How many layers of which type of fiberglass

[rberrey]

I looked for some spec,s on the Baltic birch ply and found some out of Latvia , I am assuming it is the same Phenolic resin used in the form ply I have used . It meets BS 1203 standards , it can get wet and dry , wet and dry . It is not meeting the standards for voids as in marine grade ply , but I can tell you in the few thousand cuts I have made on 3/4 Russian Baltic birch form ply I have never seen a void . I would think Finn Form would be as good or better than Russian form ply , I have never used but a few sheets and they were not cut . I would have no problem using a birch marine grade plywood .

 

[wet feet]

You are quite correct,the glue used conforms to the requirements that describe marine plywood.Unfortunately birch doesn't and for some uses that won't matter.I've used stacks of Finnish birch ply for plug building and there is no other ply that comes close.The Latvian stuff tends not to be as finely sanded on the surface and occasionally has a core void.For applications where getting moist is a possibility I'd rather use a meranti ply with bonding to BS1203 and a WBP stamp.

 

[rberrey]

There is Birch marine grade plywood online for sale , so it have to conform to some kind of marine grade standards and be stamped . My thinking on marine birch or birch form ply on a house boat build is that it may be cheaper because of his location . Years back I could buy a bundle of Russian birch form ply cheaper than HDO here in the States , and the HDO was very much inferior . I have 22 sheets of 3/4 Russian birch ply I have saved over the years for building a concrete retirement house , I am about a month off from drilling tie holes in them .

 

[Dave G 9N]

See post #3. Some CSM's uses a binder that needs styrene (from polyester or vinylester resins) to dissolve properly. It can be had compatible with epoxy as well.

I have found it difficult to find CSM that is compatible with epoxy. It exits, but almost all CSM in my experience was for polyester, not epoxy.
Fiberglass Mat for Composites | Chopped Strand Mat | Fibre Glast https://www.fibreglast.com/category/Fiberglass_Mat

Note: All Fiberglass Mat is made to be used with resin to create hard, composite parts. However, it is NOT compatible with epoxy resin. Mat has a light binder that holds it together. During lay-up, it requires styrene to break down that binder and allow for complete resin saturation. Epoxy does not contain styrene and therefore cannot be effectively used with the mat. Use polyester or vinyl ester resin with these applications.

British plywood grades and wood species availability are similar to but different from those in the US. In the states. For a houseboat used on protected waters using the US grading system, I would consider ACX or ABX sanded SYP or Douglas fir. It will not be as void free, impact resistant or expensive as marine grade. It will hold up much better than OSB in the long run in my opinion.

You can use polyester on wood. It is not generally recommended because adhesion problems are common. The cause appears to be the tendency for the wood to absorb resin enough to cause a resin starved interface between the wood and fiberglass. Some early strippers were built with poly before epoxy was readily available and most had adhesion problems. One builder in Madison used a lacquer to prime the wood and was able to produce good results. The specific brand has been discontinued for decades, so a test panel would be a good idea before settling on any brand. The other approach is to apply an unwaxed layer of polyester and let it begin to set up before applying the glass. My pet hypothesis is that the lacquer might be better than the polyester as a primer because it seems plausible that there is enough oxygen in the wood to inhibit the cure. No proof, no data, just speculation.

Fiberglassing Decks, CLICK BELOW PICTURE, For Full Directions. https://fiberglasssite.com/fiberglassing-decks-click-below-picture-for-full-directions/
Installing Fiberglass Roof Decks https://fiberglasssource.com/blogs/blog-post/installing-fiberglass-roof-decks

 

[fallguy]

The binder in csm is weaker than epoxy, and csm is loose enough where that binder is a big fat nothing in layups and the epoxy takes over.

I've not seen coupon testing on the subject, but I have to believe it'd pull foam.

 

[Tops]

I got mine from Express Composites in Minneapolis last year.
They have a warning on their 'regular' mat not to use with epoxy.
I would call them first to make sure they still have it.
Some places call the epoxy compatible 'powder bound'.

PS An objective test would be worthwhile

 

[fallguy]

I got mine from Express Composites in Minneapolis last year.
They have a warning on their 'regular' mat not to use with epoxy.
I would call them first to make sure they still have it.
Some places call the epoxy compatible 'powder bound'.

PS An objective test would be worthwhile

Interesting.

The person using csm is typically using it so it conforms to odd shapes. Thus the binder that solves in esters.

But I doubt the binder negates the strength of epoxy.

I've used csm and epoxy in small repairs and they are stronger than a polyester layup.

I've been a customer of theirs and I would say their assessment is not fully accurate. What they understand is the use of polyester allows the cam to 'fall apart' and conform and epoxy does not solve the binder. It doesn't mean you cannot; it simply means the csm will not behave the same way with epoxy.

 

[Dave G 9N]

The binder in csm is weaker than epoxy, and csm is loose enough where that binder is a big fat nothing in layups and the epoxy takes over.

I've not seen coupon testing on the subject, but I have to believe it'd pull foam.

Strength is not a factor. The mat is coated with a binder that is soluble in polyester resins. Epoxy and epoxy hardeners do not dissolve the normal binder, so the fibers in the mat remain stuck together. On a flat surface this is not important, but when the fubers need to move independently on a curved surface, the mat will not fall apart as needed.

 

[fallguy]

Strength is not a factor. The mat is coated with a binder that is soluble in polyester resins. Epoxy and epoxy hardeners do not dissolve the normal binder, so the fibers in the mat remain stuck together. On a flat surface this is not important, but when the fubers need to move independently on a curved surface, the mat will not fall apart as needed.

There are times when mat is desirable in epoxy layups if you need the glass to hold its shape a bit when carrying to substrate wet and/or you want thickness for build up. Ironically, the epoxy wetted 1708 tends to hold its shape better. I would not say only on a flat surface, but on surfaces that are not compound.

For the OP, there is little need to use 1708 on a plywood hull. I recommended it on osb for a buildup to prevent ingress.

On a straight plywood layup; if he only wants a protective layer; I'd recommend a single layer of db1700 or two layers of db1200 which is easier to wet and offers a bit more abrasion resistance. Or, he could also use 1708 which would also offer a bit more wear, but is a bit harder to wetout than two layers of 1200. The two layer wet on wet 1200 is easier to do while keeping resin ratio below 1:1.

 

[wet feet]

There is more than one type of binder used on csm,the most common by far is emulsion based and this resists epoxy.The less common and more expensive mat has a powder binder and this will yield to epoxy..
Regarding post #19,I don't know if you noticed that our original enquirer isn't in the USA but in the UK and if he asked his local suppliers for ACX or ABX they would probably ask him what exactly they might be.
Polyester on wood is absolutely fine and bonds very well as long as you take the precaution of using a generous primer coat of resin.Failure to do so can lead to the wood leachng the resin out of the initial plies of glass and a compromised bond and is the sort of thing that gets the resin a questionable reputation.Normally caused by a production crew trying to meet a time target in order to claim a bonus payment.

 

[TeddyDiver]

Forget CSM, use 600gsm Biaxial with epoxy. You end up stronger laminate with much less material used. Read Gougeon Brothers book before starting, it's free online..

 

[wet feet]

I often think this section of the forum should be titled the "use biaxial and epoxy" section.It seems to be the answer to every single boatbuilding question.Yet the volumes used by commercial builders are only a fraction of those used to build most of the world's GRP boats.It is almost axiomatic that infusion will be advocated,whether the poster has ever done it or not.Why?

 

[TeddyDiver]

I often think this section of the forum should be titled the "use biaxial and epoxy" section.It seems to be the answer to every single boatbuilding question.Yet the volumes used by commercial builders are only a fraction of those used to build most of the world's GRP boats.It is almost axiomatic that infusion will be advocated,whether the poster has ever done it or not.Why?

For wood (and ply or OSB) it's easier, faster and better, I've done both CSM/Poly and Biax/epoxy so know the difference. Even if epoxy costs more than Poly you need less of it to and better results. Solid laminate in mold is totally different task and there CSM/Poly can do the job cost effectively.

 

[Rumars]

Let me put on my Sherlock hat:

1. Location:
Stink up the neighborhood and it's not gonna be fun.
2. Wood:
Epoxy simply outperforms poly. It's an actual glue and it requires thinner coats for effective waterproofing.
3. Suppliers:
In the 400-600gsm biax is often more available and cheaper. Only very well stocked shops will offer woven rowing in this weight category, and it's only marginally cheaper then biax.

I think ply/epoxy vs. poly/CSM with hollow or wood stiffeners is a question of price and preference. I would take the polyester and use hollow stiffeners, this application doesn't require a great panel thickness, just a few millimeters.

 

[Dave G 9N]

There is more than one type of binder used on csm,the most common by far is emulsion based and this resists epoxy.The less common and more expensive mat has a powder binder and this will yield to epoxy..
Regarding post #19,I don't know if you noticed that our original enquirer isn't in the USA but in the UK and if he asked his local suppliers for ACX or ABX they would probably ask him what exactly they might be.
Polyester on wood is absolutely fine and bonds very well as long as you take the precaution of using a generous primer coat of resin.Failure to do so can lead to the wood leachng the resin out of the initial plies of glass and a compromised bond and is the sort of thing that gets the resin a questionable reputation.Normally caused by a production crew trying to meet a time target in order to claim a bonus payment.

Does it make a difference whether the generous primer coat that prevents leaching is air inhibited? That is one piece of information that I have had a hard time finding.

Post #19 includes a link to a site that describes the face veneer grades used in the UK for that reason. The OP is in the UK, the boat is a house boat and the panels are flat, and the glass is being used above the waterline. The panels are also thick and the fiberglass is being used for waterproofing and to prevent checking, but apparently not to improve strength or stiffness. I have worked with both cloth and chopped strand mat (CSM), and for covering wood I much prefer working with cloth. Cloth is easier to handle and CSM tends to be messy, at least if you don't have a lot of experience handling it. For large flat panels, the stiffness of CSM might make it easier to handle. The drapability of light woven cloth might not be an advantage here. 600 grams per square meter (GSM) is more than adequate, even excessive in some respects. In the video I posted in #19, they were using 2 oz chopped strand mat, which is only about 50 gsm of CSM. If I were using plain weave cloth 2 oz (50 gsm) is likely to be more than adequate. 6 oz (~140 gsm) plain weave glass cloth is adequate for walking surfaces and is used for strip canoes where the strength of the cloth is important. Using heavier cloth will significantly increase the amount of resin, weight and cost while not improving weather resistance, which appears to be the only reason for the glass. Epoxy has very poor UV resistance, but this will be painted, so that should not be a consideration. Below the waterline is a different situation and heavier layers of cloth are needed there.