We just had a retaining wall constructed today between our house and new pool with split face block and while it is exposed on the back I am wondering if I shouldn't put some type of water seal on the back.

What type of product would you use for this?

Our pool contractor is going to run black perforated drainage pipe along the back on top of the footer and then back fill the lower part with gravel prior to back filling the remaining gap with dirt. It would seem some type of water proofing would be ideal here as it would keep the blocks from leaching water through to the face.

Any suggestions?

 

The wall is 60 feet long with about 15 feet being nearly 6 feet tall and then stepping down along the grade. At about 40 feet into the wall it is only one or two blocks and a cap block high. Our deck is in the area between the house and the retaining wall followed by the pool apron.

 

It sounds like he is doing everything by the book.

Keep going by the book and do not put any sealer on the back side of the retaining wall block (SRW units to engineers). It sounds like he is using the correct backfill material. The perforated plastic pipe will collect the water from the backfill and remove it. Putting a sealer on the back of the block will not prevent water from leaking through the joints. If any water does leak through it would be very very small and of no consequence. One of the benefit of the open joints is the ability to relieve the hydrostatic pressure behind the wall.

I can't think of any benefit in sealing the back of the block. This system has been used on hundreds of thousand of walls around the world and has performed well without sealing the back of the block. Your local city and county probable use this system and probably do not seal the back side.

Gravity walls have been around for centuries.

Dick

 

Thanks for your reply!

I have been doing a little digging on this since my post and I agree he seems to be doing it by the book. One thing I have read that seems to be recommended is putting landscaping material over the gravel before completing the back filling with dirt to keep it from clogging it up over time. Seems like a pretty good idea!

 

The fabric is time and money well spent. Sometimes the silty clay soild can plug up the rock put in for drainage. It is the same material you would use around the interior and exterior draing for a basement wall footing.

Dick

 

Hi tthurman,

Sealing the backside of a segmental block retaining wall would pose no threat or advntage to the wall. Sealants generally break down from ultraviolet exposure in a matter of a few years. I expect that prolonged moisture exposure would result in the same. I do have a concern however. Since your wall has a footing and is being drained with corrugated tile, it must be at least a few feet high. How high is the wall? I ask this because if the entire wall has been built, and the drain tile hasn't yet been installed(which should be installed behind and below the footing in free draining sand or aggregate, before or during the process of installing the footing), I am curious as to how they intend to compact the backfill. My concern isn't with the drain tile, because you probably really don't even need it. But if the wall is four feet or higher and somehow standing on it's own(assuming there are 1/2" - 3/4" setbacks)then I would simply want to know how they intend to effectively compact the backfill, especially at the lower levels.

Of course if this wall is only two feet tall and the soils behind it have been excavated below the footing for placement of the drain, then all sounds peachy keen.

As far as the fabric goes, skip it. The dirt will more likely clog the fabric. the back of the wall will be filled with crushed stone almost to the top. Then use sand to fill the last six iches. If the sand leaches into the stone it will still allow water to pass right through. Then put two or three inches of topsoil over the sand. That's your best bet.

George Nicula
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Now that i've read the other replies I see the dimensions of the wall. And I am completely confused. If there are no setbacks on these units, then this wall is standing six feet tall with no reinforcement whatsoever. What kind of split faced blocks are these? Are they split faced cinder blocks? Because if they are, you are going to find yourself in a situation in a matter of a couple years. If these units have setbacks, then the wall couldn't stand on it's own. Not at six feet. Unless the setbacks are negligable. Which would be inadvisable in this application. I would really like to know what kind of wall units these are. Also, is this a retaining wall contractor, or a building contractor? It seems that someone has forgotten the geogrid?!!? If this is by the book, could someone tell me what book that is?

George Nicula
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Yes they are split faced cinder blocks. Our pool builder contracted this to a company he uses for retaining walls. There is no set back involved as they are not dry stack blocks. The wall is only 6' high for about 15 to 20 feet of the run and he had them fill every other hole in the cinder blocks with concrete. The footer he poured is huge, enough for 3 deep on the cinder blocks and he intends to lay the drainage pipe down in the bottom level with the first block and back fill the first foot or so with gravel. He also has a truck load of sand in the back which I assume he will also use during the back fill process. At first I was concerned about this thinking it may disrupt the drianage but it seems this isn't the case. I am sure they will back fill the majority of it by hand but will do some areas they can reach with the bobcat. I am not sure what you mean by corrugated drainage tile. On the front side of the retaining wall they have installed a deck drain that after the concrete was poured part of the apron around the pool. It drains everything away and down grade that would otherwise be trapped in the apron area due to the slight pitch he has running away from the pool.

 

To add to my post, even though the wall is at its highest 6' it is on a down hill grade and he has allowed for the wall to extend at least 1 1/2 above grade so they will only be back filling about 4 1/2' at the most and this quickly starts dropping. The run of the 6' area is about 15' in one direction then turns and runs another 5' before it starts stepping back down to grade again.

 

Just to clarify, I was assuming you were having a mortarless wall built and not a rigid cantilever wall. They are two different animals. My comments were aimed at a SRW wall.

A SRW wall works with and uses the soil and its characteristics. It never has a concrete footing. A rigid wall is an attempt to control mother nature with brute force and rigidity. You know what will win. Concrete always cracks and you want to minimize it.

A proper rigid wall needs to have steel to hold it together and minimze movement. I hope the contractor used horizontal steel (joint reinforcement) every second or third course of block. If there was no vertical steel in the cores that were filled, see if it is possible to put steel and grout in the cores that were not filled. Concrete in the cores without steel does little to tie the wall together.

A rigid wall requires good drainage to reduce the pressures that cause movement and cracks. If possible, get the drainage pipe behind (or lower than) the footing rather than on top of it. This will lengthen the wall life by improving drainage. In all cases make sure the wall is well drained.

Dick

 

The wall sounds like a mess to me, a footing is used to support a load with the weight bearing down on it, your wall will not sink, but it will topple over in a few years, I do not think its tied into the footing, does it have any rebar in it?

 

I will check and verify with them that rebar was used. I requested that it was installed in the filled cores. I checked building codes concerning the wall and from what I can determine he has done the footer correctly.

The wall itself is shaped like:

back fill area side

6' area (4' of backfill)---------60' length---------2 blocks high area

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Above is a lame attempt to show what the wall looks like on the high side. I have had a difficult time describing the orientation of the wall to the grade and hope this helps.

The area on the back fill side has been cut out since October during construction and hasn't shown any severe movement, actual little if any during this time. I realize this is to short of a time span for a long term evaluation.

This area is approximent 17' from the back of our house and much of the area is covered by our deck.

 

First off thanks for the replies!

My first question here about sealing the back of the blocks lead to a completely different topic that greatly increased my concern of the long term strength of the wall. I tend to over build things that I build and have been concerned since reading some of these replies since it didn't appear this was constructed correctly from day one.
I thought I would follow up here and give you an update on our wall. Every other cell doesn't appear to have been filled with concrete, in fact it would seem that only a few cells were filled and none appear to have been consistent top to bottom but instead just various cells along the way sometimes skipping as many as five cells. Apparently rebar was not used either! I know this judging from what I can see as the wall has completely failed after a tremendous rain last night and is currently laying on its side covered in backfill dirt.
Although it is difficult to judge the amount of damage at this point I would imagine it is fairly severe. Split face block falling on a concrete pool deck would in itself cause a great amount of cosmetic damage to the surface of the deck not to even mention possible cracking. This all coming at one or two days before completion is incredibly frustrating to say the very least.

 

I have a question for you regarding a 6 foot retaining wall. I put stucco on this wall and it peeled off due to moisture coming through the back of the wall. I scraped it off, replastered and applied acrylic instead of stucco, which has since bubbled and started peeling. I have now peeled off the acrylic and am down to the graycoat. Do you have any suggestions on a sealer I might use before trying to stucco or acrylic again?? There is no possible way I can dig out behind the wall due to the location.....help!

 

The only thing that might possibly work is a product like thoroseal, and then only if you prep the surface meticulously.

As for the poor original poster, I wonder if his wall has bowed by now?