Removing grey underneath varnish

[Brans]

Hello everyone,

As you could read in the post below, last year I built this garden table and I have finished top with three layers of Ronseal yacht varnish (undiluted).

Now I have plenty of grey areas underneath this varnish and even a wood mould on one place where I made a dent by keeping sander too much in one place.

My plan to fix this is:
- Plane all varnish and grey spots with the electric hand planer
- Sand everything down to 240 grit
- Apply Oxalic acid to bleach the wood
- Apply yacht varnish again but this time first two coats will be diluted for better tack

Can anyone recommend is this good plan of action or should I add something else to it?

Also, does anyone knows why did this happen? I know I have used very bad wood that I found outside but I sanded everything down and it was in very good shape before I applied varnish. Also, I did not seal any knots prior to applying varnish. Or is it maybe that I did not dilute the first two coats of varnish?

 

[MikeG.]

I wouldn't use the planer. That will create an awful lot of work in trying to flatten the mess it leaves.

This sort of thing is virtually unavoidable with timber left out all year. Whatever you do to it now, you'll be back repeating the job in 2 or 3 years time.

 

[Brans]

No problem I can use a belt sander to remove existing varnish as I am only working on top of the table. I won't remove varnish between planks.

So you think it is no varnish applying technique but rather that wood is mouldy on the inside?

Is there some other chemical that can stop this from happening?

 

[MikeG.]

No. Even if you seal it under an epoxy, this will happen in the end with pine.

 

[profchris]

Most finishes aren't actually waterproof. Your varnish allows water in, just very slowly. So your timber eventually looks just the same as unvarnished timber left outside, but it takes longer and happens in patches, not evenly. There is no magic way to stop wood weathering!

If you want to keep it looking pristine, then every Spring you'll have to sand it back to a fresh wood surface and re-varnish. At some point the top will become too thin to be usable, but by then the feet will have rotted anyway

This is why most outdoor furniture is made from hardwood species which resist the weather better, and weather gracefully. Oil them once a year and accept the change in colour and texture as part of the ageing process.

 

[Bod]

Normal weathering, I'm afraid.
Sand out effected areas, re varnish.
Keep under cover as much as possible, certainly over winter.

Bod

 

[ED65]

Also, does anyone knows why did this happen?

Water got through to the wood, it's as simple as that.

Also, does anyone knows why did this happen? I know I have used very bad wood that I found outside but I sanded everything down and it was in very good shape before I applied varnish.

It's not about the wood or your prep, it's mostly about the varnish you used. Consumer-level yacht varnishes are barely worthy of the name, in actual fact the Ronseal has done pretty well all things considered; horizontal surfaces are the absolute worst for both UV exposure and standing water, which are both very damaging to finishes. And you only applied three coats, which is perhaps okay for a front door but not for a tabletop exposed in the garden year round.

If you do go ahead and plane and sand this you're unlikely to need to use oxalic acid. On wood much more weathered than this the most superficial planing can remove the greyed surface, just a handful of passes with a smoothing plane can reveal bright fresh wood.

 

[ED65]

Greying like this under varnish is NOT the inevitable outcome of wood exposed outdoors, pine or not. In actual fact the wood is almost irrelevant here, it's almost entirely about the coating. We just need to look at boat woodwork. But this tells us just what's needed to prevent this: the wood might be sealed first with a penetrating epoxy, then on top of that a good coating of a proper marine varnish is used, followed by religiously keeping up with maintenance. Which means you look out for failure in the varnish surface, sand it off as soon as you find it and coat again.

Brans, given the price of these varnishes (quite eye-watering some of them) and the necessary maintenance schedule it's important to ask yourself, is it worth it for a garden table?

 

[Bm101]

Would stripping the top of varnish and applying a teak oil type finish be a better solution?
It's a 5 minute job then to just clean up the surface of dirt in the spring and autumn on a sunny day after good weather with a low grit (40 or 60 and a sanding block and get at it like a monster) paper by tool or by hand and apply another coat or two. Easy to apply, won't bubble and skin. Easy life.
Personally I don't see the appeal of varnish except if you really know what you are doing and why you are doing it. There are so many easier options to use available now.
Just my humble uneducated opinion. I'm about as far as you can get from an expert so fair warning. (hammer)

 

[Brans]

Thank you, lads, for all the answers. I will strip it back to raw wood and apply 5-6 layers of yacht varnish again (with penetrating epoxy first if I get any cheap) and I will try to get some cover for this table in wintertime.