Fiberglass Bonding Adhesives

[CarlD]

I am looking into the various types of adhesives used in fiberglass trailer construction, repair, etc. to use in my Lil Hauley buildout. I will be bonding wood to fiberglass (gelcoat). Here are 3 that look acceptable, Methyl Methacrylate (MMA), polyurethane and epoxy.


ASI MP 55310 MMA 3000+ psi and flexible.



3M 5200 polyurethane strength is 700 psi, is flexible.


ASI MP 5405 epoxy strength is 2400 psi, flexible impact resistant



What did you use? What were you doing? How was it to work with? Prep work required? Any failures? etc.


Any real life experience in this area would be greatly appreciated.

[FRED SMAILES]

Hey Carl, been hacking on our '74 boler since 2003 with many fiberglass mods, ad ons etc.
I only use polyester resin and glass. That is what the trailer was made with and takes just a little prep to add more. Lots a pics and lnfo in a thread called "there's a hole in my boler" or something close to that.

In the 80's I did a lot of stockcar racing and built body panels from polyester and glass.
I don't remember ever having a delamination on anything. Those stockcars took a lot of abuse too!
Fred

[charlsara]

It is hard to beat epoxy from West System. A stronger bond to old fiberglass than the poly stuff. You will need to sand through the gel coat or it may pull off. 5200 is a really good sealant but it may not hold up to constant hanging weight. I am not familiar with the other,

[Raspy]

Carl,

Fred knows more than I do about using polyester, but I can tell you, from boat building, that 5200 is a permanent way to glue wood to fiberglass. It is a one part caulk gun fed material, about the consistency of toothpaste, so it fills gaps and it will not let go. Plus, no mixing. Just squeeze some onto the piece and push it into place. Great for mounting blocks to the hull to screw things to.
If you want to mount a bulkhead directly to the hull, you can run a bead of 5200 along the edge and set it in place. That allows the joint to flex a bit. For even more strength, glass over the joint with 2" wide fiberglass tape and either polyester or epoxy resin. I used many gallons of System 3 brand epoxy over the years and it bonds to polyester very well. But remember, polyester does not stick to epoxy very well, so if you go with epoxy, you should stay with it.
If you need a high viscosity glue for filling large gaps, you can add a thickener to epoxy, or add saw dust from your project until you get the consistency of peanut butter.
Another easy to use epoxy is Marine-Tex. It's white and has the consistency of putty. It is good for repairs and mounting blocks of wood to fiberglass.
Polyester may be easier to work with in some cases, but I'm not familiar with it.

[k corbin]

I use epoxy, typically the MAS brand as it does not contain skin sensitizers. I use epoxy because I am right smack in a boat building community and I can get it easily and for a more affordable price. If your budget it tight then the cost of it is likely a deal breaker even though it is reputed to be stronger.



For bonding wood to the fiberglass I thicken the epoxy with a filler. I feel the filler is important because the fiberglass shell is rarely perfectly flat. A thicker epoxy will give you a better bond plus for vertical applications or overhead work it does not drip and run.


For filler sometimes I use wood flour other times I use the Mas brand of Cell-o-fill. It is not all that critical for bonding wood blocking to the walls which one of those two I use. The choice is more to do with what do I have on hand or what was the store sold out of that day.



If I need a lot of strength such as bonding wood to the ceiling where it might need to support the weight of a cabinet I would also add in some thickening fibers that are made for higher strength situations. But those fibers are somewhat coarser and more difficult to spread so if I don't absolutely need that extra strength I don't use them.



The weather is cooler now, that makes epoxy slower to set. At this time of year because where I am the outside temp is in the 40s 50s or low 60s so I put the part A and part B containers into a hot tap water bath. That will accelerate the cure time to about the same as on a warm summer day. Otherwise you might be in a situation where getting a proper cure is iffy because you are at the low end of the recommended range for product use.

[Dan-NS27]

I know people in the boating world who call 5200 "devil's glue". Only used if you never intend to remove something. If you were to try removing it in the future, it could damage the surfaces it's on.

I'd recommend epoxy or polyester resin and use a filler to thicken it

[Raspy]

Originally Posted by Dan-NS27

I know people in the boating world who call 5200 "devil's glue". Only used if you never intend to remove something. If you were to try removing it in the future, it could damage the surfaces it's on.

If you want to remove a block of wood previously glued to fiberglass with 5200 you don't pry it off, you split the majority of it off with a chisel and sand the rest away with a coarse disk on a high speed sander. Prying it off will separate the fiberglass. Be sure to wear gloves when applying it. 5200 is moisture cured. What you get on your hands will cure to where you can't wash it of. If you don't wash it off within a few minutes with paint thinner, it will take about a week to wear off. It is similar to what is used to bond the upper and lower shells together on fiberglass trailers. There is no stronger or easier way to bond wood to fiberglass. No mixing or thickening required.

[CarlD]

Lots of good advice. Thanks.


From what I read MMA adhesives are what boat builders and I think Lil Snoozy use to bond the fiberglass shells together. I saw some big tubes of Acralock MMA at Lil Snoozy when I visited the factory in the spring. MMAs require little prep work and hold like death. It is also quite expensive. Bond strength is 4-5 times stronger the 5200, however, if 700 psi is not enough to hold stuff together in a trailer then I am probably doing something wrong. If you think about it, a 4 square inch block bonded to the roof of a Lil Snoozy would be strong enough to pick up the whole trailer! I will attaching walls, cabinets, shelves, etc.. I plan on having the weight of these items transferred to the floor thru wood components, such as the bed divider, shower wall, floor to ceiling cabinets, etc. That being said the adhesive will only be required to keep stuff attached to the walls so they don't tip over, which is a relatively small load. It looks like MMA is overkill and epoxy is also overkill and requires fillers. 5200 remains flexible when cured (good for vibration), provides a permanent bond, (which I want), fills gaps and has minimal surface prep. Even though it is rather expensive ($20-$25 per 10 oz tube), it sounds like the best solution so far.

[charlsara]

Originally Posted by CarlD

Lots of good advice. Thanks.


From what I read MMA adhesives are what boat builders and I think Lil Snoozy use to bond the fiberglass shells together. I saw some big tubes of Acralock MMA at Lil Snoozy when I visited the factory in the spring. MMAs require little prep work and hold like death. It is also quite expensive. Bond strength is 4-5 times stronger the 5200, however, if 700 psi is not enough to hold stuff together in a trailer then I am probably doing something wrong. If you think about it, a 4 square inch block bonded to the roof of a Lil Snoozy would be strong enough to pick up the whole trailer! I will attaching walls, cabinets, shelves, etc.. I plan on having the weight of these items transferred to the floor thru wood components, such as the bed divider, shower wall, floor to ceiling cabinets, etc. That being said the adhesive will only be required to keep stuff attached to the walls so they don't tip over, which is a relatively small load. It looks like MMA is overkill and epoxy is also overkill and requires fillers. 5200 remains flexible when cured (good for vibration), provides a permanent bond, (which I want), fills gaps and has minimal surface prep. Even though it is rather expensive ($20-$25 per 10 oz tube), it sounds like the best solution so far.

I had a problem awhile back with a wood bulkhead pulling away from a fiberglass wall. I used 5200. Two things I didn’t like . It was too runny and after a year it failed. Looking back it is possible I failed to get the silicon properly cleaned out of the crack. But I just can’t trust 5200 now. That’s just me. sad because I have always got good service from 3m products.

[Dan-NS27]

Originally Posted by charlsara

I had a problem awhile back with a wood bulkhead pulling away from a fiberglass wall. I used 5200. Two things I didn’t like . It was too runny and after a year it failed. Looking back it is possible I failed to get the silicon properly cleaned out of the crack. But I just can’t trust 5200 now. That’s just me. sad because I have always got good service from 3m products.

That's why silicone is generally a bad thing with fiberglass. Once it's used, it's hard to get anything else to adhere to the same surface.

[charlsara]

Yes I know. I will never use the stuff in a trailer.

[Shanos]

Hi Carl,
I can't call myself an expert on adhesives but I can share my experience. I stripped the interior of my Boler with the plan to attach wooden cleats with a 2 part product called PLIOGRIP®, which is a 2 part urethane structural adhesive. To my dismay, I discovered that many of the blocks could simply be pulled off the fibreglass. I prepped the fibreglass by sanding and wiping with acetone before applying the blocks. My guess is the blocks were too small to have enough surface area for spreading out forces over a larger surface area...not sure. I didn't feel like I wanted to fiberglass all of the blocks in place so....back to the drawing board. After more research, what I came up with was using Sikaflex 252 which is a polyurethane adhesive that cures in atmospheric humidity much like 3M 5200. From the spec sheet, it doesn't look like Sikaflex 252 is quite as strong as 3M 5200 but is rated at 435 psi tensile strength and 400% elongation at break. The representative at Sikaflex that I spoke to recommended using a 1/8" thick bead for greater strength. Prep was sanding and cleaning the surface with water and a bit of soap to degrease (as per the Sikaflex rep). As you can see from the enclosed photos, I have really committed to this product working for me! I think by virtue of a large surface area in the long strips, there will be adequate strength to support the 3 mm thick paneling and interior cabinets. I have also had spray foam insulation sprayed to the thickness of the strips so this will add further strength and good insulation. Time will tell...hope this helps

[CarlD]

Shannon,


You sure did a lot nice looking work on your trailer. Custom fitting all the curves must have been fun. I will take a look at the Sikaflex 252. The strength should be more than adequate for my application. thanks.

[Pete Hein]

Re bonding to fiberglass...

Most of the commercially-produced fiberglass laminates use polyester resin. There are a lot of reasons but IMO the big one is that it's cheaper than epoxy. It used to be said that epoxy wouldn't bond well to polyester laminate, but I've used epoxy on boats for years and I've never had a bond fail.

That said, you have to accept that the key to a good bond is PREPARATION. You need to clean the surface thoroughly, grind it or rough it up, and pay attention to the design of the joint. And silicone is absolute poison to adhesives. Once you put it on the surface, you will have the devil's job getting anything to stick to it (except for more silicone).

As to additives, there are numerous fillers and such, from a fine floury filler through chopped fiberglass (messy), microspheres, and "kitty fur" which I think is another version of chopped glass. (Don't really know, never used the stuff.) You can even use garden limestone, but that will add a lot of weight, and will have a toothy surface that will chew up tools if you ever need to cut it.

As to 5200 - the OP's have pinned it: It's wonderful stuff, IF you never intend to take the surfaces apart again. (And if you've prepared the joint properly.) Be sure to have good ventilation if you use it... it's a polyurethane, and those are known sensitizers: You can be put into serious respiratory distress by the fumes.

I have no connection, either personal or financial, with the company, but I have used Gougeon Bro's "West System" epoxies and other products with great satisfaction. (No connection with West Marine, AFAIK.) They have plenty of free information on their website, and they USED to send out "how-to" literature by mail. (Might not, any more; I'm referencing 20 years ago.)

Just remember to keep good ventilation - epoxies and polyester aren't great for you either - and wear gloves... it's a lot easier on your skin than trying to clean partly-cured resin off.

Oh... last point - when working with epoxy, keep a container of vinegar handy. It will kill the curing reaction and make it possible to get the stuff off your hands (and your tools).

Good luck. Research, research, research.... And don't give up.

[CarlD]

Thanks Pete,


I have heard others mention that you should not bond polyester to epoxy, but it is ok to bond epoxy to polyester, it is certainly beyond my experience level. Many posts reference West Systems resins. I have not looked at sourcing it yet and hopefully will not need it in my build. At the moment I think 3m 5200 or possibly Sikaflex should be adequate. My design has all the structure weights transferred to the floor. I will only require adhesives for fastening them to the walls, so the loads will be relatively small.

[Pete Hein]

Thanks, Carl...

I think you're right about epoxy-to-polyester. Certainly that's been my own experience.

As to 5200, people see the tensile strength compared with epoxy and think "that's weak"; but 750 PSI is anything BUT weak. Especially combined with 5200's flexibility.

Here's a good example of "weak" and flexible vs "strong" and rigid... I'm a hobbyist blacksmith, and at one point had a loose hammer head. I drove out the wedge and took out the handle, cleaned everything up, and reassembled it with steel-filled epoxy. Did a very nice job, for about two weeks; after which the epoxy cracked from the repeated shock loads, and the head loosened up again. Next time I needed a similar repair, I used a polyurethane glue (Dow, I think; it's no longer around). It foamed into all the crevices, and at this point the hammer head is still nice and tight - 30 years later.

One last thing about urethanes -- they require moisture to cure, so if you're gluing two impermeable surfaces, the "cure" will happen from the outside-in, and may take a LONG time... like days. To speed things up, you should put the adhesive on one surface, and wipe the other with a damp rag immediately prior to assembly.

Cheers, and Happy Thanksgiving...

[CarlD]

Thanks Pete,


Your example is the reason I like the 5200. Strong and flexible. Unless congress does something about infrastructure, my trailer will have to endure a lot of vibration. I will be bonding wood to fiberglass and will have adequate time for full cure.

[Raspy]

Originally Posted by Pete Hein

Re bonding to fiberglass...

Most of the commercially-produced fiberglass laminates use polyester resin. There are a lot of reasons but IMO the big one is that it's cheaper than epoxy. It used to be said that epoxy wouldn't bond well to polyester laminate, but I've used epoxy on boats for years and I've never had a bond fail.

As to additives, there are numerous fillers and such, from a fine floury filler through chopped fiberglass (messy), microspheres, and "kitty fur" which I think is another version of chopped glass. (Don't really know, never used the stuff.) You can even use garden limestone, but that will add a lot of weight, and will have a toothy surface that will chew up tools if you ever need to cut it.

Epoxy adheres to polyester just fine. It's excellent for any glass repairs or for applying fiberglass tape to mount bulkheads in place. It is available in viscosities ranging from from honey to gasoline and it is available in various hardening times from a couple of minutes to 48 hours. The slow setting, thin viscosity stuff will wick into hairline cracks and fractured areas to make them strong again. It will also soak into rotten wood and set up to fix small areas of bad wood, or seal edges of plywood.

Polyester won't adhere well to epoxy. So once you start with epoxy, stay with it. You can switch from polyester to epoxy, but not epoxy to polyester.

The filler I've used far more than any other is sawdust. Just keep a small bucket under your table saw as you work and you will collect a lot of filler. It also sands well and costs nothing. This can be mixed to the consistency of peanut butter for mounting blocks to uneven surfaces, filling holes, making the edges of bulkheads match a curving wall, or for making a nice fillet to accept fiberglass tape along the edge of those bulkheads. Then, when painted it makes a nice looking and strong transition.

Epoxy is also excellent as a first coat or two of varnish. It soaks in to seriously strengthen the wood. Makes it absolutely water proof. Builds thickness and fills imperfections well. Then a top coat of real varnish finishes the surface and adds UV inhibitors. One of the most beautiful wood surfaces I know of is Mahogany coated with epoxy. It soaks in and deepens the red of the wood while making it very strong. When done it seems you can look down into the surface. It's the kind of thing you see in fine yachts.

Epoxy is also easy to mix in any size batch. One gallon jugs with pump tops, allow you to just pump once from resin and once from hardener, or whatever ratio your particular brand wants, or ten times from each for larger applications. This means you can mix it easily as you go or make small batches to do tiny jobs. So you are never trying to hurry up before it hardens, or wasting it, or measuring it. Tongue depressors work well for mixing and small China Bristle brushes are good for applying it in all but varnish type applications. Then just toss the brushes as you go. Cases of these are very cheap at Harbor Freight. Mix it in small SOLO cups that can also be tossed, but be careful of it getting too hot if it sits and begins to harden. Small batches are best. Sometimes small paper plates work even better than cups because it won't harden as fast or get as warm.