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Pointing with lime mortar ~ Part 3 = Technique

Category: Starter for 10 February 24th, 2011 by mbc




Lime Pointing Tips

Here’s my take on how to go about pointing with a lime based mortar – others may have differing guidelines – this is very much my take.

This post is this third in the series.

In the first instalment, I covered the tools of the (pointing) trade.

The second instalment was about lime mortar and how to go about making it.

Now in part three I’ll address – pointing technique

Technique

Firstly the old mortar joints will need cleaning out. If the old mortar is really rotten or dirty then a pressure washer can be used initially to clean down the masonry and blast out any really lose rotten mortar.

With a hand pick work back the mortar to give a repointable joint. When repointing over old mortar, a joint of around 25mm / 1 inch depth will allow a good packing in of fresh mortar that will be able to carbonate externally and remain stable over time. Too deep a treatment and the deepest mortar, deep in the joint and away from the air will remain too moist and too flexible and potentially be unstable. For deep joints point in ‘shifts’ of 25mm or so at a time, allow the mortar to go-off between applications. If you can’t get down to the ideal 25mm joint don’t worry too much, I’ve pointed plenty of shallower joints that are still sound after several years.

Some advisors on the subject talk about the need for a squared internal surface to point up against (in contrast to a rounded one). Whilst probably ideal, this is time consuming to achieve and so unless you’re lucky enough to have abundant time for your pointing project I wouldn’t worry too much about it. Square the corners if you can, but don’t fret about it if you can’t.

If the existing mortar is sound, then I leave it in place – if it ain’t broke

Before applying new mortar, damp down the wall before pointing. Use a bristled brush and a bucket of water. Personally, I favour a ‘flick’ technique – water in bucket – dip brush and flick! Get right into the joints that you’re repointing. The warmer the day the keener you’ll need to be. On a generally damp, cold, dismal day (not that we get many of those in Wales!) your damping down will likely be minimal.

It’s best to point a wall top-down – that way you can damp down the wall without damaging or washing out previously pointed joints lower down the wall.

So, to work…
Load your small pointing hawk with a trowel full of mortar, then using your trowel of choice (either a ‘normal’ pointing trowel or a smaller ‘trowel and square tool’ as I discussed in part 1) take up a sliver of mortar on the back-face of the trowel appropriate to the size and shape of the joint you are pointing and push the mortar into the joint. Use the trowel to work the mortar fully into the joint and tidy up any that doesn’t go where you want it to.

After pointing a length of joint or a discrete area of wall then go back over your work, tidying and smoothing along the length of joints to get a consistent finish.

…and repeat…

Where you have wide and / or deep joints it’s important to use pinning stones to reduce the width / depth of the joints and so reduce the amount of mortar you need which in turn will reduce the time needed for setting and carbonation of the joint.

For very narrow or very shallow joints do what you can. Sometimes you’ll need to pack the mortar into a very narrow joint – place a blob of mortar on the joint and repeatedly press the mortar into the joint, hopefully filling it slowly. I’ve been known to build up very shallow joints to stand proud of the masonry surface, although this is more of a cosmetic affectation than a practical necessity.

Cleaning up
I must admit to being a bit lax when it comes to finishing the joints. Ideally, after around 24 hours you will tidy up your pointing. At this stage the surface of the mortar will be hard with softer mortar underneath. A brush with stiff bristles (but not too stiff as you’ll just end up ruining your good work of the day before) can be used to tidy up the joints, remove excess ‘tags’ of mortar and mortar that is misplaced on the masonary.

When to point
You can point for most of the year in the UK (except perhaps in the far north), I tend to ‘retire’ over the Winter – Novemberish to Marchish. Keep an eye on the five day forecast when pointing and have a tarpaulin or sacking ready to cover over any pointing should a sharp shower unexpectedly arrive. Don’t let rain anywhere near your freshly pointed joints. Beyond that, fill your pointing boots…

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