WEEK COMMENCING 14 JULY 2019
I hope you’ve had a good week, I had a trip down to my old stomping ground of Kent to visit the good people at the Axminster store in Sittingbourne for some training in how to get the best from our finishes. They’re all experts now so do pop in and pick their brains!
By the time you read this I’ll have been to Norfolk Woodturners on Thursday night, a return trip, but I’m writing this in advance so will report on it next week. (Sorry to disillusion any of you who think I get up early on a Friday morning to write this. You want it to make some sort of sense don’t you??)
On with the questions…
(My thanks to Chestnuteer Mike F (to whom we send our best for a speedy recovery from a minor operation) for asking this question after last week’s Newsletter which fits in nicely with some other questions asked of late, so this week’s edition is going to be a bit of an intercoat preparation special).
I mentioned cutting back between coats, and Mike asked me to clarify this a little bit more.
Most of the products we supply are designed to bond together coat-on-coat; waxes will stick to pretty much anything including themselves, and lacquers chemically join together – commonly called ‘burning in’. Unlike paints, in most cases they don’t really need a mechanical ‘key’ (a roughened surface) to adhere to.
But intercoat sanding is still important as part of the preparation process to make sure that the coated surface is smooth, meaning the next coat will also be smooth and give a brighter finish.
That sanding should be gentle though; the coating is hopefully already pretty smooth, we only want to remove any minor imperfections (nibs) that might have been left behind. Unless the finishing has gone a bit wrong (as if!) and needs to have some of it removed, a cut back with a fine abrasive is all that is needed. Usually I’d use the same grade as I last used on the bare timber – possibly 320, 400, or NyWeb, any of these will be more than sufficient. This can be done with the lathe running if that’s suitable, or not if that’s easier. The shape of the item will have some bearing on this of course (and whether it’s on a lathe at all!)
This leads me to another question, from someone using our Tack Cloth after sanding between coats of oil. They wanted to know how to stop getting a residue left behind from the cloth.
This concerned me on several fronts; the resin on the Tack Cloth shouldn’t come off in normal use. The only way I could think of that this could happen is if too much pressure is being applied when using it; it requires just a light wipe over in use, not being pressed down hard. It should be like dusting a surface to remove a layer of house dust.
But along with this, there should be no need to use a Tack Cloth between coats; the amount of sanding dust generated, if any, will be infinitesimal, so there should be nothing to remove. Intercoat sanding is about smoothing and flattening the coating, not removing any of it.
Which brings me to another question I’ve been asked, about whether to use a Tack Cloth between each grit of abrasive. I wouldn’t bother, I’d wait until the end to remove the sanding dust. The comment that has been made is that using the Tack Cloth every time would remove any rogue grit particles that might have come off the abrasive – if this is happening, throw the abrasive away and buy something better! The aluminium oxide (which it usually is) should be so well bonded to the backing that it doesn’t come off.
And a little extra comment, some people use an airline attached to a compressor to blow away dust. This is fine as long as there’s a water trap in use as well. Air contains moisture; if you compress it there’s a higher amount of water per cubic metre. Thus, if you blow this over timber you’re spraying moisture over the surface which isn’t ideal. A water trap extracts the water which means that only air is sprayed. This only applies to conventional spraying with a compressor, it doesn’t apply to HVLP systems – but they don’t really generate enough air current to do the job anyway!
Next week I’m planning to get up to Spalding for one last check on the venue for our Woodturning Weekender. If you’re still thinking about it be sure to check our Facebook and Instagram for details of the goodie bag we’re making available for everyone who books in advance. It might just help you decide.
See you next week