Mold

[Drew]

can anybody shed some light on this issue I'm having. 2 years ago I build a garage for some clients. 32x24 with a bonus room. The lower level is partioned off, 2/3 garage space, 1/3 heated work shop area with steps going up to the bonus area. The entire structure is well insulated, wall profile consists of hardy siding/tyvek/osb sheathing/2x4 studs with fiberglass, vapor barrior and sheetrock. Electric base board heat in lower level workshop and entire upper level bonus room. The garage is located at the customers cabin which is important to mention as they are not at the place on a regular basis and the structure is closed up for a week or two at a time. The customer called me today with a mold issue. Concentrated on the lower level partition wall wall is "spots" of mold. More heavily towards the bottom of the wall but also scattered up to the ceiling and also some spots on the ceiling. Nothing up stairs in the bonus room. When I was their this afternoon to check out the problem I lifted up a piece of cardboard they had laying on the concrete slab and the bottom side of the cardboard was soaking wet (as well as the concrete). I also noticed the walls were never painted by the homeowner. The walls were primed and than textured (orange peal) at the time of construction but the homeowner wanted to paint to save some $.

What is the source of this mold. Is it a combo of the garage being sealed up for days on end, the extreme heat and humidity we have been having and also the fact that the drywall was never primed and painted after the texture was finished??

[Stratosman]

I'm guessing less to do witht he paint and mostly to do with the humidity in the space, need to get fresh air in the space, I am assuming that the mold is only on the finished space side of the partition? First thing I would do is find a way to ventitlate the space or use a de-humidifier in the space. How about a window ac unit, ceiling fan(s), something to keep some air moving... That might be tough if it sits empty for weeks at a time though. My bet is that it is also starting to smell a tad mildewy as well.

[Drew]

Both sides of the partitiion are finished, the entire garage is rocked and finished. That was my thought as well that windows need to be cracked open or the neighbor needs to stop over and open the place up now and than. Of course when the word mold is mentioned everybody freaks out.

[CAMAN]

Sounds like the place needs an air exchanger and to keep it running all the time.

[Tom7227]

My garage floor has been either damp or just plain wet for the past 10 days at least. Three car with a spancrete ceiling well sealed with a roof membrane. Concrete block walls as it is partially underground on the back side.

It simply is the humidity that we have been having. I am doing a kitchen remodel and all the old counters are sitting in the garage. If I move one, or a garbage can or something there is standing water. A fan has done nothing to dry it out. Thursday when the humidity was down it finally dried out and started getting damp again Friday. A lot of rust is starting to form on tools hanging on pegboard.

IMO The garage is simply too tight. The owner is putting stuff away wet and there is no air movement in the building at all. The humidity of the past week would cause problems anyplace and can't be the basis only for the mold problem. No way the guy is going to run an AC in a closed garage at a lake cabin. Assuming you have some sort of warranty that you have to honor my solution would be to paint the walls with some decent sealer and tell the guy he has to crack a window or something in the summer to air the place out.

[Surface Tension]

Cold slab + warm moist air = condensation on the floor. Without fresh air moving through you'll get mold.

Till the slab warms up some it is going to sweat no matter what you do. With the latest heat wave and high humidity, walking into the garage I could not help notice it was considerable cooler in the garage. Of coarse when I open the garage door the slab is going to instantly sweat. This will go on till the slab has warmed up some. Till then keep air moving through, keep stuff off the floor that would impede air movement to the floor and worst yet absorb moisture. The unpainted sheet rock will absorb moister as well and the mud from the orange peal is a straight shot to pick up moisture.

Not being there to monitor the temps and humidity levels and acting accordingly isn't helping.

What I mean by that is opening windows in cooler temps and low humidity level. closing windows during high heat and humid days, running AC or a dehumidifier when the windows are closed. I think leaving the windows open(more then just cracking a window) or an air exchanger is about all you can do. Bad part there is the windows are open during high temp and humid periods.

[Tom7227]

The deer shack was having mold problems. We would fill the place up with moisture for 3 weeks and then shut it up tight for the next 49. Put in two gable end vents and that solve the problem. A couple of pieces of plywood that we could put down over the vents when the building was in use avoided the heat loss when we needed it. You're going to have to do some sort of passive ventilation system because I don't think anyone is going to power up a system in an unused garage at a cabin. If the guy was too cheap to paint when/where needed he isn't going to spend $25 a month on juice to vent the building.

[CJH]

Dumb idea of the day: how about some type of solar roof vent to get air moving? Wouldn't have to be there to monitor and wouldn't cost a penny once installed.

[Down Deep]

Three conditions have to exist to have mold. Lack of sunlight, moisture and food for the mold. Remove anyone of these three and there will be no mold. It is probably not practical to add sunlight. The sheetrock is the likely the source of the food and I doubt if the client wants to remove that. The only choice he has is to add ventilation.

I have a large garage that is similar in construction and have no mold. In the summer I keep the windows on both sides open at all times. I also have two vents installed on the floor level and leave the access door to the attic open. I also don't store large boxes or items top to bottom on the walls. Any items stored on the floor either have stands or sit on pallets or rails so air can move under them. Nothing is pushed up against the wall. I always leave a couple of inches between the wall and stored item.

Sounds like the problem is a lack of adequate ventilation not its construction. I would find out how the garage is being used and go from there. The web has a lot of info on mold and its abatement, but to get a permanent fix one or all three of the three causes has to be eliminated.

[RumRiverRat]

Not a construction issue.

You do not need to fix it for the owner.

He needs to get some ventilation in that garage.

[LightningBG]

Dumb idea of the day: how about some type of solar roof vent to get air moving? Wouldn't have to be there to monitor and wouldn't cost a penny once installed.

Good idea for sure, but they are expensive. $400 to $600 range from what I've seen.

Ventilation is the issue for sure. You built the garage too good! I wouldn't put any $$$ towards it. The owner is going to need to pony up for some venting or dehumidifiers. You could donate some labor, but I wouldn't provide any product.

Maybe a couple of these that are set on timers to run an hour here and there. or a dehumidifier set to run only when the humidity get above a certain point (piped to the exterior so it doesn't need to be emptied.)

[bobbymalone]

Cold slab + warm moist air = condensation on the floor. Without fresh air moving through you'll get mold.

yep. I think the ventilation would help, but cold slab plus the air we have right now is gonna cause condensation no matter how well you ventilate it.

[BoxMN]

How about bathroom venting fans that are on a temp control? I know humidity isn't really totally temp controlled, but you can guesstimate pretty good - temp gets about 70 in the garage and it turns on? Like the summer version of temp controlled heat tape, or dog water bowls, etc.

Heck, the fans can even be temporary rigged ones that just plug in. I know prolly not code

[crothmeier]

my garage floors were soaked with condensation during that heatwave. i'm echoing the air movement as a solution.

[Justfishing]

Could very well be the lack of paint. Drywall paper is a great mold food. Mold is in the air everywhere so you have 2 of 3 things needed to make it grow. Add moisture, humidity above 60& and you have mold groth. Unfinished drywall is very good at sborbing moisture. So at times of high humidity it will absorb humidity and allow mold growth.

Paint is a vapor retarder and only allows small amounts of water vapor through. A glosss or semi gloss is the paint you want to use. You can also get a mildicide mixed with the paint.

Did you put a plastic vapor barrier under the concrete?

You can get a bathroom fan with a humidstat that can turn on automatically. If you get an energy efficienct fan is will use less than 100w. I do question whether that will pull enough air but maybe you just need to purge a little bit.

[Eelpout08]

Did you put a plastic vapor barrier under the concrete?

Exactly what i was wondering, also wondering if there is proper drainage under the slab. Even then i think with the long strech of hot humid days you are going to have moisture in an unconditioned space. they need to get a dehumidifier going and seal up that rock. ventilation is also a good idea but when the humidity gets above 65% or so it wont do much good

[Justfishing]

i have had a garage floor sweat but the painted walls (gloss) didnt sweat. Now if the walls are not painted they will absorb the moisture increasing the moisture content enough to support the mold growth.

its like an interior door that isnt sealed on all sides that swells and sticks. but it all sides are sealed it doesnt swell.

old building materials are diffenent than new. Solid lumber is better than plywood, plywood is better osb, etc. The more processed the material the easier it rots, supports mold growth etc.