# Glassing Floor Question



## cwalden (Jun 24, 2011)

I guess that I am starting to overthink this and am now second guessing myself. 

I am wanting to install a floor in a boat that previously did not previously have one. Of course, I am trying to keep it as light and low as possible. The outside edges of the floor will be glassed directly to the floor, filleted in with cabosil, and tabbed to the gunwales. The centerline of the floor will only be about 1.5-2 inches off of the hull. This will have a pair of central "stringers" spaced 12" apart to support the floor. Under the floor will be poured with 2 or 4lb foam for additional support. Pics of the boat can be seen in this thread: http://www.microskiff.com/threads/new-life-for-an-old-skiff.40640/

Now comes the questions:

A) Would you use 1/2 or 3/4 ply for the floor? The floor will be 60" wide and will be installed in 48" sections that will be lap jointed together and glassed. Both sides of the floor panels will be glassed. At every lap joint there will be a bulkhead/rib under the floor as well. But I want no "bounce". Not that I expect any with a foam supported floor.

B) What would you use to glass the floor? I was originally going to use one layer of 1-1/2oz mat on bottom and two layers of same on top. I know that mat is supposedly not compatible with epoxy, but I have been using them together on lesser projects for years. I have never had an issue and went 10 years without knowing that they weren't compatible. haha
I've considered using 1708, but am scared of the weight that it will add. Especially 2 or 3 layers of it. Even more so if I use 3/4 ply...


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## yobata (Jul 14, 2015)

If using epoxy, you do not need chopped mat. I used 3/8" marine fir plywood with a layer of 6oz cloth on the bottom and top. 

1708 is 17oz biax cloth with 8oz chopped mat on the other side - I believe the mat is needed to catylize the poly resin, whereas epoxy does not need this chemical reaction and therefore mat is not required.

1.5oz cloth vs 17oz cloth (with the 8oz mat if 1708) is a huge jump. I have successfully used 12oz biax for areas with lots of abrasion (like a floor). I would recommend the 12oz biax with epoxy. 

For the floatation foam use 2# if you plan on stringers/ribs. 4# foam is considered structural and often the ribs are ommitted when using "structural foam".

You'd be surprised how well the 3/8" will do with glass on both sides and foam under. I think 3/4" is overkill... 

All of the decks on my Johnsen build are 3/8" - front deck spans 6' with a couple of supports, and I used 12oz biax on the bottom and 7.5oz on top. My fat ass is quite comfortable with no noticible "bounce"


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## cwalden (Jun 24, 2011)

I already have several sheets of 3/4 and 1/2 left over from another project.

As for the mat and poly question. No mat is needed to catalyze poly. It is catayzed with MEK (methyl ethyl keytone). Most mat has a binder glue to hold it together that is disolved by poly resin, but is not dissolved by epoxy. Thus, they say that mat will not properly soak in epoxy resin and will have air pockets due to the binder holding the mat. But, I have used mat with epoxy many times over the years and never had a problem wetting it out. So I dont know. The more I read on the internet, the more I second guess whether I should risk it.

As for my 1708 comments. I have never used it before, so I dont have a feel for what it looks like in my hand. But it does not have the binder normally used in mat. the mat layer is stiched to the cloth layer. I have used various mats and glass in 6 and 10oz weights, so I am familiar with them. I want something heavier than 10oz cloth, or even 2 layers of it.


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## predacious (Sep 1, 2016)

cwalden said:


> I already have several sheets of 3/4 and 1/2 left over from another project.
> 
> As for the mat and poly question. No mat is needed to catalyze poly. It is catayzed with MEK (methyl ethyl keytone). Most mat has a binder glue to hold it together that is disolved by poly resin, but is not dissolved by epoxy. Thus, they say that mat will not properly soak in epoxy resin and will have air pockets due to the binder holding the mat. But, I have used mat with epoxy many times over the years and never had a problem wetting it out. So I dont know. The more I read on the internet, the more I second guess whether I should risk it.
> 
> As for my 1708 comments. I have never used it before, so I dont have a feel for what it looks like in my hand. But it does not have the binder normally used in mat. the mat layer is stiched to the cloth layer. I have used various mats and glass in 6 and 10oz weights, so I am familiar with them. I want something heavier than 10oz cloth, or even 2 layers of it.



MEK is a solvent/thinner,think of it like acetone

MEKP - that's a catalyzer,for polyester resins


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## WhiteDog70810 (May 6, 2008)

cwalden said:


> I already have several sheets of 3/4 and 1/2 left over from another project.


You said you wanted the floor as light and low as possible. If you want to use the heavier ply, you are only fighting yourself. 3/8" ply with 6 oz cloth on both sides will be fine over foam (I'd center a stringer every 15" instead of every 20" underneath the floor, but I'd do that regardless of the ply used). 1/2" ply with 6 oz cloth on both sides would be hella stout. 


cwalden said:


> I know that mat is supposedly not compatible with epoxy... ...But, I have used mat with epoxy many times over the years and never had a problem wetting it out...


Why use the mat if the materials are not compatible? What does it add other than visible thickness? Just because your previous efforts haven't failed does not mean the mat brought anything to the party. Even if you get the mat to visibly saturate, you will have weak areas that undermine the strength of the composite. You'll also add more weight than necessary.

Nate


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## cwalden (Jun 24, 2011)

I already have the 1/2 ply. I had to drive 400 miles round trip to get it. I'm not driving another 400 miles over the weight difference between 1/2 and 3/8 ply. haha. I want to keep it as light as practical. I could drive a 200 mile round trip to the Coosa Board factory and buy some of that. By the time you factor in time off from work for trip and gas, it works out cheaper to buy Coosa. The only place around here that can get quality ply only sells wholesale and I do not have a business lisc #. So they will not sell to me. I checked.

Why use the mat? That is what I was asking. I read on the internet that they are not compatible, but I have never personally experienced this in 20 years of working with glass... But I was asking because there might be those that have... So what do you think? 1708? Two layers of 10 on top and one on bottom? Other suggestions.


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## WhiteDog70810 (May 6, 2008)

Don't use any mat. 

Use the 1/2" ply with one layer of 6 oz cloth on both sides. That will be as solid as anything in a boat needs to be. Hell, the bottom of my boat is 1/2" ply with one layer of 6 oz cloth on both sides and I have stood on it while upside down many times.

Nate


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## DuckNut (Apr 3, 2009)

I agree with all of the above.

BUT....a clarification needs to be made. It was said that 1708 was 17 oz cloth and 8 oz mat. The 17 oz part is correct. The 8 oz is incorrect, it is 3/4 oz.

It also comes in two variants. +45/-45 or +90/-90. The 90 is best for flat surfaces. The 45 is better for curves as it is way more flexible and can wrap tighter.


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## yobata (Jul 14, 2015)

DuckNut said:


> a clarification needs to be made. It was said that 1708 was 17 oz cloth and 8 oz mat. The 17 oz part is correct. The 8 oz is incorrect, it is 3/4 oz.


Someone at a supply shop told me that, I have never worked with the stuff - it actually confirms my suspicions about that particular sales person's knowledge...


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