Fasteners and Fiberglass for a Plywood Squaredrop Build

[MojaveD]

Thanks for the add, glad to find a community of tiny trailer builders. Two questions so far, and please let me know if there’s a better place to post them: 1) can I use fiberglass just on the corners where the plywood walls meet (plus seems) and 2) are drywall screws okay for attaching plywood to spars? I saw 1/4” crown staples recommended but I don’t currently have a staple gun/compressor. TIA

 

[Tony Latham]

1) can I use fiberglass just on the corners where the plywood walls meet (plus seems) and 2) are drywall screws okay for attaching plywood to spars?

What are you finishing the plywood with? Aluminum? Paint or something else? Here's a link to what can happen to plywood with a paint product –including bed liner– directly over plywood.

Wood sided trailer is having issues. Suggestions wanted

Fiberglassing the entire cabin isn't difficult, as long as you mix small batches of epoxy to avoid it from popping off in the cup.

I think you need an exterior screw for exterior purposes. Sheet rock screws can rust (and I hate Phillips head screws). Something like this:

Amazon.com

Of course, you'll need to select the right length of screw and the correct adhesive.

Tony

 

[KCStudly]

Drywall screws are high strength steel which allows them to be thin so they go into drywall easily, but have adequate strength. However the high strength alloy also makes them more brittle, so in our dynamic load environment they can snap when jolted. Standard wood or deck screws are better. Gluing and screwing is always better... the glue typically does most of the work.

 

[MojaveD]

What are you finishing the plywood with? Aluminum? Paint or something else? Here's a link to what can happen to plywood with a paint product –including bed liner– directly over plywood.

Wood sided trailer is having issues. Suggestions wanted

I think you need an exterior screw for exterior purposes. Sheet rock screws can rust (and I hate Phillips head screws). Something like this:

Amazon.com

Of course, you'll need to select the right length of screw and the correct adhesive.

Tony

Plan is to sand with orbital sander, apply an exterior primer/sealer followed by exterior acrylic enamel. The camper will be garage kept and will see scant rain (I’m in the desert southwest). For sealing seams, is fiberglass a good option? I would round over the sharp edges with a router. Aluminum is beyond my budget.

Thanks for the tip about screws. Is DAP Dynaflex Ultra acceptable over screw heads? Claims to remain flexible.

 

[MojaveD]

Drywall screws are high strength steel which allows them to be thin so they go into drywall easily, but have adequate strength. However the high strength alloy also makes them more brittle, so in our dynamic load environment they can snap when jolted. Standard wood or deck screws are better. Gluing and screwing is always better... the glue typically does most of the work.

Thank you for this, will pursue a deck screw. Speaking of glue, do you recommend construction adhesive, or will titebond 3 suffice?

 

[KCStudly]

I mostly only used construction adhesive for my wall to floor joints (wood-to-wood) where I wanted to be sure I had good gap filling and working time (long before I made the switch to working with epoxy and fillers). For wood-to-wood cabinetry and framing joints where I could control the fit well, I mostly used TB2. For the foam I used a variety of products in "the grand experiment"... TMI to go into here.

 

[Tony Latham]

Plan is to sand with orbital sander, apply an exterior primer/sealer followed by exterior acrylic enamel. The camper will be garage kept and will see scant rain (I’m in the desert southwest). For sealing seams, is fiberglass a good option?

I believe it's best to cover all the surfaces with a 6 oz layer of glass/epoxy. You don't want the plywood to check down the road, and in your heat, it may. Call it insurance.

I didn't cover the seams of my cabin, nor did I suggest it in my book. After seven years, it's fine. Covering a 90% corner with fiberglass is difficult. A roundover is easier, but the radius needs to be about 1/2". A bias-ply tape–if you can find it–makes it doable.

Tony

 

[MojaveD]

What are you finishing the plywood with? Aluminum? Paint or something else? Here's a link to what can happen to plywood with a paint product –including bed liner– directly over plywood.

Wood sided trailer is having issues. Suggestions wanted

Fiberglassing the entire cabin isn't difficult, as long as you mix small batches of epoxy to avoid it from popping off in the cup.

I think you need an exterior screw for exterior purposes. Sheet rock screws can rust (and I hate Phillips head screws). Something like this:

Amazon.com

Of course, you'll need to select the right length of screw and the correct adhesive.

Tony

Hi Tony, just now watched your video applying fiberglass to the roof. How do you then seal the seam where roof and side walls meet — do you fiberglass that as well? I know some guys use aluminum 90 degree trim but I like the look of radiused corners — I’m trying to mimic the Freedom foam camper that way. I’m doing a squaredrop if that makes a difference, framing with 2x2 and 3/16 sheathing.

 

[Pmullen503]

There is a way to get fiberglass to conform to a 90 degree outside corner.

Apply fiberglass and epoxy. Then tape a larger piece of polyethylene plastic over it. Use tape strips every few inches to apply tension to the poly to pull the fiberglass tightly to the corner. Keep moving the tape and pulling the poly tight, eliminating wrinkles, until the fiberglass conforms to the corner. Don't use too much resin as the poly will squeeze any excess out of the fiberglass cloth.

Once the epoxy cures, remove the poly and block sand the corner flat. A couple layers of lighter cloth works better than a single layer of heavier cloth. Cutting your cloth on the bias allows all the fibers to cross the corner, not just 1/2 of them making a stronger corner.

 

[KCStudly]

A flocked or flox corner works, too. Bevel the corner; build a dam with packing tape release flush to one face; pack the corner with thickened epoxy; remove the dam, fill and fair any small stuff in the filler; then glass up to the corner from each side. The flocked corner allows you to knock the very sharp corner off (or suffer contusions) without lifting an edge. This works good where you want crisp lines, like door or galley hatch lines, but I prefer a nice big radius on my profile corners between roof and walls.

 

[Pmullen503]

A flocked or flox corner works, too. Bevel the corner; build a dam with packing tape release flush to one face; pack the corner with thickened epoxy; remove the dam, fill and fair any small stuff in the filler; then glass up to the corner from each side. The flocked corner allows you to knock the very sharp corner off (or suffer contusions) without lifting an edge. This works good where you want crisp lines, like door or galley hatch lines, but I prefer a nice big radius on my profile corners between roof and walls.

It helps to radius that corner under under the flocked material to solidify the edge, especially if it's in any area subject to dings and chips.

In my case, I had a high stress area with inadequate wooden structure underneath to handle the loads and racking alone. Having continuous fibers around the joint to hold it together was essential. The sharp corner was an aesthetic choice, a radiused corner could have been stronger.

 

[Tony Latham]

How do you then seal the seam where roof and side walls meet

I butted the side and roof glass. No issues in six years.

Tony

 

[MojaveD]

I believe it's best to cover all the surfaces with a 6 oz layer of glass/epoxy. You don't want the plywood to check down the road, and in your heat, it may. Call it insurance.

I didn't cover the seams of my cabin, nor did I suggest it in my book. After seven years, it's fine. Covering a 90% corner with fiberglass is difficult. A roundover is easier, but the radius needs to be about 1/2". A bias-ply tape–if you can find it–makes it doable.

Tony

Would a 3/8” radius suffice for 6oz fiberglass? The 1/2” radius bit won’t fit in my router (the shoulder is too wide).

 

[KCStudly]

I found 3/8 to be okay, but bigger is better. Easy enough to make another shoe out of some scrap ply.

 

[MojaveD]

Thanks for this KC, I considered that but wound up widening the hole in the plastic one. Routing is done. Next is sanding and epoxy/fiberglass. What do you like for filling screw holes and gaps? I see that the epoxy suppliers sell “micro balloon” additives that make sanding and shaping easier. TIA

 

[Pmullen503]

Microballoons are what you want. Be aware that you want a very high % of microballoons to make a fairly stiff consistency. The higher the %, the easier to sand. Start with a very small batch of epoxy for your first attempt!

 

[KCStudly]

I don't have experience with micro balloons, just West System fairing filler and their structural filler. My understanding is that micro balloons leave open pours when sanded that then need a dedicated filler/sealer coat to prevent blisters later (keep in mind that I'm not an expert and my research on the subject was some time ago). Either way, when using fillers a barrier coat of neat is recommended before primer and/or paint.

 

[KCStudly]

... either way, it is best to do any touch up sanding immediately following the manufacturer's recommended cure times... generally next day... so as to catch it when it is still "green". The linger it sits the harder it gets. Also, don't forget to wash amine before sanding.

 

[KCStudly]

Sorry to say, but if I'd had a chance I would have advised against opening the stock base plate/router shoe. They make guide collars that would have fit the stock size hole; could have been an easy upgrade.

 

[S. Heisley]

"I think you need an exterior screw for exterior purposes. Sheet rock screws can rust (and I hate Phillips head screws). Something like this:"

I hate star screws! To each their own, but Tony is correct when he says use an exterior screw. I used mostly #2 Philips head deck screws (plus Titebond glue on every joint), but again, Tony is right that Philips head screws can strip if you aren't careful (even though I don't think he said that! Also, Titebond glued well can make a permanent attachment that will shred the wood if you try to pull it apart! There are plus and minus points to everything.). Probably the most important thing you can do, other than choosing an exterior screw, is use the same type of screw throughout, all Philips or all star or whatever... That way you'll know what you're using and will have less worry over what style and size of screw drivers you need, both when your at home and on the road.

As far as using fiberglass only on the corners, recognize that the tape sides will most likely show. I taped my seams, and if you're looking really closely, they show. But, they've held up 15 years now, So, I suspect a quality application has more to do with how well you do it and also the products you use. Take your time; read, study; select quality products. I used mostly marine products, which are more expensive. Don't plan on using just one coat of a product and done, either. Take your time and money and do it right. You won't be sorry.