Fiberglassing a land-boat (aka homemade camper trailer)

[tessabeth]

Hello all,

Not entirely sure how forums like this work. I have a couple questions about fiberglassing over plywood, but it applies to a camper not a boat so if this breaks the online forum rules I will take it down.

I am building a teardrop camper. The walls and roof are 1/2” plywood, and it is already quite structurally sound as is, but I want to make it a little more durable and more importantly make sure it’s completely waterproof, so I decided on fiberglassing the outside. I bought 6oz woven fiberglass cloth and epoxy resin but have not started the process yet. Here are my questions:

1. Where pieces of plywood come together and there is a seam do I need to glue (wood glue, epoxy, caulk?) them together first before fiberglassing over the top, or as long as they are fairly flush i will get a waterproof seam just with the glass and epoxy?

2. should I use fiberglass tape on the all the seams first then cover the rest with my sheets of cloth?

3. do I need to cover screw heads that are in the plywood with something before glassing over the top?

4. lastly, I bought epoxy pigment to hopefully dye the epoxy and fiberglass so I don’t have to deal with painting over it later, has anyone had success with this coloring method?

I am obviously an amateur and greatly appreciate any feedback you have! I have attached a picture of the trailer body.

 

[gonzo]

You need to fill all the gaps and screw holes with thickened epoxy.
All the edges need to be routed or ground to about 3/4" radius minimum
Epoxy with or without pigment has very little UV resistance. You absolutely need to paint it.

 

[KeithO]

You will have to paint the final product, since the exoxy will not tolerate UV well and it will fail in the direct sunlight quite quickly. There may be special epoxies which are made for treating natural wood and being glass clear, but I would say it is a much more sure bet to paint it with a proper exterior paint.

A general suggestion would be to fill and fair the surface before applying glass and epoxy. The better you get the finish, the more likely you are to have a good result from it. Filling is usually done by mixing a batch of epoxy an when mixed, stirring in microbaloons until it has a "peanut butter" consistency. Then apply it with a wide squeegee like you would put mud on a taped joint on drywall. Better to put on too much, if not enough there will be a low spot that you will have to fill a second or third time.

Remember to round over external corners using a router, fiberglass will not drape over a sharp corner, there will always be unsightly air bubbles. These bubbles would be future leak spots too. Internal corners, you can add a fillet in the corner with the microbaloons mix and use something like a tongue depressor or the tip of your finger to get a nice smooth radius in the corner.

Once the surfaces have been prepared, filled, smoothed, corners rounded appropriately, now it is ready for glassing. Something to remember with glassing is that fiberglass has no strength if the fibers are not straight and taut. When applying epoxy, try to start in the middle of a surface and work outwards. It will not take long for the fiberglass to become transparent and you will see the surface underneath. Make the epoxy in small batches and after thorough mixing, pour it into a flat tray like you would use for paint. By pouring it into a tray, the depth of the epoxy is thin and it has a large surface area which is good since the chemical reaction generates heat. If you leave the epoxy in a cylindrical cup, it can get so hot it solidifies far too quickly and in some cases it can even catch fire. Not good... Make several small batches, work in the shade, try not to put too much pressure on yourself. Make sure you get each area properly wet out and get the bubbles out before moving on.

 

[tessabeth]

Thank you so much, this is incredibly helpful! For the fill and fair step, does the thickened epoxy just need to cover screw holes and the seams or should I be covering the whole camper in a layer of this first? I bought some “SculpWood Spreadable Epoxy Wood Filler Paste” is this the same as making the filler with microballoons and epoxy or will this product not work? Thank you again for the help!

 

[tessabeth]

You need to fill all the gaps and screw holes with thickened epoxy.
All the edges need to be routed or ground to about 3/4" radius minimum
Epoxy with or without pigment has very little UV resistance. You absolutely need to paint it.

Thank you! I will definitely be painting it now.

 

[Blueknarr]

The sculpt wood is essentially the same thing as the thickened epoxy mentioned earlier. It will be more expensive than mixing your own. But it will be more convenient and consistent than self mixed.

I highly recommend giving the whole structure a sealing coat of neat (un-altered) epoxy. Then a light sanding with 80-120 grit before fairing or wrapping with fabric. Raw wood will absorb some epoxy out of the fairing/cloth producing a resin starved weakly bonded zones.

If the plywood seams are sufficiently secure then all is good without seam taping. However, taping the joints is cheep insurance against the seams opening up. Tape after sealing and before fairing. Bias cut or +/- 45° tape will provide the most strands of glass crossing the joint.

Good luck

 

[KeithO]

You will need a lot of filler usually. I wouldn't think that sandable wood filler would be economical. What you have was created to fill divets in wooden parts where you want something that will match wood color and texture. You will see that glass fiber will very easily snag on any tiny wood splinters. That's why you want a smooth surface before trying to lay the fiberglass on it. If you google "moldless fiberglass" on youtube you will find quite a few videos on the topic.

Thank you so much, this is incredibly helpful! For the fill and fair step, does the thickened epoxy just need to cover screw holes and the seams or should I be covering the whole camper in a layer of this first? I bought some “SculpWood Spreadable Epoxy Wood Filler Paste” is this the same as making the filler with microballoons and epoxy or will this product not work? Thank you again for the help!

 

[Dejay]

There is also a video for the CLC teardrop camper that might give you some insight.

Also make sure to wear gloves. And while sanding a respirator / N95 mask.

I'm a bit confused how varnish works. Is it just opaque in UV spectrum and block it all? Is there a PU varnish that completely blocks all the UV and protects the epoxy?

 

[Blueknarr]

I'm a bit confused how varnish works. Is it just opaque in UV spectrum and block it all? Is there a PU varnish that completely blocks all the UV and protects the epoxy?

I think of varnish like frosting. I have to lick it off before biting into the cupcake of epoxy.
Or it can be likened to a sacrificial zinc anode. It absorbs most of the UV energy, so it degrades instead of the underlying epoxy. To be most effective the varnish needs to be replaced before it becomes too regraded. The epoxy still degrades but very slowly, eventually all of the coatings will fail and the wood will need to be completely stripped and the finish restarted.
Ancient varnish contained ground amber to allow a thick film to form. The amber also inhibited UV breakdown. Metallic oxides perform these functions in modern varnish. The more metallic oxides the greater the UV protection and the less opaque the varnish will be. Put enough pigment in varnish and paint is produced.

 

[Dejay]

Does mixing translucent pigment like red into the varnish help? After all it lets through red and blocks blue so presumably also blocks UV.

 

[Blueknarr]

Sort of. But not as you think. UV is not on the visible color wheel spectrum, sot our perceived color of pigment doesn't matter. But iron oxide and chromium oxide are really good UV blocking pigments which happen to be red.

Aluminum, titanium and zinc are common white UV blockers. Depending on how many oxygen atoms are attached to chrome it appears as red or yellow. Uranium is yellow as well. Colbalt is blue and lead oxide white while lead sulfate is black.

 

[ondarvr]

Red pigments tend to be very costly, and don't hold up well.

To achieve a meaningful improvement in UV resistance you need to make the coating opaque, but the epoxy at the surface still degrades, chalks, and sloughs off rather quickly.

Painting it is the lowest cost and longest lasting solution.

If you want it clear so you can see the wood, then no fillers can be used in the resin for fairing the surface, they will make the resin cloudy or opaque depending on loading.

There are clear coats designed to be used over epoxy to significantly reduce UV damage.

 

[fallguy]

You really need to precoat that plywood with 2 oz per yard epoxy with a roller and then sand it to smooth with about 80 grit. The reasons for this are to reduce outgassing, but more importantly, to avoid drysucking that light woven. All plywood seams need to be fairly smooth or you will develop voids under the glass. Say like a chip out, for example.

All fiberglass seams need to overlap 2". 6 ounce woven is technically a little light, so the precoating to avoid dry suck will also help you avoid ingress.

To finish.

You will experience print through. My advice to deal with print through is one of three ways.

1. Don't worry about it and paint it and let the weave show.

2. Fair with Totalfair or Quikfair appearance areas or the whole boat(camper).

3. Neat coat with epoxy within the recoat windows. I would do two neatcoats after glassing at 2oz per yard plus some epoxy forbthe roller. A 7" roller works best. Then sand the 2nd neat coat with 80-120 grit depending upon if you are cutting glass too much. Then a final neat coat; sand again and paint.

 

[hoytedow]

Having built one, I recommend white. It's for the heat of the Sun. I had painted it in other colors but they allowed too much heat inside.