Fiberglassing Wood (Does anyone have any experience on putting fiberglass on wood)

[Gary Thinglum]

We own a winter home in Florida. Last year, I and a friend built a porch. I wanted something different so, we made a curved rail for the handrail.
I spoke with 3-M (maker of the Bondo "Brown Fiberglass Resin") about what I was planning on doing with their product. She said I could apply it directly to the bare wood, without using the cloth. Said to give it several coats. I think I gave it about four coats. Then, I painted it with the paint she recommended.
It looked fantastic. We went home last April, and came back in November. The fiberglass, and paint cracked and blistered, it looked horrible. The sides still looked great, but the top, was where it had peeled, blistered. (The top is where the exposed ends, "pieces of 2" x 4" x 3/8" strips" are layered on end, and then they are glued and screwed together, to make the curve).
Talked with 3-M again in November,
(Said to sand wood to remove all the paint) this time they told me to use cloth. I have never used cloth for fiberglassing before. My questions are: 1) do you only use one layer of cloth or do you use numerous? 2) After you use the cloth, it sounds like you sand your seams, and rough spots smooth and then fiberglass again?
3) Can you paint it after this, or do you need to use a plastic filler like they use on automobiles, prior to painting?

Would appreciate some guidance from someone who has more experience than I do, which is very little.
Open to any suggestions.
Thanks for your help. Gary

[Mike Kees]

I have fiber glassed Plywood carpenters hand tool boxes that I used to leave in my pickup. They always got beat up and wrecked until I decided to wrap the outside corners with fiber glass. The cloth comes in mesh or matt form and different textures from fine to coarse. You would want the mesh in a fine weave. You just coat everything with the mixed resin and then embed the mesh into it,a rubber sqeegy thing would help here. After it cures sand and fill till you are happy and then paint.

[Andrew Nemeth]

Boatbuilders fiberglass over wood all the time. If you don’t find the answer your looking for here, you may want to try a boatbuilding forum.

With the proper epoxy mix, fiberglass cloth can be water clear so it can be finished ‘bright’ by top-coating with urethane, varnish, or painted. As far as I know, most epoxy products need some form of additional topcoat for UV protection and without it the epoxy will degrade. Was the product you used before designed to be used as a stand alone surface coating in an exterior environment? If not, you may need to top coat it with something else to protect it or you may want to switch products to something designed for this application. I might be missing something, but I’m a little perplexed how adding glass to the mix is going to give you better results if you are using the same epoxy product as before.

Now for how you actually apply the glass cloth, if this is the route you go, you can wet out the surface with epoxy first, then place the cloth on top and press it into the resin with a squeegee as Mike has already suggested. You may need to add more epoxy on top of the cloth if the cloth does not completely ‘wet out’ when you squeegee the cloth into the epoxy. I find this method works best for smaller jobs where you are just reenforcing a corner or seam. For larger jobs, I prefer to lay the cloth out over a dry subsurface, smooth the cloth out and cut away significant excess, then pour the epoxy on top and work the epoxy into the cloth from above. Since I’m not a fiberglass pro, I feel a lot less rushed getting the cloth to lay just right without having to worry about the epoxy curing before everything is where I want it. In either case, you may need to roll on a coat of epoxy that you let partially cure, prior to adding the glass and epoxy layer so that the wood does not absorb too much epoxy causing the fiberglass to get starved. After your fiberglass layer sets up, you can squeegee on one or more additional layers of epoxy to fill the weave. You should sand lightly between these filling coats to help fair out the surface (if your going for smooth). Once the surface is as smooth as you want it, it should be top coated with urethane, varnish, or paint to provide UV protection.

[Ron Citerone]

If you use multiple coats of resin you need to be aware that some resin (I think it's called finishing resin) has wax in it that comes to the surface to make the resin cure. If you add more coats of resin, the wax needs to be sanded off or the next coat won't stick. I replaced the wood core in a large deck cover for my boat and then fiber glassed it with 2 or 3 layers of cloth and then resin and was happy with the result.

I suggest you do some utube homework, there are many boat repair video's out there. I would utube fiberglass transom repairs. Most older fiber glass boats had transoms and decks made of plywood or balsa wood encased in fiberglass. I think it's worth the time to do some homework before proceeding.

Good Luck, ron

[Richard Coers]

Yeah, boatbuilders do it all the time, but they always put spar varnish on top of it to block UV rays. I'm guessing you have a UV issue, or wood movement issue.

[Lee Schierer]

We own a winter home in Florida. Last year, I and a friend built a porch. I wanted something different so, we made a curved rail for the handrail.


If you fiberglassed the rail shortly after construction, the treated lumber still had a very high moisture content, which most likely caused the failure to bond. The wood would shrink as it dried putting stress into the epoxy resin coating. Without the glass matting the epoxy would have debonded and probably buckled and cracked. It is a well known practice not to paint treated lumber for at least several months after construction.

[Zachary Hoyt]

I've built a couple of wood strip canoes, which were covered with fiberglass cloth and epoxy, then with spar varnish. Fiberglass is the glass fibers which are made into cloth or left as shreds, or a combination of these with an adhesive. If you just used epoxy with no fiberglass in it then it is not fiberglass. As I understand it it is the glass fibers which are susceptible to rapid UV degradation, and not the epoxy, but I may have misunderstood that. When I built the canoes the wood was thin and well dried before it was glassed, and the wood was fully encased by the fiberglass so that no air could get to it. If the bottom of the rails was open to the air then I would think that the wood would be able to expand and contract with changes in humidity. I've had the second canoe for 5 years now and it is still as watertight as ever, though I recoat the varnish once each year. I have spent many days out in the sun with the canoe, but I store it inside an outbuilding at home, so it is not in the sun all the time like your railing.

[Bill Dufour]

Ask in the boat building section. of this site.
Bil lD

[Gary Thinglum]

Thanks for your thought/input guys. The wood I used was not "treated". This was the second attempt at making a curved rail. The first we tried was "treated" however, after gluing several strips together the glue would not dry as the wood was wet. So, I used a regular 2 x 4. It did have a chance to dry out prior to putting the resin on. Zachary may have hit on something: "if the bottom is open the moisture, and humidity could allow the wood to expand and contract."
The bottom for the most part is open except for some supports. Closing the bottom in, and using cloth to seal the entire rail make a lot of sense.
I did sand the resin between coats thinking this would give better adhesion.
What type of paint should be used to finish the fiberglass.
I will check out the boatbuilding forum and youtube videos.
Again, thanks.

[Eugene Dixon]

You might check with Jamestown Distributors and get their thoughts.

[David Publicover]

Fibreglass resin and epoxy resins are quite different in respect to sealing wood in my experience. Fibreglass resin seems more brittle to me. Epoxy would be my preference in a situation like that. With epoxy, you need to use appropriate primers and fairing compounds before painting. Marine polyurethane holds up well. Single pack is easier to touch up than two part poly. West Systems epoxy is a popular brand and they offer technical advice if you want more specific advice.
Best of luck!

[Dave Mount]

Not sure what the "brown fiberglass resin" is, but from the price I saw here in Minnesota ($40/gallon) I'm guessing it is a polyester resin and not epoxy.

My guess is that the problems started with wood movement, with cracks forming at the lines between the plies of your lamination. Once water gets under an otherwise waterproof layer, be it varnish, paint, polyester, or epoxy, it will fail.

Before you attempt a repair, you need to get the railing into a controlled environment to let it dry out thoroughly (I'm assuming if the finish failed then water has gotten to the interior wood). Remove (sand, grind) all poorly adhered material, down to bare wood would be best. If the sides are intact, you can probably get away with just scuff sanding those.

Fiberglass is usually added to increase strength, which isn't needed here, but it may help with "armoring" the top side of lamination to avoid cracks in the future. A single layer should be fine, probably a 4, or 6 oz cloth in standard weave have it overlap the top corners over onto the sides at least some to cover all the seams in the lamination; running it all the way down the sides is fine too. When used with epoxy, you can wet the wood with epoxy first, then lay the glass on, then wet it out with a saturating layer of epoxy, or you can just lay the fabric on dry and wet it out. Wetting the wood first just keeps the wood from sucking the epoxy out of the weave if it's particularly thirsty. You want the fabric saturated, but not a bunch of excess on top of this first coat. Foam rollers (short nap, 1/4" or less) are good applicators. You can also make a good applicator by buying a foam roller, cutting it into appropriate lengths, then splitting the cylinder into thirds and attaching a handle made of scrap wood (just cut a slot in the wood and wedge the edge of the roller piece in there).

Following the first layer, you apply additional coats until you have the build you want. The goal of subsequent layers is just to fill the weave and provide a smooth surface. Epoxy forms an "amine blush" that can prevent subsequent layers from adhering properly. Your choices are to either apply the subsequent coats before the previous coat has completely set (usually 2-4 hours depending on the hardener, and temperature) or to wait until the previous coat has set and wet sand it. Applying multiple coats before setting is a lot less hassle if you can handle the schedule.

Although there are UV-resistant (that's a relative term) epoxies, not even they can handle the kind of sun this is going to get. Sounds like paint is your preferred finish, that should work fine as UV protection. The West System site says epoxy does not need to be primed, unless you need it as a fairing layer. Just sand the final epoxy layer to the desired smoothness; the paint will fill the texture, 80 or 100 grit is fine. I'd recommend a marine paint for the topcoat, probably a 1 part urethane paint. I don't think you want a traditional oil paint because this assembly is going to expand and contract with temperature changes and you need a flexible topcoat or the paint will fail. If you want to have a little grip to the handrail, they make non-skid paints for the topsides of boats.

I get epoxy and fiberglass from raka.com, and boat paint from jamestowndistributors.com. No affiliation with either one, just a customer.

Best,

Dave

[David Sharp]

Resin is generally one of three types. Polyester, vinyl ester and epoxy. If you used polyester that would explain the problems that you had. It is the least desirable product to use on wood. I haven't used vinyl ester so I don't know how it would hold up. You want to use epoxy resin. Sand it off and go back with 2-3 coats of epoxy then 3-4 coats of marine spar varnish for uv protection. The sun is going to require an annual coat of varnish, unfortunately. You can use cloth if you are trying to minimize the wood moving. If your rail is laminated I don't think that a layer of cloth is going to gain much. It's more for impact and abrasion protection. A single layer of 6 once cloth will be easy to apply. just brush the resin on then lay the cloth down and add more resin until the cloth becomes translucent. If you catch it before it completely kicks you can trim the bottom edge of the handrail where the glass hangs down with a utility knife. I wouldn't even try to add cloth to the underside of the rail. To finish it off West makes a talc based powder to add to the resin to make a fairing compound to fill the weave. I spent about 30 years in the family boatyard hell if that matters.

[Gary Thinglum]

I purchased the Bondo Fiberglass Resin at Lowes. Lowes web site says it can be used on wood. In the Lowes Q & A someone said it states Polyester on the label. Someone said it does not contain wax. It is an epoxy as you mix a hardener in the resin.
I'm not sure as the can I used is at the house in Florida.

[Dave Mount]

Having a resin and hardener component doesn't mean it is epoxy. Epoxy refers to resin that cross-links through an epoxide group (a chemical structure). The characteristics of the cured material derive from the chemical components that react. Think of the range of characteristics that different plastics have.

The fact that this product failed in this application doesn't mean it can't be used on wood. Further, it's not clear whether the problem here was necessarily the product you used, or issues with the structure it was covering (i.e., wood movement).

All exterior finishes over wood fail with time; the choice of the best finish is just a combination of how long it needs to last, and how well it can be maintained to compensate for failure. My covered porch and deck have white oak planking (don't pass out, this was from pallet grade logs, I paid $0.36/bf rough 20 years ago). Under the porch roof, the finish (Sikkens DEK) lasts for years between recoating. The deck, however, has to be re-coated annually to maintain its appearance. After 20 years, I had to sand it all down to bare wood and recoat. This is not the "fault" of the Sikkens, it's just a consequence of brutal conditions (beating sun, water, freezing while wet) and, to some degree, the choice of a difficult wood to cover. That said, I wish I had a time machine 20 years ago so I could have traveled forward 20 years to understand how much maintenance was going to be required. I would probably have chosen another material.

Best,

Dave

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