grouting inside rubble wall -not urgent any more

[charlie-ia]

what mix do we need / how much sand do we use?
is the grit sand we've been using for mortar ok, or do we need something really fine?
im assuming pouring it down a funnel/hosepipe is ok?
do we just keep pouring until it stops and the jobs done, or will we have to do it several times (over what period?)
any other useful hints?
thankyou

 

[Gervase]

You should be OK with the sand you're using, although seived sand of 3mm and under is better - use a mix of 1:2 NHL5 to sand and make it into a slurry. Start near the bottom and use two holes near each other and at the same level - tube in one for the grout, and when it comes out the other, plug them both and move upwards.
You can also use a pointing gun if the area you're grouting is small and you don't mind having to unclog the nozzle every few goes.

 

[NT]

You definitely need a hydraulic mix, dont want a ropey wall full of a ton of unset lime!

Why 2:1 rather than 3:1? It costs more, is weaker and would crack up on setting.

Any sand works. I'm wondering why your advisor hasnt said what materials to use though.


NT

 

[charlie-ia]

thanks for the quick reply - would you believe im up a mountain in the rain in ireland talking to you on a mobile telephone?!

the nearest (only) supplier of hydraulic lime we can find is right at the other side of the country. can we add wood ash (which we have plenty of) or brick dust (we'd have to make this with a hammer i think)? if so, how much?

if you recommend nhl5, would it be so bad to use cement?

how important is it to have two holes? id really like to avoid making any more holes as the wall appears to be loose fill. the wall we are mending is where smoke percolates through from the chimney, so there is some kind of exit hole(s).

dont want a ropey wall full of a ton of unset lime!

"well, lets give it a go with what we've got, cant do much harm, surely" :shock: THANKS!

I'm wondering why your advisor hasnt said what materials to use though.

erm,... you are my advisors.(mostly!)

 

[NT]

thanks for the quick reply - would you believe im up a mountain in the rain in ireland talking to you on a mobile telephone?!

Think I'd believe anything of you Charlie

the nearest (only) supplier of hydraulic lime we can find is right at the other side of the country. can we add wood ash (which we have plenty of) or brick dust (we'd have to make this with a hammer i think)? if so, how much?

if you recommend nhl5, would it be so bad to use cement?

This seems to explain it quite well:
http://www.buildingconservation.com/articles/pozzo/pozzo.htm

Also bear in mind with cement that either you use 1:1 lime to cement, in which case it can do damage later, or you use less cement, in which case premature failure is a risk. Yes low levels of cement is a pozzolan, but it comes with some risk of failure. How much risk I've little idea.

I'm wondering why your advisor hasnt said what materials to use though.

erm,... you are my advisors.(mostly!)

Well, only you will know if grouting is the solution then. Going round plugging all the cracks worked for me in a similar situation (but brick), though it took a few goes to get every leak stopped. Grouting would certainly be a more robust option, but will use a lot of material and reduce insulation value.


NT

 

[Gervase]

I recommend 2:1 based on experience of a less lime-rich mix not flowing down the tubes well enough. I can't say I've had any problems with the grout cracking; the voids being filled are not individually huge (In my experience you don't get many open spaces larger than an orange), and the main purpose of grouting is to consolidate what's in there and 'join the spaces together' as it were.
I wouln't recommend cement as the grouting would then be stronger than the stonework, and that is a recipe for disaster. I'm of the opinion that any material used for bonding should be weaker than the stuff it's holding together.
If you can't get NHL5 then go for a pozzolan and hydrated lime, or even NHL3 - they'll all carbonate eventually in a wall (though it make take a couple of months for less hydraulic limes to get up to strength, and they won't be as strong as an NHL5. The '5' representing the strength in terms of withstanding a force of five Newtons in crush tests. Cement can resist up to 70!)

 

[chuckey]

What are you groating? (and why?) The man on my lime coures, had pump groated loose cob walls, 2 holes fill the bottom one, when it dribbles out of the top one, plug bottom one fill the next one up. This is to ensure that the voids is filled to overflowing each time and not just dribbling in at the top filling hole and appearing out of a lower hole. St Astier reccomend using hydraulic (which they make!) and water only (see back of their bag). Any sand will impede the flow of the lime.
Frank

 

[charlie-ia]

we were thinking of grouting the gable end. the chimney leaks smoke in odd places (several feet horizontaly).
according to the local joiner, in around 1920 the entire roof was raised using car jacks :shock: and the walls built 3 feet higher. you can see cracks in the render on the outside corresponding to the old roofline. the smoke comes out in various places along this line, and through the bedroom wall. we thought grouting may solve/ help this. the chimney is very narrow already, so we dont think we can flueline it and still use it for an open fire. we may have to rebuild the chimney, but obviously wanted to hold off if we can. there are holes in the bedroom wall (appeared to have bits of wood in -old rawlplugs?) and you can see that the mortar is full of gaps (yes, about the size of an orange or smaller by the look of things) you can't see directly into the chimney.

what you say about using hydraulic makes good sense to me, but im having trouble with an apparent contradiction.if we're supposed to match with existing mortar (which is mud) how can we use something as strong as nhl5?
now im sure the phrase "where possible" comes in somewhere, but if its a balance, what are the pro's and cons?

i read that article- it does seem to imply that we can use wood ash, any idea how much we'd need? i suppose mix a small batch and test it.

 

[charlie-ia]

is there any reason why we shouldnt grout? the wall seems good and strong with no settlement cracks in the old render