Convert Hatch to AC & Roof Patch

[DeMac]

After completing all of the rivet work, I circled back to my original leak over the rear engine deck.


The rear AC evaporator was previously mounted, using lag bolts, through the roof. Sealant coated Aluminum channel helped support the load outside.


I removed the Aluminum channel strut to find (worse than) what I expected. Rot, caused by bolting Aluminum to Steel. (Galvanic reaction).
Directly under the Aluminum supports. This is the only exterior rust, that I have found.


The most corrosion is present where there are no holes, only pressure/friction. Note the rivets. Both bolts were near the rear/center.


Note the distance from the only two bolt holes as compared to the most severely affected areas.



I expected some amount from at least one bolt. Three of four were shinny, one was corroded and moist.

[DeMac]

The other two units were hung on these terrific brackets. They were pop-riveted to the ceiling skin only. I drilled & saved both sets of those for reuse.



Here, only through-bolts and leaks.

[DeMac]

After mechanical sanding with 60 grit Gator paper. I applied Ospho and brushed several minutes with a wirewheel.

Photographed while temporary plugging holes using 3/8" automotive retainers & insulation seam tape. (on hand items)


Ospho & wirewheel twice, two days in a row. Sanded & cleaned the area, then coated with bare metal primer.


NEMA 4X, k/o seal, 1/2" knock out, see electric supply, $7 each. Larger sized available.


Approx. 1-3/8" dia, steel convex head with included, neoprene (I know) washer. Kit also includes a snug convex steel washer washer & wingnut.


We swapped the wing for a flanged hex nut. (5-.80 metric thread). Dry fit pictured, Dynatron 550 added on reinstall.

[sealguy77]

Great thread DeMac! Super detailed!

I'm looking to redo the sheet metal I installed on the sides of my bus after a roof-raise due to some major leaking (I was a bit rushed installing them and wasn't as OCD about them). I noticed the bus manufacturer used sheet metal screws as opposed to rivets on the sides and that is where many of my small leaks are coming from. I think I'm going to use rivets on the side and am trying to figure out if I want to use solid or closed-end, blind rivets. Solid rivets are significantly cheaper, but considering I would have to purchase/rent an air hammer, compressor, et cetera and have someone hold a bucking bar, I'm considering closed-end, blind rivets and your meticulous methods. Just hoping I can apply the same methods to a large 4x10' sheet of metal.

Also considering using thicker metal than I originally used. I used 20-gauge sheet metal. Now considering 18- or 16-gauge.

Decisions, decisions...

[EastCoastCB]

Originally Posted by sealguy77

Great thread DeMac! Super detailed!

I'm looking to redo the sheet metal I installed on the sides of my bus after a roof-raise due to some major leaking (I was a bit rushed installing them and wasn't as OCD about them). I noticed the bus manufacturer used sheet metal screws as opposed to rivets on the sides and that is where many of my small leaks are coming from. I think I'm going to use rivets on the side and am trying to figure out if I want to use solid or closed-end, blind rivets. Solid rivets are significantly cheaper, but considering I would have to purchase/rent an air hammer, compressor, et cetera and have someone hold a bucking bar, I'm considering closed-end, blind rivets and your meticulous methods. Just hoping I can apply the same methods to a large 4x10' sheet of metal.

Also considering using thicker metal than I originally used. I used 20-gauge sheet metal. Now considering 18- or 16-gauge.

Decisions, decisions...

20 is ok.18 is perfect. 16 is overkill and way harder to work with.

[sealguy77]

Originally Posted by EastCoastCB

20 is ok.18 is perfect. 16 is overkill and way harder to work with.

Awesome! Thank you!

[sealguy77]

Originally Posted by EastCoastCB

20 is ok.18 is perfect. 16 is overkill and way harder to work with.

EastCoastCB and DeMac,

Another question. I'm in the planning phase of putting up the skin and am wondering how y'all would handle overlapping the sheet metal over a hat channel support.

I'm planning on being OCD like DeMac, which I think is simple enough to do with patches and deletes, but large 10x3' 18-gauge sheet metal is another matter.

My question is this: how would y'all install the skin considering the sealant drying? Referencing my picture below, I'm thinking I should install the orange sheet except for the rivets and sealant over the hat channel, using clecos, then prep the green sheet and before installing it, added sealant between the orange sheet and hat channel support and over the orange sheet (between the orange and green sheet).

Thoughts?

[EastCoastCB]

Looks like a good plan to me. The seam sealer doesn't dry up or harden so you don't have to worry about that. It stays workable for a good while.

[DeMac]

Originally Posted by sealguy77

EastCoastCB and DeMac,

Another question. I'm in the planning phase of putting up the skin and am wondering how y'all would handle overlapping the sheet metal over a hat channel support.

I'm planning on being OCD like DeMac, which I think is simple enough to do with patches and deletes, but large 10x3' 18-gauge sheet metal is another matter.

My question is this: how would y'all install the skin considering the sealant drying? Referencing my picture below, I'm thinking I should install the orange sheet except for the rivets and sealant over the hat channel, using clecos, then prep the green sheet and before installing it, added sealant between the orange sheet and hat channel support and over the orange sheet (between the orange and green sheet).

Thoughts?

There is space for two rows of rivets. Two through the orange sheet, one through the green and orange.

My ribs actually have space for three rows. (see pics below)


For the purpose of preping the second (green) sheet, I might consider altering its placement and rivet pattern.

The first sheet is could be completed normally, with rivets on all sides (IF) the nearest vertical edge (green dotted line) of the hat channel, were used to secure the first piece (orange sheet) while still over-lapping the entire hat. Wide spacing ok, we're just holding it tight. You could then clamp and predrill pilots on the forward vertical edge of first piece and hat channel, together.

On the second (green) sheet, I might predrilled one pilot hole (measured thrice) and cleco it in place (smaller clecos, pilots). Probably place the sheet aestheticly short of touching the first row, then add the second tighter row of tightly spaced pilot holes, on the orange dotted line, through the other side of the hat channel. You could finish the perimeter of the second & each consecutive sheet, separately.

The second, green sheet would eventually have only one row of rivets on its trailing edge, while passing through the first orange sheet & the hat channel (longer rivets?) Similar to the the factory rivets on my IC roof. Wide spacing first row, with a tight spaced second row near the edge.

I don't know of it's a better way of aligning and sealing, maybe, mostly just a different way to accomplish the same thing, while breaking the work hours up into stop points.

Piloting from inside out is better, to see the factory space points, but the finish size ought to be drilled from outside-in. The tooling blow-out affects the seal on the rivet head.

[MzNix]

Excellent walk-through!

Couldn't think of a single question since you covered so much detail. I'll be giving this a go this weekend 😊

I may end up using fasteners instead of rivets since my rivet gun apparently needs Arnold Schwarzenegger strength to clamp without destroying the hole and rivet :/

Any tips on applying a rivet cleanly if you don't have a pneumatic gun?

[DeMac]

Originally Posted by MzNix

Excellent walk-through!

Couldn't think of a single question since you covered so much detail. I'll be giving this a go this weekend 😊

I may end up using fasteners instead of rivets since my rivet gun apparently needs Arnold Schwarzenegger strength to clamp without destroying the hole and rivet :/

Any tips on applying a rivet cleanly if you don't have a pneumatic gun?

---------------------

Pneumatic tool,
I wish. I purchaced this lever operated rivet tool online, when it was $35.

(Amazon - Proferred Store)
Any two handled model requires exponentially less strength. Harbor Freight sells a $20 model.

Musigenesis's suggestion (slide pipes ever the handles) is the go-to method to gain more leverage.

If you do choose to use fasteners, I suggest using size 12-24 bolts & nuts to retain lasting clamping force. I used 10-32s to temporarily clamp the disks into place, while drilling. After a couple uses, the threads stripped.

[sealguy77]

Originally Posted by DeMac

Spritz on ospho wait 10 min.
Wire wheel until shiny. Wipe away residue w/ cloth. Reapply, wait 24 hours. Brush off residue, wash & dry before primer.


After cleaning each patch with Ospho and a wire brush, each was water rinsed & wiped. I then applied Apple Cider Vinegar and scuffed the surface using wire wheel to remove powdery scale. Wiped clean with ACV. Allowed to dry in the sun 45 min. Finally, brush painted with Clean Metal Primer.

After battling rust and such before painting my bus, I highly recommend that apple cider vinegar IS NOT USED AT ALL on metal. Apple cider vinegar is used to flash rust metals.

For this step, I recommend that after the Ospho has had 24 hours to sit, that the zinc phosphate and iron oxide is removed with a wire wheel, sanding, and/or paint scrapping wheel. Next, wipe the surface with acetone to clean it before priming. Priming needs to be accomplished relatively quickly after removing the Ospho residue.

Steps:
- Spray Ospho on metal surface
- Let Ospho sit for 24 hours
- Remove Ospho residue with wire wheel/sanding/paint scrapping wheel
- Wipe clean with acetone
- Prime

[EastCoastCB]

Originally Posted by sealguy77

After battling rust and such before painting my bus, I highly recommend that apple cider vinegar IS NOT USED AT ALL on metal. Apple cider vinegar is used to flash rust metals.

For this step, I recommend that after the Ospho has had 24 hours to sit, that the zinc phosphate and iron oxide is removed with a wire wheel, sanding, and/or paint scrapping wheel. Next, wipe the surface with acetone to clean it before priming. Priming needs to be accomplished relatively quickly after removing the Ospho residue.

Steps:
- Spray Ospho on metal surface
- Let Ospho sit for 24 hours
- Remove Ospho residue with wire wheel/sanding/paint scrapping wheel
- Wipe clean with acetone
- Prime

Those are the steps I've always used!

[DeMac]

Thanks for the update sealguy77.

Thank You, to Polarweasel for making the corrections to post #3

[Diverdude0075]

Great write-up! I'll be tackling the task of repurposing my escape hatch and this gives really all the info needed.

How's your build going? I noticed this thread started a few years ago.

[cadillackid]

how do you handle the curved bus roof, yet from what i understand RV roof A/C units are designed to sit on a flat roof? do you mill out a "curb" for the unit to sit on that gets placed on the roof?

[Diverdude0075]

Originally Posted by cadillackid

how do you handle the curved bus roof, yet from what i understand RV roof A/C units are designed to sit on a flat roof? do you mill out a "curb" for the unit to sit on that gets placed on the roof?

I would think that being in the center of the roof minimizes the curvature enough that the provided gasket will create a seal. This is what I am hoping anyway.

[DeMac]

Originally Posted by cadillackid

how do you handle the curved bus roof, yet from what i understand RV roof A/C units are designed to sit on a flat roof? do you mill out a "curb" for the unit to sit on that gets placed on the roof?

---------------

As DiverDude wrote, 'being in the center of the roof minimizes the curvature enough that the provided gasket will create a seal.'

I found this to be true.

In the photo below, we can see the slight curvature, causing a 1/8" gap to the flat frame. This is prior to adding the 100lb HVAC and squeezing the unit's four corner clamps.


The corner clamps squeeze the wood frame and roof steel together. I used Locktite urethane sealant between the wood frame & roof steel.


The seal on the unit is very thick and pliable, so it gives way to the outter roof shape when its compressed.


factory replacement shown, our seal came preistalled onto the unit

[cadillackid]

good point in that you can sort of flatten the center of your patch and still allow the outer to mate to the roof.. 1 inchy gasket shou;d be good.. I never knew they were that thick..

[heimlich]

I'm doing mine pretty soon. I already have the 16 gauge panels. I bought aluminum rivets instead. I tried the stainless rivets but you need the heavier tools in order to pop them in. I figured the bus (and airplanes) are build with aluminum so I expect it will work fine.