Concrete Slab Slow to Dry
Slab poured July 15, 2021 in Central TX zone 2 on post and tension with 30″ deep of total pour. Total 3700 sq ft Ranch single story- with 3 car work shop garage (1000 sq ft). Barrier was used. Cement was 4000 psi with no additives and wet dried for 7 days. Framed in November and used Tyvek sheeting and windows in place. Shingled roof on Nov 27. Would think the cement floor would be dry by now but various areas of the slab floor have visible wetness through out the house. Roof not leaking. We did 4000 psi with no additives with intention of polish cement floors–have since change mind and plan on tiling. Is the cement slab still wet and drying?
We are very concerned and hesitant on proceeding with any flooring until wetness is resolved. Any thoughts on why this is happening? Any resolutions besides abandoning project? Thank you for any assistance and information!!!
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Concrete doesn't dry, it cures -- the water in the mix reacts chemically with the cement to form a new substance. If there is more water in the mix than is needed for the reaction, the excess will seep out as the concrete cures and will typically dry within a few hours. If your slab is wet months after being poured, it's not because of the water that was mixed into the concrete. Water is getting into your slab from outside somehow.
It's not the end of the world, but you really want to get it fixed before the house is finished. The fix could be as simple as putting gutters and downspouts on the roof.
Hi You All,
I've heard of cases where the homeowner runs a lawn sprinkler that saturates soil at the perimeter (or one edge) of the slab, leading to a damp slab due to wicking of water horizontally through the concrete. Make sure your sprinkler's spray pattern stops short of your slab edge.
Thank you, no landscape yet so not a sprinkler causing it, but there is only 6-8 inches of exposed slab on the back side of the house due to ground dirt pushed up against it. We will remove it and expose more slab and add the gutters and downspouts put in sooner!
Is there a bed of gravel under your slab?
How much higher than the surrounding is the gravel under your slab?
Was a drain install around your footing?
Do you have enough slope on your lot so your footing can drain to daylight?
What is normal in my location is likely to be very different for the normal in your location so internet advise may not be very helpful.
Often where a bath tub will be located there is a opening in the slab for the tub drain. I would look for such an opening and dig out the gravel about 14 inches below the surface. If this opening is full of water, you have a major problem.
Walta
How are the edges of the entire slab detailed? Like is there a membrane and drainage board on the edges?
Also did the polishing contractor measure with a moisture meter? What was the RH? If you manage to get one, take measurements every 10' radius or something to that effect. It might give a better sense of what's going.
You're right in that you should get this handled before moving forward with any flooring. It will ruin any floor you put overtop of it, and waste your money/time.
As DCC said, this isn't water left from the pour 6 months ago. Water is getting in somewhere. Wether is ground water from the outside wicking in from the edges, bad vapour barrier details and a high water table, or a supply plumbing leak within the slab.
I'm sure there are other possibilities here, it's hard to say when you're not there looking at it. So Systematically go through each scenario.
Jamie
Thank you! We do not have water or septic connected to the slab yet so not a plumbing leak. The slab area was dug in 30 inches around the perimeter and all the mounds, then plastic membrane (don't know the quality or thickness) was put on top of caliche (not gravel) then the post and tension cables then the cement. No slab drains put in. Surprisingly the bathrooms drains (shower and tub) do not have the water issue. We did not call the polishing contractor back since we have so many cracks and had decided to tile. So we will get a water meter and measure the RH. The moisture/water is in consistent spots and happens after rain. We are building a berm or retaining wall to help direct rainfall around the house since we are on a slight slope, And have moved dirt away from the back side since it only had 6 inches of exposed slab compared to the front where there is 14-24 inches of exposed slab.