I've read that wood conditioner (also known as pre-stain) helps prevent blotching, but it 'designed' for use with soft or porous wood.
I've got an 80x36x1" red oak panel that I think I'm going to stain. Red Oak is not considered a soft wood, but would Pre-Stain help my staining project turn out more uniform anyways?
Furthermore, if I change my mind on staining, but still wish to do a poly coat, does Pre-Stain do anything beneficial for that?
It depends. On blotch prone woods such as pine, poplar, cherry, and maple, yes. On oak and walnut, it depends. A pre-stain conditioner can limit absorption and therefore the shade of the stain - it may not be as dark. Pre-stain conditioning will even out the color tone across the piece, and this may or may not be desirable, i.e. for a more rustic look don't condition. End grain, especially for red oak, will absorb much more stain. It can be conditioned by itself, but that can be difficult. I prefer to sand the end grain to ~600 and then burnish it with a polished piece of metal. This closes off the pores and limits absorption.
There are multiple approaches to pre-stain conditioning. The solvent based products I am aware of are simply solvents that are absorbed by the wood grain until saturated, and then begin evaporating. You need to stain within a time window - too early and not much stain is absorbed, too late and more blotching occurs.
Thinned topcoat finishes, such as shellac and lacquer can be used. The problem is they dry quickly, and don't allow the uneven absorption by the wood grain to occur.
The best conditioners are water based, and can be used with solvent or waterbased stains and topcoats. About any water based topcoat can be thinned 50/50 with water and used as a pre-stain conditioner. Also, PVA glues can be used, thinned with water 4-10 parts water to 1 part glue. I use Elmers Glue All 4 parts water to 1 part glue. It is the cheapest and dries clear.
Water based are best because of the long open time and relatively quick dry time. The long open time allows the conditioner to be absorbed unevenly by the grain. the water evaporates leaving more sealer in the more porous areas resulting in more even stain absorption. It will not affect the amount of pigment deposited on the surface for a pigment type stain. It effects the dye portion of the colorant. Solvent poly could also be used (long open time) but has a very long dry time. I have not tested it and don't know the thinning ratio.
Apply the water based conditioner by flooding the surface (spray, brush, sponge, doesn't matter) then using a brush keep spreading and adding until the surface stops absorbing, then wipe it off with dry rags/paper towels and let dry. Sand lightly with either the last grit used or the next one up - remove the raised grain but don't cut too much away. Pine will swell significantly, and leveling the surface will remove the conditioner in spots. It needs a 2nd application. Stain and topcoat with solvent or waterbased products as usual.
Yes, a coat of solvent poly (or a water based finish) can be applied over any of the conditioners described. Allow the solvent conditioner to evaporate completely, and let the water based conditioner dry, then apply the poly.
It is highly recommended to test any new finish or preparation method on scrap first.
Red Oak is an open pored wood vs. White Oak which is a closed pore wood. Using a pre-stain on red oak can help close the pores to reduce the stain absorbed.
Here's a video by Bruce Johnson recommending pre-stain and he's working with Oak cabinets. He says it's best for pine and problem woods like aspen and alder.
So what I get from that is, it can ensure you get a nice even stain on any wood, but many hardwoods don't usually need them. But if you are worried, then better safe than sorry.
While it will probably have a greater effect on softwoods, it certainly won't hurt to use it on hardwood. As minwax's faq says, hardwoods have more even pores and thus take stains better. Bear in mind, this is for oil based stains. The pre-stain is oil based just like the stains, so if you use it, you'll probably get poor results with a poly finish even if you don't stain.
If you use a water based stain, then you can use a water based pre-stain and then polyurethane should be fine.
Another option would be to use a one-step product which stains and finishes.
As with any project, test on scrap before you do it on your finished piece.
I've read that wood conditioner (also known as pre-stain) helps prevent blotching, but it 'designed' for use with soft or porous wood.
More accurately wood conditioners are designed for blotch-prone woods, which softwoods are known to be. But a few species of hardwoods are also prone to blotching too, including American cherry and birch.
More on this at bottom, but what conditioning does is partially seal off areas of the wood that are particularly absorbent, so that they don't soak up a greater amount of stain than the surrounding areas that are less absorbent.
With your panel specifically it may help somewhat or very little, there's no way to predict in advance (normally it would be advisable to run a quick test, check for results before committing to the workpiece). Given the size of the panel you mention it is obviously a glue-up or plywood, and on the former it could well help even out the results if the grain orientation is less than uniform from one board to the next, or if the boards are taken from more than one tree which is possible. On plywood I wouldn't want to predict any benefit, but pre-sealing can't hurt.
Note: you can sidestep the worries concerned with blotching by using a colouring product that doesn't stain the wood itself. Gel stains are the classic answer here, and coloured varnishes can give similar benefits.
Furthermore, if I change my mind on staining, but still wish to do a poly coat, does Pre-Stain do anything beneficial for that?
Not as a rule no. But it shouldn't do anything negative either (depending on specifics).
Commercial wood conditioner/pre-stain conditioners are merely proprietary products designed to partially seal the wood.
But prior to the introduction of such products this wasn't impossible, the same result was achieved by using something the woodworker prepared himself, e.g. using a 'spitcoat' or highly thinned layer of shellac. More recently both heavily diluted varnish and a watery mixture of PVA-type wood glues have also been utilised for the same end. All three methods are currently in use by someone and they work about as well as the commercial product, sometimes not as good sometimes better, because of the usual reason that wood is a natural product and varies so much.
I have never used any of the pre-stain wood conditioners but I have used a very thin coat of shellac for the same purpose and can verify that it works on both pine and cherry. The shellac method also seals the end grain somewhat and thus prevents it from absorbing too much stain which is also a common problem.
Watco Danish Oil might also work but I've never tried any of the colored varieties on cherry; I've only used the clear stuff.
