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Thin brick or stone veneer over existing brick wall

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The thin veneers for the outside seem to be more and more common. How do most of these applications hold up over time? I would think they would need to be completely moisture proof to keep moisture getting in and freezing causing problems already seen with some old masonry work. Like using a sealer ever few years.

Looking at one where the brick chimney cap failure has caused much spalling, someone mentioned to them about going right over the existing brick chimney with thin brick or stone, then use a new cap of some sort.
I would think the potential problems here would be amplified if moisture got behind.

What do you guys suggest or think of these masonry systems?
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Thin brick and thin stone can be applied with the same materials - sheathing, metal lath, scratch coat, thin set and grout. In this system, I would recommend adding a weeping system to help water move through the system. These systems are generic but have stood the test of time in most applications.

However, there is nothing in this system that is 'waterproof'. Using a system of cement board, liquid applied water proofing membrane, latex modified thin set and grout will give you the warranty you need. Laticrete MVIS is such a system.

For thin brick and certain thin stones, you can employ a metal support system like Tabs II, Thin Tech, etc. These are directly applied to the substrate, include a rain screen and eliminated the need for thin set.

You question is valid, but there is not a single answer. The answer is to work with a thin masonry expert and recommend the best system for your application - not a popular answer, but the real answer.
If the chimney is beginning to spall you cannot go over it with thin brick/stone. it needs to be put up over SOUND material.

If you put up thin veneer over a wood substrate there needs to be a drainage plane installed behind the scratch coat. 2 layers of WRB at the least. Best if the 1st one is actually crinkled. There are also rain screens on the market but they aren't cheap, not expensive either but they add $0.50-$1/sqft.

When thin veneer is installed over masonry the masonry substrate should have the drainage plane.

Nothing is moisture proof. assume that water wins. water always wins. If you give the water somewhere to go it isn't an issue
How do you leave a drainage plain with rocks stuck to brick?
Sticking rocks to bricks...
As Dom-Mas stated, the drainage plane is the air space between the brick and the substrate. In theory, the brick is sound, the brick is cleaned and you have used a latex modified mortar to apply the stone to the (I mention again) to the clean and sound brick. Moisture will enter the wall system via the grout joints - specifically the hair line cracks that form over time. Water can also enter at the top of the wall if not properly capped and sealed.

The dangers with applying thin stone directly to brick are many. top of my list are movement, bonding and moisture retention. You will have 6 plus inches of clay, mortar and stone (of concrete if you are using a mfg stone veneer). That amount of material will hold a lot of water and take along time to dry out.

There is a cold joint between the brick and stone that can hold water, freeze thaw and start to delaminate over time. Mechanically attaching metal lath and a scratch coat will assist in preventing delamination. Installed and maintained properly; this will last your lifetime.

I have a full brick home and my chimney cap was all cracked to hell and there was a drip line inside the flue. I had the previous homeowners inspect the chimney and fix the cap before we closed. 14 years later, we never have had an issue and I have it checked every 2 years. Maintenance is an equally important issue - regardless of the system.
clean..wet...parge...apply cultred stone...joints in brick make good anchor points for a brown coat..clean before starting key...l parge a section then apply stone while its still moist...pargeing all at once then laying stone on a dry or browncoat that has been sprayed with water before applying is just a warrentee isse down the road imo...brick sucks up the moisture to fast as dose a brown coat
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