Resin infusion with wood veneers

[mckenzie.keith]

I am wondering if it is possible to do resin infusion with wood veneers. The problem as I see it is that there is no resin flow channel between the veneers so resin can't get in there. But maybe there is some kind of scrim or something you could put between the veneers that would maintain a channel and allow resin to flow in there. The scrim would obviously become a permanent part of the lamination.

Or the other idea would be to finely score the mating faces of the veneers to create a channel.

Anybody ever do anything like that?

 

[SimonGH]

I've not done it with wood veneers...

As you've deduced, when you do it under vacuum, the plies will be squeezed together with significant force.  if there is not something incompressible between the layers, you're going to get a wet edge (as far as the resin will "wick" into the material), but that's about it.

So as you state, the trick is to get resin flowing in all areas enough to saturate the fibers of the wood.  The idea of channels or scrim could work, but you'd need to consider (and perhaps experiment first):

1. The depth of saturation is going to be dependent on the veneer type.  Wood is like a fiber composite, but it's already got a "matrix".  So a more open & porous wood would allow resin to penetrate deeper into the structure (also depends on the viscosity of the resin).  Consider that something really thin like water can penetrate pretty deeply even into hardwood.  So if i were trying to figure this out, I'd take a sample of the veneer and the resin and see how far it would "wick" into the wood.  Then you can determine the spacing for your grooves etc.  I would guess that the denser the wood, or the thicker the resin, the closer the "grooves" would need to be.

2. What are you trying to accomplish?  You may be better off just "pre-loading" the layers with resin (like brushing it between each layer), and then just using vacuum to press it together.  

Are you basically just trying to make you're own plywood with veneers?

 

[mckenzie.keith]

I've not done it with wood veneers...

As you've deduced, when you do it under vacuum, the plies will be squeezed together with significant force.  if there is not something incompressible between the layers, you're going to get a wet edge (as far as the resin will "wick" into the material), but that's about it.

So as you state, the trick is to get resin flowing in all areas enough to saturate the fibers of the wood.  The idea of channels or scrim could work, but you'd need to consider (and perhaps experiment first):

1. The depth of saturation is going to be dependent on the veneer type.  Wood is like a fiber composite, but it's already got a "matrix".  So a more open & porous wood would allow resin to penetrate deeper into the structure (also depends on the viscosity of the resin).  Consider that something really thin like water can penetrate pretty deeply even into hardwood.  So if i were trying to figure this out, I'd take a sample of the veneer and the resin and see how far it would "wick" into the wood.  Then you can determine the spacing for your grooves etc.  I would guess that the denser the wood, or the thicker the resin, the closer the "grooves" would need to be.

2. What are you trying to accomplish?  You may be better off just "pre-loading" the layers with resin (like brushing it between each layer), and then just using vacuum to press it together.  

Are you basically just trying to make you're own plywood with veneers?

I may or may not actually do this. But yes, the thought was to experiment with making my own plywood with veneers. Thank you for validating my thinking on it, and I like the suggestion for empirically determining the groove spacing.

I have already made small panels by brushing on the epoxy and then just vacuum bagging. When I cut through the samples there was the odd small void here and there. Not large voids. Just kind of like "bubbles." My thinking is mainly that infusion might produce a void free result, and perhaps be less wasteful of epoxy compared to slathering it on and letting it ooze out everywhere in the hopes of eliminating voids that way. I also think controlling the thickness of the glue line might be valuable.

I do have a sizeable amount of wood in my barn that I could cut up for this purpose. And it is redwood. You can't buy redwood plywood as far as I know. So if I do this it will produce something that is unique, which might be a good enough excuse to at least build a few test panels.

 

[BurnsideStyle]

Are you bagging your test panels with thick platens top and bottom?

How thick are the veneers you are using? Seems like you are talking about shop sawn - the hard part for larger panel sizes will be edge gluing the sawn veneer pieces together, flattening those layers then pressing them all together into the ply sandwich. Got a wide belt?

I think that the way to add veneer to an infusion stack would be for it to be on the bottom, with f/g and scored foam on top.

 

[mckenzie.keith]

Are you bagging your test panels with thick platens top and bottom?

How thick are the veneers you are using? Seems like you are talking about shop sawn - the hard part for larger panel sizes will be edge gluing the sawn veneer pieces together, flattening those layers then pressing them all together into the ply sandwich. Got a wide belt?

I think that the way to add veneer to an infusion stack would be for it to be on the bottom, with f/g and scored foam on top.

In my test panels I did it with about 1.5" wide strips of wood. About 2mm thick. Cut on a bandsaw.  They were a bit uneven in thickness. I vacuum bagged them with moderate amounts of weight on top. The vacuum kept plenty of clamping pressure on them. The idea of the weight was to prevent warping.

My thinking going forward is to plane the strips then edge glue them vacuum bagged down on a very flat table (probably a glass table top) to create a ply. That step would not use any infusion. But the vacuum should keep the faces even. Then I will vacuum bag multiple layers together, clamping them down to the glass with vacuum pressure. This is the point where I am trying to figure out how I can get infusion to work, to let the epoxy infuse between the plys.

 

[CaptainAhab]

You need to work on your vacuum bagging techniques. Infusion should not be considered for wood veneer. It's simply wrong. No benefits many problems. We do wood circular staircases, boat hulls, boat decks all vacuum bagged with no issues.

 

[SimonGH]

Yes, after thinking about this, if you're trying to make plywood you're not trying to saturate the wood completely like in a laminate - you're just trying to glue things together.  Otherwise you're creating a solid resin soaked wood lump - it would be quite heavy.  The idea behind vacuum bagging is to consolidate the layup and actually minimize resin content (while avoiding voids) in a laminate - compared to the fibers the resin is extremely weak and heavy, so less is more.  Properly done infusion actually allows you to very accurately control the amount of resin going into the laminate.  All things irrelevant to your use case!

You need to experiment with the adhesive you're using.  If you apply prior to vacuum bagging, then you may actually want something with less viscosity (add thickeners), so it doesn't squeeze out as readily.

If you're trying to make flat items then you want to use the substrate as part of your vacuum bag - so a glass table or a sheet of melamine (waxed!) over 3/4 MDF would work well.  You tape the bag directly to the table.  Then you have 14.7psi keeping everything flat.

 

[Feisty!]

I would expect that wood would outgas slowly under vacuum, possibly producing bubbles. Simple vacuum bagging would preserve the bubbles when cured. Infusion, with a suitable dwell under vacuum and before introduction of resin should reduce the bubbling as well as pressure impregnating the surface of the wood.

There are products available for use as flow media that can be left in the composite. For small areas and slow kicking epoxies, common wedding veil from a fabric store seems worth trying.

 

[BurnsideStyle]

If you're trying to make flat items then you want to use the substrate as part of your vacuum bag - so a glass table or a sheet of melamine (waxed!) over 3/4 MDF would work well.  You tape the bag directly to the table.  Then you have 14.7psi keeping everything flat.

I second this above method.

You are going to have to hand lay it up and vacuum bag each sheet. Attached a photo of a small piece of Mahogany shop made plywood, this was to replace the pierced, ornamental back on a dining chair.

Re-saw, edge glue each layer, flatten layers (both sides), layup into plywood, vacuum bag.

Also, have you thought about just using your Redwood as veneer layers on nice plywood? Why do you want to produce redwood veneer cored ply?

 

[mckenzie.keith]

You need to work on your vacuum bagging techniques. Infusion should not be considered for wood veneer. It's simply wrong. No benefits many problems. We do wood circular staircases, boat hulls, boat decks all vacuum bagged with no issues.

Thanks CaptainAhab. How thick are the veneers usually, and what epoxy do you use? Do you apply copious amounts and let it squeeze out or do you control it carefully? I realize I am asking a lot of questions. I appreciate your suggestions. I am just trying to get as many tips as I can.

 

[mckenzie.keith]

I would expect that wood would outgas slowly under vacuum, possibly producing bubbles. Simple vacuum bagging would preserve the bubbles when cured. Infusion, with a suitable dwell under vacuum and before introduction of resin should reduce the bubbling as well as pressure impregnating the surface of the wood.

There are products available for use as flow media that can be left in the composite. For small areas and slow kicking epoxies, common wedding veil from a fabric store seems worth trying.

This sounds good. I have seen wood under high vacuum produce loads of water vapor. But both vacuum bagging and infusion are done on balsa core, so this by itself should not be a show stopper. It may be necessary to use fairly dry wood though.

 

[CaptainAhab]

This sounds good. I have seen wood under high vacuum produce loads of water vapor. But both vacuum bagging and infusion are done on balsa core, so this by itself should not be a show stopper. It may be necessary to use fairly dry wood though.

I have no idea what you are writing about. Seeing water vapor??? The wood is 6-8% moisture content. It effectively can't get any lower in the real world. 

Veneering and plywood has been done all over the planet for a long long time. Old old school is to manually apply pressure with a tool, old school is weight, clamps, or a press, new school is a vac pump.  

This isn't complicated. 

 

[Feisty!]

Vacuum has effects that mechanical compression does not - like causing things like water and polyester resin to vaporize (boil) ...

 

[mckenzie.keith]

I have no idea what you are writing about. Seeing water vapor??? The wood is 6-8% moisture content. It effectively can't get any lower in the real world. 

Veneering and plywood has been done all over the planet for a long long time. Old old school is to manually apply pressure with a tool, old school is weight, clamps, or a press, new school is a vac pump.  

This isn't complicated. 

Well, technically you can't see the vapor because it is transparent. I have seen condensation in the vacuum tube caused by vapor leaving the wood and then condensing in the tube. The wood I was using was probably not very dry.

In my mind what I am saying is not very complicated either. You are probably aware that some people actually use vacuum kilns to dry wood. Gallons and gallons of water can be removed from a batch of wood in a vacuum kiln. I can't really tell what point you are trying to make other than you think I am over-complicating this.

 

[CaptainAhab]

If you have wet wood and pull a vacuum on it you will pull water out of it. 

Your project is bonding a wood veneer that is millimeters thick. It has the moisture content of a piece of dry paper. You are bonding it to a substrate that in real world terms effectively has no water in it. If it has enough water in that you are pulling it out with a vacuum pump you should not use epoxy resin. Waterbased adhesives would be the obvious proper choice.

Resin infusion under veneer or between any other pieces of wood is over complicated. If you were trying to create some kind of composite panel with dry fiber between two pieces of wood you could in theory resin infuse it. In that case, there are other ways to accurately control the resin content instead of infusion then bag it.

I'm trying to help you from making this project into a fool's errand.

 

[mckenzie.keith]

If you have wet wood and pull a vacuum on it you will pull water out of it. 

Your project is bonding a wood veneer that is millimeters thick. It has the moisture content of a piece of dry paper. You are bonding it to a substrate that in real world terms effectively has no water in it. If it has enough water in that you are pulling it out with a vacuum pump you should not use epoxy resin. Waterbased adhesives would be the obvious proper choice.

Resin infusion under veneer or between any other pieces of wood is over complicated. If you were trying to create some kind of composite panel with dry fiber between two pieces of wood you could in theory resin infuse it. In that case, there are other ways to accurately control the resin content instead of infusion then bag it.

I'm trying to help you from making this project into a fool's errand.

So I should just apply resin between layers with what a chip brush or notched spreader or something? Then bag it down to the flat table and pull like half an atmosphere of vacuum or something?

 

[SimonGH]

yes.

If you find that a lot of the resin oozes out and you get voids, then I would play with thickeners..