PVA leeching through maple veneer RESOLVED

[Peter Sefton]

I have seen the black on Maple/Sycamore veneers when using PVA and Titebond. My feeling is that the water content restarts mould within the veneer or as Custard mentions reacts with iron within the veneer.

We usually veneer with UF glues, resin powder mixes. The product market is in the process of change my favourite Borden UL39 has just been discontinued and replaced with F120.

http://www.hallmarkfraulo.co.uk/productdetail/F120

Cheers Peter

 

[Graham Orm]

I've only veneered Maple a handful of times, but I've veneered hundreds of square metres of Sycamore which is a closely related species. Bleed through is the biggest problem, most makers using a UF glue go for the fastest hardener they can find as once the adhesive has set there's no longer a risk of bleed through. Heating the press is another strategy for speeding up pressing times. The other main option is thickening agents, which are mixed with UF glues to block the veneer pores and prevent bleed through, there are commercial UF thickening agents available which are added at 10-15% by weight, but I've known people use corn flour and achieve good results!

If all else fails you could use paper backed veneer which kills the bleed through problem dead, or alternatively size the veneer with glue size first, a giant faff but it's also a reliable solution.

Veneering PVA's (such as Titebond Cold Press) are also popular as they reduce both the risk and the impact of bleed through, they also have the advantage over UF glues that UF resins can sometimes cause a green tinge that's particularly noticeable on the most desirable, very white grades of Sycamore. i've never heard of, nor experienced, a black stain. Complete guess but I wonder if there was some iron dust/filing contamination, maybe if something like steel wool had been recently used in the vicinity?

Thanks for the input Custard. I've used fir burr on the same piece which is light in colour with no problems. There are no foreign bodies present either. I've also used maple plenty of times as well with no problem.

 

[Graham Orm]

I have seen the black on Maple/Sycamore veneers when using PVA and Titebond. My feeling is that the water content restarts mould within the veneer or as Custard mentions reacts with iron within the veneer.

We usually veneer with UF glues, resin powder mixes. The product market is in the process of change my favourite Borden UL39 has just been discontinued and replaced with F120.

http://www.hallmarkfraulo.co.uk/productdetail/F120

Cheers Peter

Thanks Peter. I've had a look and saved the link, it must be good stuff if it's your go-to adhesive. I've ordered some Titebond now, so we'll see how that does.