View Full Version : How to fiberglass upside down?


kach22i
05-23-2008, 10:04 PM
HOVERCRAFT HULL

I would like to fiberglass over the aluminum, fiberglass shower panel, ABS plastic and wood rails/landing pads on the bottom of my hovercraft hull.

I painted the area with West Systems resin but the heaviest fiberglass cloth I selected would not stay up. A lot of the resin was soaked up by the wood, other surfaces were very wet and drippy. I have several weights of cloth I purchased a while ago.

I have some very light weight fiberglass cloth which I used on my tail cone. Will the lightest weight cloth soak up the resin better and stay on the surface upside down all on it's own?

Screws with washers are an option.

Wax paper strips/stripes and duct tape are a consideration.

I'm out of ideas - help.

http://i184.photobucket.com/albums/x295/kach22i/Skid-Again-3.jpg

afrhydro
05-23-2008, 10:23 PM
small thin coats dont forget the bubble buster roller
you will have to kick it far faster than normal

the1much
05-23-2008, 11:34 PM
like afro,,hehe,, said,,thin,,and small,,and 2 more guys,,,and some good arm protection,hehe,,,(upside down glassing was the first thing i did in a shop,,,i almost quit),,and alot of 3 inch masking tape,,,and roll the crap outta it,,,and too much resin will be your worst enemy.,,that stuff weighs alot,,and dont let the ry part of ya fabric pull ya wet down,,the glass really sticks up easy,,even before you wet the glass,,,wet ya area,,and tape the begining up,,then press with ya hands a foot down the line,,then wet out the glass.,and the lighter the glass the better it will stay up for ya,,some times if your gonna need "layers",,its best to do them 1 at a time.

PAR
05-23-2008, 11:42 PM
There are a few different methods to work overhead. Apply a wetout coat of unthickened resin, then let this sit until it's kicking off, but still tacky, then apply the fabric, pushing it against the partly gelled goo. In this high tack state, it should stick, then you can wetout the fabric with more unthickened resin, being careful not to float the fabric off the surface with too much resin. Lighter weight fabrics will work better, because they will not get so heavy with resin that they pull off.

Another trick I use, is to very lightly dust the area with 3M 77 spray adhesive, then stick the fabric to this, which holds it in place, while you wetout the fabric with resin. The 3M 77 will not affect the bond.

ABS and aluminum are difficult to bond to, with over head work making this more critical. I think you'll have a very difficult time getting resin to stick to ABS, but aluminum will if it's etched first then has resin applied directly after it's dried off.

Stick a small patch of fabric to the ABS, give it a couple of days to cure then grab an exposed edge with a pair of pliers and yank. This will test the bond. Another method is the scratch the surface with a razor, in a crosshatch pattern. Apply some duct tape, pressing it down real well, then yank it off to see if any epoxy comes with it. If it does in either case, then you may want to consider other options.

Another note is the photo shows many crisp edges along the aluminum and plywood edges. 'Glass will not adhere well to these edges, leaving you a very weak blister or pucker. The exposed screw heads should also be faired in for the same reason, other wise the 'glass will "dome" over it and leave you with the same deal as along the crisp edges. Radius all edges, so the fabric will "lay down" and use some light weight fairing compound around the screw heads.

KnottyBuoyz
05-24-2008, 06:40 AM
That's a tough one Kach. I don't think you'd be able to glass over the aluminum as was mentioned before. It's such an irregular shape you'd have a tough time getting a vacuum bag to hold.

You could try making a plywood pattern of the shape to be glassed. Cover it with poly film, lay out your glass on that, wet it out and jack it up into the space to hold it against the bottom until it kicks. I've seen this done in parking garages when they make repairs to ceilings with concrete.

Anytime I've done overhead or vertical glassing I've tacked it into place with 3M77 and vacuum bagged it. It's a bugger gettin' cured and uncured epoxy out of your hair.

Fanie
05-24-2008, 07:33 AM
Is there no way you can turn it ? It's really going to be a LOT easier... For one your arms won't break off after the first two hours or so.

Maybe get a bunch of people to help you do it. Buy the beer, it's going to be worth it. Take into consideration that's a relative large area you want glassed, it's going to take a while and you probably want a couple of layers on it.

I would defenately turn it, even if I have to put scaffolding up.

kach22i
05-24-2008, 10:49 AM
Thank you for all the input everyone.

Thoughts about fiberglass not helping 90 degree bends and comments about the difficulty of covering odd shapes and sharp angles are making headway with me. My goal on this part of the project is to add strength to the beveled pieces of wood lagged into the aluminum bar on the sides (at the wide part - set in place after the first picture was taken).

Yesterday I filled some gaps with resin soaked fiberglass twisted up and jambed in cracks with a screw driver. However it's still a piece of work to deal with.

I have some microballons and shredded strands which I also purchased at the same time as the cloth/matt. I've been meaning to learn how to best use them and experiment a little. The bottom of the craft with odd joints to fill will be a good place to do this.

I may leave the very bottom of the aluminum parts exposed, it was never my goal to cover them up. My goal is to secure them better, and I might be able to do this on each side without overlapping or covering them.

I forgot to mention that I will be fiberglass covering the modified plow plane. If I have to I will use a combination of screws, wax paper and duct-tape in some sort of band pattern and multi-step process.

Peel-Ply was mentioned in a hovercraft forum, I'm going back to the hardware store where I picked up the West Systems and see what they have. I read in an aircraft forum to stay away from the cheep knock off Peel-Ply they sell at Walmart. It does not work they said.

http://i184.photobucket.com/albums/x295/kach22i/Plow-Plane-1.jpg

The white fiberglass shower panel (I should be able to bond) is on the bottom of the ABS hull was because the hull was ripped open from front to back (6 inched from the side edge) in an incident approx. seven years ago. The fiberglass shower panel sheet was the only way at the time that I could figure out to get some sort of hull continuity, and I was not having much luck with test samples in bonding to ABS plastic. This was all done long before I had access to the resources of this forum. It is secured to the ABS with heavy duty contact cement and over one hundred S.S. screws. I did this with the craft on it's side and leaning on my house - a crazy thing I do not wish to repeat.

afrhydro
05-24-2008, 11:57 AM
kach
i hate to say it but you should have left that job to a pro
i am afraid you have a mess now that is not recoverable
you really need to flip it over and glass it all up that way (tow truck crane something)
i cant tell 100 % of what you have there but a 3 mil or so shower panel is not very strong and most of them have a plastic coating over the fiberglass and gel
does it melt if you put a grinder to it

kach22i
05-24-2008, 01:05 PM
3 mil or so shower panel is not very strong and most of them have a plastic coating over the fiberglass and gel
does it melt if you put a grinder to it
The shower panel has been on for many years and has gone through many test flights without any problems. It's doing it's job of connecting the two lower hull pieces of ABS hull under it. It is in theory only being asked to take small forces in tension distributed over a very great area.

I don't see a reason to grind it and would expect it to melt like you said. If I grid over it to polish off some stray hardened strands I have a sandpaper wheel in addition to cutting and grinding stone wheels.

One thing for you boat guys to remember is that the hull of a hovercraft is not in the water. All the typical quality of finish for hydrodynamic reasons are pretty much out the window. I'm much more concerned about sharp edges though because if the hull impacts something and pins the skirt between the hull and a hard place it may damage or cut the skirt. Trust me, I've done this several times and have plans/design solutions to avoid it.

I now have S.S. self tapping screws and S.S. fender washers and masking tape. I plan to tape as much as possible after using the tacky resin method. I will then use the screws and washers to help hold things in place before I roller a light coat of resin. I plan to leave the screws in place and may apply liquid tool grip rubber over the heads when I'm done.

I also have a little Peel-Ply cloth and may experiment with that method in larger areas just to get the feel of it.

I'm not glassing the whole hull, I'm just doing the spot areas of plow plane and landing pads. If I get around to it; all exposed foam will get get resin or resin and a layer of fiberglass cloth.

afrhydro
05-24-2008, 01:18 PM
oh sorry i didn't catch it was a hover craft
we had one once in the shop for repair just a little yellow thing it had a prop on the back as i recall kinda like a air boat
anyways we all tried it out i was the only one who could drive the thing around
they we got in trouble cause we blew dirt all over the place and the boss got mad made us leave it alone before we broke it


way way long time ago back in my first few years of fiberglass repair

lol

kach22i
05-24-2008, 02:12 PM
we blew dirt all over the place
Yea, that's what they do best, blow dirt on land and water spray over water around.

I just tried those brick red micro-bubbles. I made it just a little too thin but I like the way they work.

I also tried the chopped strands of fiberglass. Too darn slippery for horizontal surfaces, but I managed. It's slippery nature makes it almost self leveing on horizontal/flat surfaces. I'm worried about sanding and finishing it. I suspect that a layer of micro-bubbles or cloth will be required.

I also have some white 3M ballons which are next on my list to try.

I'm still having fun.:)

ondarvr
05-24-2008, 11:04 PM
Glassing the under side is going to be difficult for a first timer, this looks like job for a spray on truck bed coating product. It's fast, easy, waterproof and sticks to almost every thing. It will most likely cost less too.

the1much
05-25-2008, 08:05 AM
Glassing the under side is going to be difficult for a first timer, this looks like job for a spray on truck bed coating product. It's fast, easy, waterproof and sticks to almost every thing. It will most likely cost less too.

and SLOW the craft down by ALOT. that stuff is heavy, and will cause so much drag and friction,,that he may not even get it off the ground,,hehe,,k thats a little overboard,,but,,it does do that stuff.and im not sure how the stuff would handle being in the water all the time

ondarvr
05-25-2008, 09:38 AM
Glass is very heavy also, and it depends on how much of each is applied. Friction is not an issue, there's nothing coming in contact with this surface during normal operation, only when things go wrong.

If it was flipped over and he could cover the whole surface easily, then epoxy and glass would be much easier to do, but with all the angles, different substrates, then doing it upside down, I think he'll end up with a mess.

northerncat
05-25-2008, 09:51 AM
stianless staples around the edges fired only halfway in so they can be pulled out or tapped in as needed and start rolling from centre out
sean

kach22i
05-25-2008, 12:20 PM
stianless staples around the edges fired only halfway in so they can be pulled out or tapped in as needed and start rolling from centre out
sean
I like this idea northerncat. I'm going to do similar with the screws and fender washers. I hope the fabric does not twist up.

Would you pound the staples with a hammer into ABS plastic, shower stall panel, wood and existing fiberglass work? I'm afraid to do this, the staples would have to be razor sharp to get away with this. If the staples were not pounded all the way in, the cloth would still move and be able to pull off, if even just a little.

How do I prevent the fabric from stretching and puckering once wet?

Limit the amount of resin saturating it?

SamSam
05-25-2008, 03:37 PM
and SLOW the craft down by ALOT. that stuff is heavy, and will cause so much drag and friction,,that he may not even get it off the ground,,hehe,,k thats a little overboard,,but,,it does do that stuff.and im not sure how the stuff would handle being in the water all the time
kach22i...One thing for you boat guys to remember is that the hull of a hovercraft is not in the water. All the typical quality of finish for hydrodynamic reasons are pretty much out the window. I think with all the fiberglass panel, aluminum, plywood, screws and washers, glue and other gunk, there wasn't a whole lot of concern with weight, although you may be right in that there might be now. The thing is not meant to sit in water, and although bedliner might be heavy, compared to all the resin needed to adequately cover all those rough edges and sharp corners, exposed screws, etc. it could end up lighter. Coupled with inexperience in laminating, I have little doubt it would be a better idea.
I would like to fiberglass over the aluminum, fiberglass shower panel, ABS plastic and wood rails/landing pads on the bottom of my hovercraft hull.How well does epoxy stick to ABS plastic, anyways?

kach22i
05-25-2008, 07:41 PM
How well does epoxy stick to ABS plastic, anyways?

The resin is sticking to everything much better than I ever expected. Of course it may be a different story after a few hours of operation and several Michigan winters.

Weight is always a concern, the things added should by now equal the weight taken off; battery removed, starter removed, seat removed, etc.....

I need some more advice.

I used both the micro-bubbles (red) and 3M-balloons (white) as filler around my landing pads and landing rails. The thickest part is a 45 degree filler approx. one inch each leg along the aluminum tube seen in the first photo. I do not want impact shock or hull flexing to loosen the bond the filler has. The filler seems seems rock hard and very strong, does not look like it's ever going to go anywhere.

I figure there are three ways to proceed.

1. Do I just grid down and sand any rough edges and call it a day?

2. Do I just brush some resin on it after touch up finishing and call it a day?

3. Do I finish it with a layer of fiberglass cloth and resin?

Jratte
05-25-2008, 11:14 PM
Ok, I'm coming into this a bit late but my first large fiberglass job was an upside down repair on the bottom of a hull. Here's how I did it.

The first thing that was key to this working was being able to vacuum bag the repair.

We erected a good size table, larger then the laminate we would be adding. Covered the table in plastic. On top of that we laid the vacuum bag material with bag tape applied to the edges. Next we laid down the breather material, a layer of release film, and then peel ply.

Under the boat we had a few jack stands set up with some plywood laid across them.

We wet out as many layers as we felt we could handle, usually 5-8 layers of glass. After being wet out, each layer was laid on top of each other on top of the peel ply, breather, bag stack. Once all the layers were together, we shuffled the whole pile onto the plywood and jack stands.

Then we wet out the underside of the boat with un-thickened and thickened epoxy and proceeded to screw the stands up until the pressed the laminate on the boat. The we pulled the edges of the laminate up, made it nice and did the same with the peel ply, breather, etc. until we got to the bag. Having the tape already on the bag made it go very quickly as placing darts were no problem.

Turn the pump on, check for leaks and let it cure. I can't imagine doing any substantial glass work upside down any other way. If doing something similar is an option I would consider it. Best of luck.

kach22i
05-26-2008, 07:43 AM
Under the boat we had a few jack stands set up with some plywood laid across them..............proceeded to screw the stands up until the pressed the laminate on the boat.

Your method sounds top rate, I'm not in a position to do it the same way, but it's given me some ideas.

I'm considering a layer of sponge rubber or acoustic foam with wax paper on one side and plywood on the other. If I lay resin soaked cloth on the wax paper and press the assembly to the face of my anti-plow plane it should press flat on the flat area and still be able to form around the odd fluted edges which are all around the half-circle anti-plow seen in the second photo. I would have to figure out the best way to screw/strap/tape/bungie or maintain pressure during the curing process.

It's just an idea.


EDIT: Pictures...........needs sanding and coat of fiberglass cloth.
Not going for looks or finish awards under here obviously. :D
http://s184.photobucket.com/albums/x295/kach22i/
http://i184.photobucket.com/albums/x295/kach22i/FILL1.jpg
http://i184.photobucket.com/albums/x295/kach22i/FILL3.jpg
http://i184.photobucket.com/albums/x295/kach22i/FILL2.jpg
http://i184.photobucket.com/albums/x295/kach22i/FILL4.jpg

kach22i
05-29-2008, 10:46 AM
I did some glassing last night. Problem areas as expected were the many flutes and curves on the ABS plastic. The flat areas were easy. Even the funny folds and bends on and adjacent to the landing pads went up quickly.

The little bit of chopped strands I used as a filler on my diverter/splitter sanded down just fine with a stick on pad triangular power sander.

I went to the local/wonderful Stadium Hardware in Ann Arbor which stocks West Systems this morning. I picked up some fine filler to finish my fan cone/spinner with (410). I also picked up some low friction mixing powers (graphite) 423 & 406 to coat "first contact" areas and problematic intersections on the bottom of the hull.

I'll post pictures, verbal descriptions will not suffice for the "seat of the pants" method I came up with.

kach22i
06-02-2008, 03:22 PM
UPDATE: June 02, 2008

The key to working upside down I found is to get your resin into a paste-like state. You do this by adding fillers. Use the graphite additives for a slippery hull bottom and the recommended filler for body. It also helps if you duct tape one end of the cloth so you can have a good starting point which does not move around on you. Also the duct tape allows you to pull on the fiberglass cloth so there is no stretching or slack.

Much of the cloth texture is left exposed using this method, even if laying it on thick. I used one thin layer of paste-like resin followed later by a thinner finish coat to really gloss it up and seal it good.

http://s184.photobucket.com/albums/x295/kach22i/
Duct tape both ends and each side so that the fabric is stretched flush.
http://i184.photobucket.com/albums/x295/kach22i/HULL-CLOTH.jpg

After curing, cut away with a mat knife unresined or unused cloth and any lose parts which you can pull off with a little tug.
http://i184.photobucket.com/albums/x295/kach22i/HULL-OFF-CLOTH.jpg

Cut away openings so that a second lap layer can be done.
http://i184.photobucket.com/albums/x295/kach22i/HULL1.jpg

I used 2 inch wide cloth at the edges and pressed in with more resin mud. Reinforce high wear or high stress areas too. Then the whole thing gets painted with resin to soak in and protect intersections of differing materials.
http://i184.photobucket.com/albums/x295/kach22i/HULL2.jpg

Just another picture angle, this area received more colored resin in the air lift supply holes to seal the open cell foam. Open cell foam is bad, some of the expanding foam in a can is almost as bad when it comes to absorbing water.
http://i184.photobucket.com/albums/x295/kach22i/HULL3.jpg

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