Florida home - new construction - concrete block on mono slab. Heavy rains washed out about an 18" by 48" by 9" deep area of soil/sand from underneath the slab/footing on the front corner of the home. The home is complete minus a few finishing touches. What would be the proper method of replacing this soil/sand other than just shoving it back underneath. How can you get it compacted to restore it to the way it was. Sorry no pix.
If it was my house I would want a concrete slurry grout pumped into the cavern.
And have fixed whatever caused the washout to begin with…grade etc…
i agree. drill a hole in the slab at the shallowest point, build a “form” at the expossed edges, pour concrete and let dry. you’ll never get added soil to compact the way it should. 'course Florida itself will never compact the way it should.
Thanks all, kind of my thinking also.
I agree
The owners contacted the builders concerning this. The builders said they would merely use a tractor w/blade and compress the sand back underneath to fill the void. They asked me what I thought of this. I told them; not my choice but I’d do a little research and let them know. Would really appreciate your opinions.
If the contractor won’t budge, make sure the client has a very good warranty!
Thanks William, I’m still looking for opinions on whether this may or may not be adequate. We photo documented everything and they do have a ten year warranty on structural. Just want to know if I should advise them to push further for a more proper repair. I didn’t state this before but it is on the front of the home (right side) but does not wrap around the corner.
Once the problem of erosion has been corrected for any further problems in the future, other than pumped or pressure grout that I would not recommend, I would entertain what they call flowable fill. It gravity fills all voids and stabilizes voids to the natural state of what was there before without causing any upward pressures causing an unequal grade support. Flowable fill is usually available through any Concrete Supplier.
Just my nickles worth.
Marcel 
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Not my choice either or the best option, as it could just wash out again and the soil will never be compacted the same as other soil under the slab. This could lead to some future movement/cracking, but may not be such a huge deal if a small area with a uniformly loaded slab. If it was my house I would want it grouted.
JMO & 2-nickels … 
P.S. “Soil Cement” (simple mixture of backfill with cement and some water) is another good option for the repair, which is easy to handle for your average contractor. Gets worked in like stiff backfill and hardens like a weak concrete.
JMO & 2-nickles … 
Robert, around here we call that mudjacking, even listed that way in some of the phone books, had it done to a patio years ago, still no problems
Hey all,
i just purchased a home and need to fix some washout under the edge of the concrete slab in the back of the house. I am also in Florida.
At the back of the house, under both the living room and the florida room, there appears to be water erosion under the slab. see pictures:
there are 2 landscape beds abutting the house within my lanai, the water must have washed out under the slab?
It also appears that the back portion of the living room as a slight slope to it towards the back where the washout occurred. I was told my the neighbor that the listing agent backfilled under the house some sand material.
I am wanting to know what I should do to fix this issue and make sure everything is structurally sound. do I dig down and form a concrete knee wall with some blocks and fill in with concrete? then pump a concrete mix in behind the knee wall?
I also was told by others that i could dig out the sand, and pack some soil cement under the house??
looking for suggestions, I would like to get this handled on the cheap, not jacking the house up and pouring jacks in place etc, i think that is overkill.