veneer problems

[pip1954]

hi i have made some tables for her in doors and veneered the tops with walnut with pva type glue and sprayed with morels laquar after a couple of weeks the veneer is starting to lift in lines across the tops (along the grain) it looks like cracks the tops are mdf two skins of 12mm glued together
question what have i done wrong
veneered some other bits and they where fine glued and finished the same way with same glue
could the glue be of
would i be better of using casamite
pip

 

[custard]

Pip, a few questions,

1. Is the veneer knife cut commercial veneer or did you bandsaw them yourself? What were the veneers like before you laid them, flat and well behaved or wrinkly and brittle?

2. How did you press the veneers after laying them?

3. Is the veneer lifting ( ie delaminating from the MDF ground) or is it splitting (ie shrinking and pulling apart)?

4. How big is the top?

5. Did you put a balancing veneer on the other side? Has the top stayed flat?

6. Did you lay a single piece of veneer or did you join a number of veneer leaves? If you joined multiple leaves are the joints separating?

 

[pip1954]

hi custard thanks for reply
1 commercial
2 weighted board on top and c lamped
3 it is lifting splitting not shrinking
4 500 x 600 mm
5 not 2 skins mdf glued top flat
cheers
pip

 

[Chrispy]

Hi Pip,
I think it sounds like not enough press power, by my maths you have about 500 square inches of surface there at say 10 pounds per square inch that would be 5000 pounds of weight you would need and then you need to get it even over the whole area and within a few minutes does that sound feasible.
Also how did you spread the glue it has to be very even ie a roller it won't spread its self like a rubbed edge joint would.

 

[Peter Sefton]

Hi Pip
What PVA did you use, make, D rating and age?
Has the backing veneer been finished in the same way and has that also suffered?
Peter

 

[wellywood]

Pip. Did you rough-up the mdf surface first? I often use mdf as a ground for veneering but find I have to get rid of the 'shiny' finish first to get a good bond. Having said that, I do use animal glue rather than PVA so perhaps it's less of an issue.

 

[custard]

Hello Pip, I suspect lack of clamping pressure plus the possibility, as Peter Sefton pointed out, that it could be old glue or PVA that the frost has got at. If PVA starts looking the slightest bit "stringy" or has watery fluid separating out from it, then it's time for the bin.

You can sometimes recover a lifted PVA veneer by ironing it on a medium heat then rollering it back down hard.

 

[mailee]

I always use PVA for veneering and have had no problems so far. It could be that the glue has gone off as I have just lost almost a gallon due to the cold temp. :roll:

 

[pip1954]

hi all many thanks for all replys
sounds like not enough pressure maybe to much glue if that possible i put it on with paint brush maybe i will have to have a rethink
how do most people do veneering what tools do you use :shock:
a bit annoyed have wasted my time they looked good now they look a mess a bit disheartened
cheers
pip

 

[custard]

Pip, I've been veneering for nearly forty years. You can do it with just a few quid's worth of simple tools, or you can have state of the art equipment costing millions and veneer on an industrial scale...or you can be anywhere in between!

I'm surprised traditional veneering isn't more popular amongst hobbyists as it's a way of using extraordinary woods at modest costs.

If you want to learn to do the job properly (and believe me, basic veneering really isn't that complicated) there are some excellent books out there. The Complete Manual Of Wood Veneering by William Lincoln was for a long time the bible of veneering, I think it's out of print now but copies aren't too expensive. More modern and properly a better guide for beginners is Veneering, A Complete Course by Ian Hosker.

 

[wellywood]

Hi Pip. It's a fair sized subject and like most you'll get a lot of conflicting advice
You could do worse than get a good book on the subject. I started off with Burtons 'Veneering - A Foundation Course'. He takes away a lot of the mythology.
As to tools, sure you can invest in commercial veneering saws, veneer hammers etc. but I use a simple lino cutters knife (the type with the hooked blade) ground flat on one side to follow a straight edge and bevelled the other to suit if your a left or right hander. BTW if you are a lefty, try finding a left-handed veneer saw! The veneer hammer I made myself from some scrap wood with a dowel handle and with a blade of 5mm thick acrylic rounded at the corners and along the edge.
Also have a think about the glues you are using and initially go for those with a longer open time so you can more easily correct any mistakes at the time until you become more proficient.
Oh. And don't be ashamed to ask questions on the forum. There's a lot of experience here and the blokes like to share

 

[RogerS]

Both John Lloyd and Peter Sefton run excellent veneering courses.

 

[pip1954]

hi wow thanks to all
i have just bought the book recommended by custard
complete manual of veneering
can't wait for it to arrive
all the best
piop