xps pre-lam epoxy sealer coat?

Has/does anyone, besides stoneburner, put a thin epoxy coat on an xps blank prior to glassing, and, if so, did you find a noticeable difference compared to a non-sealed blank?

One obvious thought I have is, it should make laminating the glass much easier, as there wouldn’t be as much resin being absorbed into the perforations/heavy sanding scratches (for better adhesion).  

Down sides/Thoughts?

Thanks, TaylorO

I got the idea for the epoxy pre-seal when Kayu in Oz mentioned he had used an epoxy preseal on a shaped XPS blank (believe he only sanded to 150-220 grit), no perforations.  Said the board held up well for years.  I don’t trust a blank that hasn’t been perforated with “many small holes close together.”  I like the idea that the pre-seal fills all the perforations (creating many small anchors) before lamination. 

The first time I did it was by accident.  The lamination had gone south in short order.  Lots of small bubbles under the saturated fiberglass cloth.  Ripped the cloth off and let the epoxy coated foam go tack-free before lamming another piece of FG.

But the tack free, epoxy-coated surface had lots of small little bumps.  Decided the next pre-seal should be cured and sanded smooth to 150 grit.  Easier to laminate, with less resin, than direct lamination of FG to foam.  The sanded pre-seal should bond much better with Epoxy than bare XPS.

Not too long ago, Gene posted that he preseals blanks before laminating.

Thank you sir!

Pre sealed should be the standard way when laminate on porous materials. Best is to laminate on green still tacky but set resin so add chemical adhesion between each layers. With modern “no blush” epoxy mechanical adhesion on well prep cured epoxy is effective for us. Welcome to the sealer world of eps guys LOL. 

Thank you too sir!

The first few times I laminated XPS without a sealer coat on the blank I ended up with dry spots once everything had cured. The extra roughness I left on the blank surface for better adhesioin had sucked resin out of the fully saturated cloth in spots that obviously weren’t saturated enough. A sealer coat eliminated that problem on the next build.

And thank you too RDM!

I’m getting excited to do a white pigmented sealer coat over my pink/purple blank.

It make great sense, and I’ve been spending alot of time babysitting the lam job popping “blisters” as needed, granted, it got may better one I got the roller, but this leads to a chain of helpful step reduction.   I’m gonna do blue piment on the lam, so that’s a new trip too!!!


For me, the opaque white sealer is to insure I end up with a uniform white base after I lam the first layer of lcloth with white pigmented resin.  The sealer coat may not give you a uniform white base.  Some pink may show through, especially if you sand the sealer smooth.

If I wanted to add color, I would use a white sealer.  Next, I would lam the first layer of FG cloth with opaque white pigmented resin.  Then, I would use the colored pigment to lam the next layer(s) of FG cloth and also for the fill coat, to get a more uniform color.

If your second layer of cloth has uniform color after the lam with colored pigment, you could use a clear fill coat, instead of colored, if you wanted to.  (Sort of like the clear coat on a car.)  But a colored fill coat will help insure even color though.

But if you use 3 layers of cloth, coloring the last two lam layers will help prevent white burn throughs.

EDIT:  First time, I used a clear sealer coat and I could see some pink through the white FG lam.  The white fill coat fixed it.


Thanks again Bill.   

Here’s to hoping to learn from another’s experiences!

Thanks again Bill.   

Here’s to hoping to learn from another’s experiences!

Found Kayu’s old post at the link below.  But my final grit for the shaped blank is 100.  I vacuum the shaped foam surface before perforating and sealing.  Rather than do all the pressing and scraping, I add just enough resin to ensure a thorough coating and then sand smooth with 150 when cured.  With the small-hole, perforating rollers , thats enough for me.


Also Gene’s # 6 at this link


In air plane garage builder world, guys used to sealer coat the xps “spyder foam” with an epoxy slurry, a 50/50 mix of epoxy/microsphere then most laminate directly on this fresh coat. You can add pigments for more opaque, you can add cabosil to gelify the slurry, easier to squegge “in” the core. 

Thanks lemat - I greatly appreciate your varied background and experience. 

I’ll see how the lamination goes - I just did my first sealer coat - so the stoke increases!

Taylor--  My glasser on Maui used to seal coat EPS blanks instead of Spackle or Microballon.  Just brushed on a coat top and bottom the night before a next day lam.  This was back a few years when glassers first started doing a lot of Epoxy.  I still spackle and as long as I only fill the voids have no delam issues.  I have no XPS experience.  From what I have been hearing here on Sways; there must be a bit of delam issue with XPS.