Protecting Mortar Joints: The Weak Point in Brick and Stone Cleaning

Mark Cave

Brick is tough. Everyone knows that. And that is exactly why so many contractors get caught out by it. Because on most walls, the brick isn't the weak point. The mortar is. Treat the joints as an afterthought and you can finish a job that looks fantastic on the day, then end up with a repointing claim a few months down the line.

Mark Cave

I'm Mark Cave from SoftWash UK, and today we're looking at why mortar joints need special attention. If you caught our recent episodes on surface porosity and low pressure rinsing, this is where those ideas meet a real wall.

Mark Cave

Let's start with what mortar actually is. It's designed to be softer than the brick or stone it holds together. That's deliberate. It's more flexible and more permeable, so the wall can move with temperature changes, and moisture can evaporate out through the joint instead of through the face of the brick. In effect, mortar is the sacrificial element of the wall. If something has to give, the joint gives first.

Mark Cave

Now, not all mortar is the same. Modern Portland cement mortars are relatively hard. But older lime mortars, which you'll find on a lot of buildings from before 1950 and across heritage properties, are softer, highly porous and chemically delicate. And here's the thing. A fired clay brick will shrug off a lot of chemical exposure. The joint next to it is cementitious or calcareous, and it soaks up water and chemistry far deeper and far faster. So on one elevation you've got two materials reacting completely differently to the same product. That's porosity in action.

Mark Cave

That gives us two big hazards. The first is mechanical. Pressure washing along a joint, even at moderate pressures, around 1,500 to 3,000 PSI, can cut away the outer face of the mortar. You're left with joints that are recessed, sandy or hollowed out. And if you spray straight into vertical or horizontal joints, or into weep holes, you drive water deep into a cavity wall or behind a veneer. What follows is internal damp, efflorescence bloom weeks later, and freeze and thaw spalling when winter arrives. Other industry sources make the same point: the damage often doesn't show on the day, so nobody connects it back to the wash.

Mark Cave

The second hazard is chemical. Strong acidic washes, things like aggressive brick acids or unbuffered rust removers, can dissolve the calcium carbonate in lime mortar and weaken cement binders. And sodium hypochlorite isn't innocent here either. If it's too strong, or it's left unrinsed, it gets absorbed into porous joints. As it dries, it can leave mineral salt crystals behind. Then, as moisture cycles through the wall, crystallisation below the surface can fracture pointing that was already deteriorating. You never see it happen. You just see the result later.

Mark Cave

So what do you do about it? It starts before you quote. Look properly at the joints. Are they soft or sandy, shedding aggregate? Are there missing sections? Open hairline cracks? Crumbling pointing on a chimney? Is there growth rooted inside the gaps, where roots can open up the joint line? Those are all warning signs.

Mark Cave

Watch for efflorescence too. That white, chalky bloom tells you moisture is already travelling through the wall. If you blast it or saturate it without finding the source of the leak, you simply make the salt migration worse. Often the real problem is a leaking gutter or a failed coping stone, and no amount of cleaning will fix that.

Mark Cave

Whatever you find, photograph it and write it down. Pre-existing deterioration needs to be on record before you touch the wall. And if the pointing is severely degraded, the repointing by a qualified mason needs to come first. Either that, or you adapt the job, or you decline it. Washing over failed mortar doesn't restore it. Walking away from the wrong job isn't losing work. It's protecting your business.

Mark Cave

When the joints are sound, here's the workflow. Pre wet the masonry to manage how much chemistry it absorbs. Apply at low pressure with a wide fan nozzle and a sensible stand off distance, and never rake along the joint lines. Use a bleach stable surfactant, like Clever Wash, so the mix clings to the vertical face and gives you dwell time without flooding it. Flood coating is exactly what forces chemistry into the voids. Then rinse gently across the face, working with the fall of the building, not driving water into joints, air bricks or weep holes.

Mark Cave

Notice that none of that is about the product. It's about understanding the substrate. Knowing when mortar is sound, and when it will blow out under a rinse, is what separates a professional from a splash and dash operator. Knowledge comes before chemicals, every time.

Mark Cave

So here's your action step. On your next brick or stone job, before you mix anything, spend five minutes along the joints. Look, touch, photograph. Then decide the method. That habit alone could save you from a very expensive phone call.

Mark Cave

Podcasts like this are a great way to learn. But if you're serious about offering softwashing professionally, the CPD Certified Softwash Training Course at softwashing.uk goes much deeper. It covers surface assessment, chemical selection, safe application and avoiding the mistakes that lead to claims. It's online, so you learn at your own pace. And completing it gives you the chance to become an Approved Softwash Applicator, with a directory listing and a place in the National Association of Softwash community. The aim has always been to raise standards in this industry. Thanks for listening, and I'll catch you in the next one.