Sanding Fiberglass

[Pamela S.]

Anyone have a preference among the following tools?
Dremel tool
Dremel Multi-Max with the triangular sanding pads
random orbital sander

Thanks in advance.

[Raya]

Pamela,

Sanding fiberglass can mean a number of different things, and thus "best" wouldn't be the same across the board. Can you explain more about what your situation is?

Raya

[Pamela S.]

I need to repair a couple of cracks in the Fiber Stream. One is fairly large, probably six inches long, inside, and there are a couple of pretty small ones on the outside. Everything I've read about fiberglass repair says you need to sand it before applying the resin and cloth to fix it. I'm just wondering what has worked best for others. (I'm trying NOT to re-invent the wheel.)
Thank you!

[Raya]

Fair enough

Okay, when you say a 6" long crack inside, does it go through to the outside? Is there any way you could photograph that and the other cracks and show them to us? I would be happy to make suggestions (as I'm sure others would too), but I'd like to see it. That way I could think about how I would repair it if it were mine.

The thing is, depending on the exact type of crack, where it is, and how one plans to fix it, different tools and techniques might be used even by the same person. And of course there are usually multiple ways to do it.

I don't want it to sound like I'm discouraging you asking, because I'm not at all! Just, if your camper were here, I would be wanting to walk over and take a look at it and it would be nice to do that virtually too.

Raya

[Perry J]

I need to repair a couple of cracks in the Fiber Stream. One is fairly large, probably six inches long, inside, and there are a couple of pretty small ones on the outside. Everything I've read about fiberglass repair says you need to sand it before applying the resin and cloth to fix it. I'm just wondering what has worked best for others. (I'm trying NOT to re-invent the wheel.)
Thank you!

You should also drill a small hole at the very end of the crack. This will help prevent it from cracking further.

[Pamela S.]

OK, I am attempting to attach two photos of the largest cracks, one inside and one outside. They were taken with my cell phone camera so the inside one isn't very good. I will try to borrow a real digital camera so I can get some better shots.










OK, it worked. The cracks do NOT go all the way through to the outside.

[The Hobo]

Looks fairly serious.

What I would do, is definitely reinforce the inner side, by placing flat paint sticks across the cracks,while applying fiberglass cloth, and resin.(that will prevent you repair from cracking again.
As for the outside, fill the damage area with fiberglass,and make sure you sand it where you want to repair it, or the resin won,t stick/cure properly.

Hope this helps.

When ever I,ve painted fiberglass(after any repairs), I then epoxy primer, then grey primer, then paint the color of your choice.

[Raya]

Pamela,

I understand the outside crack completely; the inside one, I can't tell exactly where it is (to understand why it happened), but in looking at it, I think you should treat both of them as "serious" cracks and repair them as such.

I would repair both of them from the inside, if you have access.

Okay, for now I'm not going to elaborate on every step, but I will give you the general idea; if you do go ahead with it yourself, we can always get down to details.

Essentially, you need to grind/sand the inside out around the entire crack into sort of an big oval. You would want the sanded area to extend out, oh, say 2-3" on each side and each end past the crack. (More is fine too; but not less.)

Once you have everything prepped, you make a pattern of that whole area and lay it on top of some fiberglass cloth. I would use biaxmat 1708, 1508 (or similar) because it is structurally strong. You shouldn't need wood, holes at the end of the crack, or anything else given that this is not a cored structure to begin with. The repair will be many times stronger than the original construction.

You then cut 2 or 3 pieces of cloth, with one full sized and the rest staggered a bit smaller. Then you wet out the shell with neat epoxy resin, and then wet out the cloth on your plastic work bench. If you want, you can stack the patches right there and then transfer them en masse to the wall.. Place the patches on the wall with the largest one against the wall and the smallest one towards you, then squeegee the excess resin out, and let it cure. If it wants to "flop," you can use some strips of blue tape to hold it in place.

If you have insulation, etc. on the inside, you will not need to fair the repair; if the walls are "bare painted," then you will want to fair (I'll leave that out for now).

On the outside you would clean out the crack (after the inside is repaired) and then fill with fairing compound (depending on how large/deep the wound and then gelcoat. Of course you can ignore this on the one that does not extend to the outside.

Now, as to what caused it, at least on the one near the door I would say either weight on the roof (A/C/, snow load, etc.) or possibly a cracked frame (sag). Although the repair will be many times stronger than the original shell, it would be good to make sure the force that broke it is no longer there.

To effect these repairs, you will need to have supplies on hand. A partial list would be as follows:

Epoxy resin and hardener
Fairing fillers
cloth
wet-out surface (plastic, paint tray liner)
squeegees, disposable brushes
nitrile disposable gloves
acetone/vinegar/or denatured alcohol
sanding discs
respirator, goggles, hearing protection
Tape, newspaper, plastic sheeting, etc.
mixing cups for epoxy
stir sticks
tyvek suit or junk clothes

This gives you the basic idea, anyway. Feel free to ask questions if you decide to go ahead with it. It's not that hard once you have the supplies on hand. But, like cooking stir fry, you do want to have everything laid out and ready to go.

Raya

[Raya]

Oh, but you asked what to sand with, sorry!

I use a Porter Cable DA sander. Mine has a 5" round disc. I would typically use 40 grit to prepare for a patch IF I needed to make a "dish" so that the patch would end up flush with the original surface. If you are putting insulation or etc. back over the inside, then you may not need to worry about that, and will only need to rough up the glass enough for a good physical bond. Say, with 80 grit.

Before you start sanding, wipe the surface with something like Interlux 202 to remove any mold release wax or other contamination (MRW will mostly be on the gelcoated surface). This way you are not driving any contaminates into the laminate where you are going to be putting on new 'glass.

Now, when you are cleaning out that crack on the outside of the shell (after you have patched the inside), you may find a use for a Dremel or the like. But on the inside you are going to want "bigger," flatter paper, in my opinion.

Raya

[Pamela S.]

I just found a 5" sanding pad attachment for my drill. That looks like it should work well, and it was very inexpensive. I'll start collecting my protective gear and other odds and ends. I am definitely doing the repair. I have a friend who has actually worked with fiberglass before; not a lot, but a least a few times, which is more than I have done. At this point all my fiberglass repair knowledge is theoretical.

Could you explain more about fairing? The crack that is inside is definitely near a support point. That arch support is roughly in the middle of the camper, between the kitchen and dinette areas. It is plain fiberglass with no insulation, but it has been painted over.

The outside crack is behind a cupboard and I haven't had a chance yet to see how easily I can access it from inside.

Can't think of anything else right now.

Thank you so much for all the information.

[Dave Bese]

I worked 36 years as a Toolmaker/machinist at Boeing so played with a lot of 'glass. The best scuffing for paint is a palm sander with Scotchbrite.

As far as the cracks; drill a hole at each end. Simply patching will not stop the crack from growing. Resin will not adhere to a waxed surface, so Simonize the inside, make a temporary false oatch on the inside. Bondo and f/g screening works good. 1/4" thick. Now sand out as much of the crack as possible without breaking thru. Feather the edges out from the crack about 1". Then lay in new wetted fiber; layer upon layer until it's just above the original surface. Once cured you can sand it level and apply a seal coat

[Raya]

Hi Pam,

Fairing is what you do after you make the repair, in order to make it blend in. Basically, you take mixed epoxy, add one or more ingredients (we can talk about those) to make a more peanut buttery consistency, and then "frost" your repair, squeegeeing off as much excess as you can (you can sand it later but it gets relatively hard, so better to be tidy in the first place).

You can also buy pre-mixed fairing fillers, which can be a good idea if you don't feel like mixing your own. They are very creamy and consistent.

I would highly recommend that you pick up a copy of WEST System's free epoxy manual. It is excellent and will tell and show you how to do everything, in a very easy to read format (with illustrations). There are videos there too.

They speak of their products, but you can use any generic or other-brand epoxy as well (although WEST is usually one of the easiest to find at the "corner" marine store and it is a good product.

You can also view the manual online at their website. Here is the link. The illustrations below are each one chapter of the book.

http://www.westsystem.com/ss/how-to-use/

System Three is another brand and they have an epoxy handbook too, The Epoxy Book, which you can download from their website.

http://www.systemthree.com/reslibrary/m_pu...-literature.asp

Epoxy is a good resin to use because it has excellent secondary bonding characteristics (you can no longer get a primary, chemical bond because your trailer is already built and cured).

You know, as I'm looking at that crack over the door again (on the outside), I'm not sure but that you might want to put some cloth on the outside too. That is a fairly serious crack. And as Dave mentions, you need to be sure it is supported while you are sanding on the inside, so that it doesn't get "broken out of shape." I think I would still patch the inside first (and then consider how to handle the outside) because you only need to scuff up the inside and then once patched you will have a rigid shape. Whereas if you grind the outside first, you have to get rid of all that "bad" material and you will have a larger hole to deal with before you have support.

At least that's how I'm thinking about it from here; it's always easier when you can lay eyes and hands on it.

Raya