A bagging idea

[drewpster]

Has anyone tried to vac bag fiberglass down to their stringers after they have been installed? I was thinking of using an a/c vac pump and some plastic. Simply cover the stringer after the initial wet out and suck it down to the stringer. I know very little about bagging, any thoughts?

 

[jonesg]

Re: A bagging idea

why bother?
sounds too clever by half.

Done properly theres no issue anyway,
capillary action puts the glass right on the wood,
too much resin and the glass floats away from the wood surface,
too little and it doesn;t get saturated properly.

The thing is, its so simple to just do it right.

 

[drewpster]

Re: A bagging idea

Saturation is not the problem.
The problem is the shape of the stringers. Even with rounded and filleted corners I having a problem with the roving bridging and pulling away. It is most evident at the tops of the stringers. Perhaps I selected a weight of woven roving that is too heavy. The had no problems with the 1.5 csm I used.
Doing it simple did not work for me.

 

[erikgreen]

Re: A bagging idea

I've been meaning to try this... it should work quite well for stringers. The ability to glass around any shape would be nice, as well as getting the optimum amount of resin.

Somewhere in another thread Yacht Dr. posted about vacuum bagging repairs to a hull core... vacuum bags are a well known way for pro boat builders to "clamp" odd shapes and make sure fiberglass lays down in place. If you're good you can get a similar ratio of resin to glass in hand layup, but you have to follow the rules of filleting and rounding edges so bubbles don't form. Not so much with a vacuum bag.

The big thing is that you have to have a good vacuum pump setup... a shop vac won't even come close. You need a real vacuum pump, preferably a backup in case the first one flakes out, fittings, bags, tubing, and various other items, preferably including a vacuum switch to turn off the pump when the vacuum is holding and turn it back on if a leak happens.

But you can get most of this stuff or substitutes for it pretty cheaply, so I'm going to be trying it soon using polyethylene garbage bags for the outer plastic, polyethylene pillow fill for flow media, nylon taffeta fabric for peel ply (non stick layer against the glass) and custom made fittings from my shop, with PVC tubing for catching extra resin and as a "vacuum store".

I would think the hard part for stringers would be sealing the edges of the bag against the inner hull.

Do this and post pics

Erik

 

[drewpster]

Re: A bagging idea

I am thinking of using the technique for "clamping" more than for infusing the resin. My idea is to wet out the roving in place just as you would in hand layup. Then cover the area with plastic film or polypropeline (sp). Tape it down around its perimeter and pull a vacumm through a hose at one of the corners.
I know that the resin will not bond to the plastic. (hope) I also know as the film sucks down it will tend to wrinkle and bunch up. After the vac is applied use a plastic spreader to smooth out the wrinkles and remove air from the resin. Leave the vacumm in place until the resin tacks and stays in place.
Peel the plastic off when the resin is hard enough, and your bonded.
Good plan? :redface: maybe

 

[erikgreen]

Re: A bagging idea

Sure, give it a shot.

I use plastic all the time on top of resin to give me a smooth surface. Just do your layup then put the plastic on top, and roll out any bubbles.

Post pics and let us know how it goes. Be careful not to use too much resin, since you're not giving it any way to get out it'll tend to form a crust on top if there's extra.

Erik

 

[geedubcpa]

Re: A bagging idea

I have used wax paper on top of the glass as a way to work the glass down - the wax paper keeps your hands clean and you can work out bubbles and stuff - then when you are done you peel off the wax paper.

 

[redfury]

Re: A bagging idea

I think I'd use some kind of rope caulk or something to seal the edges of the plastic as well as using tape to hold it down to help create a good seal, or perhaps 2 faced tape would be a better choice. You can get a good thick carpet tape that is 2 sided and is plyable enough to fall into lower areas that might give you sealing problems, as well as it is wide enough to bridge any possible air gaps.

 

[MrPhotographer06]

Re: A bagging idea

I have used wax paper on top of the glass as a way to work the glass down - the wax paper keeps your hands clean and you can work out bubbles and stuff - then when you are done you peel off the wax paper.

Thats what i use, and then you can push it down and wherever you want, when you get through,and it hardens, you go back and peel it right off.

 

[ondarvr]

Re: A bagging idea

The stringers can be bagged, it can be somewhat involved and expensive for a one off project, or to just get around some air in the stringers though.

If you still have an issue with air in the radius at the hull, use an extra strip or two of mat under the roving in the radius, you can also use mat over it to hold it down. The other solution is to make a larger radius.

On top of the stringer can be a little trickier if the radius is tight, mat can help again and so can making the resin slighlty thicker, a small amount of cabosil may help.

 

[erikgreen]

Re: A bagging idea

The wax paper or plastic idea works well. One trick I've used to get glass to lay down is to cover it with plastic, then use clamps or weights to hold it tight until it cures.

Vacuum bagging is a really strong clamp, and can get you the optimal amount of resin, but if all you want is the glass to lay down, then put plastic over the glass after wet-out and lay something like bean bags or small plastic bags filled with sand over the top (seal the bags obviously).

The bags will conform to the top of the stringer and press down, and once they're on you can roll the sides of the stringer into place using the plastic to smooth them. Once it's all in place, wait for cure then remove the bags and plastic.

I'm going to use something like this for the edges on my hard top project... I'll see if I can illustrate it.

Erik