Flowcoat over vinylester

[Weyalan]

Any reason why a standard flowcoat (probably International) wouldn't go over vinylester resin?

[Alan Wheeler]

Are we talking new or old resin? New should not give any problems as far as I am aware. Old will need to be sanded and cleaned with a solvent wax cleaner before applying. Nothing special, it's just a prepaint wax/degreaser you would buy at a paint store.

[Weyalan]

We are talking brand-spanking new vinylester resin, as laid (by me) last weekend. So new, in fact, that I probably wouldn't even bother wiping it down with acetone!

[Alan Wheeler]

Flowcoat and Gelcoat are basicaly ester resin with pigment in it. Once the original layup has reached full cure, any further applications of resin only stickk to the surface. When I said "new", I was refering to it being layed and only starting it's initial cure. During initial cure, any further applications bond to the layer underneath it and the entire layup becomes one solid layer. Ester Resins are very poor at "sticking" unlike Epoxy.
Issues can occur when a layer has been allowed to fully cure for several days and then another layer applied. However, it's not like the flow coat is structural. It is only a coating, so not so much of an issue. However, I would still give it a wipe down with a solvent. Ester Resins have a natural wax substance that occurs on the surface and this needs to be wiped down to ensure the best adhesion of the flowcoat.

[Weyalan]

Thanks for the advice, Wheels. It will be a week (or more) since the glass & resin was laid, so I shall heed your advice and wipe it all down with acetone prior to flowcoating. Is there any point in giving it a light rub with sandpaper to "key" the surface?

[BBill]

If you used poly laminating resin it should still (1 week) be tacky and require no prep. If you used finishing resin it will have the wax and need prep. That's the difference between laminating and finishing resins.

Wiping with styrene gives superior secondary bonding compared to using acetone. Styrene chemically links the old and new resins...while acetone merely cleans the surface and can't be trusted to remove all the wax. Sanding is required if using acetone on fininishing resin if you want to be sure.

[Weyalan]

Thanks for the info BBill. I used vinyl laminating resin... if that makes any difference?

[BBill]

Vinyl or standard polyester...it doesn't matter. If it's still tacky you don't need to prep...however a light wipe with styrene will make any dry spots ready again.

[Alan Wheeler]

Thanks also BBill, I didn't know about the styrene. But it also begs the question, can styrene be easily bought??

[BBill]

Originally Posted by Alan Wheeler

Thanks also BBill, I didn't know about the styrene. But it also begs the question, can styrene be easily bought??

Don't know about where you live but styrene is sold here at fiberglass supply companys. If you can't find it retail locally try a surfboard or boat mfg. Take an empty jug to their shop and ask if they will sell you some.

Bill

[Talbot]

readily available in UK as well.

I understand that if you are trying to stick grp to ply, a 50% solution of resin and styrene helps the penetration of that first important coat.

[BBill]

Some people use acetone for thinning poly and it works ok, but styrene is actually the "official" thinner made for polyester. Poly is mfg with styrene and that acrid smell you get from poly is the styrene.

Years ago I did empiracle tests using styrene with small glass blocks made from polyester resin. I wet wiped sanded mating surfaces of one set with styrene and used plain poly resin to "glue" them together while the styrene was still wet. The other set I sanded and wiped with acetone, then "glued" them together with polyester resin. The styrene set held almost like they were epoxy glued together and the acetone set broke apart much easier. This is typical of the difference in bonding. There really is no close comparision between chemically cross linking VS tenacious bonding.

Bill