bondo and gelcoat

[JJB]

I know you cant use epoxy but wanted to know if I can use bondo filler under gelcoat . I have a small spot that needs a little fill 3' above the water line in the front of the boat . Will gelcoat bond to it ? thanks for the input ! JJB

 

[Shife]

Re: bondo and gelcoat

You can use epoxy under gel coat. You just have to properly prep the surface before applying the gel coat.

I would avoid any automotive type fillers. They are polyester based and absorb water like a sponge. I wouldn't even use an automotive poly based filler on a car, let alone a boat.

3M makes a vinylester based filler for marine use. I am not fond of it. If you do not carefully prep the surface and follow instructions, you will be re-doing this repair in a few years after it blisters and cracks.

Personally, I would mix up a batch of fairing compound using a quality epoxy and the proper filler for your application.

 

[ondarvr]

Re: bondo and gelcoat

I wouldn't use epoxy, gel coat just doesn't stick well enough to it, it can easily pop off when the area gets stressed or bumped.

How big of a repair is it, it will make a difference in what products are used and how its done.

 

[Shife]

Re: bondo and gelcoat

I wouldn't use epoxy, gel coat just doesn't stick well enough to it, it can easily pop off when the area gets stressed or bumped.

How big of a repair is it, it will make a difference in what products are used and how its done.

As long as the proper tie coat is used it sticks just fine.

Like everything if you don't do the job properly it won't last no matter what product you use.

 

[Greg Mrozinski]

Re: bondo and gelcoat

J,

Evercoat makes a marine filler (Formula 27) that is polyester based and works well under a gel coat finish. Formula 27 is for above the water line and should work nicely for your surface repair.

 

[ondarvr]

Re: bondo and gelcoat

As long as the proper tie coat is used it sticks just fine.

Like everything if you don't do the job properly it won't last no matter what product you use.

Where is a DIY guy going to find the proper tie coat?

The correct polyester fillers are easy enough to find that you can typically have it in your hand by the end of the day.

 

[Shife]

Re: bondo and gelcoat

Where is a DIY guy going to find the proper tie coat?

The correct polyester fillers are easy enough to find that you can typically have it in your hand by the end of the day.

Lots of places. There is this magical thing called the internet which has opened all sorts of doors to common folk who would have been otherwise left in the dark about this stuff.

 

[srimes]

Re: bondo and gelcoat

Yup. It's also full of smartasses who speak up with nothing constructive to say

 

[Mark42]

Re: bondo and gelcoat

In place of bondo type fillers, regular poly resin can be mixed with thickening fibers and/or milled fiberglass to make a putty that will not absorb water. Use it to fill the void and gel coat over it.

Complaints of auto filler used on boats comes from most auto filler containing talc, which is reported to absorb water over time. Personally, I have never seen it happen, on a car or on a boat.

Like with anything else, proper prep will give the best results.

Another thickener you might find in the hardware store is wood flour. Used to thicken resin. I have used plain old cooking flour (a tip I got from the wood boat building forums) to thicken poly and epoxy. Both are holding up as good as any other thickener. Mix up two oz of resin and mix with flour and see what a great thickener it really is.

BTW, a half pound of commercial thickener and another of milled glass will last a very long time for repairs, and is very cheap, and being light, is cheap to ship too.

 

[woodjm]

Re: bondo and gelcoat

i patched a few spots on my boat. Found a guy close by that had a fiberglass shop and he filled up a few jars with filler, gelcoat, and hardener for about 10 bucks

 

[Outsider]

Re: bondo and gelcoat

Yup. It's also full of smartasses who speak up with nothing constructive to say

Case in point ...

 

[DJ]

Re: bondo and gelcoat

Automoticve "Bond O" does absorb water, after time. At least, it has in the past.

There are too many good marine fillers to risk it, especially under gel coat.

 

[NSBCraig]

Re: bondo and gelcoat

Bondo is poly resin with talc mixed in it. I could walk out side right now and show you wet spots since it just rain and in an hour they will be dry. It doesn't hold water.

If you fill a dent with it and then cover it with poly gel coat there is no way for it to get wet unless you damage that area again.

After damaging the area if you left it exposed to water it will have issues, but then so will wood flour because unlike talc wood flour is more likely to hold water.

That's why it's not recommend for use under the water line on boats that sit in the water.

Before I'd even think about going out and buying epoxy and a quart of tie coat primer $$$ I'd definitely look at other options.

Do you have a pic? it really helps us answer your questions to suit your situation better.

 

[Chuck Gibson]

Re: bondo and gelcoat

How about Evercoat "Z-Filler"? Some people at a body shop told me that this is the best filler they have ever used and it dries like plastic. They said the industry is filled with "putty" that won't even harden right. I have been using Formula 27 with great results but it is quite a drive to get it if you need it right away.