Sanding sealers

[Student]

My apologies if this has been covered here recently but, as a newbie, I'm a bit clueless about the uses of the various types of sanding sealer. Up until recently, all my painting has been of internal joinery or outside window sills so no sealer has been needed just primer/undercoat/topcoat(s). Now that I have started trying to make some bits of furniture for the house, I am using MDF, hardwoods such as oak and beech and softwoods such as pine. Painting is no problem except getting a decent finish on the machined edges of MDF but what's the best sealer for wood if I want to stain and either varnish or oil or wax afterwards.

Looking at the Axy site they sell MDF sealer, cellulose sanding sealer, acrylic sanding sealer, spirit based sanding sealer and shellac sanding sealer.

Can someone please let "Confused of Bristol" have an silly person's guide to what sort of sealer to use where?

P.S. I hope that this is not going to open a can of worms like asking the best way to sharpen chisels or the best way to set out dovetails!

 

[Grahamshed]

Oh, you haven't heard about the great sealer wars then ?

Seriously though, I look forward to the answers as much as you.

 

[Terry Smart]

A sanding sealer has many purposes; to fill the pores of the wood to stop a finish coat from soaking in, and to bind the fibres of the timber together prior to sanding to give the best possible surface for finishing among others

There are thee main types:

Cellulose - suitable for finishing with most things afterwards (wax, polishes, lacquers). This is nitro-cellulose based and very quick drying.
Shellac - mainly used for overcoating with wax or French Polish or Friction Polish. Slower drying and useful if you're trying to keep a wet edge running on a larger area. Meths based
Spirit based - as shellac but without the shellac in it! Uses a cheaper substitute.
Acrylic - water based, overcoat with wax, polishes or Acrylic Lacquer. Slower drying, no smell and no flammability.

Opinions vary, as they always do, but we wouldn't suggest putting a sealer on before oiling. If you must use a varnish then either Cellulose Sanding Sealer or a thinned coat of varnish can be used.

That's a real 'in a nutshell' answer, don't want to get bogged down with too much information, but feel free to ask any other questions.

 

[RogerS]

Terry's got it in one.

The only advice that I would give and applies to all consumables such as finishes, stains and adhesives ...namely to write the month/year of purchase on the tin. A lot of this stuff has a limited shelf-life and the last thing you want to happen to your pride and joy is to screw it all up because the finish has gone off in the tin. It's a false economy. I will bin my stuff after a year (ready mixed, naturally...stuff like Van Dyke crystals have a longer shelf-life)

 

[marcros]

good point. they can look perfect in th tin/bottle/container, and can go onto the piece as normal, but remain tacky etc.

I also but small amounts of adhesive, often. Aim for pva, for instance, to last between early spring and late autumn, then get rid of the littke that remains. for things like shellac, i will buy flake now and mix my own, because it soon amounts up if you have bought a few finishes and used very little before they go off.

 

[Student]

Thanks Terry. It looks as if, for what I shall be doing, cellulose or acrylic are what I will need depending on drying time.

Thanks also to Roger and marcros for their input.

Martin

 

[Roughcut]

I don't bother with specialised mdf sealers.
I find "paint grade" edging applied to edges of mdf with a household iron gives a good finish.
And Acrylic Primer Undercoat (I use Leyland paints) dries quickly with no strong smell.

 

[Grahamshed]

Good information Terry. Thank you.