Fiberglass on Pressure Treated Wood

[dillonheath08]

Hi everyone,

I read an article online last night that stated laying fiberglass over pressure treated wood was a major mistake. It said that it would not stick to the treated wood because of all the chemicals. So this lead to me spending the next few hours researching and reading forum after forum regarding this issue. I am currently undergoing a restoration and have already bought some of my plywood. And yes, it is pressure treated. I know I am new to the boating world and boat restoration so I thought treated was the way to go because moisture is the enemy when it comes to boat structures. I have read account after account giving reasons why you should or should not use pressure treated wood. Anybody tried it? All tips and advice are more than welcome. I just want to get my supplies ready so when the deconstruction is through I can go straight into planning and then eventually into cutting and glassing. Thanks in advanced.

 

[Woodonglass]

It's not the chemicals that make it not stick it's the wetness of the woods if you dry the wood out really well for about 10 days to two weeks you should be able to get the fiberglass to stick to it with good results with no problems others have done it in the past with good results

 

[Bob_VT]

Well...... some people age and dry the PT wood before they attempt it and epoxy works better.

 

[kcassells]

Hi everyone,
I read an article online last night that stated laying fiberglass over pressure treated wood was a major mistake. It said that it would not stick to the treated wood because of all the chemicals. So this lead to me spending the next few hours researching and reading forum after forum regarding this issue. I am currently undergoing a restoration and have already bought some of my plywood. And yes, it is pressure treated. I know I am new to the boating world and boat restoration so I thought treated was the way to go because moisture is the enemy when it comes to boat structures. I have read account after account giving reasons why you should or should not use pressure treated wood. Anybody tried it? All tips and advice are more than welcome. I just want to get my supplies ready so when the deconstruction is through I can go straight into planning and then eventually into cutting and glassing. Thanks in advanced.

Then you have the "Proper Screw" issues. Stainless screws react to the chemicals in pressure treated. I'd say return it and get bc exterior grade and eliminate metallic reactions etc. altogether. If you keep researching as you said you will find it's really not the wood to use. IMHO.

 

[tpenfield]

PT wood needs to be very dry . . . I would leave it out in the direct sun for a few weeks and let it get weathered a bit.

There is also "Kiln-Dried After Treatment" (KDAT), which is pressure treated wood that has been dried at the lumber mill. Most boat manufacturers that still use wood have switched to KDAT.

Product name are "Greenwood XL" and "Inland Perma-Panel". Not sure where you can get this stuff at a retail level. Most of the KDAT stuff available at retail is dimensional lumber.

Anyway, as stated, it is the moisture content of PT wood that causes the adhesion issue. Would be the same issue if you tried to fiberglass wet wood of any type.

 

[dillonheath08]

I've had these sheets for the better part of a month ands still have a ways to go before they will see any fiberglass. The wood is very dry. It's getting plenty of air to dry it out even more. It's not likely to get used for another 2-3 weeks. Surely it would be dry enough by then? It's not like some sheets I've bought that were dripping wet. I just don't wanna make a mistake and end up restoring it again 3 years down the road

 

[tpenfield]

Since it is subjective as to how dry the wood is, you could do a couple of things to verify . . .

1) get a moisture meter at HD or Lowes (about $30) and check the PT wood as compared to a regular piece of plywood that you have lying around.

2) do a test of the fiberglass adhesion in a small area. If you can pull the cured fiberglass off without delaminating the wood, it is too wet.

 

[Chris1956]

Dillon, I think your wood is plenty dry. I have used PT plywood that I dried for only a few days, w/o any issue. Poly resin and cloth stick quite well to it, and I used stainless steel screws, and they have lasted a decade so far.....

 

[Georgesalmon]

As said, dryness is the most important. Really dry PT plywood is hard to find for a retail consumer and I don't think a couple of weeks inside is really going to help a lot. Just ask the Navy, they built several big wooden ocean going mine sweepers that were polyester and WR over dry oak and it all fell off. In truth fiberglass doesn't stick all that well to any wood in the first place. In time the natural movement of the wood fibers from temperature and humidity changes will "unstick" the glass. This might take 30 years but it will happen. I always try to think as the wood as a form and use enough fiberglass to be the structure. If I do that I don't care if the wood rots or the glass gets unstuck. Except in the transom where using enough glass to provide the stiffness needed would be extremely heavy and cost prohibitive. When I do stringers and bulkheads I use an extra layer of biaxial or WR over the wood and then the wood becomes unimportant in the structure. Now-a-days builders eliminating wood are using PVC or polyurethane foams just to support the glass until it hardens. The really high tech guys are building hollow stringers on a mold and glassing or gluing them to the hull. Yes there are some glues that are stronger than the interlaminar sheer strength of the fiberglass composite. Just ask the airplane builders. Google "itw plexus" adhesives.

 

[Ned L]

" a couple of weeks" isn't going to do it. It will take a couple of months in a warm dry environment. Remember that the glue holding the layers together is waterproof, so the inner layers (of wet wood) are all sealed with waterproof glue holding the moisture in. Pressure treated can be used properly, but why go to the expense, time and effort when a long lasting proper job can be done with regular BCX.

 

[jigngrub]

Most of the advice above is good advice, except for the waiting for a few days or a couple of weeks for the wood to dry... it takes a lot longer than that for PT wood to dry. there's a reason PT wood and paint manufacturers recommend not painting PT wood for at least 6 months after installation.

Another reason for not using PT plywood that no one has touched on yet is that it is a cheap grade of plywood, a CDX sheathing grade with lots of large core voids. You'll find this out if and when you have to cut your plywood.

You can buy kiln dried marine grade CCA pressure treated plywood that won't rot even if it gets wet and it has a lifetime warranty, but you'll have to look around to buy it locally. This is what it looks like and a product description:
http://www.pontoonstuff.com/collect...et-flooring/products/3-4-marine-grade-plywood

 

[dillonheath08]

Okay, so I called the people at Lowe's and after sweet talking one of the clerks that works in the Returns Department they have agreed to take the 1/2" ply back upon inspection of the sheets. Completely understandable. I know the wood is pretty dry but I have always found that it is better to be safe than sorry! So i am gonna return the PT and get untreated. This way I know the fiberglass will adhere to it. I plan to soak the sheets in Poly Resin a couple days prior to laying the glass over them. As far as tabbing goes I am going to use two layers of overlapping 1708 Biaxial Mat. That stuff, from what I know of it, is crazy strong. Once it has finished hardening I am going to add two layers of 1.5 oz CSM. The original deck had fiberglass on the top and not on the bottom. I will definitely be covering both sides of the deck as added protection. Seems pointless not to.

As far as my transom goes I am going to cut out two pieces of 3/4" ply (untreated) and soak both sides once again in the Poly Resin to waterproof the wood and promote adhesion. Once it has soaked that up i am going to use LOCTITE adhesive to glue the two pieces together and make one piece. I believe that adhesive takes anywhere from 24 - 48 hours to completely dry. After that time period I am going to wrap it in two layers of 1.5 oz CSM. Once that has hardened I will glue it the back of the boat using the same adhesive. To tab it in and cover it I am going to use 2 layers of 1708 Biaxial Mat. These 4 Layers should give me close to 40 ounces of fiberlgass over the entire transom.

Clamping it down to bond the two pieces of 3/4" ply and then clamping it keep in place in the boat are the two problems facing me as far as the transom goes. Any ideas?

 

[JASinIL2006]

Lost of restoration threads that show variations on what you're planning, but the place to start when planning your transom (IMHO) is Woodonglass' primer on transoms, stringers and decks: http://forums.iboats.com/forum/boat...1961-lonestar-flamingo-splashed-w-pics/page42.

You can't go wrong following his method. I was going to refer you to my restoration thread so you could see on method of clamping the transom in place in the boat, but it appears that all the pictures were lost when the forums switched to the new software. :grumpy:

I'll see if I have a good pic or two and post it when I'm home later.

 

[dillonheath08]

I am thinking about going ahead and drilling out the motor mount holes and using 4 pieces of all-thread and 4 2x4s to clamp it

 

[kcassells]

Okay, so I called the people at Lowe's and after sweet talking one of the clerks that works in the Returns Department they have agreed to take the 1/2" ply back upon inspection of the sheets. Completely understandable. I know the wood is pretty dry but I have always found that it is better to be safe than sorry! So i am gonna return the PT and get untreated. This way I know the fiberglass will adhere to it. I plan to soak the sheets in Poly Resin a couple days prior to laying the glass over them. As far as tabbing goes I am going to use two layers of overlapping 1708 Biaxial Mat. That stuff, from what I know of it, is crazy strong. Once it has finished hardening I am going to add two layers of 1.5 oz CSM. The original deck had fiberglass on the top and not on the bottom. I will definitely be covering both sides of the deck as added protection. Seems pointless not to.
As far as my transom goes I am going to cut out two pieces of 3/4" ply (untreated) and soak both sides once again in the Poly Resin to waterproof the wood and promote adhesion. Once it has soaked that up i am going to use LOCTITE adhesive to glue the two pieces together and make one piece. I believe that adhesive takes anywhere from 24 - 48 hours to completely dry. After that time period I am going to wrap it in two layers of 1.5 oz CSM. Once that has hardened I will glue it the back of the boat using the same adhesive. To tab it in and cover it I am going to use 2 layers of 1708 Biaxial Mat. These 4 Layers should give me close to 40 ounces of fiberlgass over the entire transom.
Clamping it down to bond the two pieces of 3/4" ply and then clamping it keep in place in the boat are the two problems facing me as far as the transom goes. Any ideas?

Good move, try to get BC exterior, forget the loctite and just make your own peanut butter spread. Any screws you use have 5200 ready to fill and dip or use the peanut butter aka PB to do the same thinh while clamping.

 

[Rickmerrill]

One trick I learned here is that when you are waterproofing your wood you are better off putting the csm on, once you wet out the wood, sooner rather than later. If you saturate the wood and wait two days the poly layer without reinforcement is going to be more brittle so the csm you put on it is going to be more of a mechanical bond than a chemical bond the longer you wait. Once the poly starts to tack up it's not going to saturate into the wood any more. It's better to apply the CSM once the resin on the wood starts to tack up so you get the chemical bond. I don't know about the Loctite but most here seem to be putting a layer of CSM on the back side of the transom wood and using PB to glue it in. The front side then gets tabbed with 1708 and then two layers of 1708 to the hull. If you need more thickness you can add it to the inside surface of the transom. I'm new at this so still learning but that is my understanding.

 

[jigngrub]

One trick I learned here is that when you are waterproofing your wood you are better off putting the csm on, once you wet out the wood, sooner rather than later. If you saturate the wood and wait two days the poly layer without reinforcement is going to be more brittle so the csm you put on it is going to be more of a mechanical bond than a chemical bond the longer you wait. Once the poly starts to tack up it's not going to saturate into the wood any more. It's better to apply the CSM once the resin on the wood starts to tack up so you get the chemical bond.

This is absolutely correct, dried polyester resin without cloth or matt is about as useful as dried Camel snot.

 

[Chris1956]

How do you intend to soak the plywood in poly resin? Poly resin will harden in an hour or so, unless it is uncatalyzed.

 

[Woodonglass]

I really think you would benefit a lot from studying the drawings and details in this link...Fabricating Decks, Stringers, and Transoms

 

[dillonheath08]

Okay, just got back from swapping the plywood at Lowe's. Wound up finding some really nice sheets of BC Sanded 1/2". Even saved 3 dollars. As far as soaking the sheets in resin I'm just soaking it in resin until the resin becomes tacky and then laying down my CSM. It'll help promote adhesion for the first layer of CSM. Oh and I just discovered a hole in my hull... Happy Birthday to me?