2 years ago I had a cement wall built and when spring came there where hugh white spots on the cement taking up about 50% of it. I called the contractor and he said it was curing. This year I have the same problem. I bought a corn broom and it will not come off with this. What is the cause and what should I do?


Bob

Its from water seeping through it. Its normal. If you want to stop it, then paint it with something like Drylock

Curing has nothing to do with this
The with powder is salt coming out of the block. It also comes out of brick and once in a while flagstone. Its not mold. The block is effervescing. This is mainly caused because the block is remaining wet to long and the salts are weeping out of the block and drying as it hits the air.( powder) The contractor may not have Sealed the back of the block wall against the bank properly. This is usually the main reason but not always. If the block stays wet long enough it will do this also brick façades above grade will show the white powder.

As a mason I can't tell you how many retaining walls and foundations I built. Not one effervesced and I'm in a wet area.

Effervescent is the alkaline components that make up masonry materials. They are being leached out of the masonry and collecting at the surface. Often light deposits can be removed with water and a scrub brush but heavy deposits will need more work.

For interior areas use TSP, trisodium phosphate, and a lot of scrubbing. Plain white vinegar and water, mixed 50-50, can also neutralize these deposits. The vinegar can damage delicate materials and change the color of brick, be careful.

For exteriors a pressure washer is the best tool. This alone can remove most deposits.

Commercial masonry cleaners also do a good job on heavy deposits. These are available at your local paint store or home improvement center. A strong TSP solution can also be injected into the water stream if a commercial pressure washer is used. It is most likely that a little scrubbing will be needed.

Both interior and exterior masonry can be treated with the same chemicals. Make sure you rinse the affected areas well. Don’t worry if a little effervescent still remains, this will be neutralized and sealed with a good masonry primer like Zinsser 123 or a sealer like Seal Krete Heavy Duty Sealer.

The contractor is blowing smoke when he says its "curing" I Can show him, 30 year old block "curing" and has white powder He more than likely knows the wall not being sealed properly is the cause. If it was sealed right there would not be powder on 50% of the wall. I'm been doing masonry work over 30 years and never saw 50% of a new block wall doing that.

Part of what I do for a living is replacing failed retaining walls. Maybe I shouldn't say this but cement block can ROT like wood in the cores. I have seen a 30 year old walls do this that had water puddling in the cores. And yes it effervesced all the time. I guess what I'm saying if that wall was parged/ pitched and stone with perforated pipe out the end to drain this probably would never happen. At best it would be a couple of blocks if at all.

I just got off the phone with the contractor and he said that I should wash the walls with muratic acid and then hose the walls down. Can this be right?

Bob

No muriatic acid. That etches the mortar joints. That's very caustic and its for cleaning brick that has mortar deposits on it and mortar dust.

Hydrochloric acid - Wikipedia, the free encyclopedia

A pressure washer will do the trick. The acid won't "clean it" its not dirty from mortar blobs etc. Its basically salt crystals. The trick hear is to get the wall to dry out to seal it so it doesn't effervesce. But in turn we are trapping all of the moisture in the wall. Weep holes at the bottom may be needed hear to drain the block cores as water and moisture builds up inside the wall.

Sorry I do not agree, Effervescence also has to do with the area you live in and the brick you are using. There are many place that have effervescence all over new england you can't say there all wrong. How abour errervescence on a sealed building? Both sides there is not water. It had do with the area and the are I sure water struck or what are call city hall pavers which have water and effervescence will leak. The on time you can not use acid is on color motar.

Hi imfcgold welcome to AMHD.. Just for a heads up you answered an old post.

Effervescence has Nothing to do with anything but how much salt is in that masonry/concrete product and the amount of moisture to set it off. Add the right amount of moisture sealed Building or not as you call it an it will happen. As an old Mason I see it all the time.

Have to have Salt to effervesce and moisture to activate it

My new brick retaining wall is effervescing. I understand I will need to clean it off but will sealing it keep it from doing this. I have a feeling it was not sealed from the inside

I forgot to mention is is a garden retaing wall so its got a dripper system inside so it is constantly getting moisture