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I have a client here, (Lafayette, Louisiana,) with a strange moisture-mildew problem.
His home is an upscale, ten tear old one storey brick veneer on a slab.
In his panelled library, (stained and varnished birch veneer plywood in molded frames,) he has several framed, (behind glassd,) art prints.
One of the prints, hung on an exterior wall, between two windows, recently
developed a large patch of mildew in a lower corner.
The paper backing behind the print is un-stained but the panelling behind
the mildewed corner has a blackish stain. The staining also appears on the same side above the print.
The birch plywood is not warped,cracked or de-laminated as you might expect
it to be if it got wet enough to blacken the finish.
Inspecting the exterior I found no masonry cracks, caulk gaps, roof or gutter problems in the surrounding area. In fact the entire exterior
elevetion is perfect.
This is a prime area for mildew and other moisture problems but this has been an exceptionally dry year. Almost no rain, other than a few showery days, all year. Also, this has been an exceptionally hot summer; high 90’s
and low 100’s for the past two months.
My problem is two-fold: Figure out what happened and fix it so it doesn’t
happen again. Remove the staining from the existing panelling and re-finish.
Any ideas out there what caused the mildew and staining? Moisture sources?
How to remove the stain? Would sandpaper and household bleach work?
Replies
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s....
seems like that little patch is below the dew point..
either elevated localized humidity..
or a cool moist draft from one of the two windows
could maybe increase the air circulation in that room to even out temp / humidity...
time to break out the old sling psychrometer...
*S.Doane:I just covered bleachs in a thread in Knots entitled "Blue-grey stain in maple". I suggest you refer to my advice there as a start.I do not know the cause, but maybe the solution (bleach that is). DO NOT SAND -- at least not initially. It may be possible to attain effective bleaching through the finish.Choose what ever bleach type you prefer - I would start with sodium hypochloride because there is probably some at the site. Mix as recommended in the Knots thread. Several ounces should be sufficient so you might want to use teaspoons/tablespoons for measuring the bleach and water. Find some Q-tips (cotton swabs) and slightly dampen them with the bleach solution. VERY CAREFULLY treat ONLY the affected area. You may want to get a fine pointed art brush because you definitely do not want to bleach ANY of the surrounding area or you will likely get a bleached border. Don't apply in excess such that you get drips or runs. Let it sit for a bit (say 5 or so minutes) and wipe with a dampened rag and then a dry rag. Repeat as needed or use a slightly more concentrated solution or let it sit longer before wiping.If you are lucky, you might be able to solve this problem in an hour or so without having to mess with the finish.My brain of limited capacity cannot comprehend dew points and such relative interior building applications as it is saturated with too many wood facts (or maybe it's residual from living during the '60's). Maybe it might be worthwhile to get a dehumidifier for the house or room.Let me know how it works out. If you are sufficiently grateful maybe you can come to Orygun and take back all your F#$%ing possums. We have a joke out here --- Why did the chicken cross the road? --- to show possums that it could be done! They are not native to here; Supposedly they were introduced by somebody from Louisana in the '30's.Stanley
*DoaneI am from North Louisiana near Monroe. Dont know about your possum count down there but I can relate to the hot dry weather we have been having. could it be that an a/c vent is blowing on the print and moisture condensing on the back side of the glass on the print. condensation always occurs on the warm side of a cool surface. Also Im curious if the a/c unit is oversized and not running enough to lower the humidity. It appears this area is isolated and this is not occuring throughout the house so I would opt for an a/c vent blowing on the print. As hot as its been I cant see an a/c unit turning off anywhere in louisiana until this week after our cool snap. The only other thing I can think of is heat coming thru the print from the wall if it is uninsulated. Hope you figure it out. Also I learned in a continuing education class last yr. that the louisiana dept. of natural resources or energy has some folks that will come out and diagnose moisture and infiltration problems in homes. Might want to give them a call
*s.doaneMoisture moves from high vapor pressure to low vapor pressure and from hot to cold.Your building is in a climate that drys to the inside of the building. The back of the glass in that particular area is the first condensing surface.Brick serves as a large buffer for moisture storage, and then if the sun heats it you have both heat and high vapor pressure pushing the moisture through the walls.So despite being a dry summer, rain can induce larger moisture differentials than ongoing high relative humidity can.I would not be surprised to find some sort of defect or anomolie right behind that spot.Are there other pictures on the same wall?What exposure is the wall?Where is an A/C outlet relative to the picture?How long after it last rained did this happen?Can you pull off a receptacle cover and look inside the wall anywhere?And the last question - the big one - Where is the vapor diffusion retarder (vapor barrier) and what type of insulation?-Rob
*Brian; Thanx for the wood bleaching info. I'll give it a try. Sorry about the possums.I'm afraid they don't add much charm to their surroundings. s.doane
*Rob; thanx for your input. I think you may have nailed it. s.doane