& sand, and then linseed oil&sand mix for finishing coat (far less common I think in general this method was)

I'm not sure that a solid Roman cement stucco was often used originally, probably on cost grounds as much as anything else. But I'm no expert on this... Do you know what the full depth of your stucco is formed of?

It does depend on how wide the cracks are, but in my opinion you could consider repairing them with 'burnt sand mastic', essentially that is linseed oil and dry fine sand mix. As long as the crack is not damp, this mix should bond well and be durable, but still have a small degree of flexibility, which a modern cement repair will certainly not. The downside is that it cannot be painted until it is dry& cured, which unfortunately will take a quite a while.

Perhaps one of the stronger hydraulic limes with a finer sand could be suitable. Unless you are sure the stucco is solid cement the whole way through then a modern cement repair would be a prime area for a crack to (re)form in future years

 

[chuckey]

How wide are the cracks? if they are only hairline, then you will need a very small particle fluid to get good penetration. Or they will need opening up, say "V"ing out to a width and depth of at lest 1/4" to get the new material into the crack and allow it to be flushed off. The other thing to consider is the final surface texture, too many times I have seen cracks repaired and then the top of the repair floated off, leaving a nice shiny outline of the crack about 2" wide under the coats of paint. I think the finish must be done before the mix has cured and do it with a soft paint brush and loads of water. If you have used sharp sand you will get small pebbles exposed which might or might not match the existing surface.
Frank

 

[c r]

whilst searching for info on another topic, I just stumbled upon the link i couldn't find/remember before on stucco, an interesting read:

http://www3.westminster.gov.uk/spgs/publications/Stucco.pdf


(although for reference the 1:2:9 cement-lime-sand 'repair mix' quoted in above document is now considered not good practice)

 

[Nigel Watts]

For some reason I missed this thread. See the link in my more recent, and very similar, thread. I too am contemplating this issue just now.