Cupping veneer problems

[Ricardo 53]

Hi

New to veneering and have a query for those with more experience than me who's slowly learning. I veneered some jarrah, elm burl and maple burl veneers onto 3mm mdf. At the same time i veneered pine onto the other side and left it for a day. Result cupping of varying degrees to the non-pine side.

I assume the problem stems from one side being hard wood and the other softwood. Would the boards straighten if I veneered another layer on the pineside at right angles to the original? Any advice would be very welcome.

[joez]

I wouldnt have thought the different materials would have much too of an effect unless you are using thick veneers.

How were the boards stored during drying? If you simply left the boards show side up the pine side might still be wet and the bow might be a result of un-even drying.

If this is the case flip the boards for a few days, or even try stacking/stickering them to promote even drying.

I have had this happen to me on occasion when using a timber substrate but never mdf.

good luck


joez

[Ricardo 53]

Thank Joez

I had them show side down and dried them between two chunks of benchtop left over from the kitchen reno, 35m moisture resistant chipboard with the laminex sides on either side of the veneer pieces. Perhaps I should try to moisen them and leave them to dry for a couple of days??

Ricardo

[joez]

I would just flip them for a day or two, and let it sit on some stickers to promote a more even drying process.

3mm Mdf is fairly flimsy, a little bow is probably ok from most projects.

If you want to try something faster put it in the sun for a few hours (bump side up).



joez

[pjt]

I have used 3mm mdf to veneer onto before with mixed results, upshot of it is I think that it is not strong enough, I had some that pulled apart (both side veneered) solid wood or good quality 1/4" ply is a better option I think.



Pete

[Ricardo 53]

Thanks Pete

Any thoughts on whether sticking another sheet of veneer on the pine side at right angles might straighten (un-cup) the board. They all cupped on the shorter side not down the length if you get what I mean!

Cheers
Ricardo

[pjt]

Yep, it might straighten a bit, it might not to, if it does straighten each side is then trying to pull away from each other and this is where the mdf starts to split, you might be ok if you can capture both sides of the panel in a frame but it might also still have a curve shape in the panel give it a go and see what happens,

Is it a large panel? What glue did you use? How thick is the veneer? How did you apply the veneer? Clamps/veneer hammer? Did you do one side then the other?


Pete

[Ricardo 53]

Thanks Pete, will give it a go and see what happens. I used Titebond, glued both sides at the same time and the 3 bits are 370 x 260 (jarrah), 280 x 260 (elm) and 180 x 130 (maple). The veneers were less than a 1mm I reckon.

Oh its all learning processes. Primarily I'm thinking box lids for these, inside a 12mm mitred frame.

Cheers

Richard

[pjt]

Thanks Pete, will give it a go and see what happens. I used Titebond, glued both sides at the same time and the 3 bits are 370 x 260 (jarrah), 280 x 260 (elm) and 180 x 130 (maple). The veneers were less than a 1mm I reckon.

Oh its all learning processes. Primarily I'm thinking box lids for these, inside a 12mm mitred frame.

Cheers

Richard

Your main issue is the water based glue, I have used Titebond (pva) for gluing veneer in some circumstances, e.g. if the base is solid and thick ~>10mm but for 3mm thick mdf the outcome is less than assured, a non waterbased glue (epoxy) will give better results if you are going to use 3mm mdf.


Pete