Did I lay fiberglass wrong or just simply not layer enough

[04silverz 10+ year member]

Started work on my new box which will have a fiberglass bottom. Dimensions are roughly 26L x 16D. I did three layers yesterday afternoon and when it cured it seemed really flimsy.

I've glassed door pods before and tweeter pods but never a box so I have no experience doing such a large piece and am curious if I just simply need more layers or did I lay the glass wrong. From the research I did I've gathered that there is no magic number of layers as it is all install dependent for layering. But before I go and potentially waste more time and money on another package or two of fiberglass I figured I'd ask here first.

With the other stuff I've done I cut the mat into strips or squares as it required lots of shaping but with this being just a giant rectangle I just cut three big pieces and laid them on top of each other.

Box is going to be for 2 Boston SPG555 powered by Orion 2500D and the only part that is fiberglass will be the bottom. Also is going to be a sealed box.

So to sum up do I need more than three layers or was I supposed to cut into small strips?

Click to read more...

 

[Wingman0121 10+ year member]

You should be able to stand inside/on top of a well-done fiberglass box without seeing any flex.

 

[RAM_Designs 5,000+ posts]

Fiberglass is not real good at being rigid on flat planes, that's a place where you'd use MDF. Just use the fiberglass on the more rounded parts of the box. And yes, you should use more than three layers; 5-7 normally works well, but it depends on the application as well.

 

[fasfocus00 5,000+ posts]

use a 4mil core mat after 2 layers of fiberglass mat and another 2 layers on top of the core mat.

 

[04silverz 10+ year member]

Alright thanks for the tips guys. Was just surprised at lack of rigidity when compared to the pods I'd made in the past

 

[BASSMEKANIK89 10+ year member]

If you check with your local fiberglass distributor you can get a perforated foam fill(usually white in color) that can be sandwiched between 2 layers of fiberglass mat. This is what most boat manu. use to get rigidity in thin fiberglass panels. If used correctly you can get the strength of a 3/4" peice of fiberglass out of 1/4" fiberglass, and it is still lightweight. With it being against the floor you should be able to get away with what you have done and maybe a layer of foam fill and a nother layer of glass to seal the foam fill. Also, when you let fiberglass cure it gets a shine to it. If you are going to apply more glass after full cure, sand away the shine for a better bond. Hope this helps.

 

[04silverz 10+ year member]

Thanks for the tip on sanding. I was wondering about that. I'll have to see if there is a distro like that here is so md. Might have to run to dc or baltimore

 

[ramos 5,000+ posts]

Started work on my new box which will have a fiberglass bottom. Dimensions are roughly 26L x 16D. I did three layers yesterday afternoon and when it cured it seemed really flimsy.I've glassed door pods before and tweeter pods but never a box so I have no experience doing such a large piece and am curious if I just simply need more layers or did I lay the glass wrong. From the research I did I've gathered that there is no magic number of layers as it is all install dependent for layering. But before I go and potentially waste more time and money on another package or two of fiberglass I figured I'd ask here first.

With the other stuff I've done I cut the mat into strips or squares as it required lots of shaping but with this being just a giant rectangle I just cut three big pieces and laid them on top of each other.

Box is going to be for 2 Boston SPG555 powered by Orion 2500D and the only part that is fiberglass will be the bottom. Also is going to be a sealed box.

So to sum up do I need more than three layers or was I supposed to cut into small strips?

you should always alternate the bias each layer of mat or cloth. One direction first layer, turn the piece 90 degrees for the second layer and so on. Like has been said flat is easier and quicker done with mdf or plywood. Since your already half way there, glass some thin scraps of mdf in, or some 1/4'' poly rope in. Then do a couple more layers on top to add stiffness over the large flat area. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Fiberglass is not real good at being rigid on flat planes, that's a place where you'd use MDF. Just use the fiberglass on the more rounded parts of the box. And yes, you should use more than three layers; 5-7 normally works well, but it depends on the application as well.

werd number of layers also depends on weight of mat or cloth used //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

use a 4mil core mat after 2 layers of fiberglass mat and another 2 layers on top of the core mat.

werd best for lightweight. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

If you check with your local fiberglass distributor you can get a perforated foam fill(usually white in color) that can be sandwiched between 2 layers of fiberglass mat. This is what most boat manu. use to get rigidity in thin fiberglass panels. If used correctly you can get the strength of a 3/4" peice of fiberglass out of 1/4" fiberglass, and it is still lightweight. With it being against the floor you should be able to get away with what you have done and maybe a layer of foam fill and another layer of glass to seal the foam fill. Also, when you let fiberglass cure it gets a shine to it. If you are going to apply more glass after full cure, sand away the shine for a better bond. Hope this helps.

^ foam core , they also sell plywood and other composite core materials as well. the shine on cured resin occurs when using finishing resins. it is a wax added to the resin. as the resin is curing, the wax rises to the surface to protect the surface from the air while it cures fully. Brands sold at the big box stores do indeed have wax. if you buy online or from a supplier, simply buy layup resin and have no wax //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[fasfocus00 5,000+ posts]

Thanks for the tip on sanding. I was wondering about that. I'll have to see if there is a distro like that here is so md. Might have to run to dc or baltimore

also, if you get marine/boat resin it doesn't have that much of a shine to it b/c it doesn't contain wax plus the marine/boat resin is cheaper. you can usually get a gallon for $20 and 5 gallons for $75.

 

[BASSMEKANIK89 10+ year member]

Make sure that the resisn you are buying is fresh, it does have a shelf life and needs to be rotated when sitting on a shelf to allow mixing. The GP product that you find in alot of autopart stores is the leftovers out of the 55 gallon(or larger) drums at the distibutors. It is just all mixed together and packaged at a cheaper price to make it go away. That is why when you pour the resin some spots will be clumpy and other parts will be very viscous. if it is within your budget try and get "LOW SHRINK" resisn so it will not warp your project while it cures.

 

[BASSMEKANIK89 10+ year member]

also, if you get marine/boat resin it doesn't have that much of a shine to it b/c it doesn't contain wax plus the marine/boat resin is cheaper. you can usually get a gallon for $20 and 5 gallons for $75.

Be carefull with the price on that resin. For that kind of money you will not get a quality resin. Those prices were right in line before the gas prices went thru the roof. We buy alot of resin and we pay about $118 (wholesale) for a 5 gallons of quality resin. We have found it cheaper, but it created more problems than it was worth.