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Thread: Red Brick as veneer over cinder block chimmney

  1. #1
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    Red Brick as veneer over cinder block chimmney

    When my house was built, the exterior chimney, which is about 7-8 feet wide, as it is a double flue chimney, for an oil furnace and fireplace, was built with cinder blocks from the ground up to about 7 feet and then the rest is red brick.

    The reason was because a garage was supposed to be attached to to the side of the house, and you would not see the cinder blocks from the outside.

    I can buy red brick that is used like a veneer and would be attached to the cinder block to look like a complete red brick chimney.

    I would buy thin set or use the correct cement to face the cinder block like a stucco, and then butter the red brick veneer with thin set and apply it to the stuccoed chimney.

    My concern is that over time, will the red brick veneer fall off with the freeze thaw cycles that New England has.

    Any advice from anyone with experience in doing cement work that could advise me would be greatly appreciated.

    Some may say that this sounds like a job for an experienced mason, but I feel capable, as worse comes to worse I would just put a thin layer of cement over the cinder block with a color additive if the red brick veneer sounds undoable and not recommended.

  2. #2
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    You should be fine if the cider block is clean and in good shape. Stone and brick veneers are used all the time in new England. I'm in the midst of putting stone veneer on my pizza oven.

    Talk to the folks at your local masonry supply and watch the various youtube videos. If the block hasn't been painted you should be able to just wash it, apply an adhesion promoter, and put your brick veneer on directly. Most folks here recommend Ardex x77 as mortar. It is a polymer modified mortar with reinforcing fibers. It sticks tenaciously! Only downside is that it's about $40/bag.

    Chances are the veneer won't be a perfect match to your brick, I'd choose something obviously different so that it looks like a design choice rather than an accident.

  3. #3
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    Roger, The cinder block is in good shape. My only concern about that is I think I sprayed Thompson water seal on it about 20 years ago. I don't know if I need some kind of acid to etch the chimney block.
    I will inquire about the Ardex x77 as a mortar. That sounds like just what I was looking for. I appreciate the comment.
    Good luck with the pizza oven.

  4. #4
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    I would want to install furring clips.

  5. #5
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    I don't understand Bill. How would the brick attach to the furring clips?

  6. #6
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    If you want the belt-and-suspenders approach you can screw wire mesh to the wall, apply a scratch coat of mortar, then veneer on top of that. I really doubt that is necessary in your case.

  7. #7
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    Quote Originally Posted by michael langman View Post
    I don't understand Bill. How would the brick attach to the furring clips?
    They extend from the existing CMU into the mortar joints of the brick "veneer". Easier done on new construction but it truly ties the two materials together and creates a monolithic finished product.

    If you are proposing actual veneer (say 1/2" thick) then it is more important to achieve a continuous bond like Roger has outlined.
    Last edited by Bill McNiel; 06-21-2019 at 10:48 AM.

  8. #8
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    I had known about the wire mesh, and too thought it unnecessary, because I have the cinder blocks in good condition as a base.
    The furring clips sound like a similar approach, but the same outcome.
    I'll probably do this without either one.
    I will try to waterproof the heck out of the chimney afterwords so water penetration does not cause problems down the road.
    Thanks for the help roger , Bill.
    Last edited by michael langman; 06-21-2019 at 11:25 AM.

  9. #9
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    Shouldn't be much harder than setting tile, and that's a pretty easy job. It might even be worth using tile spacers for the "grout joints". I wouldn't use the type of spacers that you leave in, or at least not put the crosses in the corners, but just use them for the thickness, and pull them out before grouting.

    A bit of testing to find the exact right size notched trowel will let you find just the right one which allows setting without hollows between the ridges as you press the brick in place. Those hollows might hold water, and freeze-pop the brick off.

    Measure your water before mixing the thinset, and find the exact right ratio for it to act like you want it. Repeat exactly for the rest of the mixing. I'd mix a whole bag at the time, so it's always the same. Depending on what sizes the bags come in, it would be worth a few dollars more not to have to mix, and deal with large batches at the time-at least for the first go.

    Doing all that, it would be fine just stuck to the blocks.

  10. #10
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    I was hoping I would hear from you Tom. I thought you might have some of this type of experience.

    It sounds like a good idea to mix smaller batches, and I will spend some time getting a trowel or modifying one to give me that spacing.

    I will look for tile spacers too. I appreciate the help.

  11. #11
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    Probably a 3/8, or 5/16 notched trowel will be right. No need to buy the expensive ones for this job. I have one 5/16's trowel that I ground the notches out a little deeper with a 4-1/2" sidegrinder, that I use a lot for outside stuff, like our screened porch that I just put 12x12's on. Normally, you would use a 1/2" trowel for 12x12's, but I didn't want to leave voids under them.

    Set some of your bricks for practice to start with. Pull them up to see if the coating of thinset is complete on the back without grooves in it. Adjust the trowel accordingly. If the trowel is just right, you can do that, and not squeeze up too much into the joints.

    If you use too much thinset, or it's too soft, it's a big mess to have to get it out of the way if any squeezes up too high. Too stiff, and it causes several other different types of problems which can be worse. This is why I measure the water, and don't just guess.

    Soft enough, and there is no real reason to back butter. Too soft, or too much, and it makes a big mess. The amount of water I use is usually close to the maximum recommended on the bag. I always start with that, and adjust a little after the first batch, using a container with measurement lines on the side.
    Last edited by Tom M King; 06-21-2019 at 7:20 PM.

  12. #12
    I did brick veneer on a 100+ year old masonry wall inside my house and it was fairly easy, granted doing it outdoors is a different set of challenges. One thing I learned is that it helps to cut wood strips to use as spacers on top of each course because the brick is a lot heavier than tile and will sag if held with just the mortar.

  13. #13
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    Thanks for that tip Gunter. I will need a lot of strips of wood. 50 rows across to get to the top. But it will be worth it if the bricks begin to move down.

  14. #14
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    Michael, if you have 50 courses, why not just lay brick? The corners would look better, but you would have to provide some footing for it. You could put a Rowlock at the transition, and it would look like it had always been that way. It might seem like a lot more work, but by the time you tuck point that much of the tile laid bricks, the pendulum might swing the other way. I don't know if you can grout rough faced brick, and not get it all in the faces.

  15. #15
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    Make your mortar a bit stiffer if they are slipping. With a mortar like the Ardex they shouldn't be slipping. Press them into place and don't move them again. Lots of folks set rock and brick veneer from the top down. (Not sure I understand why)

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