Musty Smell in basement only in summer

Liberty2November 16, 2013

I am in a new home and my basement only smells musty in the summer. its unfinished and appears its the inside exposed concrete picking up the outside humidity in the air and condensates on the walls, then smells. i dont have a water problem and my walls leaking in from outside they are sealed with rubber on the outside of the foundation. I want to paint my walls to brighten it up and dont plan on finishing for a long time maybe never. What do you recommend that will help knock out the smell and seal the concrete to prevent it from absorbing the moisture. I run a dehumidifier and keep it below 50% all year. Thanks for your recos.

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If moisture is condensing on your basement walls in the summer, the humidity is still too high. Be sure all your basement windows and or vents are closed in the summer. Adding foam board insulation would also help. But then you would have to cover it and finish the walls. Add another dehumidifier if you have to. I run two in the summer in a 1,700 sf uninsulated poorly air-sealed basement.

    Bookmark   November 16, 2013 at 12:26PM
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Liberty2

Basement is sealed very well around windows and door. Will dry lock stop the concrete from absorbing condensation thats in the air is my question? i dont have water coming in from out side, appears to just be on humid hot days that it condensates. Does a sealer stop this?

    Bookmark   November 18, 2013 at 5:36PM
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Condensation occurs when the humid air of the basement hits the cold basement wall. A sealer will not help. Lowering the humidity will as will adding a water insensitive insulation.

Here is a link that might be useful: Building Science Corp.: Basement Insulation

    Bookmark   November 19, 2013 at 8:58PM
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Liberty2

Basement is sealed very well around windows and door. Will dry lock stop the concrete from absorbing condensation thats in the air is my question? i dont have water coming in from out side, appears to just be on humid hot days that it condensates. Does a sealer stop this?

    Bookmark   November 20, 2013 at 12:44PM
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dgeist

It's entirely likely that the humidity is not coming in via your windows or door. The moisture is coming from somewhere. It's possible that it's coming through the block, but not if your symptoms are only on certain days. As a test, put a couple square feet of thick plastic sheet (industrial garbage bags, 6-10 mil plastic from a home store, etc. seal it around the outside edge to the block with a seam sealer tape or a bead of silicone. If the water condenses on the inside, then the water could be seeping through the block. If it forms droplets on the outside, then the air is the problem, not your wall.

Get an inexpensive humitistat at your home store and take readings upstairs. If humidity is high up there, it will naturally be high anywhere in the home air can flow, but only condense where it's cold.

Above the foundation, what is the construction of your home? If you have rim joists that aren't sealed, you could be taking on warm damp air from outside through the siding/framing on the house. The plastic trick works in lots of places. seal pieces against the wood framing to see if you're getting water vapor ABOVE your foundation.

Do you have a sump or a drain in your basement? They can both be sources of humidity in the area if not setup properly. Again, though, it would be happening all the time, not just on certain days.

    Bookmark   December 6, 2013 at 11:58AM
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Water vapour moves from warm to cold. On humid summer days, that means it's moving from the outside to the inside, right through your blocks. And, as pointed out above, it's being circulated in the home itself, moreso if the home is not air conditioned.

Some people put great faith in sealers.

As pointed out above, a sure way to reduce the uncontrolled inward movement of water vapour is to properly insulate and air seal the rim joists with either spray foam or blocks of XPS, EPS and caulk.

The mould smell is quite common in basements everywhere. The surest remedy is to reduce the humidity well below 50% RH.

    Bookmark   December 7, 2013 at 8:34PM
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