Question
I would like to install a block retaining wall system on the concrete pad that is my front yard. I am told that as long as the wall is not over 4ft I can just glue the first course to the concrete and then do the next courses normally. However, the person did not seem to know how I prevent water from draining onto my exterior wall and therefore into my foundation through the weep holes. I have a finished basement so this would be a problem. I wonder if I can backfill gravel against the exterior brick wall just like I will behind the blocks so that any water can drain away from the house and also so the damp soil will not be in contact with the brick wall and block the weep holes. Or is it a bad idea altogether to build it against the wall?

Answer
In general it is definitely a bad idea. However, if it is something that is important to you  let me explain the steps you need to follow.
1. You must apply a 'fluid applied' water proof membrane to your existing exterior wall face. This is typically a 'thermo-plastic' that must be heated and then sprayed on or applied with a roller. It is self healing rubberized material that waterproofs the exterior wall face.
2. Apply a 10mil poly liner to the membrane. This is simply black plastic you can buy at your home store in rolls. It is a secondary waterproofing and serves as a line of first defense.
3. Now you build your masonry wall. First clean the slab with bleach and water. Then use muriatic acid to etch the concrete for better bond with mortar.
4. Use mortar, not glue, to build the wall up from your slab. To be sure the wall stays in place consider drilling 1/2" holes every few blocks and putting in some rebar pieces that go at least 2" into the slab. Epoxy these in place with two part epoxy rated for masonry anchoring. Then apply mortar or grout(watered down concrete) in the cells where the dowels are. This will ensure no lateral movement in the wall. It is best to do this at the corners and then a few spots in the length of the wall.
5. Once you finish the wall you need to apply the same waterproofing to the inside so water doesn't leach though the wall, which looks bad. You also need to provide some form of weep holes in the front face of the wall to let trapped water out. I'ld drill several 1" holes across the front. Not less than 48" on center. You could also place 1/2" pvc pipe under the first row of block and make the first mortar joint wide enough to accommodate the PVC width.
You also need a french drain across the back that will drain water away from the house.
6.Place a 4" perforated pipe at the back where the slab meets the house wall and cover it with gravel. Add soil in the front and add gravel at the same time in the back make sure you keep 4 to 6" of gravel across the face of the wall(with the 10mil poly liner pinched against the wall). Either end of the pipe under the gravel should either come through the wall or be routed to weep holes so water that drains down through the gravel has an outlet.

That should be fairy safe but rather expensive and difficult to do right.
Good Luck
Sean J Murphy, LA,ISA, LEED AP
Please check out my blogs and articles on landscape topics like this on my websites.
http://www.seanjmurphy.com
http://amenityarchitects.com




6. Now you are ready