Existing Slab Concrete - Do I Repair, Replace, or Pour Over?

[VinceGarage]

Hey guys,

I'm very new to this, and am in the preliminary stages of planning to convert my detached ~ 200sqft garage into an office space.

It is old, having been built in 1943; all wood construction with vinyl siding. Roof looks to be in good condition. It is on a concrete slab which is cracked in a few places.

Given that I'm in Southern Ontario, winters are such that I will need decent heating and summers are such that I'd like decent AC. I intend to put in a portable AC (installed permanently with a hole in the wall) and a wall-mounted heater. Insulating the walls and ceiling will be no problem, but I'm curious about the floor. I would like to keep it concrete, so that it can still be easily used as a garage if needed in the future. But I have no idea what's under the current slab, if anything.

I guess my question is two-fold:

1) Should I be concerned about heat-loss or moisture issues through an existing slab-concrete floor if the rest of the building is thoroughly insulated?

2) For the floor cracks, can these be filled, and then the whole floor painted /sealed? Or would I be better off completely re-doing the floor?

 

[dcg9381]

I'll defer #1 to someone who knows about slabs up north as they are very different from slabs where I am.

As to #2, post photos of your slabs cracks.. I've seen some substantially cracked floors that are filled, sanded, then refinished to the point where you cannot tell that they were ever cracked. Here, a "re-do" would mean pouring at least 4" of concrete on top with it being much more common to cut out the entire existing slab and start over (expensive).

 

[ConCretin]

Too many variables to offer an informed decision but in general, moisture through a slab while not ideal, isn't a major issue unless you want to apply an adhered floor covering. Likewise heat loss isn't a huge issue either. Unless you are planning on in-floor radiant, I've become convinced the natural heat from the earth under a slab is a net gain over an insulated slab that blocks it.

The serviceability of the existing slab depends on the nature of the cracks. Are they minor shrinkage cracks or are they structural resulting from an insufficient base underneath or excessive loading If it's the former, the cracks are cosmetic and can be hidden pretty well. If it's the latter, they are pretty much impossible to repair.

It probably comes down to how pretty you want the slab to be and how much trouble it is to maintain and keep clean.