ACX VS Marine Plywood

[tank1949]

It seems that I have read something concerning the usage of ACX vs Marine plywood to rebuild a transom but I cannot find it on Iboats. If anyone knows if the ACX glue is more waterproof than Marine Plywood's, please respond. Where I live, ACX is $50+ a 4x8 sheet where Marine is 70+ a sheet. Coosa is 250/sheet but I need 2 sheets. Coosa is out of the question.

 

[oldrem]

I believe the only real difference is marine has fewer voids in the layers. I used ACX for mine

 

[Mad Props]

Yep, "marine grade" is a loose term... in general, it will have less voids and potentially more layers, but the good stuff is BS 1088 certified, it is made from tropical hardwood veneers which tend to be more rot resistant, but your not getting that for $70 a sheet...

all that said, use ACX, if properly sealed, it will last decades.

 

[tpenfield]

The exterior rated and marine rated plywood all have the same glue. As stated, it is just the quality of the veneers that is better with marine. Many boat manufacturers don't even use marine rated.

 

[chevymaher]

ACX is alot better than Four winns used in the original construction. I am sure of that. What I Put in mine was alot better than what came out.

 

[Scott Danforth]

same glue, slightly different wood,

 

[tank1949]

Thx to all!!!!!!!

 

[sutor623]

What are you guys sealing this with?

 

[Mad Props]

Always give the wood a coat of resin and let it tack up before you start to apply any glass/resin. If you don't do this, it will pull resin out of the first layer and give you a dry layup which can delaminate.

 

[kcassells]

2 steps;
Fill all voids you find from cuts etc with a putty, then 1st wet out all wood surfaces and edges. Especially edges. Let cure.
Step 2
Quick smooth sand, wipe with acetone
Then go back wetout to lay glass.

 

[CrazyFinn]

ACX is fine for a transom. Glue is the same as marine ply. Marine ply will rot if not sealed, same with any other plywood. Marine ply has no real advantages when used as a core in a glass boat.

The real advantage of marine ply is when you're building a WOOD boat - there are no voids so the strength is a lot more consistent across the wood, less issues with cracking when it is being formed into a curve, etc. That's really what marine ply is intended for. Back in our racing days we were running tunnel hulls, built entirely of marine ply, epoxy coating on the bottom, only a few mm thick. No glass reinforcement (to keep things light). Good marine ply was mandatory.

 

[Woodonglass]

Check the second link in my signature below. You should find it informative.

Marine Plywood uses the same Glue but...The wood that's used for the veneers and the number of veneers is better than ACX. And it does have less imperfections. Having said that, ACX is perfectly acceptable IF you heed the advice above. The KEY to using it IS filling all voids, especially in the edges, and then giving the edges a thorough coating of resin. And as stated all the flat areas should receive a thorough coat of resin too. Read the Link and you should have the info you need for a transom

 

[tank1949]

A local glass shop uses thinned poly with acetone to coat bare plywood. The thinned poly soaks in deep! Lots of hardener... After tacking, then he adds 1708 on bare plywood and coats with poly and then applies thickened poly and applies to plywood or inner boat skin and presses wood into cutout area. It is important to have the required number of turnbuckles and the plywood replacement marked to fit exactly where you want it. The clock is ticking!!!! C clamps if possible. I prefer and will be using epoxy, since curing time is more forgiving and you don't need the 1708 layer between ply and inner boat skin.. Coat regular epoxy onto bare wood and apply thickened epoxy with grooved trial to fiberglass inside transom skin. Press together and pray u aint screwed up too bad because once it cures, it aint coming off easy! Sandwich second 3/4" ply onto first ply using thickened epoxy. I'd like to find some inexpensive ACX but around here it is hard to find. Marine ply is more cost effective here. For I/Os, after drilling out transom assembly holes (in my case 8 1/2" holes) and testing to make sure assembly will fit, including y pipe on the inside and tiller movement, coat inside boat holes with epoxy by using q tips. On final application, 5200 thin layer in holes too. Bare wood need to be coated or rot will find it.

 

[tank1949]

Always give the wood a coat of resin and let it tack up before you start to apply any glass/resin. If you don't do this, it will pull resin out of the first layer and give you a dry layup which can delaminate.

U got that right. I always thin first coat with acetone! It really gets in deep and allows next coat to bond very well!.

 

[kcassells]

Hmmmmm IDK, I would think thinned out resin with acetone would flash/set up faster than undiluted resin.

 

[Woodonglass]

Yup you NEVER want to thin Epoxy, If you want it to have lower viscosity, set your cup in warm water and it'll flow much better. Chemical thinners destroy the GOOD properties of Epoxy.

 

[tank1949]

Hmmmmm IDK, I would think thinned out resin with acetone would flash/set up faster than undiluted resin.

U can thin with styrene or acetone and its soaks in great. Add 200% acetone and then hardener. It works great. Great for protecting or coating bare wood like boat seats too providing u finish with last coat containing wax, sand and then top coat. Applying full strength poly on plywood will not penetrate as well.

 

[Woodonglass]

Again Thinning Epoxy is NEVER a good idea. Our forum has one of the Leading Epoxy experts in the industry. ondarvr (On the River) is his handle. He has taught a lot of us that thinning it destroys the innate properties of the resin and yields an inferior product that is NOT as waterproof. When glassing wood the penetration into the wood is not as important as the total encapsulation of the wood with the resin. And then ensuring this encapsulation is not compromised. With Plywood the top lamination at best is 1/16" That's ALL the penetration you'll get even with water. The laminate resin blocks any further penetration. The Edges are the critical area and again as long as they're properly sealed and maintained, epoxies innate properties will ensure a very good waterproofing. Thinning is NOT required OR Recommended!!

 

[tank1949]

Again Thinning Epoxy is NEVER a good idea. Our forum has one of the Leading Epoxy experts in the industry. ondarvr (On the River) is his handle. He has taught a lot of us that thinning it destroys the innate properties of the resin and yields an inferior product that is NOT as waterproof. When glassing wood the penetration into the wood is not as important as the total encapsulation of the wood with the resin. And then ensuring this encapsulation is not compromised. With Plywood the top lamination at best is 1/16" That's ALL the penetration you'll get even with water. The laminate resin blocks any further penetration. The Edges are the critical area and again as long as they're properly sealed and maintained, epoxies innate properties will ensure a very good waterproofing. Thinning is NOT required OR Recommended!!

I never mentioned thinning Epoxy. Only POLY... The thinned POLY seals the plywood by penetrating deeper than regular strength. Then, u can encapsulate with regular strength POLY or epoxy. As I wrote earlier, I prefer epoxy because it is more forgiving while applying. Hopefully, a boat owner only has to rebuild a boat's transom once in his lifetime.

 

[kcassells]

Look to clarify things you mentioned eeepppoooxxxyyy in line 13. As if you may go that way with eeeepoxxyy. Getit, got it, geez Louise. We're just countering that approach.
Moving along....