Sanding Sealer versus Grain Filler

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Blog entry by Tootles posted 07-21-2011 11:36 AM 23410 reads 4 times favorited 5 comments Add to Favorites Watch

I’m probably writing something that many people already know, but I’m writing this as much for myself, to remind me later what I’ve learned, as for any others out there for whom this is new.

I’ve just recently made a box, mainly out of Tasmanian Oak. It’s my first real project of any significance in over twenty years and I’ve had fun doing it. But I got to the stage where it is complete bar the finishing and that’s where I got a little stuck.

In the past I’ve always applied sanding sealer, sanded it back really well and just polished with wax polish. This simply brings out the natural colours of the wood with some shine. It is also has a really silky feel to it. Trouble is that when I did my last project, I lived in a different country with different products available so I’ve had a learning curve to be able to do this again – if that’s what I do choose to do.

So, first lesson: This came about quite accidentally, but I cut a few squares of left-over timber from the box to test different finishes before I pick the one tht I will use on the box. Good move – must remember to do that again in the future.

Second lesson: We have two products available here in Australia, sanding sealer and grain filler. Now I always thought that sanding sealer worked by filling the grain so that when you sanded it, all you did was take the sealer off the top of the surface leaving the sealer behind in the gaps between the grain so that the wood surface comes up really smooth. Well, it turns out that my woodwork teacher was wrong on that one. And that means that sanding sealer and grain filler are not equivalent – in fact, they are quite different.

When sanding sealer is applied to unfinished wood, which is what is should be applied to, it raises the grain – in other words it basically causes the surface fibres of the wood to swell up so that they can be easily sanded off and, I presume, out sideways to close the gaps between adjacent fibres. You then sand (most of) the residue sealer off leaving the wood exposed to form the surface. This means that it is as amenable to absorbing oil or polish as it is to being varnished or stained.

Grain filler is not applied to unfinished wood. It is applied after at least one coat of finish has been done, be it stains, french polish or lacquer, but before the final coat is applied. Grain filler does fill the gaps between the grain and so is intended for open grained wood (walnut, maple, cedar, meranti and, I’d say, oak). It does not affect the surface fibres of the wood in any way. That means that you cannot sand it after application and before the next coat of the finishing product. It also doesn’t seem to take polish very well – though that is more my observation than a fact stated by the manufacturer.

Some other points:
- Sanding sealer can be sprayed, brushed or wiped onto the wood, grain filler must be applied with a course cloth such as hessian.
- Sanding sealer is sanded off when dry, grain filler is wiped off (excess only) again using a course cloth such as hessian. In fact, grain filler must not be sanded as it both clogs the sand paper and pulls the filler out of the grain.
- Sanding sealer is clear (though it can be applied after a stain), grain filler is also clear but can have stain added to it before being wiped onto the wood.
- Neither sanding sealer nor grain filler is suitable for use under a two-pack stain / varnish (this could be brand specific)
- Clean up for both is with Mineral Turpentine.

Well that’s it. I started out buying a tin of grain filler, but that has not provided the results that I want, because I’ve used it the wrong way of course. I have since bought a tin of sanding sealer and and have a coat drying as I type. If it works as I hope, then I still plan to polish my box. Otherwise I need to decide between a satin and a gloss finish varnish – and then the grain filler will almost cerainly be used between coats.

And when it is all done, I’ll post the project.

-- I may have lost my marbles, but I still have my love of woodworking

5 comments so far

View Chris Davis's profile

Chris Davis

1560 posts in 4153 days

#1 posted 07-21-2011 02:12 PM

Great post. Thanks for the info.

-- Watch live video from our shop.!current-projects/c3c1

View BritBoxmaker's profile


4611 posts in 3208 days

#2 posted 07-21-2011 09:43 PM

I prefer your original method. Sanding sealer then wax. Easy, true colour and silky finish.

Having said that this is all very useful information. Thanks for posting.

-- Martyn -- Boxologist, Pattern Juggler and Candyman of the visually challenging.

View Karson's profile


35139 posts in 4572 days

#3 posted 07-21-2011 09:57 PM

Something to add to your trials.

I posted a blog an grain filling many days ago. You can use punice and rottonstone as a grain filler.

You can find it in the link. There is a contuination of the blog, the link is at the top of the link I gave you.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Appomattox Virginia †

View gfadvm's profile


14940 posts in 2861 days

#4 posted 07-22-2011 04:15 AM

I apply Timbermate grain filler to unfinished wood with a credit card across the grain, allow it to dry, and then apply stain, finish, or just wax^^. I sand to 150 grit before applying the Timbermate. You can also fill grain nicely by wet sanding with BLO to create a slurry, wipe excess off across the grain and then finish however you like. I think Timbermate is an Australian product? ^^ Sand the dried filler to 150 or higher before applying stain or finish. Hope this helps.

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

View Tootles's profile


808 posts in 2673 days

#5 posted 07-22-2011 01:57 PM

Thanks guys. I have a lot to learn and a great resource from which to learn it.

I think the final decision has been made. I did say that I had a trial running with sanding sealer that would be polished, well my wife says she likes that one. Actually, I rather like it too – it has come out really smooth and silky to the touch. I wouldn’t call it highly glossed, but there is a nice gentle shine to it – and that’s the way my wife likes it. Who am I to argue?

-- I may have lost my marbles, but I still have my love of woodworking

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