Question
Sunken Bricks
I have a stairway next to a herb garden. It is constructed with 6 x 6 treated timbers, sand, landscape fabric and bricks. The rectangular spaces created by the timbers are filled with sand, then landscaping fabric is laid down on top of the sand. Bricks are then laid down on the fabric and the spaces between the bricks filled with sand.
As a result of some monsoon rains this year, the sand has washed down from the top steps to the lower steps and the bricks sunk down. I've taken the bricks out, stacked them for reuse and am planning to remove the sand and replace it with something that won't wash out the way the sand did.
Is this the best way to correct this problem and what type of base material do you recommend? Materials at Lowe's that come to mind are river rock, coarse gravel, paver base, etc. Also, what's the best landscape fabric to place beneath the bricks (if this is the correct design to use).
AnswerFirst you have to stop the water problem. For this sand to have washed there must be a problem with water intrusion into the base material. It is highly likely the bricks were loosely fit into the spaces with large gaps filled with sand and not cut to be tightly packed. There appears to be no back edge under the previous step to hold the bricks tight. The water can then easily wash out the large gaps. If this was done properly and bricks all fit tight with 1/8"(or smaller) gaps, there should not have been a significant problem.
As for the rebuild, place crushed aggregate (stone with larger and smaller pieces...none larger than 1.5" is good) down first and compact it with a hand tamper. Then place the geotextile over the gravel. Turn up the edges of of the fabric against the wood and staple it in place. Most paver companies will be able to sell you the correct geo-textile fabric. Local home stores may carry it also. Manufacturer US Fabrics recommends US 115NW fabric for this type of use.
After the geo-textile fabric place 1" of sand OVER the geotextile and screed it to a level base course. Place the bricks over the sand and lightly tamp to level them. They should probably set about a 1/4 inch above the height of the surrounding wood to account for minor settling in your base courses. Sweep fine sand into the joints. Now place a large piece of plywood over the step and tamp it uniformly to finish packing the joints. Add more sand as needed to fill any joints that open up.
Critical to success of this design is that the wood parts must be tightly held in place, surface water must not be flowing across these steps except what falls from the sky onto the steps. Sand must be on top of the geo-textile.
See
http://www.icpi.org/
and or
http://www.usfabricsinc.com/geotextileapplications/lightweightseparation
for more.
Best of luck in making these repairs.
Sean J Murphy, LA, ISA, LEED AP
www.seanjmurphy.com
www.amenityarchitects.com
www.seengineering.com
