Rippling grain on wing veneer

[Stuart Z]

Hi

Hoping for some advice on this. I glass clothed a foam wing using lightweight glass cloth and epoxy laminating resin but after a light spray I can see rippling in the finish. I sanded the wing again as much as I dare and resprayed but the ripples are still evident. I think this wing is a lost cause and will be flown “as is”. But can someone suggest what may have gone wrong? I plan to continue on the next foam wing job using glass cloth again. I didn’t use Poly C as it is water based (having said that I used it on my Magician over glass cloth and had no problems and I love the stuff as it is so easy to use and clean up after use.) I didn’t use high build primer due to potential weight issues and sprayed with acrylic over the epoxy laminating resin.

Your views and thoughts are welcome.

S

 

Edited By Stuart Z on 05/04/2018 10:04:49

Edited By Stuart Z on 05/04/2018 10:05:31

[Denis Watkins]

You have not gone wrong Stuart, when timber is processed flat, some of the grains are cut across the cells.

Sometimes, the grains are parallel on a sheet and show no lifting

Demonstrate this, interlace your fingers of both hands flat

now point both lots of fingers 45 degrees

the grains do this when wetted, either water or solutions, they spring up

light sanding will remove them

Edited By Denis Watkins on 05/04/2018 10:30:48

[ron evans]

Hi Stuart, had the same problem many years ago. The veneer grain changed direction every inch or so, not sure how the stuff is cut, but if off the log then it must have been the last cut.

the veneer was epoxy bonded but when cured was still rippled where the grain changed. I fixed it with pollyfiller then sanding back with most of the filler gone.

Today I would use a mix off lightweight filler and poly c, most will be sanded away with little weight added.

Ron

[Stuart Z]

Thanks Denis,

I have sanded the panels both before and after painting, nervous as to how far to take it. I don’t want to break through to the actual glass cloth or balsa. But thanks for your idea, I’ll try a bit more to see if that takes it down.

S

[Stuart Z]

Thanks Ron,

A good suggestion- so taking the veneer to a level with a mix before glass clothing. A good idea, hadn’t thought of mixing Poly C with a filler. I wonder if I can get micro balloons to mix in.

Thanks again to both you and Denis

S

[Engine Doctor]

Its happened to me on a few occasions with Obeche covered wings but never with balsa covered wings .. I used a high build primer to fill the uneven surface then colour coated and sanded wet using a block until flat , removing as much of the primer as possible between coats until your happy . Once flat I gave the whole wing a light coat of suitable coloured primer ready for finish coats. I think the un-even surface is caused by either poor foam cutting or the glue application as Obeche is very thin and cant mask the undulations , it certainly was with the wings I made. The grain does affect the finish but once its been raised and sanded it shouldn't be a problem . Good luck

[Stuart Z]

Thanks ED.

Glad I’m not alone with this.

With all of the above I will adopt a strategy on the next foam wing combining all the suggestions.

Many thanks to all.

S

[McG 6969]

Hi Stuart,

I wouldn't mix microballoons with filler as they are not supposed to be 'fine' sanded. You can use talc powder instead or - even better - use the genuine Freddie B Recipe.

I would try the latter in any case as it is a joy to work with. You can find the Recipe on page 43 of my Bella Ballerina build.

Above is the Fred B 'stuff' I used recently to make a cowl plug for my Vicomte build. You can apply it as thick as you want/need.

I think next time when your veneer or balsa is prepared/sanded, I would apply a thin brushed coat of 'Sand & Seal' to raise the grain of the wood, then get rid of the grain by some fine sanding (ie 400) before glassing. Also, I would go the 'hard varnish' - Ronseal Diamond or similar - route for glassing instead of the heavier epoxy or polyester resin.

Cheers

Chris

[Stuart Z]

Chris

Thanks for the “heads up” - I’ll look up your recipe. I thought sanding sealer was not good on foam wings or is Sand & Seal something different?

S

[McG 6969]

Stuart,

The Deluxe Materials stuff can be used on balsa, ply , hardwood and foam. I used it on bare Depron for my Ballerina. I don't know if other brands of sanding sealer could be to aggressive for foam, but I don't think so as long as they are water based.

Cheers

Chris

[Stuart Z]

Thanks Chris

I’ll take a look and see how it makes up.

S