Flashing

General stuff.

Contrary to popular belief, cavities are supposed to be free of pipes and wiring.
The whole idea of the cavity is to provide an air barrier between the outside and the inside of the building.
If the cavity is full of pipes etc, then mortar may fall on top of the pipe and breach the cavity allowing moisture to travel to the inside of the building.

Any overlap of flashing need to be at least 100mm.

For brickwork on a concrete slab.

Flashing is put in on top of the first course above the concrete slab rebate, weep holes are put in no more than every 4 perpend joints apart, 1200mm maximum.
Weep holes are just perpend joints clear of any mortar.

It is always better to put the weep holes closer than the maximum allowed.

Above openings.

Flashing is put in on top of the first or second course above any openings (windows, doors, etc.) and run at least 100mm past the window or door opening so that any water can drip into the cavity rather than onto a window or door.

Weep holes are put in above each opening.

Without the flashing above the openings any water that penetrates the brick will find its way down, and water dripping inside the house will be the result.








The bricks that are on edge in the pic are there only to hold the flashing in place until mortar is applied.


Cavity Flashing.skp (91.08 Kb)

For brickwork on a footing.

Cavity flashing isn't used when building on a footing, 100mm wide damp course which is slightly narrower than the bricks is used instead.

The 100mm damp course does the same job as the cavity flashing in keeping out any rising damp.

The air flow from under the floor will keep the cavity moisture free and the 100mm damp course allows any water that enters the cavity to fall to the ground.

DPC (Damp Proof Course)

• Old Methods
• New Methods

Failure

How to fix

• Mechanical

An example of a failed dampcourse, the salt from the ground has attacked the brickwork.




Cut out sections at a time say 5 bricks, leave 5 bricks etc.
Insert damp proof membrane in the cut outs and re-brick.
You have make sure that the brickwork above the cut out is securely wedged back into place after the mortar has gone off, usually achieved by driving a hard packer into the upper bed joint like slate.

Once the replaced brickwork has gone off cut out another section and repeat.

Very costly in time, but cheap in materials.

• Chemical

Two holes are drilled into each brick at the level you want the damp proofing to be.
Liquid Silicone is injected into the holes, once dried it is water proof.

Costly in time and materials.

Chemicals available here.
http://www.saltdamp.com.au/diyweb.html