Asking here because some of yarn it be that easy's know

[RJ Howell]

I'm building a XPS foam kayak to add to the toy arsenal. I do want PBF on the inside for the texture/grip. I also want fiberglass on the hull to be smooth and slip through the water.

Question really is about Gelcoat. How does it play into the game with xps foam? Can I web the hull and just gelcoat? Or is Gelcoat just a very expensive coating?

[tony.latham]

I do want PBF...

Poor Boy's Fiberglass? (Asking for a friend.)

Aren't most gel-coats polyester-based? As in, "let's eat some foam for lunch."

Keep in mind, in all my years of fiberglassing, I have never used a gel coat.

Tony

[QueticoBill]

In my experience with canoes, the gel coat adds a smoother finish, protects the resin - epoxy or polyester - from UV degradation, and adds a decorative/color option. (I'm not sure polyester resin needs protection.). Gel coat has become less common with newer materials and the popularity of the "natural" look of the fabric - aramids generically but Kevlar often, and integral color, carbon for lighter weight, or basalt/innegra for toughness - is popular. Polish with 303 and the UV issue goes away.

[twisted lines]

Small can of colored hard stuff that sticks well,
I think of polishing stainless
I hated them both.

[RJ Howell]

I do want PBF...

Poor Boy's Fiberglass? (Asking for a friend.)

Aren't most gel-coats polyester-based? As in, "let's eat some foam for lunch."

Keep in mind, in all my years of fiberglassing, I have never used a gel coat.

Tony

Spell checker spells worst than me.. Missed that one, but I'll go with it LOL.

[John61CT]

What is 303 when it's at home?

[swoody126]

gel coat = polyester

polyester no likee foam

foam go away when exposed to polyester

results are messy

check your chemistry carefully prior to applications

sw

[noseoil]

Gel coat is typically applied to the inside of the mold as a first coat, then the layup is done. As swoody said, check foam & compatibility with the resin you're using. Polyester can be a great solvent...

[John61CT]

why XPS specifically?

Gelcoat your mold, then use pourable PU foam at the correct density.

Could even use the much stronger higher density at high stress locations where it's worth the extra weight, then the lighter stuff for the rest.

[MickinOz]

Besides the obvious aesthetic function, one of the purposes of putting gel-coat into the mold (after the release agent of course)is to actually waterproof the fibreglass.
The fibre reinforced polyester isn't particularly waterproof. Water can wick along the fibres.
The gel coat is a chemically compatible coating that provides the seal.
When people say they haven't done gel coats, the might not have applied the opaque colour impregnated product, but they probably have done the functional bit, in that they probably have laid a few extra coats of resin over the wetted out mat, thereby ensuring a full seal.

[QueticoBill]

To the o.p.:
Are you covering a carved foam piece or building it in old?
Are you planning on epoxy or polyester resin?
Woven fibreglass or a fibreglass mat?

I assumed carved hull and woven fibreglass like on a stripper. Ignoring color, you could just brush or roll on spar varnish (if epoxy resin) for a smooth finish and uv protection.

[RJ Howell]

To the o.p.:
Are you covering a carved foam piece or building it in old?
Are you planning on epoxy or polyester resin?
Woven fibreglass or a fibreglass mat?

I assumed carved hull and woven fibreglass like on a stripper. Ignoring color, you could just brush or roll on spar varnish (if epoxy resin) for a smooth finish and uv protection.

Never used Gelcoat and was curious about it. My use is coating the build. Current project is a foam Kayak, yet same principles work for most any XPS build.

Love all the input folks!

[OP827]

Never used Gelcoat and was curious about it. My use is coating the build. Current project is a foam Kayak, yet same principles work for most any XPS build.

Love all the inout folks!

Hi RJ Howell,
I have considered gelcoat as a finish coat on my trailer build. Gealcoat is compatible with polyester resin (since it is based on PE resin) and epoxy if epoxy's surface is cleaned and sanded. If you can thoroughly cover XPS foam with epoxy laminated fibre glass cloth you can then use polyester based body fillers and spray gelcoat and then fine sand and polish to a mirror finish if wanted. My process was epoxy fiberglass on XPS, Polyester body filler (various brands from auto supply), high build primer, color base coat and 2K clear coat with body work before and between the steps. I must give credit to Michael Adams (Atomic) for giving advice on body finishes, fairing and much more.

Oleg