Core material for fuel deck on 253G

[slow ride]

Hey Guys, I'm getting ready to pull my fuel deck and recore it would like some opions on which material would be better. Penske board or divinycell. I understand that divinycell is a kerfed material and can conform to the slight radius on the cover. How about Penske. I'm thinking of using 1/2" or should it be 3/4". Thanks

 

[richie rich]

Slow ride, there are several designations of foam boards and they go by density...ie 4lb, 9lb etc..and the density determines where they are used and the cost goes up accordingly......they are not necessarily kerfed...you can get flat, one side and 2 side kerfed....and a flat board will bend somewhat if you really need it...if you get kerfed, the resin will fill in the cuts and add weight......you will need additionall glass when using foam board like 1708 biax.....I would contact Composites One as they can tell you what to use to replace your existing thickness that uses plywood and matt .....give them your dimensions...you probably don't want to go thicker than your original deck, so if its a 1 inch deck, you have a choice of 3/4 foam and a few layers of glass or 5/8 and more layers of glass...which also means more weight....weigh your current deck cover, then calculate what new foam, plus glass and resin will weigh....the glass is in oz per sq-yd and a hand layup will be 50/50 glass to resin ratio. You may find by the time you're done, you saved little weight and doubled your cost.....I would do some math before spending the money.

 

[slow ride]

Thanks Rich I'll get intouch with them

 

[BobP]

1/2 inch marine ply, 2 layes of 1708, core the screw holes.

If you go any thicker, you will have to router the edges otheriwse it will rise about mating deck.

 

[kevine]

I am doing this same job but I havent gotten far enough into it to post my questions, but what is 1708 ?

 

[slow ride]

Thanks Bob. Kevin 1708 is a type of fiberglass that has mat on one side and a biaxle stich on the other. Lighter and stronger than woven roving and will conform to radiuses easier. I do plan on using 1708 on the underside of the deck I'll also use a mat under what ever core material I am going to use.

 

[BobP]

And there is no radius to the cover construction.

The slight radius comes from the support structure below and the cover conforms to it.

 

[richie rich]

The 1708 is 17oz double bias glass with a layer of chopped strand matt as slow ride mentioned.....the matt is used for filling in when bonding to rough surfaces and is also used facing out as the layer that can help keep print through from showing through your gel coat. Its the first layer against the mold. If you reusing your existing deck cover and just gutting the core it will be a rough surface so the matt will take up any irregularities....but it does add weight to your part. If you have an application that does not need filler or hiding, just use DB1700 which is the same material just without the matt....the strength is in the 17oz cloth....both should work well with epoxy, but ask your distributor if the cloth they sell wets out in both polyester and epoxy as a cloth made specifically for Poly resin will have a tough time wetting out in epoxy because of the binder used when making the cloth/matt.

 

[BobP]

He doesn't have to use DB material, he can use mat like Grady used, Grady used 1.5 oz mat, one layer, that's it. Can makes up thickness with 24 oz roven, plenty of choices, thickness matters.

I wanted more deck stiffness, and since I used epoxy resin, the chopped strand mat binder makes it springy, no good for forming at the deck plate recesses and at the edges.

The stitched no binder 3/4 oz mat in 1708 makes it set thicker than 1700; thickness is stiffness. So may need three layers of 1700 to equal thickness of two 1708s.

I keep a lot of 50 inch roll 1708 around, my all purpose cloth, keeps it shape even when pulling and doesn't unravel. Cuts easy with Fiskars.
So I use it for almost everything structural.

When I removed the old core checker board ply, I also added a layer of 1708 to factory skin, and another layer of 3/4 mat, then the wood.

Wanted greater stiffness and got it , cover did finish heavier than original.

Stiffness comes from thickness of both skins, not core when given same core thickness.

 

[richie rich]

yeah, you can go with matt like GW did if you're using plywood.....but if you go with a structural foam, you really should use something like the 1700 or 1708......but matt is really a quick way to fill or build thickness but is not very strong at all....So I'd rather use better fabric to make up the thickness...at least you'll have better strength for that extra resin you'll be carrying....for a deck cover, you can even get away with a few more layers of something like 12oz....in either case, get the final thickness.

 

[ocdansar]

I have the gas tank cover out of my 330 it was a mess, it was cored with 3/4" balsa, anyhow I have it cleaned out and went over it with an 8" d.a. with 40 grit. I am planning to recore with 3/4 plywood cut into 12"x12" squares my question is do I have to use epoxy resin or will polyster resin work. This is the biggest cover I have ever done almost 5'x5' the smaller ones I have done I used polyster resin. Thanks for any input.

 

[richie rich]

Use epoxy for sure. Polyester is OK for fresh glass layup as a laminating resin but now you're trying to bond a new core to your original skin.....this is a secondary or mechanical bond. PET isn't really a good adhesive which is what's required here....epoxy is an excellent adhesive and laminating resin and will seal your wood core better than any other resin.

Is there a reason you're using small pcs of wood vs cutting out a whole or larger pieces? Just wondering..

 

[slow ride]

I was thinking of useing a vinylester resin. The product has a high mech bond ratio and you can do multiple layups in a day. That being said I do agree that epoxy is the strongest bonding agent but cost for cost vinylester is a good alternative

 

[ocdansar]

I figured with the smaller pieces it would be easier for me to work with, also on such a big piece I was afraid I might not be able to get it completly flat, any way G/W has always used small squares so I figured it wouldn't be a problem. Any thoughts on this? I definetly want to do it right.

 

[richie rich]

OCDANSAR, your deck cover had balsa core? Did you by chance weigh it? My covers weigh a ton so I was under the impression it was plywood...just trying to compare weight, but I will find out soon enough when I cut it open this spring...that means all that weight is coming from the CSMatt and resin built up in there.

Slow Ride, I agree, VE is a good alternative and many boat manufacturers use VE as it has good bonding properties and better moisture resistance than PE. But Epoxy is readily available, there is no solvent to smell or inhale and with such a relatively small amount you will need for the job, how much will you really save? If you use epoxy with a slow hardener or even refridgerate it before mixing to even slow the process down more, you can do multiple layers of glass all day. Some epoxies like Silvertip (may cost a little more) allow you to do "wet on wet" within 24 hours of the previous layer even though it may feel somewhat cured to the touch as they have no amine blush.

I dunno, you can use epoxy for a lot of things, even at home or garage....can't say you can for VE....what do you do with the rest in the can?

Using the smaller pieces will be fine, but in that case, IMHO, I would use the better glass like 1700 or 1708...not just chopped strand matt. It will give you better overall strength around those joints/seams.

 

[slow ride]

Rich, I hear you about the volume with ve, I've got a 233 formula project that I'm working on and as far as epoxy goes I use it alot on my woodworking projects so it is much more user friendly.

 

[ocdansar]

It was definetly balsa 3/4" I had a wood guy look at it to confirm my thoughts. It was so saturated with water I could hardly handle it by myself. I am afraid it is gonna be even heavier with the plywood but I already have 3/4 and 1/2" so I figured I would use the 3/4 since that is what it had for thickness. I plan to put 1708 in first and wet it out then start putting the squares in wetting them out, let everything dry, go over the plywood with my 8" and 40 or maybe 80 grit then cover with 1708 and wet it out again, let it dry and just knock any burs off.

 

[ocdansar]

What about using 2408 instead of 1708 ?

 

[richie rich]

Then I probably have the same water logged problem with mine....just add it to the list I guess.....

If you got 2408, thats OK....its expensive stuff but if you have it, why not?You just won't need as many layers....2 of those is like 3 1700s...but because its thicker, it will be tougher to wet out and bend around any curves.....if you're buying from scratch, its easier with the 1700 or 1708.....its a very good all purpose cloth.....

Just food for thought, when laminating wood, wet the wood out first and see how it sucks up the resin, and add more if you start to see dry spots....then lay in or on the glass and wet it out. Many times, if you simply put a quick tack coat down on the wood and quickly glass over it, (or in reverse order in your case ) the wood will take as much resin as it wants, even right out of the glass, leaving you with dry, or resin starved areas that can delaminate later and you'll never see it until its too late. Wet the end grain of the wood especially, until it can't take any more...that will help with the water saturation problem.

May want to add some weight on top of the wood after its epoxied....plastic pails with water works well, but don't over due it or you can squeeze out all your resin...just enough to see the resin start to squeeze. Post some progress pics...would like to see how the panels came out.

 

[BobP]

Nothing wrong with putting 3/4 inch Pro Balsa back, to keep the weight down vs. 3/4 inch ply which will be very very heavy, a bit more expensive though than marine plywood which comes in 4 x 8 sheets, and marine plywood doesn't appear to fit in one cut on your cover.

So butt them with thickened resin in the gap, so there is no gap.

If going marine ply, no reason to cut into checker board unless you want to play checkers!

Balsa comes in 2 ft x 4 ft sheets, butt it all together tight with thickened resin. Can buy on internet the stuff rolls up since it's bonded on one side with a glass mesh.

The wet problem has nothing to do with choice of core material, it wasn't sealed properly, probably at the screw holes or deck plates.

So make sure you do it right, over bore and core all holes with thickened resin from bottom side - redrill holes from top side after they cure.

I'd lay that cover on a very flat surface, I use my garage floor, 3/4 oz mat or 1.5 oz mat between wood (prewet all wood) and cover, weight it down with two bags high of 50 lb home depot sand clear bags layed flat. Use shipping package clear tape to cover topside surface otherwise resin may seep over side and get onto gelcoat. Make sure floor surface is smooth to the hand, no pebbles or anything. 3 or 4 mil sheet plastic down.

Keep sanmd bags away from edge of wood so you can fill the gap wit thickened resin as needed. Same goes for deck plate area gaps.

After cured, wet out and lay up the facing side.

Use two layers of 1708 or 1808, whatever you get.
What did Grady use on balsa?
If you make yours at least as thick, or better yet thicker - will feel more solid to the foot. 2 layers of 1708 will beat Grady's 1.5 oz mat, if that's what they used.

I would stay with lighter Pro Balsa. I prefer epoxy resins myself, nothing against the others. Just less shelf space needed.
Raka's 127 is perfect and easy to work with, no odor, lighter viscosity, plenty of set up time with slow hardener, economically priced, ships out same day, ask Larry for any advise.

I have no affiliation with Raka.

Get my 1708 there on the roll, silica, foam rollers, everything.

Good luck.