Correct Mat oz / type for decking

[Fletch170]

Hey everyone!

I am replacing the deck on my 170, What oz mat should I use? The one feedback from a prior post was 1.5 oz on 3/4 in plywood. However, the factory deck is made of 1/2 ply with glass on both sides.

I checked out bayou2 and the lightest oz mat is 3.5?

[gran398]

LilRichard is knowledgeable in all areas of fiberglass/layup schedule/polyester/vinylester/epoxy resins. Hopefully he'll chime in regarding the best and latest layup recommendations for your new deck.

Know you've posed some transom questions. Guess the big question is, how long do you think you'll keep her? If you'd like to keep her say, ten years...you may as well do the transom now. Then, when/if you go to sell her..."The transom and deck were professionally restored fall 2011 cored with all composite materials" etc. A big selling point, the heavy work is over, restoration complete, no future issues.

Will be a whole lot easier(and cheaper) tackling both jobs now than piecemeal down the road.

The term "the transom is sound" is thrown around loosely in the rebuild world. For 70's hulls like ours the quote should be "the fiberglass skins above the lower plywood mush are sound...no flex."

[Capt Matt]

1.5oz mat seems the most common out there. I'm surprised they don't have it in stock. You can probably find a 20-25yd roll somewhere. Wait till you finish all the demo before you order materials this will give you a better idea of how much stuff you will need.
Capt Matt

[LilRichard]

I would avoid using just mat - I would try to use a structural material to add strength to the layup.  A layer of 1808 followed by a layer of mat would improve the durability of the deck.  I also added another layer to overlap where the seams in the deck are.

And yes, I would also put some glass on the bottom of the deck.  Some folks just use resin on the bottom, but it can crack and allow moisture in.  Using even a very light cloth will help avoid that problem.

[Group W Bench]

How about using 3/4 inch Nidacore with a layer of 1708 laminated on both sides for the floor? The cost won't be substantially different than good marine grade PT kiln dried ply and 1.5 oz mat. 3/4 inch Nidacore is like $70 a sheet, so it is pretty comparable to good wood, but lighter and won't rot.

[Capt Matt]

I'm not a fan of nidacore, unless the cut edges are ground out and filled I have seen it crush, specially around hatch cut outs and it does not hold a screw
Matt

[Group W Bench]

It's a given that Nidacore decks require some finish work around any areas that have been cut to accept hatches. However, the same finish work should be done to wood decks to encapsulate the end grain of the wood. You are right about Nidacore not handling compression well in isolation, that is why it is commonly covered on both sides in 1708 prior to cutting and installation. Areas under high compressional loads may be better candidates for nilaboard or penske cores. When properly installed, Nidacore is a great composite deck material in terms of cost vs. weight vs. longevity.

Remember, whether wood, nidacore, klegecell, divinicell, corecell,etc. these are all simply cores. The strength comes from the grp laminates combined with the core, not the core in isolation. For each restoration, it's an equation of longevity relative to cost relative to weight. 3/4 ply with an 1.5 oz mat on each side wins in terms of low cost, but not in terms of weight or longevity. A core cell deck with postcured carbon epoxy lams on each side wins in terms of weight and longevity but certainly not in terms of cost. Nidacore has become commonly utilized in deck applications as it is a very good composite compromise in terms of low cost and low weight.

[Capt Matt]

Group W Bench
Your not a fan of coosa? I found it really easy to work with and its crazy strong
Capt Matt

[flfisher]

Rule of thumb what ever u take out put back ......but then again it doesnt hurt to thicken the deck ... I am currently redoing my deck and used  matt on the back of the core which i recommend like previously stated ....... U dont want to put all that time into a deck and cut corners!......also the ideas about composite cores if you can afford them is never a bad thing

[Group W Bench]

Matt,

I'm a big fan of coosa, nilaboard, penske, any of the composite high density Fiberglass reinforced poly boards for high compression applications like transoms. They are an incredibly expensive and heavy way to rebuild a floor. Additionally, you go through carbide bits like tic tacs cutting grp reinforced poly board. It is often called "transom board" for a reason.

[81walkaround]

the factory deck is made of 1/2 ply with glass on both sides.

fwiw, my deck was 3/4" ply with glass on both sides (250 Osprey)