Recommendations for Polyester Filler

[Frank R]

I need to fix the sagging roof. I haven't committed yet but it looks like I will be grinding off the gel coat and laying down two layers of 12 oz biaxial fiberglass cloth. After that it will be a lot of filling and sanding. I have always worked with epoxy filler and never with polyester filler.

Do you have any recommendations on which brand to use? Bondo? Eastwood? Evercoat? Total Boat?

Any other recommendations?

[Frank R]

https://help.summitracing.com/app/an...hould-i-use%3F

I just found this. Looks like a premium filler is the best type.

[wbullivant]

Originally Posted by Frank R

I need to fix the sagging roof. I haven't committed yet but it looks like I will be grinding off the gel coat and laying down two layers of 12 oz biaxial fiberglass cloth. After that it will be a lot of filling and sanding. I have always worked with epoxy filler and never with polyester filler.

Do you have any recommendations on which brand to use? Bondo? Eastwood? Evercoat? Total Boat?

Any other recommendations?

I would recommend staying with epoxy rather than switching to polyester. I worked with polyester for decades until I switched to epoxy about eight years ago. To my mind virtually all the characteristics of epoxy are superior including generous working time up to 30 minutes, generally better bonding to a variety of surfaces, and ability to completely harden in one day ready for sanding. There is no gummy surface layer that polyester often has until it has dried for a number of days. I use fillers with epoxy to obtain just the right viscosity for the job at hand.

I think if you are used to the advantages of epoxy it will be difficult for you to go back to polyester resin.

[David Tilston]

Originally Posted by wbullivant

I would recommend staying with epoxy rather than switching to polyester. I worked with polyester for decades until I switched to epoxy about eight years ago. To my mind virtually all the characteristics of epoxy are superior including generous working time up to 30 minutes, generally better bonding to a variety of surfaces, and ability to completely harden in one day ready for sanding. There is no gummy surface layer that polyester often has until it has dried for a number of days. I use fillers with epoxy to obtain just the right viscosity for the job at hand.

I think if you are used to the advantages of epoxy it will be difficult for you to go back to polyester resin.

What do you mean, "switching to polyester"? As far as I know, Scamp trailers were made with a polyester resin at the factory.

What you forgot to mention in the characteristics of epoxy is that polyester has trouble sticking to it. So, if you, "switch" to epoxy, you have to stay with it.

Since I always use polyester, I have no idea what epoxy costs. How much is a gallon of epoxy?

I don't consider myself any kind of expert, but I have sanded polyester resin a few hours after laying it down. I have not noticed any gummy surface layer, other than that time when the fibreglass was still wet from washing it. The resin never hardened and I had to sand, (wipe) it off and start again.

[Frank R]

Dave, you bring up a good point.

After I have ground the gel coat down to the fiberglass, what should I use to adhere (wet out) the fiberglass cloth I am using to strengthen the roof?

I want this to be strong to avoid sag and I only want to do it once.

[David Tilston]

Originally Posted by Frank R

Dave, you bring up a good point.

After I have ground the gel coat down to the fiberglass, what should I use to adhere (wet out) the fiberglass cloth I am using to strengthen the roof?

I want this to be strong to avoid sag and I only want to do it once.

Frank, I'm sorry to say that I think you are going about this wrong. Not that I have any personal experience with what you are doing.

As I have said elsewhere. I would use pultruded 1" square fibreglass, running side to side, on top of the roof, where the sag is worst. No need to strip the gel coat anywhere other than where the square tube is glued down. I would bevel the ends at 45° and close them off with fibreglass. I think that if this is done just to the top of the trolly roof, it would not be an eyesore.

https://www.grainger.ca/en/product/S...-FT/p/WWG4ATN8

Another approach is to use foam sandwich construction. Many boats are made this way. First you glue the foam to your fibreglass, then fibreglass over the foam. This is lighter than multiple layers of fibreglass:

https://www.fibreglast.com/product/g...core-materials

The folks at Trillium/Outback now line the inside of the trailer roof with some non-woven fabric and fibreglass over it. I assume that the fabric does not absorb the resin. Joe Thoen tells me it is quite expensive, but he didn't tell me where he gets it.

Lastly, fibreglass is plastic, that is it will deform under stress. The sag that you observe is the result. However, this process can be reversed. I use something like this in the winter, when snow load might deform my roof:

https://www.princessauto.com/en/45-t...t/PA0008822124

The upside of this is that if you support your roof over the winter, (or any extended period of time where you aren't using your trailer) then the roof could just stay that way when not supported. At least that's what happend when I did it.

The answer to your original question, I would just use Bondo™ resin, or go to your local fibreglass place and see what they have. However, wbullivant has a point about how quickly it sets. You only have about 10 minutes to work. Lower temperatures would give you a bit more time. Have everything cut and ready to go, before you mix in the hardener.

[Frank R]

Originally Posted by David Tilston

As I have said elsewhere. I would use pultruded 1" square fibreglass, running side to side, on top of the roof, where the sag is worst.

I'm sorry, but this is just not acceptable. I won't be doing this.

Originally Posted by David Tilston

Another approach is to use foam sandwich construction.

I am familiar with this. However, I do have a 4x8 sheet of 3/8" thick MDO board that I might be able to use.

Originally Posted by David Tilston

The folks at Trillium/Outback now line the inside of the trailer roof with some non-woven fabric and fibreglass over it. I assume that the fabric does not absorb the resin. Joe Thoen tells me it is quite expensive, but he didn't tell me where he gets it.

Scamp also strengthens their roofs so they are ready if you want to install an AC unit. The call it "Prep for A/C" in their Standard Features. I am just guessing but I think they just add more glass from the chopper gun. Maybe they add a piece of wafer board in there too.

Originally Posted by David Tilston

I use something like this in the winter, when snow load might deform my roof:
Attachment 145794
https://www.princessauto.com/en/45-t...t/PA0008822124

The upside of this is that if you support your roof over the winter, (or any extended period of time where you aren't using your trailer) then the roof could just stay that way when not supported. At least that's what happend when I did it.

I was already thinking along the same lines and bought one.

Originally Posted by David Tilston

The answer to your original question, I would just use Bondo™ resin, or go to your local fibreglass place and see what they have. However, wbullivant has a point about how quickly it sets. You only have about 10 minutes to work. Lower temperatures would give you a bit more time. Have everything cut and ready to go, before you mix in the hardener.

I was all set to just use my boat building fiberglass materials but then the comment about them not adhering to polyester gave me pause. That was good info. I will just switch to a polyester resin for the wetting out. It is cheaper than epoxy but it smells worse and it is not as strong.

[David Tilston]

Originally Posted by Frank R

I was all set to just use my boat building fiberglass materials but then the comment about them not adhering to polyester gave me pause. That was good info. I will just switch to a polyester resin for the wetting out. It is cheaper than epoxy but it smells worse and it is not as strong.

Actually, it is the other way around. The epoxy bonds to polyester resin just fine. However, polyester resin may not bond to the epoxy.

[Frank R]

Originally Posted by David Tilston

Actually, it is the other way around. The epoxy bonds to polyester resin just fine. However, polyester resin may not bond to the epoxy.

Thanks, that brings me back to my original plan. I just need to get some micro balloon filler material for my epoxy resin.

[Frank R]

Woo Hoo! I just found my other box of supplies. I think I have everything on hand to do this repair.

Now we will see if the weather cooperates.