how to glue wood to high top

[travlinman and wife]

Hi travlinman with a ?. what type of glue can I use to fasten wood to fiberglass high top for perment hold do not want to drill holes in in high top.

 

[Optimistic Paranoid]

I'd go with VHB tape, myself.

Regards
John

 

[highdesertranger]

inside or outside? you want to epoxy it with fiberglass resin, possibly adding some more fiber. what is the plan for the wood? highdesertranger

 

[SternWake]

Fiberglass roofs are generally made in a mold. First the mold is waxed with a mold release agent, then a Gel coat is sprayed inside, then multiple layers of fiberglass cloth and matt are applied. In some areas there is foam and or Wood sandwiched in between the fiberglass.

The resin used is Polyester resin as this is the cheapest and easiest to work with.

The Gel coat Bonds extremely well with the subsequent fiberglass, however, it is also possible to spray on a gelcoat after the fiberglass is popped from the mold, and any contamination can compromise the bond of gel coat to fiberglass.

So, a Glue applied on top is only as strong as the bond between the gel coat and fiberglass below.

Similarly if it is just painted, the bond strength of the glue is only as good as the bond between paint and substrate below.

So ideally, one would want to tape off the area where the wood would be attached, and a little more surface area 2 inches minimum, around the size of the wood, then sand down through paint and gel coat to get to the greenish/ brownish fiberglass below..

Then one would grind the wood so that it fits tightly to the curve of the fiberglass roof in the intended area.

One then would use polyester resin, sold in Home depot as 'fiberglass resin'.

The wood should be painted with the resin on the bottom so that it soaks deeply inside the grain, the sanded fiberglass roof should be painted lightly too. Do not work in direct sunlight, and be aware of the potlife of catalyzed resin. you only have so much time to work with it, and once it starts going off you can no longer manipulate it nor expect it to bond properly. The hotter it gets the faster it goes off. The bigger portion that is catalyzed, the more heat it itself generates.

Another portion of this same batch of resin should thickened with the fine wood dust you captured when you grinded the wood to fit the curve of the roof. There are many thickener options, but this one is free and more than adequate for this task. Once mixed into the resin so that it is near the consistency of peanut butter, spread it on the pre saturated wood's underside, and place the wood on the roof and place a brick or two on top and let it cure. You do not want to push out all the thickened resin, but you do not want a bubble under there either. Aim for about 1/8" thickness.

Once the resin hardens fully you should sand the edges smooth, and make sure no areas remain shiny. Precut strips of layered fiberglass should be laid on a 'wet out table' consisting of clean cardboard. these strips are to bridge the wood and fiberglass roof mating area, and also to cover the rest of the wood. Cut the fiberglass cloth patches perpendicular to the weave, not diagonally. Good sharp scissors are absolutely required for this task, and multiple layers can be cut at once so they are the same size or nearly so. but ideally each piece would be a smidge bigger than the one under it to reduce the amount of sanding needed later at the edges..

Catalyze an adequate amount of resin and stir completely and apply the resin to the patches/ strips of layered fiberglass and let it soak in until the glass turns transparent. While it is soaking in, go paint the sanded (100 grit or rougher) wood and fiberglass roof with the resin too. Go back to the wet out table, make sure there are no white patches of fiberglass left, squeeze out the excess resin from the patches, carry the cardboard over to the roof, and lift the patches off with gloved fingers and lay them over the wood footing. No bubbles. If necessary sharp scissors can be used to cut the saturated fiberglass to cut reliefs near corners/ edges where the fiberglass does not want to conform. These can also be cut beforehand, before saturating, but will make the messy job, messier still.

You are hoping to have at least 1/8 inch of fiberglass bridging the two materials and covering the wood facing the sky, and with the store bought fiberglass cloth sold at home depot, this will be at least 6 layers. On the wet out table one can drip a generous portion on each layered patch/ strip of fiberglass then flip them over and do the same to quicken wet out. Complete saturation of fiberglass is paramount.

Do not attempt more than one footing at first as the procedure is rather time consuming, and you only have so much time to do it before the resin goes off and is unworkable. If this occurs it can turn into a nightmare. One can go light on the catalyst to extend work times, but excessive dry times can be undesirable too. You want it hard before nightfall if working outside.

When the resin hardens, sand it smooth again, no shiny spots to 220 grit. At this point you can paint the footing the color of the roof, but you can also go a step further and paint another layer of resin on top( sand back to 100 grit or rougher). You could drill and drive the fasteners/ brackets where desired, then remove them and paint another layer of resin so that it soaks into the drilled holes, but does not fill them Spin a Q tip inside or even redrive the screw and remove and clean it. This will make wood screws have more grab and protect the wood from moisture intrusion better than just a sealant after the fact. Much stronger result!

Keep in mind the fiberglass resin sold at HD, is a sanding resin, meaning it has a wax mixed inside it which rises to the surface during curing, and allows the resin to be easily sanded. Without this wax, the sandpaper gets all gummed up and the task impossible. If this wax is not sanded off and the shiny parts made not shiny, nothing will properly bond to it.

This is obviously a large amount of work, but it will yield an excellent and long lived result. Wood just glued down with gorilla glue to the gel coat or paint will only last so long before it releases the brackets holding down your panels. The wood will expand and swell if not properly sealed, and UV light does a number on anything it comes in contact with.

Use Stainless steel fasteners, and squirt some paintable adhesive caulk in the predrilled holes which hold the correct length stainless fasteners on final installation. Paint does not stick well to stainless steel, so roughing it up and wiping it with acetone before painting helps a bit.

Working with fiberglass is messy work. Gloves and and acetone saturated rag help to keep your hands from turning into a fuzzy mess, and help clean the tools/ spreaders you use, so they can be reused. Working as clean as possible is mandatory, and drop cloths or more cardboard taped where resin is not desired is wise. trying to clean drips of resin later is not fun, but if waxed with car wax beforehand, and the drips allowed to cure, they pop off fairly easily.


3M 5200 marine adhesive sealant is an excellent glue as well, but takes a long time to cure. It needs humidity to do so.. it cannot be smoothed easily, and must be grinded off. One must still protect the otherwise exposed wood when using it, and paint adhesion to 3M 5200 is not great.

3m 5200 has a fast cure version too, but it is still pretty slow, and is not quite as durable in my opinion. I've seen both for sale at home depot. Once opened the product must be used within a week, or stored tightly sealed in a refrigerator.

The 3M 5200 is likely the easiest path that will yield the most durability, but in terms of ultimate durability and ultimate strength, the fiberglass is the method to use.

If you do go the 3m 5200 route, make sure to sand through the paint, if applied. The rougher the sandpaper the better, for more mechanical tooth, and before using the sandpaper, wipe the area clean with a light solvent so as to not push contamination deep into the grooves where it will compromise bond strength. If the fiberglass roof is gel coated, and it is still in good condition you might get away with not sanding down through it to bare fiberglass but it is not a risk I would take.

I once glued some plywood that only served as an antenna base to my fiberglass roof. I used a regular adhesive caulk, and I did paint over it. Within 6 months it was split cracked and rotting. At the one year point I removed it and it was so soft and rotted out it would have been useless for your purposes.

 

[SternWake]

Do note Epoxy has a higher bond strength than polyester resin, however, it must be mixed precisely, and is more expensive, and is not as resistant to heat as is the easily available home store, Autoparts store bought polyester resins.

Epoxy bonds to hardened polyester resins, but Polyester resin does NOT bond properly to hardened epoxy resins. Sometimes polyester resin will not even Cure at all on top of hardened epoxy!

Some epoxy resins like West systems have a tremendous Amine blush, which has to be removed with lots of water and a skotchbrite pad before sanding, and secondary bonding. I do not like West systems epoxy resins and favor System 3 epoxy resins. System 3 is stronger, has an easier 2 to 1 mix ratio( West systems is 4 to 1 or 5 to 1), and does not yellow as quickly. Also much less or no Amine blush depending on which formulation is used.

The Epoxy hardeners are very corrosive. Some people are very sensitive to them and have bad reactions. Some people develop sensitivity to them,

Epoxy is nice because clean up can be done with rubbing alcohol or vinegar. i use a 50/50 mix to clean my tools and gloves to reuse. Acetone must be used with polyester. Do not use Acetone to clean epoxy. it works but if it gets on your skin it puts the evil Amines right into your blood stream.

Good gloves are necessary.

Epoxy can be sanded before it is fully cured. The dust is still toxic at this stage. You do not want to be sweating and have this uncured epoxy dust settle on your skin. Fully cured epoxy is much harder to sand, but is inert and much safer to be around.

While I prefer the attributes, and working with epoxy, when I glassed my solar panel footing to my fiberglass roof, I used polyester resins for the better heat resistance/price, and the fact that the roof was made with polyester resin, not epoxy.

Here is mine before I was done painting. My Van can go 95MPH. It has multiple times since installation nearly 8 years ago.

 

[highdesertranger]

and there you go, a great detailed explanation from stern wake. highdesertranger

 

[Canine]

I've only seen one person develop a sensitivity to epoxy; he hobbies model airplanes. (Is "hobbies" a verb? Lol.) After I had seen that happen, I learned how common that actually is. I now use gloves for just about any chemical. Hard for me to tell what is or isn't going to be in the nummy ingredients and how that could affect me, so I play it safe. Gloves are cheap and take up little space. Easier clean up afterwards, too.