Fiberglass Repair

[Jared1989]

I have a 1989 Mastercraft Prostar 190. It's all fiberglass. I am working on a few spots on the inside of the boat. The holes I am repairing are about the size of a quart in diameter. And I have sanded away the surrounding fiberglass to allow for the right slope in toward the hole to allow for about three layers of fiberglass mat and epoxy. I'm new to this and have been experimenting.

What is the best way to get the air bubbles out from in between the layers of wet fiberglass? I'm going to sand the new fiberglass down and put gelcoat over it. And I am afraid that there are going to be little holes in the new fiberglass. Any advice is welcome.

 

[jbcurt00]

I'd suggest you not use epoxy if you plan to use gelcoat over the repairs.

It can be difficult to ensure proper adhesion for gelcoat over epoxy. BTW gelcoat is a polyester based product, use polyester resin for the repairs.

Matching the gelcoat for the repairs can be tricky unless you plan to recoat the entire area not just the repairs

 

[Woodonglass]

Do you have access to both the inside and outside of the repair area? What exactly are you repairing? What section of the boat? Do You mean the area is the size of a Quarter? JBC is correct about using Polyester resin if you're going to be Gelcoating for the final finish. It is possible to gelcoat over epoxy but IMO it's still advisable to use Poly. If you give us more details about the repair we can/will give much more detailed instructions on how to do the repair.

 

[Jared1989]

No Title

I'm using West Marine 105 Resin and 205 Hardener. I do have very limited access to the back side of the panel as the picture shows. I'm trying to patch the holes that you see.

 

[Woodonglass]

Ok, Here's how I've done this kind of repair and how I'd recommend you do it too!

I believe you should be able to reach up there and put some duct tape over those from the back side. That's all that's needed. Then you can make your patch on the bench and apply it in on fell swoop and be done in less than an hour. Here's how. Get a piece of heavy plastic and lay it on your bench. Cut a piece of CSM about the size of the hole, lay it on the plastic. Cut another piece about 1/2" larger than the first and Lay it over the first piece. Cut another 1" bigger than the last and lay it down and finally one more 1 1/2" larger than the previous and lay it down. I'd still recommend using Poly since your gunna be trying to gelcoat. I'd take the West Marine epoxy back a trade it in for their Polyester resin and Hardener. Mix it up per instructions and then pour it on to the patch you just created on the plastic and use a cheap paint bush to DAB the resin into the CSM. Do NOT try to Brush it!!! You'll make a Mess!! Just poke and Dab until it goes clear. You'll only need about 1/2 cup full of resin. Now carry the whole thing to the boat Plastic Too!!!! and lay it over the hole. Use a bondo spreader or a plastic putty knife to spread the patch out smooth. You prolly want to tape off the surrounding area cuz the resin will run!!!! Once you get it smoothed out leave the plastic on!!! You have about 20 mins. max to get this done once you mix the hardener in. Once it kicks off you can do your final sanding and then get some fairing material to fill in any low spots etc and do your final fairing and sanding and then the hard part starts. Mixing and matching the Gelcoat!!! That's another story and training session!!!

 

[Jared1989]

Okay. What kind of heavy plastic to you recommend? Do I need to apply some wax to it? And CSM means 'Chopped Strand Mat' correct?

 

[Woodonglass]

Any kind of plastic like a plastic bag, or even wax paper will work. CSM yup Chopped Strand mat. you want 1.5oz NOT the cheap crap they sell at Lowe's or WalMart. West Marine should have some.

 

[Georgesalmon]

A little tip: Snip a 1/2" of the bristles off of one of those cheap china brushes for "dabbing" at the wet CSM to get the air bubbles out . It will make it stiffer and work better.

 

[Woodonglass]

Good tip GS, these Cheapo Chip Brushes is what I use and like George says I cut the ends of the bristles off to make em stiffer...

 

[Jared1989]

I really appreciate all of the help. Very helpful info. I will need more help when I try to gel coat. Again, I greatly appreciate the help.

 

[Jared1989]

I didn't do something right. The polyester resin and CSM pulled right off with the mold release fabric I bought from West Marine. I let it cure for 2 hours and tried to pull the application mat off and the CSM and all pulled right off with it. It didn't bond to the existing fiberglass. I used Acetone to clean the surface too.

 

[Woodonglass]

Mold Release Fabric???? Not sure I understand. Please give details of what products you used and how you used them.

 

[Jared1989]

When I was at West Marine this morning getting the poly resin and tools, I asked them if they had any heavy plastic. They said they didn't but had a mold release mat that served the same purpose. What happened is that the resin bled through the mat and set up. So I tried it again and took the mold release mat off right after I applied the patch on the boat. It is holding. I even sanded it with my sander to check and see if the new patch would stick to the old fiberglass.

 

[Woodonglass]

Nope, Don't listen to those guys. Did you put tape behind the holes? If so just just forget the plastic and do the patch at the boat one layer at a time. Cut each layer as described and apply one at a time. Smallest first. Apply some resin on the boat then place the CSM and use the brush to dab it in place and immediately put the next layer on and dab it in place and then the next etc. 4 layers oughta do it. In and hour you should be sanding. What resin are you using?

 

[Jared1989]

I put duct tape behind the holes. I do like prepping the CSM with resin before applying it to the hole. I just remove the release mat right after I apply it to the hole. The resin I am using is West Marine Polyester Boaters Resin.

 

[Woodonglass]

OH Ok is understand what you're doing now. That should work fine as well. You May need to use some finish filler to do the final fairing or the Gelcoat paste may do the trick

 

[Jared1989]

I didn't know this, but I'm pretty sure that my boat is made out of Polyester resin material. And I'm thinking that I need to grind and sand away the other repairs that I did using Epoxy resin. I feel dumb

 

[Woodonglass]

If you want to Gelcoat over those repairs then it would probably be a good idea.

 

[Jared1989]

What kind of filler do you recommend before applying gelcoat?

 

[Woodonglass]

I make my own using resin, and glass bubbles and a bit of cabosil. OR you can buy some of this...