WEEK COMMENCING 5 JULY 2020
I hope your week has been better than mine! Just too much to do and not enough time to do it in. To cap it all, we’ve been having a few issues with our emails, some aren’t reaching us and some we’re sending are being ‘delayed’. I don’t think either of these problems is anything we’re doing, but we are investigating. If you’ve sent us an email and didn’t get a reply, do call us.
Enough of my woes, let’s answer some questions!
I expected that my ‘don’t thin Cellulose Sanding Sealer’ comment last week would generate a number of responses, and I wasn’t wrong.
The first question was about the aerosol version of this product. Surely it’s been thinned to allow it to deliver through an aerosol system? Well, yes, the product as supplied wouldn’t be able to go through the aerosol, so it has to be thinned. Most of the ‘solvent’ used for thinning though is in fact the propellant. It’s liquid in the can but turns to a gas almost instantly once exposed to the air, which is fine as it has already done its job. More importantly, we increase the amount of the ‘good stuff’ – predominantly the sanding agent – to compensate for this. So the product in the aerosol isn’t exactly the same as in the can, but by the time it hits the surface you’re spraying the difference is almost non-existent.
Another question was whether two coats of a thinned sealer is as good as one undiluted coat. When using a sealer, and especially if you’re putting a lacquer over the top of it, the best practice is to only use one coat. More than that, especially on large items, can lead to the sealer crazing and cracking. It doesn’t happen every time, and can take months to occur, but it’s a real danger.
There’s also the common practice of thinning a sealer 50/50. In this case, the first coat soaks in to dry under the surface of the wood. It will harden the wood, but it isn’t sealed. The second coat follows the first coat, but because of the way the sealer works the second coat dissolves into the first coat, forming one coat under the surface. There’s still very little sealer on top of the wood and it isn’t sealed properly.
The last one about sealers suggested that surely thinning the sealer made it easier to apply on larger areas. We concede this completely – it even says so on the can. Importantly, though, this should only be done when necessary, not as a matter of course. When working on a larger area thinning the sealer by up to 20% (and that should be plenty) will allow it to flow out easily, giving a smooth, even, sealing coat. On these occasions, the sealer is often applied by brush (rather than a cloth). This is a bonus as well as a brush can be loaded with more sealer in the first place, so a little more liquid is applied which, once the solvent evaporates, leaves a better coat.
Sealers are a particular passion of mine (had you noticed?). I think they’re very misunderstood, underrated and underused. And sometimes overused, they shouldn’t be used with an oil for example but I know that comes as a surprise to some people who call us up. I’ll try to stay away from the specific subject of how best to use sealers for a few weeks…but I’m not making any promises!
I hope you have a good week. At the very least, I hope it has been better than mine!
Take care until next week,