Thread: Flattening Veneers

First attempt for me is a good spritz with misted water then clamp between good solid and flat cauls - i.e. a cold press. Then I ramp up from there if that is unsuccessful, using warm to hot water for small sheets, to getting more serious with some recalcitrant veneers having to resort to steaming as you would for steam bending. Have to keep in mind how the water may react with the wood and any potential contaminants in your workspace though. Steelwool dust, Queensland Maple and warm water aren't a good combination.

I find layering sheets of veneers between plain (unprinted) news paper / butchers paper and alternating (flipping) the direction of veneer sheets (if consecutive sheets) so that the badly warped sections are not on top of each other works best for my small stuff.

Larger veneer sheets used for large furniture pieces require a different approach. As a kid I used to sneak in to watch the veneer & ply mills operating in Cairns in the 1960's. From memory all that was used was heat (steam) and pressure.

Originally Posted by Mobyturns

Larger veneer sheets used for large furniture pieces require a different approach. As a kid I used to sneak in to watch the veneer & ply mills operating in Cairns in the 1960's. From memory all that was used was heat (steam) and pressure.

I fear that this is the truth, especially for 3 mm veneers. All I need now is a four foot long microwave oven or to build a steamer ... something I have been avoiding.

How thick will your substrate be?
Is that ply, mdf, or solid?
If thick can you veneer individual leaves and trim, and edge join each "board"?
I was thinking narrower strips maybe (maybe) easier to manage, clamp
Judging by those photos there's some strong grain pull that would no doubt need the treatment described above too

Originally Posted by Avondale

How thick will your substrate be?
Is that ply, mdf, or solid?
If thick can you veneer individual leaves and trim, and edge join each "board"?
I was thinking narrower strips maybe (maybe) easier to manage, clamp
Judging by those photos there's some strong grain pull that would no doubt need the treatment described above too

I'd rather not have edge joined MDF boards for the doors of my cabinets and etc.

I think I need to build a steam box that will take veneers are almost 300 mm wide. Double Bugger!

Silly question, but what would be the effect of a steam iron on veneers? With a flat MDF substrate as the "ironing board". Some irons can kick out a fair head of steam !

Originally Posted by John Samuel

Does anyone have ideas to share?

Did you saw them from the solid John?
When sawing veneer from solid I machine and tooth plane the gluing face before each piece is sawn from the board. Then if it did warp a slight moisten and weighting it down with something like a sand bag or news paper first and sand bag will flatten them . One at a time though. Id only be doing that just before pressing them if it was a water based glue being used. If its not water based glue then maybe a hot sand bag or iron it down flat. The pressing when gluing will sort it out after that. The important part is having a flat side before sawing them off the solid piece at the start.

Originally Posted by auscab

Did you saw them from the solid John?
When sawing veneer from solid I machine and tooth plane the gluing face before each piece is sawn from the board. Then if it did warp a slight moisten and weighting it down with something like a sand bag or news paper first and sand bag will flatten them . One at a time though. Id only be doing that just before pressing them if it was a water based glue being used. If its not water based glue then maybe a hot sand bag or iron it down flat. The pressing when gluing will sort it out after that. The important part is having a flat side before sawing them off the solid piece at the start.

I did that Rob,

But I most commonly book leaf the veneers. That means that one veneer has the planed face to be glued face down and the other is face up.

Normally, after I saw off the veneers I immediately sand them to an even thickness ... problem solved. because the timber is dry, they will usually stay flat enough for further work ... even months later. The occasional warp can be heated with a heat gun and clamped between some boards. Again, problem solved. However, this time I have significant warping.

This time I had a green slab and nowhere to put it. I decided to cut it green and air dry it in my workshop. The drying only took about three or four weeks. But I now have warped veneers that I dare not put through the sander without flattening them first.

The only solution I can think of is to heat the veneers and then to clamp them flat. The only way I can think of heating them is to build a steam box that will hold 300 mm wide veneers. I am not at all sure that the techniques involving glycerine and etc will work with 3 mm veneers.

A steam box will work but its possibly a bit overkill for 3mm thick wood. Quite often the moisture held within the dry timber is enough to make it shift with the help of some heat. You can always spray on a bit more off course. Getting say a shoe box lid size ( or larger) flat bit of wood hot enough all over quickly is the tricky part. When I need to do such heating I have a 20 lt drum with the lid cut off and I pour 20 mm of metho in and light that up. First I do it outside to burn off the paint then it can be used inside. With that I have heated a cold workshop on many freezing Melbourne winter mornings before I had a better heater just to get the place workable first thing. And I used it to heat steel and timber cauls for pressing veneers a few times. You could heat up each piece of veneer with that holding and flipping it using cooking tongs and then flatten it with a cold weight like a sand bag. You would then have better control over moisture than the steam box.

Originally Posted by auscab

A steam box will work but its possibly a bit overkill for 3mm thick wood. Quite often the moisture held within the dry timber is enough to make it shift with the help of some heat. You can always spray on a bit more off course. Getting say a shoe box lid size ( or larger) flat bit of wood hot enough all over quickly is the tricky part. When I need to do such heating I have a 20 lt drum with the lid cut off and I pour 20 mm of metho in and light that up. First I do it outside to burn off the paint then it can be used inside. With that I have heated a cold workshop on many freezing Melbourne winter mornings before I had a better heater just to get the place workable first thing. And I used it to heat steel and timber cauls for pressing veneers a few times. You could heat up each piece of veneer with that holding and flipping it using cooking tongs and then flatten it with a cold weight like a sand bag. You would then have better control over moisture than the steam box.

Thanks, Rob.

I have 22 veneers 300 mm long and about 1,200 long. Some are warped in only one or two sections. Others are warped quite badly.

The trick is to get them hot enough. If I can get the veneer hot enough I can slip the veneers between a couple of pieces of MDF and into a vacuum press. I saw a video years ago where a bloke had built a microwave oven big enough for such jobs. I am green with envy!

Originally Posted by Mr Brush

Silly question, but what would be the effect of a steam iron on veneers? With a flat MDF substrate as the "ironing board". Some irons can kick out a fair head of steam !

Great minds think alike ...

The iron was my first attempt. It half worked. Certainly the warping was reduced, but not by enough to get me out of trouble.

The good news is that several blokes have given me what seem like workable ideas, so I'll start trying a few of them. I am sure that if I get the veneers hot enough and clamp them flat enough that the problem will be solved.

When I made my Georgian Knife boxes I had to deal with thick crotch mahogany, what I ended up doing after researching it was to spray with a homemade veneer conditioner, can't remember all the ingredients you can google it, but it included water and glycerin. After wetting down it was sandwiched between fly screen which was sandwiched and clamped between thick ply sheets. I believe because I was hammer veneering, I may have also tried sizing it with hot dilute hide glue before doing the sandwich thing...

I found the information I used when I was veneering. It was from the book Veneering : A foundation course by Mike Burton. He recommends a water spray bottle and an iron for minor flattening. Then water/glycerin/alcohol 1gallon/8oz/8oz. Sandwich between melamine sheets. Over a few hours gradually place more weight on the sandwich and after a few hours clamp it. Maybe clamp overnight. Steaming (as you've been researching). My steam generator was a 5l new petrol can, a radiator hose and a iron ring burner. You should pretreat the veneers with water an hour or so before steaming for 3-5 minutes. Oversteaming will make it brittle. You then need to add something like one-sided corrugated cardboard around the veneers in the clamped stack and leave to dry for several days. You can size with hot hide glue (one part glue 5 parts water) in the flattening stage if you are going to use hide glue to glue. It is not recommended if you will glue with PVA as they're not completely compatible. You will need to sandwich between flyscreen to prevent the glue sticking to the cardboard.

Originally Posted by mic-d

I found the information I used when I was veneering. It was from the book Veneering : A foundation course by Mike Burton. He recommends a water spray bottle and an iron for minor flattening. Then water/glycerin/alcohol 1gallon/8oz/8oz. Sandwich between melamine sheets. Over a few hours gradually place more weight on the sandwich and after a few hours clamp it. Maybe clamp overnight. Steaming (as you've been researching). My steam generator was a 5l new petrol can, a radiator hose and a iron ring burner. You should pretreat the veneers with water an hour or so before steaming for 3-5 minutes. Oversteaming will make it brittle. You then need to add something like one-sided corrugated cardboard around the veneers in the clamped stack and leave to dry for several days. You can size with hot hide glue (one part glue 5 parts water) in the flattening stage if you are going to use hide glue to glue. It is not recommended if you will glue with PVA as they're not completely compatible. You will need to sandwich between flyscreen to prevent the glue sticking to the cardboard.

mic-d

Something I've not been able to determine is whether the method using the glycerin mix method will work on 3 mm veneers. I know it works on the thinner 0.6 mm veneers, as does the spray bottle and iron method. I find myself wondering if the mixture will penetrate through to the centre of a 3 mm veneer.

Thanks for the advice about over-steaming.

Originally Posted by John Samuel

mic-d

Something I've not been able to determine is whether the method using the glycerin mix method will work on 3 mm veneers. I know it works on the thinner 0.6 mm veneers, as does the spray bottle and iron method. I find myself wondering if the mixture will penetrate through to the centre of a 3 mm veneer.

Thanks for the advice about over-steaming.

I don't know the answer to this for sure, but I suspect that because your veneers are new from green wood and only air dried they still contain a good amount of moisture as I think Auscab said too, so you should easily be able to rehydrate it and the glycerin will help in this. It may require patience like a soak overnight as a suggestion. Being fully saturated will assist when you heat it, however you decide to heat it.

How are you going to glue the veneer? If you might use a vacuum bag, it would be worth testing whether this will pull it down onto a substrate without flattening.

I suddenly started picturing you using a steam clothes press like Bee used in Prisoner to flatten that inmates hand... I'm being partly serious as I think it would be difficult to find one... EDIT - I just had a look on FB Marketplace and this is the sort of thing I mean Log into Facebook . Maybe you could find one or borrow one your neck of the woods