Natural Stone Veneer Over Painted CINDER Block

Tommy C

Hey guys,

I'm looking at an existing cinderblock wall (cinder, not concrete), that is painted. Customer wants to veneer it with Natural Veneer. Do I need to take any special precautions with CINDER block, as opposed to concrete block, when attaching the lath, seeing that cinderblock is more brittle? I was thinking of attaching the lath with a nailgun, then scratchcoat.

Here's another issue...the wall is actually 2 separate walls, which are not lined up exactly. So, one part of the wall is slightly more protruded than the other. Any suggestions on how to even out the walls during the scratchcoat phase, or at least make it slightly less noticeable? The one section of the wall is about 4" protruded out from the other section.

I was thinking of attaching strips of Durrock cement backerboard to the wall where the 2 sections of wall meet. Then, attaching my lath over that, so at least the wall will gradually taper into the other section of wall. Thoughts on this??

-TC

consolidatedbui

power wash
paint with wellcrete
build out plywood wall, felt paper
wire lath, hand bang only,potentially doubled at area of 2 wall intersection...

Tommy C

I don't feel comnfortable just installing this stone over Weldcrete, on a painted wall! Has anybody done this?

Plywood instead of concrete backerboard? How come?

jomama

Tommy, my instincts say to stick with lath. Unfortunately, I have very little experiance with actual "cinder" block, but I would assume plenty of shot nails would hold. I would also mount a 1 1/2" angle iron at the base to aid in laying the NTV. Lastly, I think I would treat the 4" return as a corner, as I don't think you can hide that much deflection in any thinstone.

genecarp

Why the lath, thinset cement board as needed to flush out condition, and thinset directly to block. depending on condition, angle iron as ledge may be a good choice. G

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Tommy C

You're suggesting to thinset the stone directly to PAINTED cinder block? I don't feel comfortable with that at all...

genecarp

What is it SPECIFICALLY that you think would fail. As long as the painted surface is SOUND----rough it up a bit, and thinset--thinset will bond, if the painted surface is not sound, clean off, prime well and go, you have a masonry surface, you are making this more complicated than it has to be. i have done this application on cement block, unless there is something about cinder block that is different, i do not see a problem--but i am all ears....G

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Tommy C

It may hold for 10 years, but it may not. I don't know what kind of paint was used, and these people are going to live here for at least 30 more years, barring any unforeseen circumstances, so I think I'm going to use lath, because I feel that it's best practice.

Now, in terms of making the 2 skewed walls flush, I was thinking of using cement board as needed, and adheering it with thinset AND screws. I need to gradually taper the 2 walls together, so the lath and a scratchcoat would also help me achieve that!

MasonryPro

Mortar does not adhere very good to a painted surface. The paint acts as a bondbreak and has potential to fall off, especially with thinstone, as the stone has a smooth back as well.

Make a decent attempt to remove the paint from the surface you want the masonry to bond to, and you'll create a stronger bond. That may be easier said than done, however!


Mastercraft Masonry
Professional Masonry Since 1974
Oregon / Washington

michiganmason

I would definately add mesh and scratchcoat. laying stone to a painted surface would be ignorant. treat the 4" difference as a corner.

MasonryPro

Natural Stone does not require mesh to adhere to another surface, unlike the manufactured variety. It requires a sound footing and a somewhat bondable surface, as well as fasteners such as galvanized hot dip "L" shaped wall ties to bond the stone to the concrete. These wall ties protrude way farther into the stone/mortar substrate than mesh, giving it a much stronger "grab" than just mesh alone.

It wouldn't hurt to install wire mesh, but installing stone ties to the cinderblock wall after the paint was removed would be the best option for durability.


Mastercraft Masonry
Professional Masonry Since 1974
Oregon / Washington

jomama

MasonryPro, this isn't your father's stone (full bed depth) he's talking about here but Natural Thin Veneer, which is sawed at approx. 1" thick and treated as lightweight "hung" veneer

rock man

Most definately used lath.drilled and pinned,we use zamac pin anchours that require a 1/4"hole, washers are required to add a bit extra surface holding area.natural thinwall can be install with out boottom angle bar but for the nominal amount it costs we use it all the time.maybe the area out of line could be handled more effectively with a combination of 4" veineer and thinwall to make surface flat. hope this helps

MasonryPro

I apologize. He posted "natural veneer" in his first post so i assumed it would be natural stone.

Tommy C

You drill in? Wouldn't a nail gun be better/more efficient?