Trying to keep dry crawlspace.

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Old 02-17-20, 05:37 AM
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Trying to keep dry crawlspace.

I just bought a 1997 home on a slope with a stream at the bottom of the hill, close to house w high water table. I have three crawlspaces. We had some high mold spore counts before we bought it and had the previous owner pay for mitigation (she and previous owner before her never looked in spaces, I am sure), including new visqueen in the spaces, drylock walls, new insulation in one of them, and closed up the vents Good readings after all of this.

Now I want to keep it healthy. Cannot afford these ridiculous prices for 3 dehumidifiers. May eventually buy 2 cheap ones as crawlspaces are 300 sq ft or less and will replace as needed.

Issue now is, we had several days of huge rain and there is considerable moisture accumulated under the visqueen in 2 of the crawlspaces. We already had slope improved next to the foundation which has helped dry things out. I also understand the visqueen is doing its job by trapping moisture...but how does it ever dry out? Was thinking of opening crawl space doors for a few hours on days where humidity is below 60%...any thoughts/ideas appreciated. Am I overreacting and just need to give moisture time to dissipate? Mold team said the space was really dry, but that was before these huge rains. I bought a humidifier measurement tool to monitor keeoing it at below 60%. Thanks for advice/input.
 
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Old 02-17-20, 09:31 AM
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Moisture trapped underneath plastic never really dries out. It will dry eventually but it takes a very long time after the source of the water has been removed. If you still have water entering the crawl space it will always stay wet under the plastic.

Closing crawl space vents is the opposite of what you want to do if you have a moisture problem. Most modern homes are required to have quite a bit of crawl space ventilation.
 
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Old 02-17-20, 06:08 PM
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The vents open/closed debate seems to be an ongoing one.

I am now not sure if we need more foundation work, or if the huge storms created an exceptional amount of runoff...but my main objective is to stop the mold from returning. Do you think the moisture under the vapor barrier is really a concern? I mean, it's doing its job and keeping it from reaching wood and insulation. Or should I rent a high power dehumidifier for a few days.
 
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Old 02-18-20, 04:38 AM
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The real question is how much money are you willing to spend to get rid of the water. The best option is always to keep the water out in the first place. Even with a dehumidifier the water is already inside and it takes time, sometimes a long time to evaporate it away.
 
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Old 02-18-20, 07:03 AM
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Right, having only had the house for a couple of months, we immediately had the grading improved so water isn't running up against the house. We do have one problem spot, I think, on one steep corner still.

This current situation may be an exception as we had several days of big rain. Also, we had mold mitigation, they did not suggest encapsulation and actually said the one crawlspace was quite dry - not any more. I guess we will rent a monster dehumidifier and see if this was a one-off event in the year ahead.
 
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Old 02-18-20, 10:48 AM
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If you have openings into the crawl space a fan would be the cheapest way to dry it out. I would only use a dehumidifier if you don't have openings you can blow fresh air in and out.
 
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Old 02-18-20, 01:26 PM
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Foundation guy came out and doesn't know why there is so much water, except that lately we had had a lot of rain and we need a humidifier. He is going to talk to the boss, and also said newer homes are putting gravel under vappr barrier. Not sure about that one.
 
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Old 02-18-20, 01:33 PM
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Option #1 - Run a fan during daytime.
More important that "humidity" (water in the air by weight) is "RELATIVE humidity"(water in the air as a percentage of what the air can hold).
Warm air can hold a HUGE amount of water. Cool air holds much less.
So, you want a simple FAN to blow air through the crawl space (warm inside air during the winter) or outside air during spring-summer-fall when it is warm enough.

Option #2 Ever eat at a southern diner?
You may notice that the salt shakers have a few grains of rice in them. That rice is there to absorb humidity that would make the sale stick together. You can use this same trick to your advantage. Figure out where your local Asian/Korean/Indian population shops - find an Asian market someplace, where you can buy rice in a 40 lbs burlap bags
e.g. ASSI PLAZA near me.
Walmart has 20 lbs plastic bags of rice if you can't find an asian market.

Get 2 bags. Think of them as giant versions of the "dessicant - do not eat - silica gel" baggies that electronics are packed in. Set the 40 lbs bag of rice on a steel tray, plywood sheet or plastic snow disk, and slide it into the crawl space. Swap out every 2-4 weeks with a new bag.

A- (boring) Take the old bag of rice and bake on low in the oven to remove moisture

B- (fun) Take ten pounds of old rice, cook it. Cook carrots, celery, green peppers (Cajun trinity)
add
6 tablespoon sweet or smoked paprika
12 teaspoons oregano
6 (18 pound) frying chicken, cut each into 10 pieces
2 1/2 cup extra-virgin olive oil
12 Spanish chorizo sausages, thickly sliced
Kosher salt and freshly ground pepper
6 Spanish onions, diced
24 garlic cloves, crushed
6 Bunches flat-leaf parsley leaves, chopped, reserve some for garnish
6 (15-ounce) cans whole tomatoes, drained and hand-crushed
6 cans beer + 1 gallon water
Generous pinch saffron threads
6 dozen clams, scrubbed
6 pounds jumbo shrimp, peeled and de-veined
12 lobster tails
3 cups sweet peas, frozen and thawed
6 cups artichoke hearts,
24 roasted red peppers,
18 cups chicken broth,

and invite all your neighbors over.
 
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Old 02-18-20, 03:14 PM
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Without being there to see the lay of the land it is hard to advise you so the following are just thoughts.

Make sure all eves trough drains drain away from the house and does not collect anywhere.
Does the house have weeping tile around the perimeter?
Water under your visqueen is not going to evaporate.so you have to wait till the surrounding earth dries enough so the water is absorbed.
You said you closed up the vents. Where and what were those vents. Usually closing vents is not a good idea as you are trapping the moisture in the space. If anything I would be adding vents.
Why are you insulating the crawl space?
Opening the doors should definitely help. The only problem is that you may let critters in.
Gravel under the vapor barrier is used because it does not hold water like soil so it will drain away quicker.
Since one crawl space is good that may give some clues as to what is going on.
Also a lot depends on the soil type.





 
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Old 02-19-20, 02:43 AM
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Rice is a new one, I'll consider that.
I have a dozen different articles saying vents open or closed and everyone has different opinions. Foundation guy said vents closed in winter and open in summer. Makes sense to me. There are even automatic vents that react to temp changes.

Anyway, we got 4 box fans last night and will fold back visqueen in sections to dry out the dirt. I can see opening vents for this but snow is coming tomorrow. Furnace and hot water heater are in the driest crawlspace. Insulation is on ceiling of 2 crawlspaces as it is the floor of the house above. This is all crazy moving from the arid SW to the rainy SE! We need to figure out a system to fight return of mold spores. Ugh.
 
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Old 02-19-20, 02:48 AM
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Oh, yeah, foundation guys made sure drains were carrying water away and none are broken, downspouts secure, etc. I don't even know what weeping tile is. He put red clay soil around the eroded area to prevent if from washing away. I don't know what is actually under the plastic.
 
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Old 02-19-20, 04:29 AM
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I would NOT put rice in a crawl space. First it can only absorb a limited/small amount of moisture before it will need replacing and it will need replacing often so it's an expensive option. Second, and this is a biggie. It's FOOD. It will attract and feed vermin, insects, mold and mildew.
 
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Old 02-19-20, 08:17 AM
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Opening up the visqueen will let the water evaporate into the air which raises the humidity in the crawl space.

Weeping tile is a corrugated pipe with holes in it. Also usually has a material sock over it so it lets water in but keeps debris out.
It buried the bottom of a foundation, then gravel and then a earth.
So any water that hits the foundation drains down to the weeping tile and then away from the building.

 
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Old 02-19-20, 10:26 AM
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Originally Posted by Pilot Dane
I would NOT put rice in a crawl space.
Should clarify that -
The rice is for one-time use, as a last-step dessicant, AFTER you get the water out.

The open bag ~ 20 lbs rice goes into a container - a 5 gallon bucket works well, with a metal screen over the opening. Other option for removing residual moisture and musty smells are unscented bags of clay based kitty litter, or stock up on a couple of bags of "real wood charcoal" (NOT the brickettes, and NOT the "easy light" charcoal).

These are fairly common real estate tricks when showing a vacant house, rice, kitty litter, charcoal absorb humidity and odors, which keeps a place from smelling musty.
 

Last edited by Hal_S; 02-19-20 at 10:43 AM.
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