Cloth instead of mat w/roving?

[erikgreen]

Hi again all -

I'm in the process of tabbing in my new transom on my 22 ft Sea Ray, and I'm planning on using some 18oz woven roving to laminate the edges to the hull sides and bottom. I've read that I should use a mat,roving,mat,roving layup with 1/2 oz. mat since the roving needs "help" to adhere properly. I don't actually have any mat, but I do have tons of 8 oz. cloth. Is this an acceptable substitute? Can I use the same layup order, IE cloth, roving, cloth, roving over the fillets?

Thanks,
Erik

 

[Robj]

Re: Cloth instead of mat w/roving?

No. I wouldn't. Go buy some matt, it isn't that expensive.

Rob.

 

[ondarvr]

Re: Cloth instead of mat w/roving?

Like EG said

Cloth isn't what you need and if you don't use mat the repair will be junk. You can even get mat at Wal-Mart, so it shoudn't be hard to find some.

After saying that, I am assuming you are using polyester resin.

 

[erikgreen]

Re: Cloth instead of mat w/roving?

Nope, Epoxy.

I bought a 3' x 3' section of mat at Home Depot, it went on ok except for a tendency for strands to come out when I pulled the brush across it. Hard to saturate the dry spots, but I eventually got it done.

Next up is the roving, then another $7 piece of mat. So far so good.

Erik

 

[ondarvr]

Re: Cloth instead of mat w/roving?

You can put all the glass down at one time, it's much easier. If you put on the mat and let it harden, you can't just put the roving down on top of it, you need to use another mat under it.

Wet out the surface with resin before you put the glass in place, it's easier to push the glass down into the resin than force the resin down into the glass. You will still need to apply some resin to the top of the glass but not as much, then put the next layer of glass on, do this until all three or four layers are in place, then work the air out with a roller.

 

[Robj]

Re: Cloth instead of mat w/roving?

If you do it one layer at a time, you have to grind in between layers, to get a mechanical bond. Much more work, plus I hate grinding. Do all you lay-ups at one time and you will also get a chemical bond between layers, which is better than a mechanical bond. Also use a roller to remove the air, I personally like the plastic ones. I have tried the rollers with bristles and did not like them.

Good luck

Rob.

 

[erikgreen]

Re: Cloth instead of mat w/roving?

Hmmm... I suppose I should have guessed that I'd need to use the mat and the roving at the same time. Well, I guess it gets another layer of mat then, along with the roving tonight.

I do use an epoxy that's very slow, 36 hour minimum cure time, and I keep the work covered, so I would think I can avoid needing to sand if I get back to it in 24 hours or less, but looks like I need to re-do the mat anyway.

I had already been rolling on the epoxy first, then pressing the mat into it, but in this case the mat was too thick? to get full saturation, so I slopped on some epoxy after with a chip brush, and pressed it in with gloved hands.

So in the case of a four layer layup, you guys put on a thick layer of epoxy, then press in all four layers of cloth at once?

Erik

 

[ondarvr]

Re: Cloth instead of mat w/roving?

Using epoxy is different, you don't need to use mat, infact most types of mat are not designed to be used with epoxy

 

[erikgreen]

Re: Cloth instead of mat w/roving?

I made sure the mat I got was ok with epoxy.. but I don't need to use mat at all with epoxy? Why does polyester need it? I thought it was more due to the shape of the weave, not adhesive considerations.

Erik

 

[Robj]

Re: Cloth instead of mat w/roving?

Oops, sorry for some reason I thought that you were using polyester. I guess the matt made me think that. What I previously posted was for polyester. Ondarvr knows much more about epoxy than I do. I still think that you should get a roller to roll out the bubbles. It works great for poly and probably do the same for epoxy. I think that you will also end up using less resin.

Good luck

Rob.

 

[Jeel]

Re: Cloth instead of mat w/roving?

Actually, the Gorgean Brothers (sp?) from West Epoxies did a study a few years back testing suposedly "polyester" mats and epoxy. Previous thought and "internet theories" was that the binders used in the mats impeded the catalyst reaction. What they found was that there was no difference using poly or epoxy with any type of mat (for strength or curing). The binders do not affect the epoxy.

Having said that, I normally just laminate with a biaxial cloth or tape (1708 or 1808). Epoxy will stick to anything (usanded surfaces, dirty surfaces, clean surfaces, doesn't matter), which is the beauty of using it.

Secondly, Mat doesn't help the binding characteristics of poly. It creates a barier for the roving. Roving alone has so many pinholes after curing it traps water. That is why you use mat/roving/mat. Roving is where the strength is and the mat is just water proofing it. And since poly is not as water resistant as epoxy you can see you need alot of layers.

If you have any other questions give me a shout.

 

[erikgreen]

Re: Cloth instead of mat w/roving?

Well, thanks to all the good advice here, I've just finished laying out two layers of 18 oz. woven roving with epoxy covering the seam between the hull and my 7 foot by 3 1/2 foot transom on three sides, the second layer being wider than the first for a good grip on the surrounding hull.

The technique I used was to use a sponge roller to wet the area the roving would cover, then laid the roving in place over it and wet it out with the roller and with a chip brush where needed.

Once I had it all wet out I used the roller to flatten it against the transom fully and into corners, and to roll out bubbles and roll out excess resin.

I don't know how much I should have used, but I went through about 1/2 gallon of epoxy putting these layers of roving on.

Next I will be using cloth with an opaque resin with UV protectant to cover the whole transom and the roving, and that should be it for the transom repair. Then on to the motor mounts and stringers

I'll take some pics and post them before I cover the transom so you can all laugh at my workmanship

Erik

 

[ondarvr]

Re: Cloth instead of mat w/roving?

Sorry Jeel

If you've ever done much work with polyester you would know that mat doe's help polyester to bond well, no mat = poor bond. That seal the roving idea has some truth to it, but is not the main reason for using mat, it's to hold the layup together. The polyester is not water proof idea is frequently thrown around, while nothing is "waterproof" and epoxy does have better resistance, polyesters and VEs can do an excellent job under water. To get good results under water, the correct products need to be used though and that's where the problem is, some boat builders use the cheapest resin they can buy, even in the hull, so some boats end up with problems. In recent years more builders started using better resins, but on smaller trailer type boats, they may still use lesser products.

One of the main reasons why people think polyesters don't bond well to things is they do poor prep work, with very little sanding and then use just cloth or roving and pour resin over it. These repairs never last very long and the failure is blamed on the resin.

While normal mat can be used with epoxy, it's not formulated to be used that way. The binder is designed to disolve in polyester resin and become limp and pliable allowing it to conform to whatever shape is needed. This may not happen when using epoxy and you end up with mat that stays stiff and difficult to work with.

Epoxy is a very good glue, so it doen't need to be used with mat, it will bond very well to far more surfaces than polyester will and in some situations it's the only thing to use. But for the vast majority of repairs polyester is all that's needed.

 

[ondarvr]

Re: Cloth instead of mat w/roving?

I almost forgot. Never Never apply epoxy, or anything else to a non prepped, unsanded, not clean surface, you're just asking for failure if you do.