3rd Jul 2003, 11:26 AM #1
Water stained window sills - How to repair and finish
I bought my first home last year and my fiancee has created a rather large list of jobs to do (at least I have an excuse to buy some power tools).
One of them is repairing our water damaged (ie: stained) window sills. To summerise, the window is a type of hardwood (I don't know how to identify it), which has been color stained, but it looks like that was all. (ie: no protective coat)
Over the past 15 years, water has condensed on the inside of the glass from time to time and caused lots of water stains (black and brown blotches) on the top of the wood. It is also very easy to scratch the stained surface with your finger.
I've found a few web pages that reconmend sanding back, applying wood bleach (oxyalic acid) solutions, washing off with alkaline water (to neatralise the acid which if left on will lighten the stain you apply - apparently).
However, before I go ahead, I was wondering if anyone had some pointers. After re-staining the window, should I give it a few coats of hard shellac or cabothane. I would like the finish to be much more resilient to water staining if possible.
Great forum this!
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3rd Jul 2003, 08:41 PM #2
The oxalic acid will remove the stains, there are also some proprietry stain removers. There's one I've used with good results, Deckswood I think it's called . It's got oxalic acid in it I believe, but also detergents. Oxalic acid can stain the timber a horrible yellow colour if applied too strong or for too long. (Idiot company I worked for once left about 20M3 of Tas oak under black plastic and it all got water stained, I told them to get Oxalic acid and showed the supervisor how it worked, he figured if a little was good then more was better and left it in the hands of one of the labourers - result 20M3 of urine yellow Tas oak!) Anyway once you've got the stains out you need to think about refinishing. Just be aware that clear finishes have no UV blockers in them at all so if the sill gets a lot of sunlight the finish will tend to break down somewhat and the timber will discolour (grey usually). However I'm in the tropics and this may not be a real problem where you are. Intergrain, Sikkens and Cabots all make clearish finishes that have a lot of UV inhibitors in them. They do tend to stain the timber in varying degrees and hues but they do last a lot longer in harsh sunlight.
3rd Jul 2003, 09:54 PM #3
The brand I have is "RecoChem" Timber Restorer. It does warn about the timber becoming "furry" if left on for too long. It also mentions that if the product is not completely removed it may darken the timber.
I read elsewhere about neatralising the acid in the timber restorer with an alkaline solution, like water with sodium bicarbonate dissolved in it.
I have in front of me a can of Cabothane, and it does not mention anything about UV stabilisation. I might go to a paint store tomorow and ask about UV stable protective coatings.
Some of the window sills are exposed to lots of sunlight, so the point you raise is very valid.
Thanks for the quick response.
3rd Jul 2003, 10:12 PM #4
A good finish that may be worth considering is Wattyl Estapol 7008 (2 pack).
I'd be tempted to just see how much of the stain you can remove by sanding. It may be enough.
3rd Jul 2003, 10:40 PM #5
2 pak estapol is an excellent hard wearing floor finish but doesn't contain UV inhibitors so the timber will still discolour from sunlight. Plus being extremely hard is a right pain in the **** if you ever need to sand it back to refinish.
4th Jul 2003, 01:30 PM #6
Well sort of.
While 7008 may not have uv inhibitors added, it probably wouldn't need it. The change in colour is probably due to the reaction (due to uv) of the wood with oxygen. 7008 will likely bond better to the wood and so prevent this. In fact a lot of research into uv degredation into resins at a place I was working showed that essentially the damage was only in the first few microns from the surface. My guess is that that is because none of the resins is a perfect barrier against air, moisture etc. If I see anyone from there again I will try and get a professional opinion.
Personally I would be too worried about some bleaching, as long as it is even and not blotchy. Mostly blotchiness is due to water settling on the wood.
I would be tempted to try it. But yes, it is a "permanent" finish.
4th Jul 2003, 10:32 PM #7
Update : I asked some helpful guys from Paint Spot in Knox (used to be called Morgans I think).
The opinion was - don't use a clear cote of any kind!
The reconmendation was to sand back to a smooth finish and use an exterior oil based stain.
His argument was that it works very well on wooden outdoor furniture so no reason why it shouldn't on a window sill. The added advantage was that it is much easier to rub down and give another coat than staining and poly over the top.
Aparently polyurethane has a tendancy to crack under intense heat and sunlight (like a window sill) and once this occurs, it takes EFFORT to sand it back.
The only other alternative suggested was a marine or exterior polyurethane but they are both gloss and require 5 to 6 coats to get the stated lifetime.
I think I'll try this oil based stain first and see how it goes. They did say if I did not like the finish I could polyurethane over the top anyway.
4th Jul 2003, 10:49 PM #8
So problem "solvered".
5th Jul 2003, 02:54 AM #9
It may be too late but my 2 cents worth..
We had the same problem, tried many stains and finish combinations (Wattyl products) and finally ended up with Sikkens Cetol HLS. As Mick sugested, it works well.
You can get some free samples, contact Sikkens / Tenaru on 1800338871 for location of their delers.
Furniture oil based stuff on window sills pickup dirt quickly, this finish doesn't, but take a long time to dry (more thAN A DAY, thin it with thinner and apply with a pad).
6th Jul 2003, 09:16 PM #10
Your comments are not too late at all. I'm in no hurry to make a decision, I'd rather do it properly the first time (and learn form others) than to learn from my own mistakes (where possible).
A few questions. Sikkens say "don't thin", but you reconmend to do so. From what I have read on the net, thinning makes it easier for the wood to absorb the product, but it may take a few more coats to get the desired effect. Is this correct?
Sikkens also say "not to be used indoors". So apart from the longer drying time, is there any other reason why I should not use it indoors.
Did you do one or two coats? I don't want to darken the wood too much. Have you tried the THB or Filter 7 Sikkens products over the top of the HLS. I believe these are available in clear too.
Sorry for all the questions. Sikkens is a bit more expensive than most, but if does the job it properly it will be worth it.
Cheers and Thanks
7th Jul 2003, 10:28 AM #11
Hmm, didn't realise Sikkens wasn't recommended for indoors. I did a kitchen in brush box about 8 years ago and the owners finished it in Sikkens Cetol HLS, still looks really nice. I don't think I'd use the supercover top coat though as it might be hard to get a really good finish with it, from memory it's pretty gluggy. Maybe this is what Theva was thinning? because from memory the Cetol consistency is like water.
9th Jul 2003, 10:00 PM #12
Spoke to Sikkens (local) and the "not for indoors" is due to European chemical regulations. As far as they are concerned, it's fine for interior window sills. I bought a can of teak and a can of natural (HLS) so we'll see how it goes.
I'm now learning all the joys of sanding off the old stain and bleaching. All those bloody mouldings make it very time consuming! Sanding in all the edges and corners is a real pain. However, bleaching does do a great job at removing the faint black water stains that remain after sanding with 40 grit.
Anyway, I've now spent the time to build some wooden sanding jigs and lined them with velcro. Seems to do the job (I have the Bosch 1/3 Random Orbital for the larger flat bits). Dust is a big problem!
What do people do for this sort of detail sanding?
9th Jul 2003, 10:03 PM #13
I mean Bosch 1/3 sheet Random sander! (woops)
9th Jul 2003, 10:08 PM #14
You might want to look at getting a detail sander. Comes with pointy bits for getting into corners.
10th Jul 2003, 12:03 AM #15
Sorry about the delay in replying, I was cleaning my nose.
I am using only HLS natural (077), three coats. Problem with filter7 & TSI is - for the trouble of using additional product types there are no major benifits (I have tried samples). Suppernatural (waterbased) clouds the grain and the finish is not exactly transparent (looks muddy). Also HLS can be overcoated with other products but not the otherway around. Sticking to one product also helps in future maintence if any.
I thin the first coat, and then the second coat depends on the temperature. The reason for thining is to improve absorption and drying times; to avoid dust getting on the coating specially in renovation enviornment.
The level of colour depends on flim thickness, if you thin it and apply additional coats then it should work out the same. As the experts say, try it on an old bit of hardwood.
The solvents in HLS can cause headache (I got one). As long as you keep the windows open it should not be a problem.
Finish sanding - if you are starting with 40grit, then there is a long way to go and more dust to enjoy. I sanded to 180grit. Sanding between coats is to remove the nap, without removing the coating toomuch- Lightly wetsand first & second coat (400 & 800 grit W&D paper as per Niel's book) to get a finer finish.
Just applied the third coat today and it looooks jjjjust fine .
Re sanders, I got a Metabo duo random orbital sander and makita random O/ liner 1/3 sheet finising sander (which helps me to cheet against hand sanding). Dust bags don't work (well). If you really want to tackle the dust you require a vac / extraction system - consider connecting vac cleaner to the Bosh with an adoptor if its worth it.
Thanks Mick, I am inhaling all the wood dust hoping I don't have to do this for another eight years?
Last edited by Theva; 10th Jul 2003 at 06:23 AM.