How to face a cinder block retaining wall with stone?
This is a long post. Apologies and thanks for your patience.
I am researching how to face a cinder block retaining wall with stone. I have a very modest experience with the materials and methods. I removed some set-in-the-ground timber stairs from the hillside in my yard and replaced them with a cinder block/concrete substructure faced with brick and hand cut stone. It was a lot of work and took forever, but it looks good, and even more importantly, it seems solidly built.
The next project: Facing a cinder block retaining wall with stone. A description:
The wall is about 70 feet long in total, surrounding the front of my rather narrow urban lot. The 40 foot long front face abuts the sidewalk and is broken by a set of cement walkway stairs. A 25 foot leg runs up the driveway on one side and a 5 foot leg anchors the other end. The front wall is about 25 inches (3+ cinder blocks) high. The side walls and stairway are progressively shorter. The wall probably dates from 1940-1960. It was capped with 3-hole brick that had been set on edge. The brick was crumbling and I have recently removed it. The wall has been painted several times. Much of the paint has deteriorated and been removed.
My main concern is avoiding mistakes that could cause problems in the near future, especially mistakes in preparing the wall to receive the mortar.
1) I will need to remove the remaining paint. On the side walls, which receive less sun, the paint is mostly intact. Does 100% need to come off, or will 90-95% do. These side walls are shorter, averaging 12-14 inches high. Suggestions? Paint thinner, scraping, sanding?
2) I had thought that the base layer (the first layer laid over the cinder block) was white paint, but upon closer inspection, it appears to be more like plaster than paint. Of course it could not be plaster (or whitewash), which are too water soluble. It is slightly soft/powdery and can be scraped away with a lot of pressure from a putty knife. It appears too thin for stucco, varying in thickness from .5 to 2.0 mm. Perhaps a very thin layer of colored mortar or Portland Cement? Advice? Ideas?
The point of ascertaining what this substance is, is to find out whether or not I should remove it, also, from the cinder block, before refacing. It would be difficult, if not impossible, to remove it all, as it is embedded in the texture of the block. And it appears to have an absorptive quality, like plaster. I think the mortar will adhere to it.
3) A neighbor who had a much higher retaining wall faced with concrete faux-stone (looks pretty good, btw) said that a professional mason would score the cinder block with saw cuts to provide a surface for the new mortar to adhere to. I have also read of facing being secured by giving the mortar something to adhere to: a) lath (metal lath maybe?) screwed into the wall, or b) metal mesh secured to the wall by screw and washer anchors.
This wall is on the short side, and seems less likely to shed it's stone face. However, it does hold back a fair amount of soil, and that soil is sometimes wet or frozen (Washington D.C. area). This project will require a lot of effort and I don't want to have it fail because I am ignorant of standard practices.
Two additional notes: I hoped to reduce possible water issues by improving the drainage behind the wall: digging out an 8 inch trench and filling it with brick rubble, and cleaning out the three 4 inch weep pipes. This is now done. But I have noticed that the mortared joints on the front of the wall now display numerous cracks. I think this may be caused by the wall drying out, caused by either the drainage work or the removal of the cap, thus exposing the open tops of the cinder block. Some of the cracked mortar may need to be removed, but I hope that applying the mortar for the stone facing will remedy the gaps. Another thought: the center of the cinder blocks is mostly hollow, should I partially fill the interior with cement (and rebar?) before recapping the wall?
Also, as mentioned, the wall is butted directly up against the concrete sidewalk. The stone face will have to extend out over that walk (not more than 4 inches at the base). Although this is a relatively new sidewalk, that doesn't mean the city won't find a reason to demolish and replace it in 5 years. I was wondering if I should run a line of standard size stone or brick along the base of the face, which could be more easily replaced if it was damaged by such activities.
I am also wondering about what kind of mortar/grout to use?
Any information you can share would help me overcome this initial hurdle and would be greatly appreciated. If anyone wants advice on building landscape stairs, I endured a number of travails.
First off, thank you for the very intricate post. Its good to see a DIY'er take such a thorough approach.
Starting off, you need to pressure wash this area with a minimum of 3000 psi and a 15 degree tip. See if you can get back down to the original concrete. This should work out just fine.
What type of stone will you be using? If your using a flat stone with joints in between then you can lay it right over the concrete. If your using a dry stack stone, it might be a good idea to score the area like you mentioned the other mason did. Dry stack doesnt lock the wall together like a flat stone so you want to be able to adhere to the wall a little better.
You will need to use masonry cement type "S". This is the strongest type currently being used. The mix should be 1bag of mortar/15 shovels of sand/ 1 bucket of water (or less). You want the mud to be just a lil sticky.
You do not have to fill the block cells with mortar. But you dont want water getting in there at all. Might have to put a cap on top (4" solid block, 2" landscape wafer)
Hope i answered everything for you. GL
Thank you, Steve
Not to burst your bubble, but the mesh may be necessary.
If you are thinking of applying a lick and stick product like cultured stone then you need the mesh. The initial scratch coat will not bond to the block if there is a paint or stucco coat still on the block. You will likely get pieces that pop off the wall if the scratch coat doesn't bond.
If you are going to lay up real stone that is about 4 inches thick then you can rely on wall ties that you would install as you lay up the stone to give you full attachment to the block.
The main concern of this type of wall is moisture intrusion. The trench you dug and refilled with rubble will help relieve moisture pressure from the soil. The cap is another area that allows moisture into the block cores and causes them to fall apart. Ideally the wall is flashed at the top and then a cap is installed. The fewer joints on the cap the better in terms of preventing moisture into the wall. The old brick cap had a joint every 2.5 inches, which allowed alot of moisture in. Look for something bigger to reduce joints.
It seems the first thing to do is to power wash, which I hope will take off most of the paint. I don't think the white coating on the cinder block is stucco, it looks more like a thin (skim coat?) of Portland cement, perhaps with color added. It has the texture of rather hard plaster. It does not have the look or feel of paint, but I could be wrong. I will examine it further.
Do you still think the wall will need Wall ties? I will see if I can locate info on the installation process.
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