Why Cement Stock Bricks Cause Damp (and Clay Face Brick Doesn’t)
October 9, 2026
Stock bricks are the most common walling brick on South African building sites, mainly because they cost less per brick than a face brick. What most buyers do not see is how the two materials behave once the rain arrives. A wall is only as dry as the brick behind its finish, and the way a brick is made decides how much water it takes in, how long it holds on to it, and what that moisture does to the plaster and paint on top.
How Each Brick Is Made
Cement Stock Bricks
A cement stock brick is made from cement, sand, and aggregate that are pressed or cast into shape and left to cure. There is no firing involved, so the brick keeps the open, absorbent structure that a cured cement mix naturally has, with tiny pores running through it.
Fired Clay Face Bricks
A clay face brick is shaped from clay and fired in a kiln at very high temperatures. During firing the clay particles fuse together in a process often described as vitrification, which tightens the structure and gives the brick a denser body and a harder outer surface. Dezyno Bricks stocks face brick made to SANS 227, which is the national standard for clay masonry units.
Why Absorption Matters for Damp
Every masonry material takes in some water, so the question is how much, how fast, and how easily it dries again. A more absorbent brick draws in rain from the outside and moisture from the ground at the base of the wall, and it then holds that moisture inside the wall for longer. Water sitting in a wall is the starting point for most of the problems we cover in our guide to what causes damp in brick walls.
One honest note on numbers: absorption figures differ between brick types, makers, and test methods, so if you want exact values for a project, ask your supplier for the test data on the specific brick. Do not rely on a general percentage quoted on a website, including ours.
| Feature | Cement Stock Brick | Fired Clay Face Brick |
|---|---|---|
| Made by | Pressing and curing a cement mix | Firing shaped clay in a kiln |
| Pore structure | Open and absorbent | Fused and tighter |
| Intended finish | Plastered and painted | Left exposed |
| Response to rain | Draws moisture in readily | Resists water better and dries out |
| Needs a coating | Yes, plaster and paint | No |
What Saturated Stock Bricks Do to Plaster
Moisture Moves Outward Too
When a stock brick wall stays wet, the water does not only sit in the brick. It moves outward into the plaster layer and carries dissolved salts with it. Those salts crystallise near the surface as the moisture dries, and the growing crystals push the plaster apart from behind.
Peeling, Staining, and Failing Finishes
On the inside of a house, wet bricks mean damp patches, stained paint, and plaster that goes soft or powdery near the base. On the outside, the same process causes blistering and flaking. The problem is the material behind the finish, which is why repainting rarely fixes it for long. We unpack the full cost side of this in the hardware store trap, and the plaster side of the story in why cement plaster acts like a sponge.
The Thermal Side of a Dry Wall
Damp is not only a stain and a smell. A wet wall conducts heat more readily than a dry one, so a saturated wall makes a home harder to keep warm in winter and cool in summer. A wall that stays drier holds its thermal performance better, which is one more reason the choice of brick matters for running costs and not only for appearance.
Where Damp Starts at the Base of the Wall
Stock bricks laid near ground level are in the worst position of all, since they sit close to wet soil and splashback. If the damp proof course is also compromised by plaster running past it, ground moisture has a clear route up through the wall. We explain that failure in how plaster bridges the damp proof course, and how a well-built face brick cavity wall copes with driving rain in penetrating damp and driving rain.
Choosing the Right Brick for Exposed Walls
Stock bricks have a place in walls that will be protected from the weather, and plenty of sound buildings use them. For exposed external walls, boundary walls, and the lower courses near the ground, a fired clay face brick removes both the absorbent brick and the extra plaster layer. Browse our face brick range and read our guide on how to read a face brick specification sheet before ordering.
Frequently Asked Questions
Do stock bricks cause damp?
Stock bricks do not cause damp on their own, but they absorb water more readily than fired clay face bricks. In an exposed wall with a plaster finish, that extra absorption makes damp problems more likely and harder to cure.
What is vitrification in clay bricks?
Vitrification is the process by which clay particles fuse together during high-temperature firing. It tightens the brick’s internal structure and gives it a denser, harder body.
Does face brick absorb water?
Yes, a small amount. Face brick is designed to be left exposed, and the water it takes in can dry out again, while an absorbent stock brick behind a paint layer tends to stay wet.
Why does plaster fall off a damp wall?
Water moving through the wall carries salts into the plaster, and those salts crystallise as the plaster dries. The growing crystals push the plaster off the brick behind it.
Where can I find absorption figures for a specific brick?
Ask the supplier for the technical data sheet for that brick, which should list the test results. Our guide on reading a face brick specification sheet explains what to look for.
Get a Quote From Dezyno Bricks
Dezyno Bricks supplies premium clay face brick, semi-face brick, and plaster brick across South Africa from our yard in Springs, Gauteng. Call us on 061 538 5968, email sales@dezynobricks.co.za, or message us on WhatsApp to get a quote for your next project.
