aluminum with/without plywood?

[alisa1965]

Everything is going up as planned. I actually found 2 pieces of colored aluminum which will match exactly the color of our little trailer. Also found the trim. I live about 5 miles from an RV surplus place. The question I have is the roof. There are countless forums and searches which show that the majority of people attach the aluminum to plywood for their roof. I haven't decided on this yet. I have the rib supports up and was planning on using 1 1/2" thick insulation board in between with the interier lined with paneling (to make it look nice). Do I need to install a plywood backing before the aluminum or can I just lay the sheets of aluminum to the framework itself? We were going to screw down the metal using either caulking with the screws or the screws that have a special gasket built for this purpose. Then it would be trimmed with molding from roof to sides. Any ideas would be appreciated.

[GPW]

IMHO, if the aluminum is thick enough, it should be no problem ...
When I built my house , I installed the metal R-panel roof directly to steel hat channel strips installed every 16" perpendicular to the rafters.. Very strong after ten years , went through Katrina with NO damage ...

Cargo trailers don't have any sheeting under the aluminum roofs , yet seem to survive very well ...

[alffink]

There is really no reason to use screws or adhesives to tie the aluminum directly to your roof, with or without a plywood underlayment.

Let it float, using the edge trim and the vent flange as the securing points

Either way you decide to go, really pay attention to your sealing of the edging, I have found that the aluminum's shrinkage - exspansion rate is more than I expected and I have worked as a tool/modle maker for nearly 30 years...this temperature induced movement has broken my silicon beads under my trim in some areas, not good when it rains or just washing the rig for a new trip....water has a tendency to wick, where ever it can find a path, usually right into the side walls.

[Larry C]

There is really no reason to use screws or adhesives to tie the aluminum directly to your roof, with or without a plywood underlayment.

Let it float, using the edge trim and the vent flange as the securing points

Either way you decide to go, really pay attention to your sealing of the edging, I have found that the aluminum's shrinkage - exspansion rate is more than I expected and I have worked as a tool/modle maker for nearly 30 years...this temperature induced movement has broken my silicon beads under my trim in some areas, not good when it rains or just washing the rig for a new trip....water has a tendency to wick, where ever it can find a path, usually right into the side walls.

You bring up a great point. How does one actually make an aluminum skinned trailer water tight if the skin is floating under the edge moldings.
I have seen Gage suggest to new builders to use aluminum because it's maintenance free. He made the comment that Wood (without alum.) is constantly needing maintenance. This statement seems like it makes sense. However, does it depend on where you live?

It seems the majority of the forum members are from CA, AZ, TX, or other dryer climate states. Is your dryer location what is giving you success with aluminum skinned Tears or are there methods you use that assure water tightness that really work without constant resealing?

Those of us in the northern states/CN/Yurp that get temperature extremes, lots of rain, and snow will see even greater expansion/contraction with aluminum skins.

I think it would be interesting to hear about water tightness issues from builders using aluminum skins from different regions of the world. Does location have differing effects on aluminum skinned trailers?






Larry C

[alffink]

I think it is more the technique/product used rather than weather
I know most people think of the temperature/weather changes and aluminum expansion and and the of the Northern climes, but the Southestern desert may actually be worse.
Just this week, we had tripple digit, afternoons, but by midnight the temps were into the 50's, a fifty degree temp variance in a few hours, one day after another, makes for a lot of movement....and I made the mistake of thinking OK, we don't have very much rain....so why worry about where I park the tear, so it is in the driveway, ready to go anytime, but that also means it is unprotected from not just rain, but the heat of the sun beating on the aluminum skin, spray from the sprinklers, and now posibly a leakpath directly to the sidewalls as I said earlier, everytime I give it a wash.

I will be looking at different products such as the butyl tape to replace the basic, sylicon sealent.

I don't think it's a condemnation of the aluminum skin, just that each building method requires a good understanding of just what it is, we are asking of it and if there is a better way of doing it.

[GPW]

Having built a good many sheds,garages, etc. with metal ....thinking this may be a good way to go ... the slight roll in the edge allows the metal to move without buckling ... Put the Al on when it's Hot and loose(expanded) , and during cold weather it will only contract ...

The rolled cap keeps the water away from the seams, like flashing ...

[madjack]

...here's what I do...first I cut the AL 1/4" narrower than the width...this allows a little "wiggle" room while fitting, along with a little expansion room...I use no underlayment(no ply) and lay the AL directly on the ribs...I basically float the AL on top with no adhesive...I do use a couple (or three) of air driven staples(per side) to help hold the AL in place until the trim can be put in place to hold it permanently...I used urethane windshield sealant on the first and regular RV putty tape on the second...they both worked just fine but prefer the putty tape for ease of use...and that is how I doit...by the way, I developed this method after several conversations with the fine folks at Camp-Inn, it is the basic technique they use..........
madjack

[George Taylor]

I used some caulking from Lowes that is made for aluminum sidding and gutters. It realy sicks to the aluminum and seems to remain flexible. even seems better than the suff that I bought from a RV store, cheaper too. Comes in clear or aluminum grey.

[aggie79]

My teardrop is not finished yet, but I did similar to others.

The aluminum was cut ~1/4" shy of profile. A bead of sealant was installed around the perimeter and openings prior to placing the aluminum. (I used 3M 4200 for a sealant.)



Enough sealant was used to have some squeeze out. (I let the sealant cure and then cut the excess squeeze out with a utility knife before installing the trim.)



I also used the same sealant before installing the trim.



I later came back and removed the screws that fastened the trim and squirted sealant in the screw holes. (In this picture, I was installing the hurricane hinge and filled the screw holes before installing the hinge.)



I'm keeping my fingers crossed that this will work.

[Larry C]

...here's what I do...first I cut the AL 1/4" narrower than the width...this allows a little "wiggle" room while fitting, along with a little expansion room...I use no underlayment(no ply) and lay the AL directly on the ribs...I basically float the AL on top with no adhesive...I do use a couple (or three) of air driven staples(per side) to help hold the AL in place until the trim can be put in place to hold it permanently...I used urethane windshield sealant on the first and regular RV putty tape on the second...they both worked just fine but prefer the putty tape for ease of use...and that is how I doit...by the way, I developed this method after several conversations with the fine folks at Camp-Inn, it is the basic technique they use..........
madjack

What I am curious about is the true longevity of the seal. I had a Jayco Pop-Up I bough used. It was only 4 years old. The Jayco owners manual suggested a complete trim reseal every couple years. Being new to me, I figured I should do it. I completely removed all the trim.

The trim running down the center of the aluminum top was in need of replacing. It was not leaking, but getting close. I could not see any problem till I removed the trim. I resealed it with RV putty tape and
attached the trim with SS screws, original screws were plated steel and rusty.

The sides were made of some material similar to FRP. The trim seals on the sides were completely compromised and leaking (not inside). RV putty was also used here originally. I tried using a marine caulk that really works great:


However, after a couple of days all the joints had pulled apart. I was completely clueless as I have used 3M 5200 for years with great results. It sticks to everything and expands/contracts better than anything I have ever used.

I removed all the side trim and resealed with the RV putty. This worked for awhile, but the joints were still pulling apart from just sitting in the sun.

The only sealing material on the entire camper that was in excellent condition was the seal at the roof vent. The material used was a very hard rubber material. It was just laying on the surface to cover the screws and the joint, but it showed no sign of expansion/contraction problems as the other trim did.

From my experience with this commercially made aluminum skinned camper that a complete trim reseal is in order every couple years. Is this something you all do with your aluminum tears?

I am just having a hard time understanding how a free floating sheet of aluminum held with aluminum trim and caulk or RV tape can stay sealed very long.

Even if your not getting a full blown leak inside, how would you know if a trickle of water is getting between the skin and on most builds the top plywood, causing mold to grow.

The reason I ask is I have considered using aluminum on the roof only of my" Woodie" build. I am sure there is an answer, as this construction method is widely used. I would just like to hear how others have solved this potential problem.


Thanks,
Larry C

[Larry C]

Aggie,
Your level of craftsmanship is second to none. You are an inspiration to all of us.......

I see you used 3m 4200 for your trim seal. This is an adhesive type caulk. I assume your trim is permanent? I doubt you could remove it without damaging it or the skins.
Do any of the commercial trailers use a permanent sealant type caulk at the trim seal? It would seem prudent to me to use a sealant that could be replaced periodically, such as RV putty.

After my experience with 3M 5200 failing quickly, I am wondering if this type of harder setting sealants are not the best choice for something that is expanding/contracting so much.

It would interesting to hear from others on this subject: permanent vs removable trim sealant.

[madjack]

Larry, I can only pass on my experience...first, I consider almost all commercially built RV to be just so much crap...I don't know if it matters what you pay, those I have looked at...even the top end ones. were just crap...crap materials and crap construction so I don't know if comparisons can be done between them and a well built finely crafted home built...no sealant will fix a poorly done construction job.............

On our first build, we used urethane based windshield sealant/adhesive, applying enough to get a good "squish" out...we only keep this unit about a year before selling, at that time it was dry and tight and had been stored outside. On the second and present build I used RV putty tape for the edges and White Lightning 3600, a siliconized acrylic sealant/adhesive(cheap painters caulk with an adhesive component) on the hinges...after 3 years sitting out in the open(partially/occasionally tarped) the RV puttied edges remain fine...the caulk did not stick as well to the living plastic hinges but it had not leaked, I did develop a leak at the corner of the hatch hinge but this had nothing to do with the caulks/tape I used but with water finding a place to seep past the weatherstripping I used.......
madjack

p.s. "floating" may be a misnomer as the AL is held down by the screws thru the trim, fan vent and hinges...although in my case, there is no adhesive or underlayment under the AL..........MJ

[aggie79]

I see you used 3m 4200 for your trim seal. This is an adhesive type caulk. I assume your trim is permanent? I doubt you could remove it without damaging it or the skins.

After my experience with 3M 5200 failing quickly, I am wondering if this type of harder setting sealants are not the best choice for something that is expanding/contracting so much.

It would interesting to hear from others on this subject: permanent vs removable trim sealant.

Larry,

As with most things on my build, I'm flying blind on the sealant. According to 3M, the 4200 can be used where parts may need to be removed. I did a simple lap test with the two pieces of aluminum sheet and couldn't pull them apart so I don't know about the removable part.

I only used the sealant at the edges. The rest of the aluminum is floating. Around most of the edges I have some sort of mechanically fastened trim.

I did take the time to prep surfaces before applying the 3M 4200. I sanded my epoxied plywood to give it tooth. I also sanded the mill finish trim. My aluminum sheeting is anodized, so it has little pores from the process. Prior to gluing, I wiped down the gluing surfaces with denatured alcohol. The 3M 4200 seems to have a pretty good bite between alumnium and plywood and the aluminum trim and sheeting.

I do plan on storing my teardrop under shelter when not in use. I guess time will tell how things work out.

Tom