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Old 01-24-2021, 07:08 PM   #1
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Condensation and mold

Hey! I just moved to the Pacific Northwest and I didn't realize the problem condensation and mold would cause in the skoolie. I thought that the walls were completed. My bf and I didn't have time to treat the wood furring we installed except a few pieces with polyurethane. Originally my bf and I cut plywood then screwed the 3inch plywood to the metal ribs. Literally every piece of metal gets wet including the screws attaching the wood to the metal which then create mold on the untreated wood. The poly furring strips look great, but the untreated wood is horrifying.

My question is how do other prevent mold on their furring strips? What do people cover the exposed metal with to prevent condensation? I need lots of ideas on preventing condensation. I am about ready to spray foam every window lol.. We were originally thinking to polyurethane all the wood furring so we could wipe the moisture off. However, painting poly takes a lot of time and I know people don't normally poly their furring. Also where does the moisture go if not into the wood? It's also winter here and I want to continue to work on the bus right now. Another thought was putting moisture wicking insulation (r1) between the wood furring strips and metal ribs and then putting more r-1 insulation over the wood furring then put whatever we will use for our walls on top of that. If you have any questions or want pics, let me know! I would love to hear what other people have done.
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Old 01-24-2021, 10:26 PM   #2
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We'll need a good prognosis to diag and treat the condensation.

Increase the amount of water the air will hold and/or decrease the amount of water in the space.

Are you using propane for your source of heat?
1lb of burnt propane releases 1.6lbs of moisture.

Some folks paint every splinter of wood in their build and touch them up if they're drilled or cut after installation. Primarily for the reasons you state.

Seems like you're considering conduction, and that's probably most of it. Also consider convection, the cold air from the door crack meeting the warm air on the metal surface in contact with the cut edge of the ply. In the top pic, the mildew is heavier at the edge, more so near the corner where there are two edges.
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Old 01-25-2021, 07:35 AM   #3
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The screws in the ribs provide a thermal bridge from the outside coolness to the inside warmer air. The water molecules in the warmer air stick to the cooler metal... condensation.

The fir strips need to be secured to a wood or plastic stand-off that is in turn secured to the ribs. This is easiest to achieve this is with a short stand-off mounted to the sides of the metal ribs of the bus. Then the fir strips attached to those. This means no screws contact outside metal will contact inside warm air. The screws holding the stand-offs should be sealed under spray foam.

In fact, any metal which touches or is bridged to the outside should be seal with something, Spray foam is the best for areas needing insulation. I like bed liner for areas like around the driver and dash...etc.

Of course, something like a mini-split will pull the moisture out of the air and will greatly reduce, if not eliminate, condensation.
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Old 06-14-2021, 02:21 PM   #4
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Quote:
Originally Posted by Tube_shuttle View Post
Hey! I just moved to the Pacific Northwest and I didn't realize the problem condensation and mold would cause in the skoolie. I thought that the walls were completed. My bf and I didn't have time to treat the wood furring we installed except a few pieces with polyurethane. Originally my bf and I cut plywood then screwed the 3inch plywood to the metal ribs. Literally every piece of metal gets wet including the screws attaching the wood to the metal which then create mold on the untreated wood. The poly furring strips look great, but the untreated wood is horrifying.

My question is how do other prevent mold on their furring strips? What do people cover the exposed metal with to prevent condensation? I need lots of ideas on preventing condensation. I am about ready to spray foam every window lol.. We were originally thinking to polyurethane all the wood furring so we could wipe the moisture off. However, painting poly takes a lot of time and I know people don't normally poly their furring. Also where does the moisture go if not into the wood? It's also winter here and I want to continue to work on the bus right now. Another thought was putting moisture wicking insulation (r1) between the wood furring strips and metal ribs and then putting more r-1 insulation over the wood furring then put whatever we will use for our walls on top of that. If you have any questions or want pics, let me know! I would love to hear what other people have done.
relevant thread:

https://www.skoolie.net/forums/f13/i...ure-35983.html
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Old 06-14-2021, 10:31 PM   #5
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So, good information from other posters, yet they appear to be assuming you're understanding how the problem is created. If you understand things like air moisture content, thermal bridging and such, cool.

If not, I'd recommend you watch a couple of videos on condensation and read about thermal bridging.

Per the idea of screwing a piece of wood (cross member) between the ribs of the ceiling, then screw the firing strips into those into the cross member, you still have a screw going into the metal and into wood...it's just that it's going into the cross member versus the firing strip. So, you can still have condensation form.

To address this, you might consider using a really good construction adhesive to glue the wood cross members in place, then screw the firing strips into the cross members. This way, you have no screws into the metal of the bus.

I screwed my firing strips directly into the ribs and coated the screw head with silicone caulk. This insulates the screw head from the air.

Of course, you have to insulate all the metal from the inside air, so whatever medium you choose (spray foam, rigid foam, wool, etc.) is key.

Once the insulation is in, it's time to combat the real culprit of condensation....the amount of moisture in the air.

If you're using any propane appliances, make sure they are vented to the outside of the bus.

When taking a shower, isolate the steam as much as possible and exhaust it to the outside of the bus.

When cooking, exhaust the moisture to the outside of the bus.

Keep the air moving! It's harder for condensation to form when air is flowing.

Absorb the moisture out of the air....dehumidifier or a wood stove are probably your best bet.

Bottom line, keep the humidity low. The colder it is outside, the warmer it is inside and the more moisture in the inside air, the more condensation you'll have.

Hope this helps.
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