Why two completely opposite faces of concrete?

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Greenwood
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Why two completely opposite faces of concrete?

Post by Greenwood »

I'm wondering if the collected wisdom of the Craftsman's Guild can tell me why the exterior facing of my 110+ year old concrete block basement is in relatively good condition, while the interior facing of the same wall is crumbling and may be irreparable?
Thanks in advance!
Andrea
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Disintegrating interior facing
Disintegrating interior facing
_DSC0152.JPG (1.56 MiB) Viewed 364 times
Reasonably intact exterior facing
Reasonably intact exterior facing
_DSC0149.JPG (1.98 MiB) Viewed 364 times

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GibsonGM
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Re: Why two completely opposite faces of concrete?

Post by GibsonGM »

Something in the concrete? Some form of salt perhaps. Interior moisture level is higher and more constant...outside has a chance to dry. So, the interior crumbles first.

Many things can end up in the sand used to make the crete - that'd by my guess (naturally occurring salts; moisture activates them).

Greenwood
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Re: Why two completely opposite faces of concrete?

Post by Greenwood »

Just to clarify, the outside photo shows where it has been excavated to the footing (or lack thereof). Ground level was just below the top course of block (you can sort of see that this first course was stuccoed).
Last edited by Greenwood on Wed Jul 19, 2017 1:39 am, edited 1 time in total.

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Casey
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Re: Why two completely opposite faces of concrete?

Post by Casey »

Maybe because the outside was not painted but the inside was?
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GibsonGM
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Re: Why two completely opposite faces of concrete?

Post by GibsonGM »

Casey wrote:Maybe because the outside was not painted but the inside was?
Casey


That too...holding the moisture is bad enough, and if there are salts in the crete, even worse...

Greenwood
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Re: Why two completely opposite faces of concrete?

Post by Greenwood »

So, if painting is bad, then parging is worse?
The interior was parged. It too had bits that were bubbling and you can see in the bottom right hand corner that the parging is turning orange in colour.
The engineer has taken the problem home to think about for the night, and it may be that he thinks the blocks are too disintegrated to work with. However, if he thinks they will be ok, any recommendations on what to do with them now? I'm thinking something like:
- remove parging
- brush or scrape away all loose mortar and block
- re-point with lime cement
- possibly parge with lime as well?

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Re: Why two completely opposite faces of concrete?

Post by Kashka-Kat »

All I can say is Im interested in this thread - since my whole exterior up to the second floor is concrete block just like in your picture and right now Im struggling with what to do with it, because it is eroding on the outside due to 100 yrs of acid rain. Something has to be done - but what?

Also, a related problem - my basement is part sandstone and part brick that has been damaged due to moisture trapped between a stupid and unecessary wall the PO built of 2z4's and drywall.

Im thinking of a silicate paint on exterior and basement interior - supposed to be very breathable allowing water vapors to go in and out, but not water molecules. Keim mineral paint is one such paint- they have US reps on their website who are helpful .... and Limeworks US is another. Oherwise doesnt seem like its much available in the US - its more o f a European thing. -

Im thinking also if the parging is a soft mortar like whats between the rocks - then how can it be any more of a problem than the mortar between the rocks? Maybe it is, but I just cant get my head abuot why that would be. In my basement I thik the parging over sandstone is original since its the smae color/texture as the mortar between the joints.

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GibsonGM
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Re: Why two completely opposite faces of concrete?

Post by GibsonGM »

Parging isn't bad, to the best of my knowledge. Applying a cement-based material to cement...the bonding agent used nowadays may help resist moisture coming from the exterior, too (?). I've parged all sorts of things with no ill results..but haven't checked 100 yrs later ;)

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