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L Gallagher 12-19-2009 12:16 PM

mildew on wood lath
I am having a bathroom remodeled. The walls need to be packed-put and the contractor is using wood lath (5/16 x 1 1/5 x 48). The lath is covered in black mildew. Is this a problem to put behind the new green board and cement board? The contractor tells me all the wood lath comes that way and is not a problem. He also told me if it bothered me, I should spray it with Clorox. Also, the wood is already very dry and splits very easily. Should I be concerned and get new lath that is not moldy before the walls go up or is this really how all lath comes?

ccarlisle 12-19-2009 12:31 PM

Well, we don't do things that way...we put back all new materials.

Having said that, I've never done a plaster-and-lath shower as we've gone new (with drywall as a replacement) every time we met a plaster-and-lath shower. Now maybe there'a reason I don't know about so I won't add to that.

And one of the reasons we go new in a mouldy shower situation is precisely because the wood may be a source of food for mould. And we don't do 'mouldy showers'...can't afford the risk. And if we can't up here in Canada, you guys sure can't in the US. Mould litigation south of our border is one of the biggest litigation categories going these days.

Spraying the mould with bleach is not the way to handle suspected mould growth either. Certainly it's not a permanent measure anyway...we don't use greenboard either, it's days has come and gone. Some codes won't even allow it.

The state-of-the-art in shower construction nowadays is to make it waterproof, 100% waterproof at that. As pointed out, I don't know why you are staying with plaster-and-lath apart from historical accuracy reasons - but not technical reasons.

That dog has already left the barn...

Due North 12-19-2009 01:40 PM

MOLD etc
Hi, You're right to ask about this matter. By pack out, I believe you're referring to what we call "furring out" with "furring strips-of course" to create a level plane to attach wall materials to. I agree that you should be concerned. I'm guessing that, if the wood is really dry-which explains the splitting (also low grade)-that it once was wet and got moldy (the black stains are still active spores)-this isn't high grade lumber- likely was in a bundle outside for a couple of seasons.

So, you don't want to introduce mold spores and I'm just a little hesitant if this guy is with it, sounds like cutting corners.

Anyway, the reason I responded is that this is a perfect opportunity to enhance the thermal and moisture environment of your home. If your house is like many, there is alot of airflow from the basement up through to the attic and coming with that heated air is moisture- even if you can't sense it. If you have condensation on your windows-that's a sure sign of excess moisture.

Back to the bathroom. Unless focussed actions are taken against it, your bathroom could add significantly to heat loss and moisture transfer problems.

So, I suggest the following: just focussing on the bathroom, I would recommend filling the exterior walls with cut sheets of polyisocyanurate insulation (thermax/Tuff-R brands) leaving 1/2" around against the framing and filling the gaps with spray expanding foam. A sheet-even one inch- over the inside of the wall framing will break the thermal bridge created by the framing. Not only will the above highly insulate but will be a 100% infiltration barrier to air through the walls.

I would also recommend a 60-90cfm fan vented OUTDOORS on a timer to get all that shower moisture out of the house..
I could go on, but I was trying to prompt your thinking about how ro really help your lifestyle as you improve your home.

Best, Will

firehawkmph 12-19-2009 08:41 PM

If I read your post right, the lathe is only to fur the walls out prior to installation of the greenboard. I would just rip some 2 x 4's to the 5/16's thickness and use those instead. Would only take a few minutes on a decent tablesaw.

What are you guys using instead of the greenboard in Canada, the mold and mildew resistant board, or something else? Thanks,
Mike Hawkins:)

ccarlisle 12-20-2009 06:56 AM

Well, we still have a moisture-resistant board (blue in colour) that we use in bathrooms - but the old greenboard has gone the way of the dodo bird for us - here in any case. But for shower stalls, we use regular drywall.

Properly waterproofed, the drywall never even gets wet. That's the key...

As I said, the old "greenboard" has been written out of many building code books.

firehawkmph 12-20-2009 10:15 AM

I guess I'm surprised a bit here. What was their reasoning for outlawing the greenboard, but still letting you use regular drywall in it's place? Was is because people would not take the proper precautions to use waterproof methods along with it, thinking the greenboard would take the place of that?
Mike Hawkins:)

ccarlisle 12-20-2009 10:21 AM

Well, paper-faced gypsum board was dissallowed by the IRC in 2006 as a tile backing in bathroom situations, so we steer clear of it.

PS: we use cbu also in shower stalls too.

firehawkmph 12-20-2009 11:11 AM

Ok Thanks,
I understand what you are saying. Makes sense.
Mike Hawkins:)

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