Do not attempt to weld to your roof! The existing material is too soft and thin to make welding even a remote possibility. My welder works with aluminum every day and we use tig welding exclusively. Even with his skills we find pin holes in thin material because it warps as you move the "puddle". You can easily melt wires ot pipes under the roof. IMHO your welder will never be able to be perfect around the entire sheet and if any pin holes occur your problems will be worse. We do not weld any aluminum under 3/32" and then only in short runs.

quote:

Originally posted by Moonbeam-Express:

There is a metalized roofing tape used in the trucking business to seal and patch over the road trailers. You could easily patch those areas with tape, or rivet down sheet metal and then seal the edges with this tape. I wish I could tell you the name of it, but it is kind of like metalized bituthene.

I have had good results with an Eternabond product that seems similar to what you describe. I was up on the roof Friday inspecting, and it still looks like new maybe 9 years later. The aluminum top layer protects the gummy sealant from the sun, but the bare aluminum also needs protection from our ocean salt fog. Even 1100SO powders up here. After a phosphoric acid wash and a little alodine, I gave it some zinc chromate and white enamel.

quote:

Originally posted by Tom K:
Do not attempt to weld to your roof! The existing material is too soft and thin to make welding even a remote possibility. My welder works with aluminum every day and we use tig welding exclusively. Even with his skills we find pin holes in thin material because it warps as you move the "puddle". You can easily melt wires ot pipes under the roof. IMHO your welder will never be able to be perfect around the entire sheet and if any pin holes occur your problems will be worse. We do not weld any aluminum under 3/32" and then only in short runs.

Yeah. I was gonna say something like that. I don't wanna start a "My welder is better than your welder" thing, but I will share some of what I have learned from my welder. Despite my airline connections, including free welding of small projects by super duper, multi-certified welders, I took all my important projects to the same guy for over 40 years. He was almost magical, but didn't like old aluminum to new, nor different thicknesses, nor corrosion. He is better than most others, in that he can weld different alloys well, (but that can be a trap if the alloys or temper are not known). To put this into perspective, he can weld alloys that are supposedly not weldable, such as 7075-T6. He can also weld really thin stuff, but likes it to all be the same thickness.

I have no doubt that he would not want to weld anything on a Barth roof, either.

I am a firm believer in 5200. It has strength like you can't believe. I saw a boat owner use it to fasten his trim tabs to his boat and they held! My only problem with using it on the roof is the expansion of the aluminum in hot weather. When a sheet that big gets hot it is going to grow. Is the substrate going to have enough give or not? I don't know - that's why I'm asking. You are not going to get a lot of give from the 5200 so something is going to have to give. Don't forget we are talking south Florida here and the sun gets HOT!

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Originally posted by DougZ:
My only problem with using it (5200)on the roof is the expansion of the aluminum in hot weather. When a sheet that big gets hot it is going to grow. Is the substrate going to have enough give or not?

At the same ambient temps, the aluminum roof will expand at about the same rate in the same temp as the panel. The panel will collect more heat than the shaded area underneath, although aluminum is a good conductor of heat, so the shaded area will have its temperature raised by the roof metal that sticks out from under it and is hit by the sun. The shaded are will also be heated by heat radiating off the underside of the panel. If the panel is white, it is unlikely to get any hotter than the surrounding roof.

I believe that a panel held on with 5200 will have less of a problem than a panel held on by rivets or (EEK) welding, as it has some give. I would just use the sealant around the edges, with a little of the extruded material formed up over the edge an on a bit of the top surface. Masking will make it look nice when finished.

I repaired a sail with 5200, and as an experiment, glued two pieces of scrap material together with about an inch lap. I put one end in a vise, and tore the material before the 5200 failed.

One thing......5200 sticks to whatever it sticks to. In the case of a painted surface, it sticks to the paint, but the overall strength of the bond is dependent on how well the paint sticks to the substrate. I always go to bare metal on a painted surface, and rough it up a bit.

Is 5200 similar to Sikaflex? I've
used Sikaflex before and that is also as good as welding.

quote:

Originally posted by Moonbeam-Express:
Is 5200 similar to Sikaflex?

Yup. Cheaper and easier to find, too. At least, if you live near water. I seem to remember that some Sikaflex requires a horribly expensive primer, as well.

quote:

I've
used Sikaflex before and that is also as good as welding.

The bus folks love it, too. Shadowman is up to date on bus stuff. Maybe he can tell us if there are any comparisons with 5200.

quote:

Originally posted by bill h:

quote:

Originally posted by ccctimtation:
You might scribe a note on the plate that this is held down with 5200 to cover misc. previous mounting holes. At some time someone may want to remove the plate and knowing it is bonded with 5200 will help removal.

I use heat whenever possible. It would seem that a sheet would be easily heated with a heat gun while a putty knife breaks the bond. I have also used an electric hot knife.

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I have not used the anti-5200 magic sauce but it is reputed to be effective.

Is that DeBond Marine Formula?

I think that is the product. As I remember the post it too is a 3M product.

Ok, i have no firsthand knowledge of either the 5200 or any of the Sikaflex products. There are guys that have used one or the other for various projects and seem happy with both. I know that one or two guys have re-sided entire buses using only the Sikaflex. Some say to talk to Steve at Sikaflex tech support in Troy Michigan and he can tell you which type of Sikaflex will work best for what you are trying to do. Even if you do use a sheet of Aluminum over the holes i would still seal the holes with something like dicor lap sealant. Kind of a belt and suspenders approach to it.

My MCI had large and heavy sheet aluminum over the window cutouts applied with only Sikaflex. The stuff held like a welded panel. I went to Sanels (a local auto body supply store) to get more Sikaflex and they sold me something 3M made that they claimed was just as good. It looked and applied like Sikaflex, but that panel fell mostly off on the road and only stayed on because I had pinned it in a few places with rivets. I wish I could recall what it was, but it was too many RVs ago.

Sikaflex 252 is used to bond sides and roofs on commercial trailers - no rivets or mechanical fasteners. Available on line from Amazon.

I've successfully used both 3M 5200 & Sikaflex on boats, wooden & fiberglass. I know that if you bond 2 pieces of wood with 5200, & try to separate them, the wood fibers tear before the bond releases.

You're not likely to find 3M 5200 in an auto supply store, it's advertised as a marine sealant.

3M makes a wide variety of adhesives including several for automotive applications, one of which is specifically for sealing body panels that have been spot-welded. I've used that one in RV & auto body work, & that may be what you got from your auto parts store. It is not compounded to take stress, & has a texture completely different from 5200 or Sikaflex, both of which are polyurethane compounds.

Sikaflex comes in several varieties, some specifically marine, others more general purpose. You can educate yourself on which Sikaflex product you need with a Google search for Sikaflex. In my book, 3M 5200 stands by itself, though I've also had success with Sikaflex.

quote:

Originally posted by Moonbeam-Express:

There is a metalized roofing tape used in the trucking business to seal and patch over the road trailers.

Just ran across this: Harbor Freight

I'll bet that's the stuff. Good find Bill!

It may not be pretty, but who are you going to impress up there anyway?

Looks like a great product BUT, If I clean to bare aluminum, rough it up a bit, use 5200 or sickaflex to seal it down, and mesh tape it before resealing with rubberoid or whatever, do I need or want another thing in the middle of it all?