Polyester coverage question

Hi,
I began laying the glass for the floor in the cockpit of my boat today.

Originally I was going to use two layers of 1 1/2 oz mat over 5/8 sealed plywood but after talking to a boat builder, who suggested that I use a mat and woven roving combination, I opted to do that.

I was not prepared for the amount of resin I was going to need!! The cockpit of my boat is only 6'X8' but as I began wetting out the glass in 38"X6' sections I began to realize that I was not going to be able to complete the job at one time due to the amount of resin this mat/woven roving combo required. I was going to apply another layer of 1 1/2 oz mat on top of this but had to stop--------no more resin.

My question is if I apply a second layer of mat over this first layer in a few days need I be concerned about secondary bonding issues. I am using laminating resin and believe that sanding between applications is not required. Is this correct?

Additionaly, after looking at the surface of the first coat, although it is still wet, I am wondering if I even need to put on another layer of mat. The roving has a washboard surface that might act as a non skid.

Any suggestions?

Thanks

Re: Polyester coverage question

You didn't say how big your boat is, but with 5/8" plywood and a mat and roving (and possibly another mat) over it, it should be bullit proof.

You didn't really need the roving, 1 layer of light cloth would have been fine over the mat and would have used less resin.

Secondary bonding shouldn't be an issue if the resin you're using has no wax in it, unless you're doing it outside in the sun or rain and you don't need to put a mat over the roving if you like the texture.

Re: Polyester coverage question

Thanks again ondarvr,

The boat is 25' and mainly used for ocean fishing. The resin has no wax (laminating) and I planned on painting directly on it. Is sanding required befor painting?

Thanks.

Re: Polyester coverage question

For a good bond with paint you should do some sanding, if you use gel coat you won't need to sand it if you put it down within a few days of finishing the glass work.

Re: Polyester coverage question

For estimating resin...Calculate resin amount by calculating oz of fabric. Mat is measured by oz per sq ft and woven roven is measured by oz per sq yard. Resin oz needed matchs fabric weight.

6' x 8' = 48 sq ft...48 sq ft of 1.5 oz mat takes 72oz of resin (48 x 1.5) and 48 sq ft of 24 oz woven roven takes 127 oz of resin (48 sq ft = 5.3 sq yd x 24 = 127).

Laminating resin will take paint no problem without sanding. Actually, if you are using laminating resin it will be impossible to sand it. To be able to sand it you will need to do a fill coat of resin with wax added or finish resin (which has the wax already). Then ylou will have to sand the finishing resin for paint. The only reason to do this is if you want to fill the cloth weave before painting...otherwise just paint over the laminating res.

Re: Polyester coverage question

Only some paints will bond to an unsanded resin finish, most will peel off after a period of time. This is due to the uncured layer of resin left on the surface, some paints sort of cross link with this uncured resin, but most won't. This uncured layer eventually breaks down and the paint flakes off. Gel coat cross links with this uncured layer and bonds very well.

Re: Polyester coverage question

I'm not arguing here or there but I've painted over laminating resin with popular brands of single part marine enamel and poly paint without long term issues. That isn't saying problems don't happen but looking back over 40+ yrs and many glassing projects tells me it may be a technically correct problem that in reality doesn't show it's ugly head often enough to be concerned with. I've always felt the tack of laminating resin is the same tack that "skip sand" provides for painting. Regardless, underneath transom wells and lockers is where I paint over fresh tacky laminating resin without doing a tackless fill coat.

peace

Re: Polyester coverage question

I too know of people that do it with very good results and I've done it myself. The problem is depending on the type of resin, how long it's been sitting, the type of paint and even the brand of that type of paint, it may or may not hold up well. Sanding and cleaning the surface ensures that you are doing as good of a job as can be done. I've seen some very big jobs that have failed for this exact reason.