Concrete holds more water than it shows
A basement slab is several inches of porous material sitting on soil. When water stands on it for hours, it soaks in, and the surface can dry to the touch within a day while the inside of the slab is still saturated. Foundation walls behave the same way, and block walls can hold water inside their hollow cores.
Basements are also cool, which slows evaporation, and they tend to have little air movement. Colorado's dry outdoor air helps upstairs, but a closed basement with wet concrete can stay humid for a long time without equipment. Dehumidifiers pull moisture out of the air so the concrete can keep releasing it, and air movers sweep the surface so the damp layer of air right above the concrete is constantly replaced.
Readings you may see on a drying log
| Measurement | What it tells you | What to watch for |
|---|---|---|
| Relative humidity in the room | How much moisture the air is holding | Should fall noticeably within the first day or two of equipment running |
| Grains per pound or dew point | Absolute moisture in the air, independent of temperature | Compared inside and outside the drying area to show equipment is removing water |
| Slab moisture readings | Relative wetness of the concrete at marked points | Steady decline at each point, compared against a dry reference area |
| Framing moisture content | Percent moisture in bottom plates and studs | Approaching the reading of unaffected framing elsewhere in the house |
| Drywall readings | Whether remaining drywall above a cut is dry | Should match unaffected walls before finishes go back |
How a typical basement drying job progresses
Actual times vary with the water source, how long it sat and how much was removed.
- Day 1
- Standing water extracted, wet pad and insulation removed, baseline readings taken and marked on a sketch, equipment placed.
- Day 2
- Room humidity drops; framing readings begin to fall. Equipment is checked and repositioned if any area lags.
- Days 3 to 4
- Most framing nears dry. The slab and block walls usually lag behind and are still reading wet.
- Days 4 and beyond
- Equipment is reduced as areas reach dry standard. Dense concrete or block cores may take longer.
- Final visit
- Readings at every marked point compared with a dry reference. Equipment removed and a final log provided.
Your part while equipment runs
Keep basement doors and windows closed unless the provider asks otherwise, leave equipment on even when it is noisy, and do not turn the furnace off or way down without asking. Keep a phone photo of each day's readings if the provider leaves a log on site. Those numbers are the best evidence for an insurance adjuster that the drying time billed was needed.
Common questions
Can I just open the windows instead of running dehumidifiers?
On a dry, breezy day it helps a little, but basement windows are small and outdoor air can be humid during summer storms. Dehumidifiers remove water steadily regardless of the weather.
General information for Englewood, not a quote or professional advice. In an emergency, call 911.