I’m building an outdoor kitchen which will have about 2 1/2 sides buried and the rest open to a sort of sunken courtyard. The agregate in the block I get has a red and brown color mix. I’m thinking of doing a sort of acid wash on the inside of the walls to bring out the color a little. Probably follow that with some clear sealer.
I poured a little muriatic acid on the side of a block and then poured a big can of water over it a minute or two later. It did bring out color, although the acid wash was uneven and thus so was the color revealed.
I’m wondering: Will the acid wash hurt the block in any way? It would be easier to wash the entire wall after it’s laid up, but would that hurt the mortar? I’d only be doing the part of the wall that will be inside the space.
One more CMU question: Do you wet the block before you lay it up? I never have, but then I haven’t laid that much block. In reading an old bricklayer’s manual it specifically says to soak the brick so that the mortar doesn’t dry out too fast “before it’s cured”. I have always sprayed any blockwork after it was laid, so maybe that’s been good enough (What I have done has held up). The FHB Foundation book is too vague to be of help, it doesn’t mention wetting block or not.
Thanks in advance for the help!
“But I say to you who hear, love your enemies, do good to those who hate you, bless those who curse you, pray for those who mistreat you…. and just as you want people to treat you, treat them in the same way.”
Replies
To get a more even color, wet the block before applying the acid.
Hey Hasbeen,
Like the last post said-- wet the block first.
Also you might experiment with diluting the muriatic acid and then brushing on the mix. Just remember to stop the acid from working too long on the block by rinsing off the block after a short time. This will help prevent the block from "burning".
PS ALWAYS wear eye protection when using that muriatic acid. Even just a little drop splashing up into your eye will truly give you the "heebee jeebees".
Cork in Chicago
Acid washing a CMU is risky due to the porousity and absorbtion. It is hard to get all the acid flushed out. If you're sure you want to do this, make sure saturate the wall first and use a low acid detergent cleaner like SureKlean 600 then rinse, rinse, rinse. If you're looking for color, think about staining the block then using a clear sealer.
Don't wet the block before laying up. The block should be surface dry and of a low enough moisture content that "suction" occurs in the mortar joint. Read more about this phenomenon at the Brick Institute of America website. Modern brick should not be presoaked either, since the rate of absorbtion is usually very low compared to old soft brick.
If you want a more detailed response, email me. It's late and I'm going to bed now.
Eric
Edited 6/7/2005 12:15 am ET by EBORG2
Try putting a clear sealer on a test block and let it dry. Maybe a second coat. Could that be good enough?
I've found that really brings out color in stone, Your block is simply a lot of crushed stones...
Do you mean putting the sealer on a block that hasn't been acid washed?"But I say to you who hear, love your enemies, do good to those who hate you, bless those who curse you, pray for those who mistreat you.... and just as you want people to treat you, treat them in the same way."
As long as there's no spilled mortar on it, yes. The sealer will most likely be enough. Although, it may be a good experiment to do it after on another block to see which look you prefer.
Thanks. I'll do some more experimenting."But I say to you who hear, love your enemies, do good to those who hate you, bless those who curse you, pray for those who mistreat you.... and just as you want people to treat you, treat them in the same way."
While you are experimenting, I wonder what using an acid stain on the CMU's would look like.
I'm not familiar with acid stain. What is it? Do you get it at a masonry supplier or a lumber yard or? What is it usually used for?"But I say to you who hear, love your enemies, do good to those who hate you, bless those who curse you, pray for those who mistreat you.... and just as you want people to treat you, treat them in the same way."
Masory suppliers."Acid Stain is not a paint or coating agent, rather, it's a coloring process involving a chemical reaction on a cementitious material. A solution made with water, acid and inorganic salts reacts with minerals already present in the concrete, the result of this reaction is color. It works very well on new or old concrete, and we've seen impressive results over decorative polymer overlays as well as self-leveling products. Acid Stain is a very durable product if properly protected with sealer or wax, and it can be applied to both interiors and exteriors."http://www.decorative-concrete.net/stained.php
http://www.concretenetwork.com/concrete/acid_etch_staining/
http://www.kemiko.com/
http://www.concrete-stains.com/Brownbag did his floors with an acide stain. The picture have been posted.
Thank you."But I say to you who hear, love your enemies, do good to those who hate you, bless those who curse you, pray for those who mistreat you.... and just as you want people to treat you, treat them in the same way."