# How many layers of material will it take?

Discussion in 'Fiberglass and Composite Boat Building' started by Bigoledude, Aug 4, 2010.

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### BigoledudeNew Member

If we must build our pontoons for our houseboat, we will probably choose to use fiberglass. My intension is to have the pontoons designed with the basic shape of a jon-boat with a top, 30 to 40 feet long.

They would have a bulkhead every 6-feet. The top and bottom would be 3/8-inch to 1/2-inch thick. The sides would be 1/4-inch thick.

An online vendor told me to use two materials. He said that 1 1/2oz mat and a combo product of 1 1/2oz mat and 24oz woven roving would make a solid pontoon.

How thick would two layers of the two products come to?

How many layers of material would it take to achieve 1/4-inch thickness and, how many for 3/8-inch?

Is there a better choice of materials to use? How many layers would it take to produce my desired thickneses?

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### HermanSenior Member

I am not good at imperial, but 1 1/2 oz mat equals 450 grams (correct me if I am wrong) which will give approx 1mm when hand laminated.

24 oz woven roving is 600 grams/m2?? Then approx 0,8mm.

1/4 inch is 6,35mm, 3/8 inch is 9.5mm, so you can do the math...

Is there a better choice? Probably not, or the combo material could be skipped if it is expensive. CSM and Woven roving are (still) cheap.

3. ### tunnelsPrevious Member

24oz roving is close to 820grams in real measurements
Im a bit like you , find it hard to think in imperial any more .
Its easyer to find a roving with a csm P matt already stitched to the back of it and then you can lay the material much quicker and better . 2x 450csm P matt to start and the the rest rovmatt (as we call it here ) with the csm facing up not down and carry o the same till its finished all the required layers !!

Anyone know why i always suggest P matt for the csm layer and not E matt ???

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### tinhornSenior Member

Nope. But I want to point out that if you're facing roving to roving, you should slip some mat in between.

5. ### tunnelsPrevious Member

The rovematt we have has a 225 gram of csm on one side only , stitched on !!!!so you always had csm between layers , wets out nicely and saves time ! .

Ok differant between p matt and e matt is the binder used to hold it all together . E matt has a emussion type binder the breaks down when the resin soaks the matt , trouble being that if the resin goes off and gells to quickly then the dinder may not have had time to dissolve 100% so the glass is not wet out properly . This can be and is bad news as the first layer of glass behind the gelcoat even if you are using Vinylester resin as a barrier and is still more likely to get osmosis !!!
P matt has a sprinkling of powdered resin as its made and then put through a oven that melts the powder and so binds the glass together . It does not have to dissolve in the resin and there for if you have a quick brew then it is far less likely to get Osmosis .
P matt also wets out much quicker and better than e matt and in some situations of multi layers of csm it gives a slightly strong lay up !
In industrial glassing we always used P matt and glass tissue ,also continuous strand matt as well , terrible stuff to use but was there for a purpose when making high pressure acid pipes and tanks etc .

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### HermanSenior Member

just to add: p= powder bound, e = emulsion bound.

Some factories like emulsion bound, as when working the dry material (cutting, tearing) there is far less material (glass fibers, binders) to be ejected into the air.

Water resistance of powder bound is higher, indeed.

7. ### tunnelsPrevious Member

A friend used to have a factory and made csm and woven matt, plus all kinds of unimatts incombination with other glasses , i used to use all the differant products he made , he'd even make special runs as long as he was given a couple of days warning . The emolssion used was almost like PVA glue watered down so it would go through a spray gun . Its never to late in life to learn new things !!

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### SamSamSenior Member

Maybe this will help....( From Ken Hankisons book " Fiberglass Boatbuilding For Amateurs" at Glen-L Marine)

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### Wynand NRetired Steelboatbuilder

Still regret the day I gave my copy of this excellent book away to an "old" GRP boat builder....

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### SamSamSenior Member

He dropped out of the boat thing for a number of years and now is back. With a new wife. The Dog. (I mean HIM, not her. Certainly not her.)

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### GGoffshore artie

Personally i would go with 2 layers of #1708 and bag it because bagging will give you the advantage of having two layers of glass being almost as thick as one and beside's woven roving is so old school as far as fabric or material goes .

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