Waterproofing a timber vanity top

[Putty]

Hi guys,

I'm willing to accept you can't 100% waterproof a piece of timber, but I have to do something with it.

A customer wanted a walnut top for his vanity and I was willing to do it. Pictures attached.

Is my best bet to coat it with polyurethane, let it dry, sand it back, recoat, repeat?

The people I bought the timber from advised this would allow the polyurethane to seep into the grain and fill any tiny gaps in the surface of the timber, with multiple sandings and recoats to ensure all gaps get filled, finished with a final layer to protect the rest of the surface.

I've given the timber a coat of feast watson kitchen oil so the customer could get an idea of what the finished colour will be. Should I sand this back before applying the poly? A lot of people say you can't add poly once oil has been applied, others say yes you can as long as the oil has cured, and from my experience doing things like coffee tables and wine holders it hasn't has any detrimental effect on the finish or the timber, but I'm happy to go with the consensus view on here.

I'm just about to cut the basin hole out, so that cut will be sealed up as well.

Any advice is greatly appreciated.

Putty.

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[Arron]

Ordinary polyurethane will disappoint.

If you want a high build, super-waterproof finish on a vanity then, I think, Wattyl 7008 2-pack poly is your best choice. I did several timber vanity/bench tops (including our own) in 2006/2007 and they are still like new. We make no special concessions to the fact it is timber, Water spills are a daily occurrence and we make no special efforts to wipe them off.

Being a high build finish it will take care of the tiny pores in a timber like walnut without needing any filling.

The only neg is that, like all polys, it's not very repairable.

[Xanthorrhoeas]

I'm not expert on this stuff so please interpret my comments in that light. I think that there are two ways to look at this:

(a) plastic seal it with a great hard-wearing polyurethane or I think there is a floor finish called isothane. Those finishes provide a seal coat that stops water ingress. As long as they are kept away from serious abrasion and UV they can last a very long time. Their weakness comes if they are punctured. Then, water gets in under the finish and begins to rot/degrade/discolour the wood. Mind you, some of them are so tough that puncturing them would take a lot of effort. I used a finish like this (a floor finish in fact) on my timber kitchen benches. it lasted about 10 years but now looks pretty sad.

(b) a penetrating oil finish. I have used a marine oil finish called Deks Olje (Whitworths Marine stock it). Oil type 1 is very thin and is applied wet on wet until the timber won't take any more. The solvent stinks so good (excellent) ventilation is required. Deks Olje #2 is thicker and can produce a really good gloss (maybe not super super gloss but pretty good). Deks Olje stands up to full exposure outside on Australian Cedar and Huon Pine. It needs recoating in that situation ever 6 to 12 months but would not require that indoors.

On small items I have used Rustins Danish oil but there are other brand (and advocates) aplenty.

A good oil finish soaks deep into the timber, often helped by the first coat being well-diluted by solvent. Once enough coats are applied and soak in you can get a wonderful finish. I like matt finishes in oil but I have seen a wonderful gloss Tung oil finish too. Theoretically, these finishes will better resist damage and water penetration though a crack or scratch. Also, to refresh them just add more oil. To repair the polyurethane you scrape/burn it off, sand it and then apply a new finish.

When I scrape back my kitchen benches (needed real soon now) I will be trialling oil finish.

[Sir Stinkalot]

If you have a look over on the renovation forums there was an in depth discussion about this along with finished photos.

[Putty]

Ordinary polyurethane will disappoint.

If you want a high build, super-waterproof finish on a vanity then, I think, Wattyl 7008 2-pack poly is your best choice. I did several timber vanity/bench tops (including our own) in 2006/2007 and they are still like new. We make no special concessions to the fact it is timber, Water spills are a daily occurrence and we make no special efforts to wipe them off.

Being a high build finish it will take care of the tiny pores in a timber like walnut without needing any filling.

The only neg is that, like all polys, it's not very repairable.

Hi Arron,

How did you go about applying it? Should I sand the current finish back to raw timber then apply, or will it be ok as is?

Did you do multiple coats/sandings or just give it a couple of layers?

Cheers,

Anthony

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[Arron]

I don't know whether it will be ok over the oil or not but I'd sand it off myself, without question. I never mix products or product families - I've been caught too many times and had weird unexpected effects. Then next time, use white spirits to show the customer what it will look like finished.

So sand well. Apply first coat by brush. Sand back, just to knock the dust nibs off. Then a second coat by brush.

There is no reason you can't do more then two coats, but I found two adequate. If you do multiple coats be careful sanding between coats so you don't sand right through a coat and get witness lines.

It self-levels very nicely and brush marks are not a big problem, especially if you aid flow-out with a bit of reducer.

I can't remember whether I used the reducer to thin the first coat for better penetration. Seems a logical thing to do though.

It's a product which I've always wondered why it's not more popular. Maybe it's because it's still marketed as a DIY level product, but being a specialised two-pack that puts DIYers off when they can just slop on some poly straight out of the can.

[q9]

Whatever you do, do not exceed the recommended thinning ratio on the tin...Makes it much worse!

If you've been here long enough you'll know 7008 is my default answer. I don't know why it's not more popular either, but smell, tendency to make bricks out of brushes that aren't meticulously cleaned, and the higher skill and patience level needed to get a good finish might explain it.

Don't be put off, it's not impossibly difficult, but it will punish impatience and carelessness.

[Putty]

Thanks everyone for their advice and product suggestions. I went looking for the 7008 at a paint store and the salesman strongly suggested I use Northane 2 pack epoxy instead. I know he wasn't getting anything out of the recommendation because they didn't stock the stuff and he sent me to the opposition.

I gave it three coats sanding between and then wet sanded and buffed at the end. The isomer is ecstatic, really looking forward to seeing it installed. Here's a shot of the finished product.

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