How To Scratch Coat A Cinder Block Wall, Just In Case

Usually you won’t need to apply a scratch coat to a cinder block or cmu wall but in some instances like installing stone veneer, you will need a good base for the material to stick and a scratch coat is perfect.

Let’s take a look at some tips before we get started to make the process go a whole lot smoother.

This is for a block wall and the same techniques will work for a concrete wall as well but does have a few different variables.

Wet Down The Wall: You will want to make sure that the wall gets some moisture before you start applying any of the mud to it.

It will help the mud stick to the wall and prevent it from drying out too quickly which could result in cracking. need to be careful on how much water you use on the wall because if the walls are too wet it will slide off and if the walls are too dry the mud will have a hard time sticking to it.

Spray Down Block Wall

Just be sure that after you wet the wall you allow a little bit of time for the water to soak in before applying any of the material. It should not be wet to the touch but the block will be darker in color.

You may need to add water a couple of times on hot days because it will soak up the moisture very quickly. As you make your way down the wall, keep misting it to ensure that it is retaining enough moisture.

Make Your Mix A Little Rich: The basic stucco recipe is 3 parts sand to 1 part Portland cement but for block walls, a little bit richer mix will help the mud to stick better.

A rich mix is simply adding a little more Portland cement in the recipe. I wouldn’t go as far as a 2 to 1 ratio, just a little more to make it adhere better. Lime would also help to make the mix a bit stickier and just a little bit will go a long way.

Mix The Scratch Coat Up

You can mix in a bucket, a wheelbarrow or a larger mortar mixer, it doesn't really matter which method you use.

Start Applying the Mix To The Wall: Start to apply the mud to the wall, starting from the top and working your way down (typically for larger walls standing 6′ high or more).

You can use a hock and trowel to lay it on (spraying it on will also work) and try to maintain a 3/8″ thick coat all the way throughout the process. You can use a depth gauge to help determine that you are within that depth.

Apply The Mud To The Block Wall

Add The Scratch Marks: After you have an even and uniform amount of mud on the wall, you will want to use a scarifier, notched trowel or something along those lines to make the scratch marks in the material.

It works best if the mud sets up for 5-10 min before scratching the surface. You can scratch it right after you apply it to the wall but it will take a bit more control on your part to prevent the scratcher from digging into the cement.

Scratch The Mud

Keep Working You Way Down: Like I mentioned earlier, keep misting the wall as you go to keep the bond strength high. You don’t need to use as much water as you did the first time around, just enough to re-hydrate the wall again.

If it is drying out fast (like on a hot day) then use a little more water so the block stays a darker in color for long enough to spread that section.

Keep Misting The Wall As You Go
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Ryan Retired Stucco Contractor

I’m Ryan, a longtime stucco contractor who has spent plenty of years getting dusty, chasing cracks, matching finishes, and figuring out what actually works in the real world. I created TheStuccoGuy.com to make stucco a little less confusing, help homeowners avoid expensive mistakes, and give you practical answers without all the fluff.

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11 comments
michael says

hi there

We just poured a cast in place concrete wall. We are going to wait 28 days for full cure on concrete. I was wondering whether we needed scratch/brown and finish or if 2 coats would do .

Does new concrete need bonding adhesive prior to scratch??

Reply
    The Stucco Guy says

    Hi Michael! No bonding agent is needed for concrete or cement walls. Simply pressure wash the surface to remove dust and debris, then apply a base coat followed by the finish coat. This method works well for new concrete. Let me know if you have more questions!

    Reply
Ray says

Ryan; I have 4 12in x8ft round cement columns holding a deck up on our house. I used sonotubes to form the columns. I would like some advice on applying stucco to these columns Thanks Ray

Reply
    The Stucco Guy says

    Hi Ray! For your cement columns, spraying is by far the easiest and most efficient option. It ensures even coverage and reduces waste compared to hand spreading, which can be time-consuming. Use a hopper gun to apply the stucco and leave it or smooth it with a trowel to match your desired finish. Thanks for the question, and good luck with your project!

    Reply
Sam Andrews says

It’s good to learn that you should wet down a cinder block wall before applying a coat to it. My brother is wanting to add a wall to his backyard. I’ll tell him to wet his cinder blocks before building the wall.

Reply
Danny Cowart says

Ryan,
Stuccoing a block wall on a crawl space . I was told to direct apply the stucco because of the mechanical bond . I did this and applied a acrylic coating over that. The stucco was taking down to the grade and cover with dirt . Now I being told that because its below grade possibility of moisture wicking up and allowing incest’s to get into house. The wood structure is 20″ or more above the grade now.
Thank you
Dan

Reply
    The Stucco Guy says

    Loaded question Danny but I would have recommended a hydraulic cement base coat and then finish on top of that. Just watch it and see how it goes, hard to say without being there and seeing the specifics.

    Reply
Dave Bramsen says

Hey, Thanks for your input. Nice site, Stucco Guy.
I’m doing a couple low block walls, 2 and 3 high to which I’m applying a flagstone veneer. I’ve been watching some local pros do a 6+ foot high cinder block wall which will probably get a sandstone outer layer — very popular in Santa Barbara’s nicer neighborhoods and has a historic Spanish look. So, I saw that they applied the scratch coat directly to the blocks today. — No wire mesh underneath. But I’m wondering what is my best scratch coat cement. I’d like to get premixed with the sand in it since I’m only doing about 45 linear feet of wall. Here’s my HDepot experience: I looked at their website but there were no good descriptions on scratch coat/stone veneer applications. So I called the Goleta store and went through 30 (thirty) “Your call is important to us” till a woman came on who didn’t know about mortar but said to go look at their website! 🙁 Some types of cement must be superior for scratch coat purposes? I have some bags of Quickcrete which has the sand in it (no gravel) and maybe some lime? I’ve noticed they don’t list cement ingredients very specifically.
Thanks!!!
Dave B. in SB, Calif.

Reply
    The Stucco Guy says

    Hello Dave, thanks! Block walls do not require lath (need to be clean though) and a premixed bag of scratch or brown mix will work. Plastic cement and sand will also work or Portland cement, lime and sand. There is no real “superior scratch mix” other than a rapid set material which gets harder than standard mixes but sets up much faster. Hope this helps!

    Reply
Anonymous says

Can I use type s mortor insead of cement

Reply
    The Stucco Guy says

    Hi friend, Absolutely, you can use Type S mortar instead of cement for your scratch coat on a cinder block wall. I’ve personally used it in some of my projects. Keep in mind, Type S mortar is a bit thicker than a more traditional base coat recipe, which can make it slightly tougher to work with. When applying, ensure you mix it to a workable consistency and apply it evenly over the surface. Remember to let the scratch coat cure adequately before proceeding with the next steps. Good luck with your project!

    Reply
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