Peelply in handlaminate: uneven surface

When I was laminating epoxy and glass fabric over wood, I ran into trouble after applying peelply to prevent sanding.

What I did:

-coat the wood with epoxy
-lightly sand the cured epoxy to get rid of the protruding wood fibers
-laminate 2 layers of 200 gr/m2 glass with general purpose laminating epoxy, nicely bubble busted and without a lot of excess resin.
-apply peelply and a bit more resin to impregnate the peelply. All went on smooth.
-some sections were left without peelply

During cure bubbles of resin formed under the peelply, which caused an uneven surface. (see photo).

The big question: What is happening. These bumps caused a lot of sanding, something I tried to avoid.

Things I tried:
I tried different peelply as the one I used was nylon (I thought the high humidity could be a problem). Originally I used Airtech Econostitch, later I tried Econoply G, a polyester peelply.

I tried different epoxy. (Sicomin SR8500 instead of West 105/205)

The Econoply G gave a slightly better result, but still caused more sanding than leaving the laminate alone.

Any hints?

 

I am not sure what went wrong here
but it is not necessary to first coat the ply with epoxy
this creates a lot of extra unnessesary work

I do it all one shot.
Lightly sand the plywood smooth and flat and vacuum properly to remove dust.
I then wash the plywood with warm water and a little dishwashing liquid soap, use a good cloth that doesn't leave behind fluff. I then wipe down with clean warm water. Allow to dry properly AND THEN wipe down with a mixture of 30% white vinegar and 70% warm water.
This will remove ALL DUST. As you can see I work very clean BECAUSE it saves time.

In small places if I am not happy I wipe down with Acetone.

The best roller is the "ribbed" white plastic type, with STRAIGHT GROOVES not spiral, this works well also on the peelply. I only use the hard flat rubber roller if I put some waxed paper over the peelply to avoid the hard roller sticking and then lifting the peelply.

You can see that I get excellent results, and you can see where I have sanded the glass lightly, I did minimal filling with glass microballons and painted directly onto the glass with a roller and a water based Acrylic PVA with Teflon. I really works well, the paint is very strong and hard to sand.

 

Yup...just like Manie proposed. Peel ply is pretty easy to get right. You mentioned that you added epoxy on the outside of the peel ply ? This is not often necessary and perhaps you are impeding the escape of air thru the peel ply ? Start with a resin rich laminate, generally compact it with your bubble buster, peel ply it, then work the extra resin out with your buster, squeegee, roller rig. Usually the only dry spots are fiddly corners. And remember plywood breaths..out gasses, when the temp of your shop is rising. Laminate when the shop temp is falling.

 

yes - as the others have said - you have been 'outgassed'

I notice you coated 'the wood' with epoxy - I presume it wasnt Plywood, I bet it had joins.

To avoid this again, unlike Mainie, I do a couple of coats of epoxy on the freshly prepared wood. If their is any outgassing, it will become apparent where you need to fill.

Then you lay the glass and peel ply.

 

I guess I did not make myself clear enough:

The bumps on the picture are not filled with air, but with resin.

After laminating, peelply, squeeging and bubble busting everything looks fine. It is just after an hour or so that the bumps form.

I have done this several times before, and without any problem. Only back in the old days I have had the same situation, but the problem was not accute then, knowledge was less and the project did not call for another laminating session.

On adding resin to the peelply: Only where a dry-ish spot was left. Large areas had enough resin.

I forgot to mention that I also made a test piece on a sheet of formica, to rule out air from the wood substrate, but that gave the same results (yet much harder to photograph with my very limited camera)

RWatson: The wood was plywood. I coated the wood with epoxy, then sanded lightly. The laminate without peelply is in perfect shape. No bumps, no voids, no air.

Could it be the high humidity? I could understand that nylon does strange things, but also the polyester peelply reacted similarly.

 

That's out gassing for sure.

You need to be careful with temperatures and humidity prior to putting epoxy on wood (or balsa core).

What happens is at night, your wood picks up some moisture from an increase in relative humidity. Once day breaks, you are quickly heating the wood, releasing gas from the wood. That released gas is what caused your bubbling and it's *not* waterproof where you have these bubbles.

Pull the peel ply and look under... you will find mini craters and pin holes.

The way to prevent this is to only apply epoxy to wood when the wood is cooling down, not when it is heating up.

Edit: If those bumps are actually filled with resin only (and definitely no air - destroy one and find out), it's just a bad squeegee job on the peel ply application.

 

-we did not destroy one or 2 bumps, but all of them. First carefully to see what was under them, but completely resin filled. Then we sanded all of them.

And also on the melamine board we had the same problem! No outgassing for sure.

The work area is stable in temperature. Variations of 2 degrees C at most.

When ready with laminating and peelply the job looked fine, so I doubt it was a bad squeegee job.

 

Hmm.. solid epoxy "Warts"...Hmm. And those warts in the picture are oriented in the same direction, almost wood grain like...Hmm...Hmmm...Hmmmm

 

Well I dont know

but another 2 cents worth

I have used both polyester and nylon peelply and no difference

 

I know where you are heading, but the same happens on the melamine board....

 

Very strange indeed.

The only strange thing i can think of if that you say you are adding epoxy to the outside of the peelply.

That is a complete waste of time. Sure, peelply is slightly porous, but you wont get enough onto the laminate to make a difference to a dry layup by applying it over the top.

Usually, when you are screeding the laminate with the peelply applied, and you notice you have a dry spot, there will be enough excess resin in nearby areas that you can 'scrape' over to that spot.

If not, you must peel back the peelply ( often better to use a razor around the spot than lift the entire sheet of peelply), and re-apply resin at that point.

The only thing I can think of is that you are somehow inducing the bubbles by your laying technique, especially if they are solid.

I have achieved minor effects like this where I have not seen a wrinkle in the peelply, and been left with a big 'blob' trapped by the wrinkle.

If the 'peelply' you are using is wrinkling from heat, or chemical action, it would create this effect. That would indicate that the stuff is not meant to be peelply.

Just to recap - you should be laying the glass (are you using chopped strand matt ?) on the surface, applying the resin, rolling it thoroughly with a ribbed metal roller to make it translucent, then you lay the peelply, and use a squeegee on the peelply to move all excess resin from the centre of the job, out to the edges. In the process, the peelply will be sitting firmly on top of the fibreglass with very little resin between it and the peelply layer.

The effect you are getting is very, very non-typical

 

One more guess. Maybe you were sold some type of inferior peel ply that is puckering after being applied to wet resin?

 

Or the layup is shrinking a lot more than the usual 1% or so and pulling the peel ply with it.

 

Thanks for the help.

RWatson described the way we did the layups correctly. First create a near-perfect laminate, then apply peelply and use a squeegee to get this flat on the laminate. On some places you have just too little resin to saturate the peelply, but when squeegee-ing you always have some resin moving around, and can use that for better saturation. Still some spots needed extra resin. It does not seem that these areas caused more trouble. The bump-effect was all over the surface.

The peelply was Airtech Econostich, and later Econoply G. I guess these do not count as cheap substitutes for the real stuff... The Econoply G was tried after recommendation by Airtech, although they had no explanation for the bumps.

My thoughts at this moment are that the nylon was saturated with water (high humidity). After application, the epoxy pulled the water from the nylon, slightly shrinking the nylon, but in an uneven way.
I am not sure why the polyester peelply gave similar results, however. Or does polyester (thermoplastic) also expand when getting wet?

I will run a test with wet peelply (stored in a bucket with water, however above the water level) and with dry peelply (1h in an oven of 120 degrees C should be enough to dry it out) See what happens then.

As I had this effect before, and no-one seems to be able to pinpoint the problem, I am determined to get to the bottom of this. I just want to understand.

 

Sounds logical to investigte the peel ply. perhaps its changing shape ? Those warts certainly look to be oriented in a fabric or grain axis.