sealing balsa core?

Are there any thin coatings that could be applied to seal Balsa so that it only soaks up minimal epoxy during vacuum bagging, especially during high vacuum pressure.

I am using epoxy so it would have to be compatiable and still acheive an excellent bond. This is a sandwich panel that is under dynamic loads.

Also reason for sealing is to keep weight down.

 

I have in the passed rolled a coat let it start to set up then start my lay up , and when i have cut my parts just looking at the edge of the core its nice and dry for the most part.

 

I was just hoping that there was some product that was low viscosity but did not penatrate the balsa so that during vacuum bagging with high vacuum or also infuzion that the balsa did not soak up too much epoxy. Maybe spray it with a light coat that would setup quickly. Maybe even an epoxy. But also an A+ bond between your laminate and the balsa was still maintained with the epoxy used for the laminate.

 

CPES will likely do the job but you better have a good ventilation system.
CPES

 

Baltek Seal Balsa

Have you tried Baltek's sealed end grain balsa. I recently completed my final year project on investigating resin absorption in end grain balsa. Reductions up to 45-50% of epoxy by weight can be achieved by using triple coated AL600/10 Baltek end grain balsa compared to non-seal.

Give them a call. Its good stuff.

I also tested single and double coated balsa too. The triple is the best and gives fairly reliable (repeatable) results.

Buckle

 

Epoxy is not a light weight sealer. Almost anything else is lighter when applied and dry. Lacquer comes to mind. Can be thinned a great deal and still seal. Which step is the more important?

 

Drop in Mechanical Properities

Just a suggestion? If you seal the Balsa with some ultra light weight crapy DIY sealer/lacquer, how can you be sure that your resin will be bonding to the balsa and not the sealer. If you dont use a proper adhesive sealer from the start, upon sandwich construction, interlaminer skin shear fail will result as there will not be aproper bond between the skins and the core due to the sealer on the core surface.

My advice would be careful when selecting sealers. You may seriously affect your resultant laminate properties at the end of the day.

What methods of laminat construction are you considering? If hand lay, there are pastes of the market designed for this. If infusion, buy sealed balsa from the start.

 

What is your SHEAR loading on each surface? What is the maximum AIR GAP that the bonding adhesive will have to bridge. Unless your moulds are almost perfect, and your balsa plugs when sealed. You will join the EPOXY or 3M compound gang.

 

This is exactly what I was hoping to find. I cannot find any info about "sealing" on the Baltek site though. I'll contact a Baltek rep though. Is AL600/10 the code for "sealed" end grain balsa? GPS core is what I'm most interested in because process will be infusion. Is Baltek the only company that does this?
Thanks for the info, Sam

 

Sealed balsa

Both Baltek (AlL600/10) and DIAB (ProBalsa Plus) supply sealed or coated end grain balsa. I don't think any other balsa supplier (like Nidacore) does though. Both products are fairly similar (I believe they both use a UV cured system).

As for using sealed balsa with GPS-cut style core, I don't know if you will see a whole lot of resin uptake reduction, as the sealing is only on the main surfaces, not in the infusion grooves or in the kerf cuts.

 

Yes, AL600/10 is the name for the formulated coating, named after one of Balteks late employee's Alan something... The /10 is meaningless so I am let to believe. Anyway I tested tonnes of this stuff. It comes in all thicknesses and cut styles in single/double and tripled coatings. Triple is the most effective.

Only the surfaces need to be coated as its the capilary action of the balsa cells/grain that does the absorption, therefore theres no need to coat the sides of the cuts/groves etc.

Hope this helps.

Buckle

 

Sealed Balsa

The kerf cuts probably won't absorb too much resin (against the grain), but the infusion grooves will open up the end grains, assuming that the coating is applied before the grooves are cut...still might not be that much resin absorption anyway.

As for double and triple sealing the balsa, it may decrease resin absoption, but doesn't it weaken the shear transfer from the skins to the core (skin/core adhesion)?? One of the advantages that balsa has over structural foams is that the resin can penetrate the gains, producing better adhesion. With the coatings, you might not get this (only a thought).