help with roof decision

[will guthrie]

I'm building the widget from plans in the Design Library. I finished putting on the 1/8 inch marine ply outer roof skin as per plans and was reading up on epoxy fillers and sealers for the outer skin in sdtripper2's index. I'd been apprehensive about the durability of just 1/8 ply with epoxy sealer and paint since the start but now I'm really nervous. I was hoping not to have to add another layer of ply or glass the top. Perhaps the design relies for strength on the radical curve of the outside ply in combo with lots of epoxy sealer. I'm really running out of steam on this project but I do want to end up with a reasonably strong product. Any thoughts out there wether what I have is gonna be strong enough and if not what the best course of action would be? How much rigidity does the sealer add?
Thanks

[Joanne]

Hi Will!

I don't have an answer for you but I did look at your build photos and they look great. I love the shape of the Widgit. You mention that you are running out of steam on the project and I just want to encourage you to persevere in your efforts. It's going to be a great trailer. I had a number of when I was overwhelmed by my build so I just started to focus on individual tasks rather than the magnitude of the entire build. I also took a couple of "vacations" from building.

Keep on buildin'!!

Joanne

I'm building the widget from plans in the Design Library. I finished putting on the 1/8 inch marine ply outer roof skin as per plans and was reading up on epoxy fillers and sealers for the outer skin in sdtripper2's index. I'd been apprehensive about the durability of just 1/8 ply with epoxy sealer and paint since the start but now I'm really nervous. I was hoping not to have to add another layer of ply or glass the top. Perhaps the design relies for strength on the radical curve of the outside ply in combo with lots of epoxy sealer. I'm really running out of steam on this project but I do want to end up with a reasonably strong product. Any thoughts out there wether what I have is gonna be strong enough and if not what the best course of action would be? How much rigidity does the sealer add?
Thanks

[PaulC]

Adding another sheet of ply will increase the strength if that's what you want. 2 part epoxy will add strength to the single sheet but it will not be as strong as 2 sheets.
What do the plans call for. This should give you the heads up on what has been done and proven.
The bottom line is what do you want to do.
I know that sounds if and buttish but that's what individual builds are all about.
Don't give up on it yet, your pics show you are making great progress.
Cheers
Paul

[BobR]

I think you would be fine with a single layer of ply with several coats of epoxy. The rigidity will come from how well it is attached to the sides and spars. Make sure you use a quality high strength waterproof glue. Then I might suggest a layer of lightweight fiberglass cloth for the roof or a least fiberglass taping the seams and edges. Just my opinion. BTW the trailer looks great, keep going...

[mikeschn]

Steve Frederick built mine with 2 layers of 1/8" plywood. I never had to worry about a rock going thru the skin.

An alternative would be 1 layer, plus a layer of fiberglass and resin.

If you're running out of steam, take a break from working on it, just don't take a break from thinking about it.

You'll come back in a week or two and be glad that you are going to add the extra strength.

Mike...

[Arne]

I plan on using 1/8 on the roof, inside and out... the insul will back up the outside, along with it being coated with cpes, which does make it more rigid.

I have some spots on my current tear where the 2 - 1/8 sheets do not touch. Yes, it does depress, but not so easily I expect it to be a problem... with the insul backing it, I don't think it will be a problem... and, it is designed to be in a constant curve.. the only straight part will be where the roof vent goes, 16" long.

But, unlike Mike, I don't throw rocks at mine/g/..

[SaGR]

Take a break and then come back to it.

You're off to a gorgeous start! I hadn't looked at the Widget much until just now. That's a pretty "sexy" trailer!

[madjack]

Will, if you were skinning in fiberglass cloth or AL, the 1/8th would be adequate but with just epoxy, I don't know, Andrew had posted some info on a "hammer" test and the 1/8th failed miserably by itself...if you must go this way, be sure the roof cavity is completely filled with a foam insulation to give it some backup, otherwise I would go with 2 layers......
madjack

[angib]

Will, that Midget's looking good - I hope you don't mind that I've 'stolen' your photos and added them to my Hall of Fame.

To add to madjack's post, I should say that I haven't got any "test results" - my point was just to copy the idea of a former boss of mine, that the thickness of many things depends not on how strong they need to be, but on how hard you want to be able to hit them with a hammer without breaking them. 1/8" is strong enough to hold the trailer together over bumps, etc, but for rock resistance, you may want to make it thicker - one idea would be to do that only on the front lower curve that will get most of the road debris.

Andrew

[will guthrie]

Thanks for all the encouragement. I think I will take a break from working on the roof to mull over my options and switch to working on the inside for a while. The roof is backed up with foam insulation but you can depress the ply a little between the ribs.
If I were to attach another layer of 1/8 ply should I roll the entire surface with epoxy to attach or just apply epoxy where sidewalls and spars are? Also what's on the roof now is marine ply that cost $200 and change(it takes 5 partial sheets) for what I thought was gonna be the only outer layer. Do you think it would be ok to add your basic (and much cheaper) 1/8 luan over the marine ply and then seal with epoxy etc? I know this would be backwards but maybe with the sealer this wouldn't be to big a deal. I keep telling myself the second teardrop will be so much easier.
thanks all

[will guthrie]

Andrew writes :
"Will, that Midget's looking good - I hope you don't mind that I've 'stolen' your photos and added them to my Hall of Fame. "

Steal away.

He also says:
"To add to madjack's post, I should say that I haven't got any "test results" - my point was just to copy the idea of a former boss of mine, that the thickness of many things depends not on how strong they need to be, but on how hard you want to be able to hit them with a hammer without breaking them. 1/8" is strong enough to hold the trailer together over bumps, etc, but for rock resistance, you may want to make it thicker - one idea would be to do that only on the front lower curve that will get most of the road debris. "

I had thought of adding another layer just to the front for road debris etc. and one to the back since I'm a dismal backer upper. Maybe I can make a detail of it of the step it would produce. Will

[Sam I am]

Will, I used two layers of 1/8" Baltic birch on my tear. One layer would probably have been enough for stiffness. Any sheeting on a curved surface makes a very rigid structure! I added the second layer for resistance to punctures from stones and road debris when towing, and sticks or tree branches falling on it at a camp site. The birch on mine was only $9.25 a sheet (5'x5'), and I used three sheets, so it only cost me about $30 for the added security. I glued it on with Titebond II, squeegeed onto the entire surface, plus some small brads into spars and the edges of the walls. It seems to be very strong! If you can get birch, it might be cheaper than the marine ply.
Sam

[angib]

I should have added that in my experience adding epoxy doesn't make a structure much stiffer or stronger overall, but it does make the surface much harder and so more resistant to local damage - you can press a strong thumbnail into most ply, but the nail will break before it marks epoxy-soaked ply.

Maybe a dumb suggestion, but if you've done the whole roof in one skin of 1/8", why not try it as it is? If you find that it's too liable to be damaged by road debris or whatever, adding a second skin afterwards isn't a huge difficulty. Of course if you were planning to apply an expensive body shop paint finish then re-doing that would be a painful, but for most paint systems all you'd need to do was sand off the paint to get a good key to stick the second skin to. At worst, that might cost you a cheap HF belt sander, but you probably have something better that that already.

Andrew