[GMCnet] Aluminum wall thickness and welding

[Justin Brady]

I have completely redesigned the interior of my coach, meaning I have a lot of holes to patch (fridge vent, bathroom vent etc etc)
I will be welding in fillers, but I'm curious if anyone has done it and if anyone knows what aluminum alloy the factory used?

Before everyone chimes in I will be tig welding it, not botching it.
--
Justin Brady
1976 Palm Beach 455

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[Peer Oliver Schmidt]

Justin,

is the GMC Assembly Manual of any help?

--
Best regards

Peer Oliver Schmidt
the internet company
PGP Key ID: 0x83E1C2EA

[John Wright]

Justin,
Tig welding here is probably not the first choice that should be used here as no matter how good or careful you are you will be dealing with warping of the panels as they are not flat but on curved surfaces. A better choice would be to use the body adhesive that GMC used in assembly.

Such as the one in the middle:
http://www.gmcmhphotos.com/photos/fixing-the-front-end-bulge/p11516.html
Summit Racing
http://www.summitracing.com/parts/trm-8115

An alternative is to use JB Weld as the Adhesive as it can provide almost the same bonding and the #M 8115 adhesive and you don’t have to clean out the adhesive from the seam points as you could just sand it.

Cut hole patch to correct size and then make an another ring piece that is 1 inch bigger and 1 inch small that the patch size using the same thickness material (.060 as measured from a piece I had cut from a new vent in the bath) as the body. Clean both the underside of the body and all other aluminum pieces with acetone to remove any oils. You may need to slightly bend the patch to fit body curvature before fastening as the top of the coach is not flat anywhere. Using the adhesive and pop rivets install the support ring and then the patch using the adhesive and rivets. Clean the excessive adhesive out of the seams between the body and the patch before it sets unless you're using JB Weld. After every thing is set, sand off the rivet heads and the area where the body part meet and I would use JB Weld type as a filler for both the seam and ground off rivets as it doesn’t expand or contract as much as automotive body fillers can and bonds better.

<http://www.amazon.com/Hy-Poxy-H-455-Alumfast-Aluminum-Repair/dp/B001RLYQ88/ref=sr_1_6?ie=UTF8&qid=1441378159&sr=8-6&keywords=jb+weld+aluminum>
or
http://tinyurl.com/o7rclsq
And regular JB weld would work OK too!

Just how I have done it in the past with good results and if done right you can’t even see the patch from the outside. Yes, I do have a Tig unit in the shop! If your that good on 0.060 thin aluminum body panels then go for it. JMHPO

JR Wright
GMC Great Laker MHC
GMC Eastern States
GMCGL Tech Editor
GMCMHI
78 GMC Buskirk 30’ Stretch
1975 GMC Avion (Under Reconstruction)
Michigan

[Emery Stora]

Another thing to consider before welding is that the sprayed in insulation is flammable. Welding could cause a fire. One would have to remove the inside ceiling panels where you are welding and scrape out the insulation. Then you should have a person stationed inside the motorhome with a fire extinguisher in hand!

Emery Stora
77 Kingsley
Frederick, CO

> On Sep 4, 2015, at 9:20 AM, John Wright <powe...@chartermi.net> wrote:
>
> Justin,
> Tig welding here is probably not the first choice that should be used here as no matter how good or careful you are you will be dealing with warping of the panels as they are not flat but on curved surfaces. A better choice would be to use the body adhesive that GMC used in assembly.
>
> Such as the one in the middle:
> http://www.gmcmhphotos.com/photos/fixing-the-front-end-bulge/p11516.html
> Summit Racing
> http://www.summitracing.com/parts/trm-8115
>
> An alternative is to use JB Weld as the Adhesive as it can provide almost the same bonding and the #M 8115 adhesive and you don’t have to clean out the adhesive from the seam points as you could just sand it.
>
> Cut hole patch to correct size and then make an another ring piece that is 1 inch bigger and 1 inch small that the patch size using the same thickness material (.060 as measured from a piece I had cut from a new vent in the bath) as the body. Clean both the underside of the body and all other aluminum pieces with acetone to remove any oils. You may need to slightly bend the patch to fit body curvature before fastening as the top of the coach is not flat anywhere. Using the adhesive and pop rivets install the support ring and then the patch using the adhesive and rivets. Clean the excessive adhesive out of the seams between the body and the patch before it sets unless you're using JB Weld. After every thing is set, sand off the rivet heads and the area where the body part meet and I would use JB Weld type as a filler for both the seam and ground off rivets as it doesn’t expand or contract as much as automotive body fillers can and bonds better.
>
> <http://www.amazon.com/Hy-Poxy-H-455-Alumfast-Aluminum-Repair/dp/B001RLYQ88/ref=sr_1_6?ie=UTF8&qid=1441378159&sr=8-6&keywords=jb+weld+aluminum>
> or
> http://tinyurl.com/o7rclsq
> And regular JB weld would work OK too!
>
> Just how I have done it in the past with good results and if done right you can’t even see the patch from the outside. Yes, I do have a Tig unit in the shop! If your that good on 0.060 thin aluminum body panels then go for it. JMHPO
>
> JR Wright

[Justin Brady]

I will do a good bit of practice before welding, I have welded .06 alum before with good results, you just go really slow.
The insulation will all be removed before patching.
It may turn out horribly! But I don't like rivets and patch panels, when the next owner repaints I'd prefer they not be able to find the patches!
We shall see.

Does anyone know the alloy used? It would be easier welding if I can match the alloy

--
Justin Brady
1976 Palm Beach 455

[Todd Sullivan]

I've patched the roof both ways mentioned , welding and adhesive patch with
aluminum sheet. The results were MUCH better using an adhesive to patch
with an oversize sheet from the interior. There is a lot of stress in the
roof sheet and it quickly deforms with the introduction of weld heat. And
if you pull that off you need to be REALLY careful while finish sanding and
grinding for the same reason. If the hole is carefully beveled on the
outside then a patch placed on the inside the repair area is much more
stable leaving only a slight depression on the visible side which is easily
filled and contoured.

My 2 c

Sully
77 royale
Seattle

[Billy Massey]

Justin
I'm sure you've checked for yourself, but the insulation on my '76 will burn
if you hold a torch to it but will go out as soon as that source is taken
away. It will burn, but will not support combustion. Trouble is, I've
heard that it puts off cyanide gas when it does burn. (yikes!) Probably
about like burning or trying to weld galvanized metal.

bdub

-----Original Message-----
From: Gmclist On Behalf Of Justin Brady
Sent: Friday, September 04, 2015 11:05 AM

I will do a good bit of practice before welding, I have welded .06 alum
before with good results, you just go really slow.
The insulation will all be removed before patching.
It may turn out horribly! But I don't like rivets and patch panels, when the
next owner repaints I'd prefer they not be able to find the patches!
We shall see.

Does anyone know the alloy used? It would be easier welding if I can match
the alloy

[Justin Brady]

So what you're suggesting is just placing a patch on the inside?
What about the .06" depression you're going to have leftover? Filler?

[David H. Jarvis]

Do both.
An inside sheet and a filler sheet on the outside.

[Todd Sullivan]

Only a patch on the inside then filler on outside. If you put a sheet on
the outside you will never get the contour cosmetically correct.

Sully
77 royale
Seattle

[Ken Henderson]

Todd,

I suspect that most folks on the 'net don't know that this is you:

http://www.yelp.com/biz/seattle-collision-center-seattle

Y'All pay attention to what he says!

Ken H.

On Fri, Sep 4, 2015 at 1:52 PM, Todd Sullivan <sgl...@gmail.com> wrote:

> Only a patch on the inside then filler on outside. If you put a sheet on
> the outside you will never get the contour cosmetically correct.
>
> Sully
> 77 royale
> Seattle

[James Hupy]

Ken, I second that.
Jim Hupy

[Kerry Pinkerton]

Justin, I shape aluminum basically for a living.


http://www.gmcmhphotos.com/photos/art-deco-roadster/p45004-d-012s.html


http://www.gmcmhphotos.com/photos/art-deco-roadster/p49529-v-0023.html

I can, with some authority, promise you that the weld will shrink. It is absolutely going to pull and distort. Going slow won't make any
difference.

Since you'd have access to the back side, you COULD planish out the welds and get it in the proper shape...but it's not as easy as it sounds. I've
seen vastly more attempts messed up than successful.

If it were me, I'd make an oversize patch with the appropriate simple roll (the aluminum curves in one direction only) and panel bond it to the INSIDE
with at least a 2" overlap. I'd then cut a patch that is just smaller than the hole and bond it to the first piece. I'd fill the resulting small
crack with quality filler and block smooth.

I'll be glad to help you make the aluminum panels if you like. If you have a slip roll, or access to one, I can tell you the radius you need or you
could trace the door frame onto a piece of plywood and make a template.

I'm not sure of the alloy but the aluminum is .063 thick. I suspect it is 5052. I would use 3003 H14 because that is what I have on hand and it will
not make any difference structurally. 5052 is not as workable as 3003 but either will easily take the small roll needed.

The "RIGHT" way to do this would be to pull the old siding off and replace it with a new sheet from seam to seam. Lots of work but it's probably the
only way to ensure you won't be able to see the repair. The problem is that the patch will expand and contract at different rates and show up in the
paint. A big filler patch will do the same thing.
--
Kerry Pinkerton - North Alabama

77 Eleganza II, 403CI, Manny Brakes, 1 ton, tranny, lots of aluminum goodies.

http://www.bdub.net/pinkerton/

'03 Fleetwood Discovery 39L

[Justin Brady]

Kerry,
First off Amazing work!

I guess I should take your advice and use a filler from the back side.
I was planning to planish the welds but you're probably right, more trouble than it's worth!
Thanks for the input!
Justin

--
Justin Brady
1976 Palm Beach 455

[Justin Brady]

Okay guys getting ready to do this, what's the preferred sealant to use to bond the new patch panels to the old aluminum?

[Todd Sullivan]

Any cross bonding 2k adhesive.
3m 8115
JB weld
Fuzor cross bonding adhesive

All are toolable and will cure quicker with the introduction of heat.

Sully
77 royale
Seattle

[Espen Heitmann]

I did my drivers side chipmunk with 3M 08115, strong stuff and holding, will do the same with some other panels and do not worry about them coming
off.

I did also use the 3M 08115 to glue one of the handles on my brake lathe to the axle, works like a charm :)
--
1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Mean Green Machine,
And just sold my 1973 26'-2 # 581 White Canyon lands under the name Dobbelt trøbbel
in Norway

[Justin Brady]

Sounds good guys, I'll get some.

So next question, do you guys recommend using only the sealer or should I use rivets as well?
I am thinking put down a good layer of adhesive, then rivet the panels on to hold them tight while it cures, then I'll sand the rivet heads off flush
once it's cured.
This sound like a good plan?

--
Justin Brady
1976 Palm Beach 455

[Todd Sullivan]

I would avoid rivets.
I would
1. Prep the inside and outside of the repair area with 80 grit or
courser to at least 2" past hole. Re -Abrade immediately prior to bonding
to prevent surface oxidation.
2. Cut the patch material and carefully arc the patch to match the panel
arc.
3. Mix and apply x bonding adhesive to patch and panel. Apply a thick
enough layer to allow some squeeze out when patch installed to eliminate
voids
4. Install patch panel and support from inside with a brace clamped onto
surrounding roof stringers, prop stick to floor/counter etc.
5. Heat with heat gun for 5-10 minutes ( just hot not burning. Hot to the
touch but still touchable)
6. Allow to cool naturally and check for cure. Bracing can now be removed
if it's in the way(prop stick to floor etc.)
For finish surfacing and shaping wait 12 hours.
7. Plane top surface to original contour and bevel perimeter of hole
8. Fill for final contour with plastic filler.
Above times assume ambient air temps above 60 degrees.

Sully
77 royale
Seattle

On Tuesday, October 13, 2015, Justin Brady <jbr...@gmail.com> wrote:

[Espen Heitmann]

Did just clean the surface and 80 grit, no rivets, bolts or screws, just clamps to give it pressure, no large gaps between the surfaces, the closer
(thin layer of 08115 is better than thick )heat and time, 24 hours is good

--
1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Mean Green Machine,
And just sold my 1973 26'-2 # 581 White Canyon lands under the name Dobbelt trøbbel
in Norway

[Gary Worobec]

I would look at 3M 5200 or 3M 4000. The 4000 dries in 24 hours, both are
paintable, have high adhesive properties are excellent for wet weather. 3M
5200 is the go to adhesive in the marine industry. They both come in white,
black or brown.


Thanks,

Gary and Joanne Worobec
1973 GMC Glacier
Anza, CA

[John Wright]

For bonding panels you want to use the 3M Panel Bonding Adhesive or these others depending on your needs.

http://www.gmcmhphotos.com/photos/fixing-the-front-end-bulge/p11516.html

JR Wright
GMC Great Laker MHC

GMC Eastern States Charter Member
GMCGL Tech Editor
GMCMI

78 GMC Buskirk 30’ Stretch
1975 GMC Avion (Under Reconstruction)
Michigan

[Robert Mueller]

G'day,

When I removed a horizontal support in the wall above the fridge in The Blue Streak I used heat to soften the epoxy that GMC used.

As I heated it I experienced a flashback to my Project Apollo days. To speed up the cure time we would put a heat lamp on the epoxy
as noted in the 3M Technical data sheet:

http://multimedia.3m.com/mws/media/594118O/3m-scotch-weld-epoxy-adhesive-ec-2216-b-a.pdf

Quote:

5. Join the adhesive coated surfaces and allow to cure at 60°F (16°C) or above until firm. Heat, up to 200°F (93°C), will speed
curing.

Unquote

The smell that the epoxy in the GMC emitted when heated was exactly like what I smelled when we used 3M EC-2216 epoxy and when I
examined the epoxy and it was the same color as EC 2216.

Regards,
Rob M.
The Pedantic Mechanic

[Charles Boyd]

Rob, don't leave us dangling. Did the stuff get harder or easier to take off???

USAussie wrote on Fri, 16 October 2015 20:07

--
C. Boyd
76 Crestmont
East Tennessee

[Robert Mueller]

Chuck,

Sorry!

Frankly the epoxy was so hard I couldn't budge the part I wanted to remove.

I had a go at heating it with a Map Gas torch but that gave off some nasty fumes so I stopped and went to a 1500 watt heat gun. It
softened the epoxy enough to allow me to separate the reinforcement from the skin.

Heating the epoxy to soften it made it possible to remove the reinforcement but it was still a BITCH!

Regards,
Rob M.
The Pedantic Mechanic

-----Original Message-----
From: Charles Boyd

Rob, don't leave us dangling. Did the stuff get harder or easier to take off???

C. Boyd

[Charles Boyd]

So it is possible to get the fiberglass shell off the the front alum frame work and it be in reusable condition with a heat gun and putty knife? I
had thought of trying a horror freight gmc tool and staying against the aluminum. Any thoughts of using freon or dry ice? My luck that would only
brittle up the smc. Any hints would help?


USAussie wrote on Fri, 16 October 2015 21:28

--
C. Boyd
76 Crestmont
East Tennessee

[Robert Mueller]

Chuck,

There's a world of difference between the SMC and the aluminum. What I removed was a piece of C channel aluminum and I heated the C
channel then shoved a narrow putty knife (less than 1" wide) between the skin and the C channel to break the bond. The first go was
the worst as I had to shove the whole blade width in. After that I went little by little until the bond between the C channel and
skin was broken. I think that Freon or dry ice would just harden the epoxy.

The problem you may have is that you'll be heating the SMC as well and you may go through it with the putty knife. I reckon the HF
tool would be the way to go. As you noted you would have to be careful and keep the oscillating blade hard up against the aluminum
to make sure you didn't punch through the SMC.

Regards,
Rob M.
The Pedantic Mechanic

-----Original Message-----
From: Charles Boyd

So it is possible to get the fiberglass shell off the the front alum frame work and it be in reusable condition with a heat gun and
putty knife? I had thought of trying a horror freight gmc tool and staying against the aluminum. Any thoughts of using freon or
dry ice? My luck that would only brittle up the smc. Any hints would help?

[Jack Ramsey]

I have used the JB weld marine on the smaller holes in the roof, with success, but there are 6 ea, 1/4in holes where a pod was bolted down and the
silicon has obviously been leaking. I have it all cleaned up, but don't think JB weld is going to work on a hole that size. Thought about plugging the
back side with foam of some sort and then JB weld marine, or the Hy-Poxy H455 might be more suited for a 1/4in hole. Any ideas that I am overlooking?

Thanks,

Jack
--
Jack Ramsey
Tulare, CA
TZE165V101526
1975 Palm Beach

[Emery Stora]

You might use the method that Dale Ropp has demonstrated at GMCMI conventions. He takes a foam ear plug and saturates it with epoxy resin and pushes it into the hole. After it hardens he trims it level with the surface and sands it smooth.

Emery Stora
77 Kingsley
Frederick, CO

[Kingsley Coach]

Brilliant !
Thanks for the 'simple' solution Emery !

--
Michael Beaton
1977 Kingsley 26-11
1977 Eleganza II 26-3
Antigonish, NS

Life is too short to hold a grudge; slash some tires and call it even !

[Jack Ramsey]

Thanks,

I have a healthy selection of foam earplugs and that sounds like a perfect solution.

Thanks again,

jack