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mortar without cement or lime  RSS feed

 
J. Tabordiy
Posts: 64
Location: north-west coast of iberian peninsula
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Hi,

we've been in our adventure timberframing a tiny house to add on top of a ruin, now we finally return to the recovering of that ruin (last year we started, then gave up on that part and started timber as it was going to rain...

last year mortar looks fine, even with pouring rain on top of it, my quest for opinion iis about making mortar without bringing new materials into to the spot (no lime nor cement or clean sand or pure clay),

our mix till now is about
3-4 parts sand (from the river stream nearby, so it's sand with biological particals - leaves, roots, a bit of soil, etc)
2-3 parts of old mortar from the ruin it self (a mix of bigger sand, clay and possible lime from the plaster of the walll)
3 parts clay soil (it's not pure clay, we collect it from a nearby forest spot, so it also includes part of leaves and other organic matter)
2-3 parts of water

we try to sieve it all and it really looks and feel nice and hard, the parts we did last year are sound and solid... but i still didn't find much info on the "organic composting matter" inside this mortar... what are the risks and any opinions on that?

another question is about holes on the wall of the ruin, probably mice, lizards and other animals opened them, we try as hard as possible to fill them up but i guess it's impossible to say there is no holes inside of the wall, what should be the approach on those cases? the wall is solid, 50cm wide....
 
Jay C. White Cloud
Posts: 2413
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Hi J.T.,

Good to hear you are still hard at work!!

"Cobb Mortars" in general are greatly overlooked accepted by a few like yourself and "Historic Preservation Artisan" that are lucky enough to be around really old structures that still have it in them. The can be very enduring, especially if not exposed to direct water degradation.

Organic matter should be avoided at all cost unless servicing a function within the matrix like, small fibers in animal dung, "rice soup" or botanical mucilage additives, etc. I would encourage doing a better job of "grading" and "sifting" the materials to go into your mortar mix.

The more enduring and stronger "pointing mixes" are going to be "lime based" then "lime-cobb" then what you have. On a scale of one to ten...cobb mortar is a 1 to 4 at best for durability compared to lime be a solid 8-10. Same goes for compression strength. Now what you can do, and was done is to use what you have and then later "rack out" the structures joints and "repoint" with a more enduring lime pointing at a later date with time and finances allow.

I would note that the old mortar as an "additive" is typically only done to achieve a "color matching" and is only meant to replace the "sand" component. It adds little to the strength of the wall if it is an "addition" to sand and not a "replacement" for it. As a "replacement" element there may still be enough uncarbonated lime to add some additional strengthening to the mix. Old lime mortars used in "core work" inside the mass of the wall or in some old plasters/renders can remain uncarbonated for centuries, if not longer, and some never reach full strength in these protected locations. This is one reasons "cobb mortars" have been used there as they are well protected from the elements...(other than digging little pawns.) "Leaching" out of these or cobb mortars are a concern if overly exposed to the elements.

another question is about holes on the wall of the ruin, probably mice, lizards and other animals opened them, we try as hard as possible to fill them up but i guess it's impossible to say there is no holes inside of the wall, what should be the approach on those cases? the wall is solid, 50cm wide....


If this is being turned back into a home...all holes...should be addressed for "occupancy" (and by what if possible??) and well filled and pointed. All stone work should be solid and not moving at all or repairs need to be made to make so. Loose stone is a serious issue on such foundations and must not be tolerated. Restoration stone work is perhaps some of the most challenging forms there are because we are "working in" and not down from the top. In some more chronic cases the wall must be "deconstructed" and rebuilt to achieve an adequate repair.

Regards,

j


 
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