Durability of Polyester Filler

[Peter_Crowl]

I've been chatting with a friend about the use of Polyester Filler as opposed to Epoxy. Polyester being hydroscopic and all.
Has anybody who uses their boat regularly noticed any failure or issue with Polyester filler?

Peter
Inquiring minds and all that...
in Denver

the major drawback you should consider is that polyester filler is never to be applied in excess of 1/8 of an inch thick. I have repaired boats using it as a cosmetic application only, and it has held up well. wether its a true fiberglass or a sheet molded compound, just make sure you build the majority up with your epoxies and keep the polyester to a minimum and you should be ok

[Peter_Crowl]

The question came up when discussing grinding gelcoat cracks. The theory was posed that filler needs a fresh bonding layer and to that end applying polyester resin was suggested - followed by filler for fairing purposes as opposed to grind and fill with polyester fillers alone.

But what of the incompatibiliy issue between epoxy products and polyesters? My presumption is that the boats of the late 50's and early 60's were made using polyester resins. So it would seem logical that applying an epoxy resin on top of that followed by polyester filler topped with polyester gelcoat would create an undesireable sandwich that's a delamination waiting to happen.

No?


Peter
in Denver

[Tim_Mattson]

Polyester filler and epoxy

Peter,
If you need someone to agree then yes polyester filler over epoxy can fail.....once epoxy is on ,you always want to use epoxy friendly stuff though for speed and if too cold ,then bondo can do.But it has to be thin.....
I`m doing a huge job in Ballard on a 95` Cruise Yacht,the Caledonia, that has up to an inch of various epoxies,fillers and putty/surface compounds.Tons of bubbles pop up on all sides/edges thru every year on the the early 70`s,welded Steel/Alum hull and with Teak railing caps and hidden steel that sees water every rainfall,it has many areas that get wet almost every day of the year.
The thicker non-epoxy repairs almost always fail ,and seem to become wet ,even when in the middle of a big flat surface.It either cracks or makes a bubble shaped blister.
West System w/thickener pretty much works every time .....except at the bow where they smash logs in storms on the Inside Passage To AK.
Epoxy will stick to any type of hull when prepped properly and whether doing a polyester-based hull with polyester filler is any better could go both ways.

Putting Epoxy onto a polyester hull would be ok if you ground deep enough and were getting into some fibers.

I try to do some hull repairs from behind with epoxy and glass and then fair the top side with the quicker drying filler.Other times it will be epoxy on both sides and in all cases epoxy primer is superior.
Dealing with the epoxy fumes and having to sand in between most applications makes it time consuming and a venting without dusting can be tricky.
As said ,keep the thickness down and use the polyester for fine feather edge and surface repairs.
Darn rain,I need to finish some painting before the drydock session ends.
Tim M
Seattle

Polyester blah blah blah

Everyone seems to be almost right here. First, it is not necessary to grind through gelcoat all the way down "to the fibers" for a good bond when applying epoxy onto polyester. Scuffing with 80 grit and wiping down with denatured alcohol or acetone will provide adequate tooth for a strong mechanical bond between any chemically compatible materials.

These are the golden rules of applying fillers and fairing compounds:

1. Everything sticks to cured polyester - polyester, vinylester and epoxy.

2. Only epoxy sticks to epoxy (effectively).

3. Vinylester and polyester are always compatible.

4. Polyester shrinks much more than vinylester and epoxy (vinylester shrinks the least). Thick polyester body filler will distort over time (that is the reason you don't apply too much).

5. Bondo is polyester based (Bondo is automotive grade at that and should never be used in a marine environment).

6. Epoxy is more waterproof and stronger than vinylester and polyester.

7. For large fairing jobs where structural integrity is not at issue vinylester will provide a better finished product than either epoxy or polyester and is considerably cheaper than West Systems.