The Astroliner

[anon1]

... I got the last of the epoxy finished up. She's glued up and sealed up. All the seams are epoxied and all 12 million or so of the staple heads are as well. ...

What did you use for the epoxy in the seams, or is that the 3M Platinum filler from above?

Did you mention carbon fiber cloth, did you do it just like a fiberglassed seam?

Is the seam usually sanded down a little before the filler & fabric goes on so that the finished seam is level with the surrounding?

Thanks.

[Atomic77]

... I got the last of the epoxy finished up. She's glued up and sealed up. All the seams are epoxied and all 12 million or so of the staple heads are as well. ...

What did you use for the epoxy in the seams, or is that the 3M Platinum filler from above?

Did you mention carbon fiber cloth, did you do it just like a fiberglassed seam?

Is the seam usually sanded down a little before the filler & fabric goes on so that the finished seam is level with the surrounding?

Thanks.

The 3M Platinum is a filler for finish work. I get mine from here because they have the best price usually. http://www.tcpglobal.com/MAR-01171_5.ht ... UgaZ_lViko

The epoxy is here: http://www.ebay.com/itm/like/2213760423 ... =82&chn=ps And yes, a recessed area on the seam and then seam tape. Probably over kill but why not. I'ts light and solid as a rock.

[Atomic77]

That's ok Dale. I'm guessing there is limited experience here with Filon on this forum. But that's OK... I'm going to try another forum that specializes in fiberglass campers and see if I get any info there...

[OP827]

Thanks for the kind votes of confidence... It's much appreciated for sure.

....
I'm still up in the air for now about gluing the entire roof or just floating it... Big decision. From previous experiences I'v seen issues because of the glue or lack thereof, if it wasn't applied properly. In fact, notice most any RV out there that has Filon on it and look down the sides. They all look lumpy to me. So I'm probably leaning towards floating with a bead of urethane on the perimeter as Dale suggested. I'm going to epoxy and mold all the edges anyway. And with windows and roof fans, I'm sure there's plenty to hold it down. Decisions, decisions. So anyway, feel free to offer your wisdom on this one. I would like to hear your thoughts...

...

I think your concern is quite valid. My feeling is that the issues with delaminating must be coming from thermal expansion difference between Filon and underlying plywood or other substrate underneath. Good glue is a big factor, but the real reason is stress created by the difference in thermal expansion properties between the Filon and material it is affixed too.

There is probably a good reason why manufacturer has published these numbers:
http://www.cranecomposites.com/pdf/7587.pdf

So Filon changes dimensionally at 1.7 x 10-5 in/in/°F or 31 µm/m/°C while plywood can be a lot less, up to 10 times. Say for 20ft long cover and 150°F temperature change, the difference could be around 0.55” if my calculation is correct, so if the skin fixed at the ends, I am not sure whether it is glue that will fail or glue and plywood can still expand together with the filon.

Teardrop roof (not the walls) is somewhat better in shape to allow for some of that expansion than straight panel like a house wall for example.

That is why there are slotted holes and special instructions for a house vinyl siding installation.

It would be a good idea to glue the Filon when the ambient temperature is in the middle of the expected future operating temperature range. That will reduce the movement potentially up to two times. Glue that allows some movement can be a good idea too.

[Atomic77]

Thanks for the kind votes of confidence... It's much appreciated for sure.

....
I'm still up in the air for now about gluing the entire roof or just floating it... Big decision. From previous experiences I'v seen issues because of the glue or lack thereof, if it wasn't applied properly. In fact, notice most any RV out there that has Filon on it and look down the sides. They all look lumpy to me. So I'm probably leaning towards floating with a bead of urethane on the perimeter as Dale suggested. I'm going to epoxy and mold all the edges anyway. And with windows and roof fans, I'm sure there's plenty to hold it down. Decisions, decisions. So anyway, feel free to offer your wisdom on this one. I would like to hear your thoughts...

...

I think your concern is quite valid. My feeling is that the issues with delaminating must be coming from thermal expansion difference between Filon and underlying plywood or other substrate underneath. Good glue is a big factor, but the real reason is stress created by the difference in thermal expansion properties between the Filon and material it is affixed too.

There is probably a good reason why manufacturer has published these numbers:
http://www.cranecomposites.com/pdf/7587.pdf

So Filon changes dimensionally at 1.7 x 10-5 in/in/°F or 31 µm/m/°C while plywood can be a lot less, up to 10 times. Say for 20ft long cover and 150°F temperature change, the difference could be around 0.55” if my calculation is correct, so if the skin fixed at the ends, I am not sure whether it is glue that will fail or glue and plywood can still expand together with the filon.

Teardrop roof (not the walls) is somewhat better in shape to allow for some of that expansion than straight panel like a house wall for example.

That is why there are slotted holes and special instructions for a house vinyl siding installation.

It would be a good idea to glue the Filon when the ambient temperature is in the middle of the expected future operating temperature range. That will reduce the movement potentially up to two times. Glue that allows some movement can be a good idea too.

Thank you for the input, that was awesome. I have witnessed what happens when there is a "pocket" behind the Filon that didn't adhere for whatever reason. The air in the pocket heats up faster and it causes a bulge from the swelling. It's all about the differences in expansion rates and the success of the bond. I've had a couple guys tell me they floated theirs on their teardrop with great success. My teardrop is larger and I'm wondering if the size will make a difference? In reality, if I use 5200 to glue the edges down, then epoxy the outside corner and seal it all up... the 5200 is actually unnecessary at that point. I read on another forum an article about urethane sealants such as 5200, expanding at the approximately the same rate as Filon. So... leaning towards floating... but still undecided!

[OP827]

You are welcome, glad I could help. The length of materials matters a lot as the absolute difference is proportional to the length. You nailed it, it is a fight between bond strength and expansion difference forces while it is glued. When it is floating, it a different picture when there is more room for filon to lift from the substrate and relax the stress, it needs very little lift up from the plywood to compensate for the difference, that is why floating setup has better success perhaps. I would also lean towards floating for such build. As far as air bubles, they need to be taken care of too. The way I'd do it, I'd drill at least one tiny air relief hole in the plywood ceiling somewhere where it cannot be seen that would allow the air pressure in between the fillon and plywood roof to escape and the problem is solved. I do not know if trailer manufacturers do that relief holes, but it is pretty common practice in engineering to manage air diffential pressure issues caused by various things.

[OP827]

if you do not drill relief hole and your plywood roof is fully sealed like you said and then filon is sealed completely around its perimiter, the roof would lift more from the air expansion under the filon, rather then filon thermal expansion itself.
This air, although in a small quantity still needs to escape to reduce any issues, it could be a relief in any place as long it is not permitting moisture buildup under the plywood. If plywood is not airtight, the air most likely would find its way out not to cause any issues.

BTW, if you are planning to only epoxy filon roof perimeter to plywood roof I would recommend to do some estimation of thermal expansion forces not to exceed the strength of the glue, filon and plywood joint on the roof perimeter so that one day the edge does not lift up. There must a good reason why trailer manufacturers keep using moulding and screws there. it is a difficult decision with your design idea, I agree.

[noseoil]

Why not drill the relief holes into the interior for venting? As long as it's well sealed, it should work. A very small diameter hole is all that's necessary for the air movement. As long as the body is sealed from moisture, it will work. Perhaps a red plastic squirt nozzle from a WD 40 can bedded in epoxy as a pressure relief shunt?

[dales133]

Micheal how good is the range of sika products avaliable there?
There is one that will stretch about 1.5 inches on a 1/4inch bead I recon would be ideal for you.
The 11fc is a high strength adhesive/sealant that has almost as good stretch.
I'd check out thier website it will have all the stats.
If the us one dosn't then check out our one and then ask the us distributor for the product

[Atomic77]

Good suggestions... all of them. I'm looking into it all right now. Thanks!

[OP827]

Micheal how good is the range of sika products avaliable there?
There is one that will stretch about 1.5 inches on a 1/4inch bead I recon would be ideal for you.
The 11fc is a high strength adhesive/sealant that has almost as good stretch.
I'd check out thier website it will have all the stats.
If the us one dosn't then check out our one and then ask the us distributor for the product

Without perimeter moulding and hard epoxy perimeter glued as Michael menitioned, the flexing glue will only help to some extend, but the roof will still be fixed and stressed on the perimeter.
So I guess if perimeter moulding and moveable flexible roof perimeter is not an option, other option would be a very strong glue bond that will stand against time and frequent daily stress caused by thermal expansion linear difference.
All polymer glues, epoxies included, can creep under stress and also age, they gradually loose their strength in time, but that is a theory.

[dales133]

Yea that's a hard one I guess, maybe some edge trim might be the lesser of several evils if it means better longer lasting perimeter bond with the rest floated

[KCStudly]

There must a good reason why trailer manufacturers keep using moulding and screws there.

Because it is a quick, easy, and relatively cheap way to make a rough edge look good. Making an assembled corner seam water tight and appear monolithic would be much more time consuming and labor intensive.

[OP827]

There must a good reason why trailer manufacturers keep using moulding and screws there.

Because it is a quick, easy, and relatively cheap way to make a rough edge look good. Making an assembled corner seam water tight and appear monolithic would be much more time consuming and labor intensive.

True, but also the corners are the stress concentrators where cracks may occur first due to vibration and more movements. Trailer is not a house, it is subject to some shocks and shakes. Fiberglassing the whole skin as monolithic is probably the best and most reliable solution for monolithic look.

[OP827]

As many of us and Michael noted before the structural strength comes from sum of all the parts. If the corners are enforced (internaly) and very rigid to the point of no flex in the right angle, the probability of cracks and skin separation is greatly reduced. It is basically to do with high quality of the materials and their geometry combination. Michael is using epoxy which is the strongest glue out there. If the wall and roof are webbed reliably (not like in manufactured wood frame trailers by staples only) the monolithic skin should be achievable, even with filon, but some trial tests may have to be designed and made from filon strips and wood for the peace of mind. That is what I would want to do in this case anyway. I do not know how strong filon will bond with plywood and epoxy and how great the forces could be from the thermal expansion in this case, there are too many unknowns related to geometry and structure, it is all my theory that seems to be showing evidence in practical issues on real trailers. I have no experience working and maintaining filon or with bonding it. Sorry for a long and potentially hijacking post here.