Proper placement of fiberglass

[bcc101]

I am about to tackle some balsa core replacement using West epoxy.
To start off there are two hatches I have already removed the core and the inner layer of glass. I intend to put down one layer of chopped strand mat, the balsa, and a layer of chopped strand and wove cloth.
This is working from what will be the inside of the hatches. The deck I will cut away the top layer and remove material to the inner liner.
My question. When putting down the chopped strand, woven cloth which side goes up and which side goes against the balsa?
I am sure I will have more questions as this process evolves.
Thanks Bruce

[brantleychuck]

The chopped strand goes against the existing surface. Chopped strand makes better contact with un even surfaces. Then cloth on top of chopped strand mat


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[bcc101]

Thank you both. I have consulted the West manual and may have overlooked the proper positioning of the cloth.
With the weather finally breaking around here I can start on this project.

[Zach]

You probably don't want to put chopped strand mat under the balsa core, as you'll end up high to the surrounding area if you lay up the same top skin thickness as is there.

Most folks use cabosil and resin, or cabosil cut 50/50 with milled glass fiber as the bonding paste to bed in the new balsa.

[Hamish_ct]

If your going to gelcoat over the repair you have to use vinylester or polyester resin. Gel coat does not chemically adhere to west systems epoxy. In 3 years you will be doing the repair again

[bcc101]

I am putting a layer of chopped strand under the balsa on the two hatches I am beginning with. The balsa is a panel on the interior and there will be room for it to stand proud a bit.

Not sure of the final coating but it will not be gel coat.
I am thinking of a deck paint and Kiwi for the nonskid.

This will be an ongoing project this Summer.
Thanks again

[leftbrainstuff]

CSM or chopped strand mat will conform to most uneven surfaces. It wets out readily. Its great for building up uneven sections too.

Woven roving likes to be flat, is more work to wet out and provides thickness.

If you plan to sand and remove material then bulk with CSM. You dont want to sand into woven roving.

For edge repairs and hard corner or edge taping then use a fiberglass tape. CSM, for example, falls apart if you try to work it or use small areas.

Finally deck cloth is like tape and has a small biaxial weave. Good for large areas where you want more strength than CSM can provide.

To determine the laminate schedule I'll often cut small sections and lay them up dry to see how best to orient them. You want to orient successive layers so the main fibres dont all align.

Do all your cutting before you start. Large sections can be hard to work. You might need some extra hands.

You can also use straight epoxy or polyester mixed with colloidal silica as a final surface coat. You can vary the viscosity to flow and leave a nice flat finish. Less sanding that way. Same applies to hard edges. Composite fibers dont like sharp corners as a rule.

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[Stumble]

I have not tried this,but after using hydroturf for a couple of projects I would seriously consider doing the structural repair then instead of painting or adding gel coat just stick down hydroturf on the raw epoxy.

[scherzoja]

I've got a couple of questions on this.

1. Has anyone successfully used epoxy with CSM? I tried it once and ended up with as sticky rat's nest of fibers because the epoxy was so much stickier than polyester that all the fibers in the CSM got all over the place and the sheet of CSM looked like a epoxied bedhead. Had to scrape it all off and not use CSM.

2. If using epoxy, is it still necessary to layer mat/cloth/mat, etc...? I thought the whole reason for layering when using poly is that cloth on cloth doesn't adhere well with polyester because poly is just not that good of a glue. Sticking a layer of mat between forms better substrate for cloth. Setting aside print-through issues with cloth, since epoxy is so tenacious, is it necessary to use mat?

3. Doesn't CSM have binder that is incompatible with epoxy? Isn't that one reason why biax exists?

[Zach]

1. It is a bit different to work with, as you have to dab a brush into it without lifting the hair if you are using continuous strand mat. I use it with epoxy to make decorative corners that won't be filleted for paint. Sort of a sheet rock tape grade inside corner.

2. Most Mat that is available for sale today, is soluble in epoxy.
It used to be that it was soluble only in styrene, if you got some off an old roll from the early 2000's, its a possibility that you got the stuff that lays out like cardboard in epoxy.

3. You don't have to use Mat with epoxy. Most Biax is 1708, which has a mat backer that makes it compatible with polyester and vinylester, without having to add a layer of mat between layers of biax. It has 8 ounces per square yard of mat attached to the back, the 08 designates that.

If you buy 1700 biax, it has no mat backer, and with epoxy you don't need any mat in between layers. You wet out with less resin as it takes 17 ounces of resin to wet out a yard, compared to 25 ounces for a yard of 1708.

I like 1708 for big overhead work in epoxy, unless the 1700 stuff is stitched very tightly the 1708 is much less "stringy" where the stitching doesn't come out and wind around your air roller quite as bad. This is more so if you have to cut a piece of cloth across the bias.

[bcc101]

I am learning a lot. I have done a bit of research prior to joining this forum.
I appreciate the way you all share your knowledge and experience.
I guess now is the time to get at it and hopefully not make too many errors.
Thanks and I will continue to ask.

Bruce