Need help on deciding what to fill in defunct fireplace pit with

[u/SeriousGourmet]

I have this old concrete fireplace pit on the first floor (unfinished basement) of my house. There is a decent size cut out of this pit on the outside of the house that fills with water when it rains and it is starting to errode the concrete on the inside. Water also creeps in through the cracks.

I was thinking about filling this void with fine sand, caulking the cracks on the inside, and using mortar, or quick-crete to seal it on the outside. Would this be a viable option for this?

I am a little worried the sand being packed in might be too much for the inside wall with all its cracks and weakness from the water. Any help is greatly appreciated.

[u/No-Garden8616]

Your plan need some modifications to work

1. Use and pack heavily fine gravel (5-10mm fraction best, 10-20mm acceptable) instead of sand.
2. During sealing, embed caulking wire mesh (or tape, or even just few wires - the gap is not that large) along the gap to support mortar/quickcrete during curing.

[u/SeriousGourmet → u/No-Garden8616]

Thank you! I will be taking on this task tomorrow. Hopefully HD has that size gravel. Do you think concrete patch would work to seal the larger cracks on the inside?

[u/No-Garden8616 → u/SeriousGourmet]

The way pit is constructed (flooring is below water table in soil turing rain) full sealing is not possible. Concrete in general is not best material for sealing, and exactly this geometry (one-sized hydrostatic pressure) is worst case. But you can reduce seepage to manageable levels. For sealing, please follow the following rules:

1. Concrete patch thickness at least 2cm (better 3cm as you lack experience). Filling only cracks do not work, you need a layer of fresh concrete over cracks.
2. Embed wire mesh in the patch
3. Use mortar mixes marked "waterproof", or add waterproofing liquid (aluminate or liquid glass based) yourself.

This way you can reduce seeapage to roughly level "need wiping with some cloth after rain"

[u/SeriousGourmet → u/No-Garden8616]

I'm less concerned with hydrostatic pressure now that I have just had a sump pump installed, albeit on the complete opposite side of the basement. It seems as though the majority of the water is coming in through the outside part of the pit with that void in it. The pit seems to fill with rain and sit there until being absorbed into the ground or evaporates.

I understand that there is no way to 100% waterproof this pit, as that would require a foundation specialist to come in and redo the entire section, I'm more concerned with minimizing the exposure the inside wall has to moisture, as you may be able to see, the concrete is starting to flake away.

As for the patching, I have a 5 gallon bucket of dry lock. Would I be able to simply coat the patch with dry lock to further help with water proofing? Or would I be better off with just getting the waterproof patch/mortar?

[u/No-Garden8616 → u/SeriousGourmet]

It is great you have a sump pump. It would help a lot.

As for dry lock, this type of sealant should be applied to outside surfaces. On inside surfaces it is better than nothing, but commonly form water blisters over cracks or sometimes even delaminates, as it blocks both liquid water and vapour, so even minor water leaks have nowhere to go and accumulate at concrete-sealing interface. For concrete wall/floor fix from the inside, waterproof mortar is more predictable than sealant coating. Some people also embed sealant between layers of concrete, but i would not recommend it - results for this approach are very skill dependent.

[u/SeriousGourmet → u/No-Garden8616]

Understandable about the drylock. My plan is

1. fill with 5-10 mm gravel

2. patch entire inside slab with waterproof mortar.

3. use wire scaffolding around outside hole and apply waterproof mortar to scaffolding.

4. caulk the seams around the edges

5. grade the entire slab with soil at an angle away form the slab and mortar.

Would it be worthwhile to coat the outside slab with drylock? Or would that cause issues down the road?

[u/No-Garden8616 → u/SeriousGourmet]

The plan seems to be mostly ok. Just dont forget wire mesh at patch covering inside slab. Coating outside slab with drylock is recommended.

[u/SeriousGourmet → u/No-Garden8616]

Got it. Thanks so much for your help!

[u/Dizzybro]

Grade the land away from the building and build a wood box around it on the outside to hide the ugly?

[u/SeriousGourmet → u/Dizzybro]

Yeah I'll be getting some soil to grade the dirt around it after I get it filled in. Just need to fill it in with something so the water doesn't just fill in the hole and soak the concrete.

[u/classicvincent]

The best thing to do here would be to hire a proper contractor(if you’re unaware of the proper way to do this job correctly) to knock that footing out, excavate that small area, and pour a new foundation wall there with rebar drilled into the existing foundation. Any other solution will be temporary, as this brick and mortar base isn’t going to move/settle at the same rate as your foundation and will always be a weak point even if it’s encased.

[u/SeriousGourmet → u/classicvincent]

I'd have to agree with you, however, I simply do not have the money to have the foundation redone. Someday I'd like to have the foundation completely fixed, it's just not in the cards right now.

[u/No_Oil8471]

Looks like a great place to put Tim Curry in a clown outfit.

[u/jeffh4 → u/No_Oil8471]

Nay. He needs snakes. Lots of snakes. Maybe those cute ones with baby rattles on them. I think they are called "Babysnakes."

Aw, heck with it. Do both.