Epoxy compatible Mat?

[Mark42]

Anyone know of a supplier or manufacturer of fiberglass mat that is compatible with epoxy resin? So far everything I found is not epoxy compatible.

If there are no epoxy compatible mats available, what do you think is a good substitute to build up thickness and strength quickly? 10oz weave? or heaver?

BTW, if you are unfamiliar with why mat is not compatible with epoxy resin, the reason is that mat fibers are held together with a glue that disolves in polyester or vinylester resin. This glue holds the mat together, and allows the glass fibers to be in direct contact with the resin when resin is applied. If the mat is used with epoxy, the glue does not disolve and the glass fibers do not come in contact with the epoxy resin.

 

[ondarvr]

Re: Epoxy compatible Mat?

I don't have a link or source for it, but most of the time normal mat will work. The softer and fuzzier the mat, the less binder it has, which means it should work better. It's not a great answer, but it might get you through the job.

As for heavy cloth, it will work, but is costly, roving is far less per lb and 24oz is less than 18oz, so you can use it to build thickness if needed.

 

[KnottyBuoyz]

Re: Epoxy compatible Mat?

Hey Mark

Try boatbuildercentral.com all their products are epoxy compatible. I don't know if you'll find just mat but they have a good range of biaxial fabrics with mat backings that are at least twice as strong as regular knitted fabrics.

What is it you're trying to do? Woven rovings and mats will add thickness (and weight) but not as much strength. Using biaxial fabrics you can add much more strength without the added thickenss and weight of conventional fabrics.

 

[oops!]

Re: Epoxy compatible Mat?

dont sweat it mark......

epoxy is so tenatious....an old sock will work.

 

[ondarvr]

Re: Epoxy compatible Mat?

To go along with NB's response, how do plan on using the mat? There are times when using epoxy that mat can make things go a little easier, but normally it's not used (that's why you're having a difficult time locating it).
Epoxy doesn't need mat to help with the bonding and since mat has the least strength when compared to other types of glass, it doesn't add as much to the strength of the laminate for the weight, so people go with cloth, roving, biax or a combination of these, but in a thinner layer. You also end up using more epoxy, the glass to resin ratio with mat is about 35/65, with woven or knitted products it can go up to 50/50, more glass results in higher strength for the same or less weight.

 

[Mark42]

Re: Epoxy compatible Mat?

I'm an old polyester resin guy. Most of my fiberglass work has been on cars and kit cars, where mat is used to build up thickness so parts match.

This glass will be used on my hard top project (take link in my signature below). I'm almost done with the foam shape, and it needs to be covered in epoxy/glass inside and out. The foam is being used as a form or mold.

I have been doing a lot of reading on fiberglass fabrication with epoxy, and I feel a little uncomforable going with light layers that seems to be recomended. From what I read, I could probably get away with two layers of 8 or 10 oz cloth inside and out. Then apply the epoxy fairing material, sand and paint. Does this sound right to you?

I also know from experience that 8 or 10oz cloth is not going to conform well to complex shapes, like the inside of a corner. Mat will conform. Just jam it in, poke around with plastic spatula for a few minutes and it stays there.

So I thought that mat might be easier to work with. I don't need high strength like Oops needs in his hull extension. This is just a top and won't take direct pounding on the water. It will take wind gusts, and maybe even a hard spray, and I'm sure sooner or later someone will try climbing on the roof, but thats about it. So I though two layers of mat, finished with a nice 6 oz cloth then fairing, sand and paint would work.

And suggestions from members who used epoxy to fabricate is greatly appreciated!!!

 

[ondarvr]

Re: Epoxy compatible Mat?

Two layers of heavier cloth should work and will leave you with a fairly good surface to work with. If you want extra protection on the top for people to walk on, use an extra layer. With a good radius in the corners I don't think you'll have much of a problem getting it to lay down.

After looking at the pic I did rememeber something we discussed when you first thought about using this foam, it was that it's not as strong as a typical foam used in a marine application, so the laminate will need to be a little stronger to make up for it. To make sure it holds up, it may be safer to add that extra layer to the entire structure.

 

[BillP]

Re: Epoxy compatible Mat?

I use epoxy mat from USComposites in West Palm, Fl and had A1 service from them.

Assuming you can even find "fluffy" mat with less binder made for polyester DON'T use it. Bury the thought. It gives a dry, weak layup. I tried it on several samples to see what happened...it's difficult to even partially saturate and harder to work bends because the strands are dry. The dry strands are easy to see...they look just like cloth without resin. It's a weak and inferior laminate.

Use epoxy mat and don't look back. It's softer, easier to work and gives 100% saturation. The alternative is to use biaxial because the mat with it is sewed and no binder used.

A couple layers of 10oz on each side is going to be very flexible without mat or 18-24oz woven. It will take a lot of glass thickness to give equal strength to a couple of wood stringers though. For stiffness use 1-1/2oz or 3oz mat. Alternate if you want with 18 or 24 oz woven if major strength is needed. Do a light cloth for final layer and fill coat it if you want a smooth painted type finish. If you are bent on not using mat be ready to do major thick laminations of cloth to get the same stiffness as one using mat too.

bp

 

[Mark42]

Re: Epoxy compatible Mat?

....
Use epoxy mat and don't look back. It's softer, easier to work and gives 100% saturation. The alternative is to use biaxial because the mat with it is sewed and no binder used.

A couple layers of 10oz on each side is going to be very flexible without mat or 18-24oz woven. It will take a lot of glass thickness to give equal strength to a couple of wood stringers though. For stiffness use 1-1/2oz or 3oz mat. Alternate if you want with 18 or 24 oz woven if major strength is needed. Do a light cloth for final layer and fill coat it if you want a smooth painted type finish. If you are bent on not using mat be ready to do major thick laminations of cloth to get the same stiffness as one using mat too.

bp

Hi Bill!

What is it about mat that gives it strength when mat is not considered a high strength cloth?

So if I understand you correctly, a layer of 6oz, a layer of mat, then a layer of 6oz would be stronger than two layers of 10oz?

I do want a smooth paintable finish coat with as little fairing and filling as possable. Should I finish with a 1.5 or 3 oz final layer?

I don't want to experiment with the layup, I just want to do what is proven to work well, especially for my application.

Thanks,

Mark.

 

[ondarvr]

Re: Epoxy compatible Mat?

It wasn't until he posted the pic that I knew how he wanted to use it.

I didn't say I recommended normal mat (I said "it's not a great answer"), but some commercial accounts do use it with epoxy, the difficulties of wetting it out are just something they work around and mat with less binder does work much better. You can also easily get biax (1708, 3208) with epoxy compatible mat attached, so that's an easy solution.

Mat does add bulk and stiffness, partially from the random direction of the strand, but to greater extent from the higher resin content, higher resin content means less strength for the weight and thickness of a laminate. I supplied information on laminate strength a while back, it compared three separate 1/4" laminates, one made with mat only, one with mat and roving and one with biax, there's a huge difference in strength between these laminates.

Two layers of 10oz cloth won't be very flexible with that thick of a foam core, it will actually be very stiff, but again stiffness is not a sign of strength. For durability with this type of foam, there should be more glass in the skins on each side, with even more on surfaces that may be walked on.

 

[ondarvr]

Re: Epoxy compatible Mat?

Woven and knitted fabrics tend to give a smoother more even laminate thickness than mat, which requires much less fairing.

 

[BillP]

Re: Epoxy compatible Mat?

Hi Bill!

What is it about mat that gives it strength when mat is not considered a high strength cloth?

So if I understand you correctly, a layer of 6oz, a layer of mat, then a layer of 6oz would be stronger than two layers of 10oz?

I do want a smooth paintable finish coat with as little fairing and filling as possable. Should I finish with a 1.5 or 3 oz final layer?

I don't want to experiment with the layup, I just want to do what is proven to work well, especially for my application.

Thanks,

Mark.

Mat isn't "weak", it's just resin rich and if used by itself gives a stiff but heavier layup...about 2X the resin is used compared to cloth. Random fibers are what makes it stiff. The same weight (fabric weight in oz) layup done only with woven cloth will give a lighter but more (WAY more not even close) flex. If you try to duplicate mats stiffness with a laminate made only of cloth the laminate will be thicker and heavier than one using mat...more tensile strength too but tensile strength isn't the only reason for glassing.

Do you want to overkill on tensile strength to get the desired stiffness? Every boat factory in the country uses alternating layers of mat instead of more layers of cloth or extra built up structure. Not using mat just because you don't need the adhesion with epoxy is basically ignoring the engineering properties of mat. That dog don't point in my woods and is missing the whole picture.

Two layers of 10oz cloth (20oz total) held up by itself will will flex way more than one layer of 1.5 oz mat and one layer of 6oz cloth (19.5 oz total)...Tensile strength on the 10oz cloth layup is stronger but I don't know the actual calculated number. BUT, flex on foam can make for pressure point delaminations. Stiff layups prevent depressions causing delamination. Highest tensile strength given with cloth isn't the final answer on all applications, especially foam.

I see negatives posted on mat often but it's usually over hyped and the engineering aspect totally ignored. Look around at the pros. Mat is univerally used throughout the boating industry because it fills a structural void that cloth doesn't. If you are using foam it needs a stiff laminate, not a flexible one. Do yourself a favor. Don't take anyone's words for what is strong, weak, resin rich or whatever. Instead, go do your own samples and get a real up front and personal idea of what is happing here. You will be pleasantly surprised at how strong and stiff mat is and how it compares to glassed panels of cloth. Just do it and go forward in the glassing world without worry.

Quiz...what type glass material was seen bound (during the foam board construction) on a structural foam used in the boat building industry. This foam sheet comes with a fiberglass covering which is ready for resin and more layers of glass. I saw this at a high end flats boat factory in Florida. Cloth or mat?

Yep, I know I repeated myself.

bp

 

[ondarvr]

Re: Epoxy compatible Mat?

The same amount (weight) of glass in knitted or woven forms yields a thinner laminate (less resin) resulting in more flex and less weight than mat. When you build to the same thickness, woven and knitted products are much stronger. Mat also has the lowest cost of any of the types of glass except for chop, which is basically the same thing. The low cost and ease of application make it very popular in most types of production, plus it does build bulk and stiffness, so there are benefits. The vast majority of marine accounts use no cloth, it has the lowest strength for $$ spent, they use roving and nitted (Biax) products.

Mat's weakness is relative to other forms of glass, not that it has no strength on it's own, many products are made from nothing but CSM and hold up fine. These are normally low tech, low cost, low stress items where weight is not the main concern, cost is. When increased strength and less weight are the goals, the amount of mat is reduced to the bare minimum and in epoxy laminates it's used even less, or not at all.

Because of the type of foam you're using more glass will be needed, you can use mat or other types of glass to get there, but the laminate does need to be thicker. Going thicker with mat tends to result in an uneven surface, so you'll do more fairing, the more mat used, the more fairing needed.

When Billp mention flex, I thought he meant the finished panel would be flexible, not just the skin, the panel will be stiff, but the skin will be more flexible if only 2 layer's of 10oz cloth are used. Mat will increase the thickness and stiffness, but add less strength than other types of glass.

Many cores can now be purchased with glass skins already bonded to them. For cores designed for polyesters, mat is used to improve the bond.

 

[Mark42]

Re: Epoxy compatible Mat?

Ondarvr and Bill, I really appreciate all the detailed info you posted. But, darn! you are making my head spin.

What I take away from your respective posts is that mat is not bad, it imparts regidity to reduce flex, but does not add tensil strength like woven fabrics.

I was thinking back on when I used to use mat on kit cars, and yes, it does take a lot of sanding and fairing to get a smooth surface.

So should a knitted biax fabric like 1708 be used instead of mat for rigidity and stiffness? It should reduce the amount of finish fairing compared to using plain old mat.

Or,

Just use 6 oz cloth, 3 oz mat, then finish with 6 oz cloth?

To reduce delamination due to flex or impacts, I plan to make a puncture tool. Think of a 4x4x1" block of plywood with sharpened nails protruding about 1/2" every inch or so. This block would be pressed into the foam to make indentations that the epoxy resin would be forced into with the first coat. This will hopefully give the epoxy some "roots" into the foam to help it hold tight.

Other than the roof, there will not be too many large flat areas that could delaminate easy. Both the front and sides will have large window openings which means that most of those areas are only going to be about 8" sections. With the windshield posts and window perimeters being "wrap around" areas where the glass wraps from inside to outside, I hope the glass will be strong whether or not there is foam inside those areas. Its really the roof and rear most side panels that could be subject to delamination due to twisting/flexing or impacts.

Ah, decisions, decisions, decisions....

 

[ondarvr]

Re: Epoxy compatible Mat?

I've seen punch type tools used to help improve the bond on different types of cores, I don't know how much it improves it, just never saw any test data.

A fine cloth should be used for the surface no matter what the rest of the laminate is, it makes filling the weave much easier.

1708 offers the best physical properties, plus you get a little mat mixed in.

I think test panels would be a good idea, then you can be confident it will hold up to what you think it may encounter in use (abuse).

 

[BillP]

Re: Epoxy compatible Mat?

Mark,

There are many ways to do what you want and all will give excellent results...so don't sweat it. A little overkill isn't going to make or break this project with too much weight, cost or labor. You aren't making airplanes or space shuttles.

I call those tools woodpeckers and use them (every time) when glassing large panels of plywood. I have one made by driving nails though a piece of wood. Overkill maybe but it makes me feel better and a whole ply transom skin can be done in 2-3 minutes.

Doing light cloth over mat makes for very tedious glassing and I wouldn't do it unless you want to invest more effort for glassing and leveling. If you just need ding protection a couple layers of 10oz cloth will work...then a sanding fill coat.

For additional stiffness and structural integrity (which is my preference on a basic foam structure)...Biaxial with sewn in mat is probably the easiest way. Then a sanding fill coat on the woven (fill the weave until you can sand the surface without hitting the cloth fibers) and sand down to get it level...then a final resin coat to fill the sanding scratchs...then prep (light sand or use skip sand) to paint.

Be aware that fill coats (aka hot coats) are way easier when using polyester because you can kick them off fast enough to prevent run off. Most of the fill coat is sanded off and the extra catalyst won't come back and haunt you later. It's been done in the surfboard industry since the 1950s and still done today. I've done "hot" fill coating with epoxy (on my own personal projects) and it seems to work the same but not going to tell you its ok. I take calculated risks only for myself.

Also remember that foam typically sucks in resin. Some foams do it fast and others slowly. It can pull resin from the cloth and make tiny pinhole bubbles. Trained eyes see them and untrained won't. The results are a dry and weaker laminate. Best way to help this is a coat of resin on the foam and let it tack before starting to glass. Epoxy is harder to deal with in this regard because you can't speed up curing (or hot coat) like can be done with polyester. So when doing epoxy for this, apply it just before it kicks but early enough for it to penetrate...or thicken the epoxy first.

Bill P.

 

[fishingdan]

Re: Epoxy compatible Mat?

Mark, I fully appreciate the desire to figure this out. However, I too am the type of person that only likes to do things once. I don't like guessing. Here is a simple suggestion. Talk to an engineer familiar with epoxy/glass lamination. If you buy the supplies from them, the guys at www.boatbuildercentral.com will work with you to define a lamination schedule that will meet your needs. The prices are the same as others and their knowledge is outstanding. They design boats based on epoxy based composite laminations that can be built by backyard boat builders. They know their stuff and you will get very specific answers. They only work with epoxy, but they also have exenstive experience with professional poly boat building processes. In 10 minutes they will tell you what you need to know.

I'm not saying that the board participants are not qualified, but sometimes the dialog gets confusing and contradictory as more people jump into it.

Dan

 

[BillP]

Re: Epoxy compatible Mat?

Get as much input as you can. Be sure to tell them what type of foam you are using...low density, non structual, for "form or mold purposes only". This isn't typical and shouldn't be a "canned" answer based on high density foam construction.

bp

 

[ondarvr]

Re: Epoxy compatible Mat?

I agree.

 

[Mark42]

Re: Epoxy compatible Mat?

Spoke to some experts and I decided to use a 1708 biaxial fabric with mat backing. Thats 17oz of biax fabric and 8oz of mat per yard. I was told a single layer of this product is more than enough for my application. Good thing too because it's so thick it sucks up resin fast.

So its off to the order website.