Hi. I have a house from 1830 with the original dirt floor still in it.

I want to concrete it over and use it for storage. What is the minimum slab thickness (or thinness) that I can go? Is there a local code or an industry standard to go by? The ceiling is only 5' high, so the thinner the better. An architect told me that a "rat" slab can be between 2-3 inches and be okay. I guess with enough aggregate and some fiber mesh, that should be okay?


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I love archetects, they always have a hand in the moneypot.

Your first question should be soil composition and moisture content.  If your sand content is high enough dirtcrete could well be your solution.

In this area we have an infatuation with concrete "floored" crawlspaces.  They're generally 3" thick rake finished & the comedians who wrote the code forgot to include a moisture barrier.

Fiber concrete would give you no benefit.  Unless your storage is going to be heavy objects on small footprints you probably don't need any mesh.

You can learn a lot from the Portland Cement Association, they support many websites with good information including cement.org

Hi-Our 1890 Q.A. also has a partial dirt floor under one or two rooms--place where coal went?  Anyway, like you we want to get rid of that dirt too!  Did you find a solution?  Thanks-and we are Stooges fans too!  M. Campbell

My 1740's colonial still has its original dirt floor. I dont want to concrete as that would be an irreversible change to the house, but I do plan to rake it out flat, lay down heavy plastic sheeting and pour gravel or peastone over it.

if one is putting down plastic anyway, why not interlocking rubber and no stone?  it would be way less microbial.

true but way more expensive

I don't want to remove the dirt, I just want to concrete it over and bring the house kicking and screaming into the 21st century. Ideally, I would like to remove the soil to get more headroom. But, a tight budget and a cheap wife won't allow that to happen. If I just concrete it over, I can get some useful storage space and maybe a little workbench to fix stuff at.

The ceiling is only 5' hgh, but, I'll be sitting down at the workbench most of the time anyway. It's not perfect, but, it's what I have to live with. I wish that we could sell and get a new one, but, houses are pretty expensive 'round these parts, so thats out the window! Most houses go for $600-800K. This one is only about $500k at the most.  

start digging.  you can make a raised bed with the dirt.  icky damp (concrete stays damp a long time) storage and a 5' work area?  not very good resale value in that.  the cheap wife will lose expensive resale.

Whatever you do, don't undermine your foundation from the inside.

I see you live in Cranbury, NJ - thats definitely a pricey area! I used to work in Princeton - lived down in Ewing. 

Every house is different and every owner is different. If your house has inherent value as a historic home then you want to keep permanent alterations to a minimum. If it is simply a quaint old house that needs updating then by all means pour a slab.

My problems are several - first I have to get out piles of rocks, then put in a drainage system and sump pump, then lay plastic and crushed stone.

Nothing really "historic' going on here. Just an old house that needs to be made more useful for it's current inhabitants.
I wish someone would've done this for me 50 years ago!

I hear you! I say that same thing everyday....

the previous owners of my house did!


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