Hi all. Please forgive the long description – this is my first house so I’m totally new at this, and don’t know what info will be helpful. I hope that I’ve used the correct terminology. Pictures are at the bottom.

I recently moved into a newly remodeled home in central Illinois; it was built in the 70’s, but torn down to everything but the studs and foundation, then rebuilt with otherwise all new materials. It is a slab on grade. There is an attached garage, which sits on a lower slab the rests adjacent to the home’s foundation.

Prior to my moving in from out of state, my parents decided to help me out (without my knowledge) by trying to seal pretty much everything in the very old garage floor. I have a ton of severe allergies, including mold and insect bites, so they essentially wanted to try to water and bug proof the garage as much as possible. It’s an old slab, so there were both large and small cracks. They filled them with sand, then covered with some sort of concrete mixture, and decided to seal the entire perimeter of the garage just to be safe, putting sand down under the caulk or concrete mixture (I’m not 100% sure what they used and neither are they – they bought what the guy at the hardware store told them to get).

Here’s the issue(s) – first, the sand is washing out, and even came back out of the cracks into the garage in many places – decent amount of sand to sweep out. A ton of it also came out into the yard during the last rain storm, making it as far as the other end of the house. There also some water infiltration via some of the stonework in the garage, it looks like, so I’m guessing there’s sort of water movement under the house, since most of the sand was in a large crack in the middle of the floor. All of cracks that they sealed had pretty much all split back open before I’d even got moved in, I stuck a knife down into the largest one, and it seems the sand is totally gone.

The biggest problem – I wanted to see if the sand they’d put under the sealant, between the home and garage foundations (along part of the garage perimeter) had dried out, since the garage was super humid from the water that made its way in. I scraped out some of the caulk along the perimeter, and used a kitchen knife to get some sand out of that crack (much of the sand seemed to have washed elsewhere, but there was a decent amount left). The sand was completely black, damp, and smelled super moldy, like a to-go container in the back of your fridge that you open after forgetting about it for several months – super potent gross mold smell. Other parts of the garage have a moldy smell, so I’m kind of assuming any remaining sand is also water-logged and moldy. Even more concerning is that pretty much each room in the house has a moldy odor, even with my heavy duty air purifiers running. My parents said they didn’t notice an odor before I moved in (they haven’t been in since before I arrived due to social distancing), but I do know I tend to have a super sensitive nose for mold so it’s hard to say if the musty smell in the home is new since the garage work was done.

So, I’m concerned that this gross moldy sand is essentially in an area that seems like it could permeate under, or even through cracks in, the house foundation (especially since some of the sand ended up washing out along the perimeter of the house nowhere near the garage – that sand wasn’t moldy, yet, but I imagine ending up under the house foundation would cause it to get gross quickly). Because the cracks around the garage perimeter (which seems to be the sand that’s getting moldy) run so deep, it seems that it will be difficult to try to get all the remaining sand out, even if I can scrape off the concrete stuff and caulk to get to it (the concrete stuff is still flimsy – seems like it never actually hardened).

I would greatly appreciate any help or advice on how to tackle this cluster f of an issue. Bless my parents for trying to help, but I wish they’d asked first – I know adding more organic material, like sand, to a damp environment just gives mold a nice big dinner, and I would have asked them to just leave it alone until we could figure out a mold resistant sealing method to use. I know that just redoing the whole garage floor with an epoxy coating is an option, but I’m concerned about just sealing moldy sand against the foundation of my house, or directly under the studs in some places. My big questions are:

  1. Could this be what’s causing the rest of the house to smell moldy? Or is it just likely that just I need to install better drainage around the foundation as a whole (grass hasn’t grown in about 3 feet from the foundation around the perimeter, so I’m guessing it’s wetter than it should be).

  2. How the heck do I address this sand issue effectively so that I can get rid of it so I don’t have moldy sand potentially wafting into the air and wrecking havoc with my asthma and allergies?

  3. What is the best type of professional to call to help fix it? I know I could call someone to just fully redo the garage floor, but I’m worried that they might approach it in a way that would be fine for someone without mold allergies, but not for me since they might just prefer to seal over everything.

  4. Would it be better to dig out some of the seal so the remaining sand is at least ventilated and could potentially dry in the meantime? Or is that likely to just make things worse?

Thanks so much for any insight or advice you can give as I navigate my way through this first time home-ownership challenge. I literally have no idea what I’m doing, and don’t want to make the problem worse. If I just wanted a pretty garage, it’d be one thing, but my main motivator is maintaining my health which makes it a bit more high-stakes.

Pictures: https://imgur.com/gallery/2SrJ9ol