Thread: Cracks on garage concrete slab

Hi everyone,

Ive noticed this crack on a garage slab and it has white efflorescence which indicates theres humidity or water coming from underneath. The slab was painted and the paint is coming of. The crack size is about 1/8'' and I wonder if I should recommand to seal the crack or to have it checked by a professionnal and if its the case, which one ?

Which criteria determines if a concrete slab crack needs to be sealed or checked by an expert ?

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Its not uncommon to see cracks of this nature particularly in a garage.

My own personal opinion is to clean the crack out and apply a good quality polyurethane caulk.

As to the water vapour there is nothing which can be done. The paint is actually hindering the evaporation of the moisture and as such is being pushed off the floor.

I just noticed Ive uploaded the wrong pictures...let me try this again !

I'm betting there are cracks all over the floor and the paint was applied to hide them and give a uniform appearance.

A garage slab is poured after the block walls have been installed.
In many cases stones or debris are left just below the soil surface prior to pouring.
Since the soil can also not be compacted well, aside from use of a vibrating compactor, voids can occur and settlement or lift can cause cracks.
Another defect with most garage slabs is that they let the garage door jambs extend down into the slab, in effect, dangling bait in front of a termite.
Termite activity under the slab, can also create voids and allow settlement.
Seal and monitor cracks in the floor.
Remember,
it's just a house, it doesn't have to fly

Parking a car covered in road salt (winter months) can get into any small cracks and cause further damage and possibly even freeze/thaw damage.

Why so worried about cracks on a slab?

First question, is there any pyrite in the area you were inspecting?
If not, ask them to seal the cracks (to avoid humidity to enter the house) and the problem is solved.

There can be debris under the slab, but you can't really suggest your client to break the slab to remove the debris, so this leaves you no choice but to recommend to seal the cracks and get your ass to the next inspection.

cheers

Cracks noted in garage floor, recommend sealing with masonry caulk. That's about it!