Expert: Stephen Major (Owner--Major Design Group) - 3/24/2007

Question
Hi Steve, I have an older mobile home that heaves and I would like to have a slab put underneath. Coul you tell me if and how this could be done?

Answer
Lisa,

You don't indicate where your mobile home is located.  The prevailing climate as well as soil and drainage conditions will dictate the best approach.  The following descriptions are for typical soil conditions and assume adequate drainage and load bearing capacity.  I am also assuming that the trailer is single-width.

There are two ways to go here.  One method is to pour individual footings/piers at each jack point.  This can be done gradually, one at a time.  Just insert temporary jacks at each side of the actual support location, remove the existing support, excavate to below frost depth (if that is a concern) and pour a footing that is about 24" square and 12" thick. Place a mat of #5 reinforcing rod (3 pieces crossed by three pieces) in the footing at 4" above excavation.  When this is set (3 days or more, depending on temperature) build up with concrete block to the frame height.  Verify and follow local hurricane codes -- ties may be needed.

If you want to do a slab, I would pour 1/2 at a time.  you will need to slide I-beams or timbers under the half trailer, jack and crib them at each end, and then remove existing supports.  The jacking and temporary supports must be done very carefully so as not to create a collapse hazard -- look for a local contractor who specializes in this work.  Ideally it would be best to excavate a few inches of soil and replace it with crushed stone (#1 or #2), but this would be very difficult beneath the trailer.  Set 2x6 forms level, and stake and brace properly.  Place 6x6 wire mesh reinforcing within the entire slab area, on "high chairs" to elevate the mesh about 2".  Pour the concrete with plenty of help, and flatten/consolidate with a long straight screed (2x6 wood or metal).  There is no need to trowel-finish the slab.  Once the concrete is set, insert new supports and repeat for the other half.  Again, verify and follow local codes.