please save a novice from drowning!

[charlie-ia]

our house has "ruled ashlar" concrete render which is fairly firmly attatched to the sandstone walls which are mortared with lime. i think the render is from around 1916.
my plan is to repair and fill using lime, and leave the rest alone.

am i right in thinking that i should fill the render cracks with a hard lime to try to match the strength of the render?
or should i use something softer, to match the strength of the mortar?
some of the cracks are settlement cracks that go into the wall.
should i use 2 different mixes?
how do i test the hardness of the original materials?

if i matched to the cement would i use a strongly hydraulic lime?
is this what a "natural cement" is?

any tips on matching what i need to use to match an original mortar?
i heard that crumbling some up in a jar with water was good, but i cant remeber if i was supposed to add vinegar, and what all the different layers show. and i think if you left it a certain amount of time it told you about the clay content. oh, i wish i'd paid more attention!

im still not sure wether or not to take off a layer of render around the bottom of the wall. would this provide much benefit to letting the wall breathe?

theres a window that has been blocked up, but cracks in the render show where it is, and have allowed water through to rot the floor of the bedroom.
if i just fill the cracks is that all i need to do? they dont look very big from the outside.

would you try to remove cement patches that were not exactly attatched to the wall, or would you leave it be if it wasnt in danger of falling off?

 

[chuckey]

I would test the whole surface with a hammer to see how much of it is actually attached. Just the "hollowness" of the sound. Mark any "hollow" spots with chalk and when you are finished make a judgement about how much is adhering properly and how much is just standing close to the wall! If the loose spots are as you thought, I reckon a patch job would be in order, if more then a third appears dodgy then its best that it all comes off
For your cracks that you think(know) are letting in water, I would "V" them out, make good the bottom of the crack with cement slurry with a water proofing additive. This should then give you your desired waterproofing, then fill the remainder with a weak cement mortar. If you use a lime mortar, its "whiteness" will show as a scar for decades.
My cottage had raised pointing and about 20% of it was missing. I thought it looked hideous and no way could I match it. So I hacked it all off, only about 5% was actually adhering properly!
Frank

 

[charlie-ia]

thanks chuckey, was beginning to get paranoid that id bored everyone to death with my questions.

are cement and waterproofing the right way to go because the cement is already waterproof? i keep hearing say no to cement.would i be able to dye the mortar somehow? im sure i heard someone muttering about bootpolish and soot somewhere...

we were going to paint the house white after we had done the pointing, but similar houses appear to be grey. quite a miserable colour when the sky is grey too. would it be out of character to paint ruled ashlar?

 

[DaveBrigg]

thanks chuckey, was beginning to get paranoid that id bored everyone to death with my questions.

Not at all. I have a similar problem I think, with an original lime render which has been patched with cement. I've learnt from your question, thanks.

 

[Nemesis]

You may of course end up with a damp non-breathing building.

 

[charlie-ia]

You may of course end up with a damp non-breathing building.

this is what im worried about. am i on the right track with the thinking?
ive never done cement or lime before, have done much reading, been on a lime course and now im feeling completely out of my depth!

thanks for your advice chuckey, especially about marking it out, thats a really good idea.
what do you mean by a weak cement mortar?
and whats your theory aiming at? i thought the best thing to do was match what you patch. surely matching concrete i would use a hard mix? or is it because the wall is likely to move more in the damaged areas, so it had better be able to move properly?

the walls are of rubblestone, so i guess i shouldnt dig too deeply when cutting out a v. how deep do i need to go? just like i was going to do normal repointing?

 

[NT]

> if more then a third appears dodgy then its best that it all comes off

Removing hard adhering cement could do a fair bit of damage to the wall, I would be in no rush to do that.

A waterproof cement coat is about the opposite of whats wanted. I think the evaporation vs absorption equilibirum is explained on the damp faq (which has now gotten sticky as well as damp).

Adding more cement to sandstone is a good way to do more damage too.

IRL whatever you use it wont match the original colour-wise. The house can be painted with lime, or other.

IOW I'd knock off anything thats loose and use lime.


NT

 

[charlie-ia]

What kinda lime?

 

[charlie-ia]

please?

 

[Nemesis]

If it was me I'd use normal non-hydraulic putty.

And I'd be inclined to limewash the lot. You'll need to add something to make it stick of course.

Limewash will have the advantage of filling in small cracks which might appear in the places where the cement joins the lime. You might get the same with any repair of course.

It's the old Irish saying isn't it - if I was you I wouldn't start from here...

But you have to.

First thing I'd do is knock off anything you can easily, and play it by ear after that.

Make sure that the settlement cracks are dealt with.

 

[charlie-ia]

If it was me I'd use normal non-hydraulic putty.

because it breathes best?

Make sure that the settlement cracks are dealt with.

youve frightened me now!
we were going to re bed any stones thats loose, and fill in the gaps (its random rubble) using lime, then repoint & watch for further movement. the surveyor didnt seem to think the cracks were too scarey.

is that what you mean by "dealt with"?
i found this page, even though its about cement. http://www.forcon.com/F92.htm

are there any good previous posts about settlement? i get too many irellevent pages when i search

 

[Nemesis]

Yes, that's what I would do to the cracks, if the surveyor thought they were OK, and yes as it's the most breathable.

It's also easy to make yourself from bagged hydrate.

It's really all a question of trial and error I feel.

But at least lime is more reversible than cement.

 

[NT]

Ditto, basic non-hydraulic bagged lime is fine.

I painted crete with limewash and it stuck no problem, no linseed or anything, just the basic lime & water.


NT