Repointing a Sandstone wall

[katmark]

Hi,

I have a wall built of random sized, undressed, sandstone bricks around my house, about 18'' thick - probably built in the mid 60's. It is in various stages of disrepair, ranging from loose pointing to totally loose stones.
I have bought a pointing gun (from turptech tools) and have been using this to put a single application of lime mortar into the missing pointing and the same mix to rebed the totally loose stones.

The mix I have been using is 3 parts BUILDING SAND:2 Parts Hydrated Lime:1 part OPC.

What I need to know is - am I using the right mix ?

Any other tips would also be appreciated

The manufacturers of the pointing gun recommend use of building sand over sharp sand as 'sharp sand does not flow under pressure'. The lime mortars I've seen on this site all seem to recommend SHARP SAND though !

I have a large area of walling to do on both sides and, as I'm trying to do lots of work on the house myself, i need something fairly fast - hence the 20 quid investment in the pointing gun - it was taking me an age to point with a hawk

Thanks to anyone taking time to reply

Mark

 

[noseall]

your mixture is far too powder rich!

6 building sand (soft sand or rinsed sand), 1cement, 1 lime.

if the joints are a bit on the large side, you can use a shovel full of sharp sand or two in place of a couple of soft ones.

 

[noseall]

p.s, throw away the pointing gun and use a pointing trowel. cut 'n' struck pointing looks good with stone walls.

 

[katmark]

Thanks Noseall,

Whats 'cut 'n' stuck' ?
I'm using the gun to get the mix into the joint then using various sizes of ad hoc pointing implements to push the mix into the joints and compact it in. I'm trying to finish slightly indented into the joints. As the stones are random, some stick out farther than others. I did some on Sun & I'm hoping to brush it off tonight (if it hasn't set too much !).
The gun helps get the mix initially deep into the wall

For the stuff I've already done, should I just leave it in or do I need to rake it out and start again ?

Some of the joints are quite wide (and some stones are completely loose, so I'm taking out & rebedding these) - will a mix of sharp and building sand be OK ?

Can you post pics on here - I'll try and put some on of what I've done and whats to do. There's no way I'll be able to do it all before winter sets in though.

Thanks again
Mark

PS The lime I've been using is just bagged 'bulders lime' from the builders merchants

 

[noseall]

if you persevere with the pointing gun, then a powder rich mix is essential.
sharp sand will be useless in a pointing gun as it is simply not 'fatty' enough.

but your wall would be better re-furbished with a decent mortar (as said earlier), a proper pointing trowel and a soft brickies brush.

cut and struck pointing will work best with regular sized squarish edged stones. it is achieved by building the mortar up almost proud, strike it or flatten it with the pointer face then cut of the excess mortar giving a fairly tidy looking mortar joint.

 

[kevnurse]

You should not use OPC for pointing sandstone. Sand and lime is all you should need.

 

[katmark]

Thanks for the replies,


I've done a bit of research on the 'net since my post. A good site is http://www.buildingconservation.com/articles/cement.htm.
It gives some + & - to gauging lime moratr with OPC, if anyones interested
I've gotten to be quite engrossed by it all !
I assume if you use Lime and sand only, it will need to be Hydraulic lime? The bagged Hydrated Lime I got from the builders Mercants is non hydraulic I suppose?


My problem is that all the joints are widely different in size - some too small to use a pointing trowel. The stones also stick out, are a wide range of sizes & are not square.
Tried to put a pic in of wall but can't do it !

How far into the wall do you need to go with new mortar ? Some of the voids appear to go all the way through the wall (14-19'' thick)

Could I use builders sand : Lime :OPC for the inner bits of the wall (so I could use the gun to get it in) and sharp sand;lime:OPC for final bit (both in 6:1:1 Ratio), OR even use hydraulic lime for final pointing ?

It's all getting a bit confusing for me now !!

Thanks again
mark

 

[amwc]

if your using hydraulic lime then a 4 to 1 mix is ok with opc then 1:1:6.
if there are just a few holes that are deep just use the same mix as pointing but force it to the back of the joint with the pointing trowel.
sand stone always goes off randomly one patch will take 10 mins another 2 days? so you need to check it regularly and you should be brushing it about an hour at the most after rubbing/striking it.

 

[katmark]

As we've had the first frost up North, I'm probably not going to do any more on this until spring.
I've decided to try and get some hydraulic lime and use various implements to fit the various sized holes in the wall. I've seen 1:3,1:4 and 1:6 mixes all recommended!
I'll give up with the pointing gun I think.
Some of the stones are just coming out easily, so I'll be taking them out and 'repacking' with the mortar from the back.

However, for the really thin joints, can I use the same ratio mix, but soft sand ? Some joints are only about 3mm wide, so it is difficult to get the sharp sand mix in.

A couple of other questions - the ground on the inside of the wall is about 3'' higher than outside the boundary - will I need to leave 'weep holes' in the wall ?
Also, part of the wall has a flat top, currently with bits of sandstone set in crumbling mortar. Do I just replace with the lime mix, or does it need to be more impervious on the top ?

THANKS TO ALL FOR YOUR REPLIES

Mark

 

[oilman]

Don't use OPC as has been said above by kevnurse, it's not necessary at best, and the stones may be damaged at worst. You could use hydrated lime, mixed with water and allowed to stand for a few weeks, then pour off the excess water. You can get the same effect as a hydraulic lime by using crushed fired clay (pozzelan). You can also get crushed chalk and some cow slurry would help too. It's also better to use some sharp sand to give some weathering ability. Get a sample of the original mix, put it in a test tube and shake it up in water, then leave it to settle. You'll see the proportions used originally.

There's loads to this lime building, and I know little. Do some more lime research it'll be worth it.