Poly resin for new Plywood deck?

[JaeVeeSport]

Hey Everyone. I have some experience with resins and a lot of experience with finish work, but I am lost. I searched extensively, and I came up with more questions than answers

I need to replace the deck on my 222. I was planning on poly and 3/4" marine ply.
I could use some advice on the glassing schedule for the "bottom" of the plywood, and the top as well.

Can I use poly resin?

I want to use some form of cloth on the bottom to help with adhesion to the glass stringers. Maybe a layer or two of simple 6oz S glass, or should I go with a layer of CSM or 1708? Also if I use a laminating resin on the bottom can I leave it tacky forever, or should I use a sanding resin?

As far as the top, assuming the ply is encapsulated in 6oz S Glass or whatever, would you guys then do a layer of 1708 with CCSM on top? Would that be sufficient?

I am looking for advice on whatever will save me time.

Also if I cut out the top layer of glass now can I re use it? If I plan on using EVA mat anyway ?

Also if I must use Epoxy on the plywood, can I finish in poly ?


Thank you so much everyone.

[Fishhead]

First thing I would do is check your transom for rot. They usually go hand in hand with soft decks, I’m living it now myself. Then a 40 year old tank with corrosion under the mounting pads or straps. The deck itself has the tank coffin glassed to it and dropped in originally, as well as wet stringer foam. It’s a lot of work no doubt just want you to know it’s not quick or cheap job and lots of time. Check my build it will show the underside of the deck, everyone’s here to help you going forward it’s a great group with knowledge of these things

[Ulysses485]

Great questions to ask when starting a rebuild or just about any fiberglass work. But the big question is what you are planning as finish. You either stick with polyester resin so you can finish with Gelcoat, or with either poly or epoxy and go with paint. You can get a strong bond with epoxy over poly but not poly over epoxy. Gelcoat is a polyester resin based material and will also not provide a strong bond over epoxy and industry standard it’s a big no no. I have laid a good bit of polyester resin over the past year (think I am at 11 gallons) and my finding from years of research is that its a great product when using composite type coring (Coosa, etc) but once you go plywood, epoxy is the resin of choice. Epoxy has a really high bond strength and therefore seals the plywood more effectively as a “repair” during rebuilds. Boats are in a wet marine environment so moisture stays high unless you are in a fairly dry climate or the hull goes into dry storage after each use. With that said, sealing a plywood deck with epoxy has less chance for resin to become brittle, delaminate from the plywood at the underside of the deck, and cause moisture intrusion. However, if done carefully and Polyester resin used generously (hot coating deck prior to laying glass), you could “get away with it”. Boats have lasted decades built with plywood decks and poly resin and it is still done today. The end goal of what you are looking to accomplish and your budget are things only you can answer. There are many ways to do it and it all becomes personal preference at the end of the day.

Note: Take a look at this build thread I remember reading through where he had trouble with poly and plywood and what steps he took.

https://classicaquasport.com/smf/index.php?topic=15112.150

Hope that helps

Ulysses

[JaeVeeSport]

Thank you guys.

I was planning on finishing the deck with Gelcoat then Marine mat or Sea Dek or whatever.

Boats were built, and repaired, with plywood and poly for a long time, but I think I will go for epoxy at this point.

How does the schedule look? If I'm using 3/4 I guess the rigidity will from from that, and I really don't need CSM, so can I just pre soak the ply in epoxy, go with like 6 oz S glass around the poly, and 1708 on top?

[Fishhead]

I just finished my deck on FF 22.2   3/4” marine ply  2 layers of 1708 on bottom with poly and 2 layers of 1708 and some 1.5 csm on top using vinylester resin. Finished deck is 1” thick. Really solid.
Epoxy would have been crazy expensive, deck has total of around 9 gallons.

[dbiscayne]

I've used plywood in the past w poly resin and had best luck with applying a thinned coat of resin on both sides and all edges of the plywood, followed by a regular coat of resin on the bottom side and two layers of 1708 on the top. Was told to do this by an old school wood sailboat builder, said the resin only coating on the bottom allows the wood to breathe. I've still got the boat I used this layup on, it's been +20 years and I do try to leave the deck hatches & bilge open to let it air out, just started noticing some suspicious but not soft spots a couple years ago but not enough to be concerned. Epoxy would be even better.

About to put a new deck on my little boat, for just a few dollars more you can use plascore with glass on both sides. I've experimented with 3/4" plascore and 2 layers of 1208 w epoxy on both sides and it's as stiff as plywood. Drawback is you can't put a screw in it so need backing plates or fill the cells with resin. But it'll never rot, is lighter, easier to cut. I wouldn't span any gaps > 3 feet without checking to see if it needs reinforcing. Pieces I layed up were about 2 feet long x 1 foot wide, supported at each end I can walk on it and no noticeable flex. Could probably get away with just 1 layer on the bottom, maybe use 1708 instead of 1208, but wouldn't reduce the top layer so you get some extra impact protection. Poly resin probably won't stick good enough to the plascore even w the veil, I'd recommend epoxy w this stuff.

[RickK]

I did the same think that dbiscayne did but with 5/8" plywood. Lasted about 15 years until I had the insane idea that I needed to do a total rebuild on it.

[umecheme]

I did the 1 layer of 1708 on the underside and 2 layers of 1708 on the topside, with epoxy... you're right... crazy expensive.... 

[RickK]

I did one layer on the bottom in epoxy (on Plascore) and everything under the deck in epoxy and everything above the deck in poly.

[JaeVeeSport]

Thanks guys! I got busy with work and Halloween weekend and the kids so I haven't had a chance to check in.

Have other people used 9 gallons of resin on their deck builds? I was thinking 5 would be enough. I have some experience with fiberglass and I know more resin = higher brittleness.

Can someone answer one more question:

Why more than one layer on top? The stiffness is coming from the Plywood. Why use 2 layers or more of 1708?

Dbiscayne, where did you get the plascore and what type etc? I googled it and there are a confusing number of results.

[dbiscayne]

I found a local supplier, they will ship but have no idea what the shipping options are I know it can get pretty expensive for full size sheets.
The plascore made of polypropylene material is usually used in boat decks, can get it with or without a veil. Get the version with the veil for better fglass adhesion. Density is about 5 pcf.
http://www.seafarermarine.com/plascoreplastics.html

I put more than one layer on top to better protect it from people dropping things on the deck.

For your total resin usage. There are ways to calculate what it should be, but realistically you'll need more. I never seem to get through a big batch without the resin kicking off and having to scrap some amount. Once it jells up thats it don't bother trying to use it. You can extend the working time by pouring a big batch into several smaller containers.

also take a look at
https://www.merrittsupply.com/product-category/plywood-composite-panels/

https://shop.fiberglasssupply.com/cart.cgi?group=67

http://store.raka.com/fiberglasscloth.aspx

https://www.fibreglast.com/category/Composite-Fabrics

https://www.tapplastics.com/departments/fiberglass

http://www.fiberglasssupply.com/Product_Catalog/Reinforcements/Knitted_Fabrics/knitted_fabrics.html

http://www.uscomposites.com/specialty.html

https://www.jamestowndistributors.com/product/fiberglass-and-building-materials

https://www.aircraftspruce.com/categories/building_materials/bm/menus/cm/foam.html

[umecheme]

Jamestown recommends 51 oz (!!!) of resin per square yard of 1708 for full wet out.  But it sure is rugged!  I'm always amazed at how much epoxy I've used when I'm done.   Might not need the 1708 on the bottom if you've got plenty of strength and you're just trying to keep the water out. 

https://support.jamestowndistributors.com/hc/en-us/articles/360016060373-How-much-resin-do-I-need-to-wet-out-fiberglass-cloth-

[JaeVeeSport]

Ok, my decks 6 x 10 feet so if I have 60 sq feet, divide that by 9 (sqft/yard) = 6.67 sq yards, mult. that by 51 oz (oz/sq yard)= 335 oz. 335 oz divided by 128 oz (oz/gallon) = 2.6 gallons. Sounds about right. I should get 5 just to be safe lol.

[umecheme]

I'd do the hot coat on the plywood like dbiscayne suggested before trying to glass.  I had a terrible time on my first attempt with the plywood soaking up the resin, which would have been avoided had I done a quick hot coat on the plywood first.  What appeared fully wetted out when I finished was clearly not when I returned to check on it an hour later.  That was my first attempt, with polyester resin, which I was able to pull off in one big sheet.  Thats why I ended up going 100% epoxy.  Never have to wonder if its going to stick.