Good primer sealer for plywood before covering?

[Edgeflyer]

What is a good sealer for a 1/64 ply veneered foam wing before heat shrink covering?

Need to avoid overheating to melt the foam underneath. Also to fill the grain.

Can water based put as in fibreglassing be good? Or thinned pva which is heat sensitive for better adhesion?

[Engine Doctor]

Provided the ply it sanded lightly to remove the release agent it shouldnt need priming. All decent ply has release agent on it to stop it stickiny in the presses. Sand with a very fine grit just enough to produce a matt finish being careful not to cut through the ply layers.  Then dust off with a tack rag before covering. The heat required to shrink and adhere the covering shouldnt affect the foam. 

Edited August 24 by Engine Doctor

[Martin Harris - Moderator]

I’ve always been given to understand that bare wood provides better adhesion for film coverings and any priming or sealing should be avoided. I would agree with ED’s advice. 

[Andy Stephenson]

Sealing wood before applying film always leads to air bubbles as there's nowhere for the air to escape to.

[Edgeflyer]

Thanks to all! I tested a bit of the foam from the offcuts by ironing on some lam film at 105 degrees. All fine. Also tried a sample of oracover on the ply after fine sanding and it adhered well and no grain showed through.

[Jim Hearnden 1]

One of my models had a home made foam wing which had been left bare (no veneer) and I covered that in Solarfilm. It worked well & lasted a long time. So no worries about temperature. 

Edited August 24 by Jim Hearnden 1

[Tim Flyer]

A late reply here, but just thought it worth it as my method is different to the above and I’m afraid i dont agree with Andy from my experience. If the air needed to escape into the surface we could not apply film on top of film. Yes sealing wood or applying film to sealed surfaces can lead to the odd air bubble which can be eliminated with a needle or prevented by careful application and ironing technique from the centre after edge tacking.
 

Applying film to sealed surfaces happens when we apply film on top of film when adding stripes and dual colour schemes or covering over wing joining areas which have epoxy.
 

I make a habit of applying light coats of diluted PVA to all bare wood and light sanding between coats and before covering. I also do this on wood veneer foam wings , but obviously being careful not to wet them out too much to avoid cracking the veneer. As dried PVA is heat activated it helps the covering stick plus adds some surface strength to avoid dings😊

Edited August 27 by Tim Flyer