White stuff appearing on wood after varnishing.

[ziplock9000]

You know when you see a new wall built and the salt releases from the concrete and bricks?... Well it looks like that (sorry no photos yet)

I make plaques on a very tight budget.

Here's my process that has been working fine for a while:

1. Cut softwood to size (redwood that is young and white, not treated)
2. Glue up with sash clamps overnight
3. Cut again to make sure lengths are the same
4. Sand with 80 then 180 grit using random orbital sander
5. Use router around the edge
6. Wet the end grain to make it protrude, let it dry and use router again x2
7. Paint stain 3 times with water based clothes dye (yes it's a cheat but it's cheap and looks good)
8. Paint water based satin varnish

This all works out fine apart from the wood sometimes moving.. but that's a different discussion.

Anyway, I've bought myself a compressor and I've started to spray the same varnish on (for reasons outside of this).. That's the only difference to the process.

However after the vanish dries in about 30m, a white powder/stuff? appears around the edges of the wood.

The first time I thought it was pollen or extremely fine wood dust as I could just brush off 99% of it.. as if it was on TOP of the varnish.

The second time I did this, it was dried inside my home and not exposed to pollen or dust.. same thing happened. White powder stuff that wipes off.

It's very weird.

The only things that are different to before when this didn't happen are:

1. The varnish is sprayed on
2. I've got to the end of a 4.8m piece of timber

Anyway I'm performing some tests to see if it's the spraying of the varnish that is causing this or not.

Has anyone seen this before?

 

[niall Y]

If it is a satin or matt finish , then there is usually a white powder matting agent added to the varnish. Maybe this is separating out during the spraying process. Might be worth checking if the product is recommended for spraying , or just for brushing.

You could try the equivalent gloss to see if you are getting the same result. This can be finely abraded to matt it down. This is a method that can often be recommended for achieving a non-gloss surface, as powdered matting agents can compromise the waterproof nature of the varnish..

It's strange that it is something that can be wiped off after drying, otherwise it could just be overspray

 

[ziplock9000]

If it is a satin or matt finish , then there is usually a white powder matting agent added to the varnish. Maybe this is separating out during the spraying process. Might be worth checking if the product is recommended for spraying , or just for brushing.

You could try the equivalent gloss to see if you are getting the same result. This can be finely abraded to matt it down. This is a method that can often be recommended for achieving a non-gloss surface, as powdered matting agents can compromise the waterproof nature of the varnish..

It's strange that it is something that can be wiped off after drying, otherwise it could just be overspray

Yeah it's very strange to me too.

I'm using 'Rustins Quick Dry Varnish Clear Satin 1l' which has the semi-skimmed milky look

https://www.rustins.ltd/rustins/our-products/indoor/quick-dry-varnish

Application: "Synthetic brush, Varnish Roller or Spray (can be diluted with water about 10% if necessary for spraying, or if the temperature is high)."

I have some gloss, but that's not water based like this is.

I'll update when I've done the test I'm currently performing.