condensation on porch

karenp · #1 05/01/14, 01:47 PM

We have a 12 x 36 porch on the side of our house that becomes unusable due to condensation in humid weather. The porch was added on to the house. It has a block foundation, filled with dirt then concrete. It is at least 15 years old, it didn't start out like this, but it gets worse every year over the past few years. Anything left on the porch like boots or such leave dry spots under them. I thought of using some type of masonry sealer, but I can't find something that doesn't say not to use it on surfaces that are walked on and since the water is not coming up from the bottom I'm not sure it would help. You guys seem to know how to fix most anything, any ideas?

DeRock · #2 05/01/14, 02:20 PM

From your description there isn't anything you can apply (sealer wise) on the concrete that will make the condensation go away. The moisture is coming from the air and applying a sealer will probably make it worse (the concrete won't be able to absorb any and it will all sit on the surface).

It's what is commonly called the Coke bottle effect. When the air is warm and filled with moisture and your concrete slab is cooler than the air it will condense moisture right out of the air onto it's surface. Just like when you put a cold bottle of Coke on the table on a warm humid afternoon it soon condenses enough moisture out of the air to soon create a wet ring on the table.

I'm betting your porch doesn't get any sun and is probably on the north side of your house.

karenp · #3 05/01/14, 02:32 PM

very little sun and yes on the north side, but why wouldn't it have done this all along?

watcher · #4 05/01/14, 02:50 PM

It probably did but either the humidity or temp variation is higher than it has been.

Most of the things I can think to do would be either difficult, expensive or both.

karenp · #5 05/01/14, 02:56 PM

We may not be able to afford them, but I'd like to hear your ideas.

7thswan · #6 05/01/14, 03:00 PM

Get an attic fan for one end and the louvers for the other end. They have an automatic thermostat. It will pull dry air in from outside which ever side is the driest and the louver opens and pushes the air out(or visa versa). I've done this on 2 greenhouses. Cheeper than regular greenhouse outfits.

DeRock · #7 05/02/14, 05:13 AM

Probably the cheapest cure would be to put wood decking over the concrete.