I am a little worried about some block retaining walls on a property I am managing. On some of the tall walls the bottom few courses seem to be flaking. They are about 40 years old. We do have a swale at the top of them but ground water is coming through. Would it be the effloresence causing the damage? Any ideas on a solution?
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Replies
Clearly there's efflorescence, but I can't see the "flaking" well enough to tell how bad it is or what may be causing it.
Efflorescence can cause spalling.
What climate are you in?
A freeze / thaw area will hasten deterioration. Usual efflorescence is the release of salts, not always a sign of block failure, but of moisture pushing those salts in that direction.
yes
Clearly efforresence but the photo isn't clear enough to show any spalling, as Dan pointed out.
Two possible steps to take to reduce the recurrance of the proplem come to mind. First is to install a drainage tile behind the wall to divert the amount of ground water getting to the bottom of the wall. Best would be at the bottom of the wall, but if the wall is really tall, that may be difficult and costly, so a mid point tile would be a less effective choice, but better cost wise. The second step would be drilling weep holes through the bottom grade course to allow the trapped water an easier wayout than bleeding through the block. Drill 1" holes through the block and insert 3/4' PVC pipe in the holes. The pipe should be about a foot longer than the thickness of the wall and have 1/4 holes drilled in the bottom half the 1' part behind the wall. Also wrap the whole pipe in a fine hardware cloth or soil seperator cloth. I preferr hardware cloth, but the hole through the block needs to be larger (1 1/4") to accomodate it. Also wrap the open end of the pipe to keep from getting the pipe plugged with dirt when it is inserted. Use the longest drill bit you can find when drilling the holes and run it in all the way to the drill chuck. That makes a pilot hole for the pipe to be inserted in.
i have used the second method to create weep holes in a poured concret curb that had a paver plock patio behind it. I wasn't going into dirt but a sand over gravel bed thath supported the pavers. Worked great, and now the patio drains much better after a hard rain. In your case I think reducing the amount of ground water that stacks up agianst the back of the wall will help tremendously.
If the wall stays dry for six months or so, you could safetly start working on the cosmetic repair of the exposed face.
Block wall failure
Thanks for your ideas. The block is spalling, sorry the photo doesn't shoe it well, I have re-attched it in hope that it may come out better this time. I am not sure what is the cause of it, but I assume it could only be the movement of water and minerals through the wall. We have a swale at the top of the wall but it is not realistic to dig down and get a french drain at the bottom of the wall.
I do like your weep hole idea.
Any thought on using a penetrating sealer on the outside of the wall to slow the movement of water and minerals, maybe it would encourage them to go through the weep holes.
Frankly, for a 40-year-old block retaining wall that wall doesn't appear to be in too bad of shape.
My gut feel is to say no to the sealer, but there could be arguments made both ways.
Sealing the exposed face of the block doesn't work. Sealers only prevent or reduce water intrusion on the face they are applied to. even a penetrating sealer is only going to go as deep as what ever cappilary action will allow.
Maybe you can't do a drainage tile at the bottom of the wall, but if you look up the construction of a true "french drain" you can do that in the swale behind the wall. My guess is after forty years that swale is not moving water away from the wall the way it was intended to do when it was new. Grass clippings, leaves. and run off sediments will change the fow rate as they build up over time. That appears to be what has happened to your swale. The lower flow rate means more water perks to the surrounding soil and finds the easiest way out,...through the retaining wall. Increase the flow rate and you will have less water perk to the bottom of the wall.
Water is going to take the path of least resistance Choose the path for it and you solve the prblem.
effloresence causing the damage?
effloresence does not CAUSE damage.
Water causes the efflourescence.
Water causes other damage.
The efflourescence is a symptom or a soign, not the cause. Deal with the water issues and drain the swale first
Efflorescence can result in crystals building up just inside the surface of the concrete. As the crystals grow they force open cracks and result in spalling. Of course, without water there would be no efflorescence.
But it's a bit late in the game to be fixing any of this, other than to drill weep holes.
frerezing water in the block causes ten times the damage the crystals might.
The problem is the water. He can fiox everything else allday long and if he doesn't comntrol the water problem, he is wasting his time
True, frost spalling is generally the bigger problem in the north. But both mechanisms occur, and efflorescence-caused spalling can occur in a wall that never freezes.