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We have a massive expanse of 30 year old Western red cedar windows and glass sliding doors that need refinishing. The internal finish has held up quite well except for some sills which can be addressed. Quite a few of the windows/doors are super exposed to the sun and elements which has caused much weathering and etching into the softer area of the wood with some of the beading disintegrating altogether. The beading will need replacing. The original finish was Sikkens HLS stain finished with 007 which was highly recommended at the time. The Sikkens 007 split and flaked away quite quickly in the exposed areas. In previous renovations the 007 was ditched altogether, lightly sanded back then coated with the HLS stain only. I have started to heavily sand back some of the windows/doors and am looking at coatings that will last longer. Upon some internet research some say the most protective finishes are solid latex paint and primer rather than transparent finishes. Is this correct? The internal finish has held up quite well except for some sills, so I don't mind having a solid colour on the outside and transparent wood grain finish on the inside if it means less maintenance in the future. All of the awnings which provide little ventilation will be replaced with Breezway louvre component system with monument colorbond aluminium frame and insect screens. I was also looking at the product called Osmo UV protection oil which is highly rated overseas but I’m unsure how long it would last in Australia. I have several questions. I know that the Osmo oil required all coatings to be sanded off which is a mammoth task. If I go down the path of primer and solid latex coating, would I need to sand all coatings off as well or would I just have to choose the appropriate primer and sand only where necessary? Is the solid latex paint really the best, most protective coating and would it require less maintenance or would it just flake and peel off like the Sikkens 007 which was an acrylic?

Woodsolutions Answer +

Clear film-forming finishes (referred to generically as "varnishes") tend to fail by cracking and peeling in exposed exterior locations. A comparison of different finishes is included in our Technical Design Guide #13 Finishing Timber Externally. A copy can be downloaded from our website via this link https://www.woodsolutions.com.au/publications. It is correct that switching to an oil finish would require all the existing coating to be removed, since oils need to penetrate into the wood. Also any remaining patches of varnish would show through the oil. Paint will certainly provide the longest-lasting finish, and paint won't fail by cracking and peeling as long as it can bond to the substrate. While remaining patches of varnish won't show through paint they may present a jagged appearance at the edges, preventing a smooth, even coating and causing localised failure of the paint if the underlying varnish starts to lift. It would be far preferable to remove all the varnish if possible. You may obtain more detailed advice on this point from a paint company's advisory service. 

Exterior finish

Answered on 03-06-2021
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.

Question

I am building a hardwood gateway and would like an effective natural ( possibly oil ) coating or coatings.
I read mention of a 'Preservative', a 'Sealant', a 'UV' and an 'oil' coatings.
1. Do I need all of these for maximum protection ?

2. Also you refer to Cabot's "Timber Shades" product but they don't seem to have such.

Woodsolutions Answer +

Our answer mentioning Cabot's Timber Shades was posted on 06-07-2017, but the product seems to have been discontinued in latter years. It was simply offered as an example of a suitable finish, and there are many others. We assume your gateway will be built with a durable hardwood, in which case a 'preservative' is not needed except insofar as an oil product will help to minimise weathering effects such as surface checking, or cracking, and thus could be said to have a preservative function. You might also want to provide some protection to any in-ground areas with a product such as Preschem No-Rot sticks, more info here https://preschem.com/products/timber-protection/no-rot. Generally we would recommend a finish such as decking oil for ease of maintenance, but the subject of external finishes is dealt with more extensively in our Technical Design Guide 13 titled Finishing Timber Externally which can be downloaded via this link https://www.woodsolutions.com.au/publications.

Oil finish

Answered on 13-05-2021
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.

Question

I have a new Tallow wood deck replacement almost completed that has extensive black marking. The builder is attempting to sand the marks out but I expect the marking will continue. I intend on applying a clear oil finish. What is the correct procedure to achieve the best finish with the least amount of black marking? Does the timber need to be weathered for an amount of time before cleaning and applying the finish?

Woodsolutions Answer +

Black marks on new hardwood suggest that the problem is 'iron staining', ie. metal particles falling on the deck and reacting with tannin in the wood when it gets wet. The recommended treatment is oxalic acid, or a proprietary timber cleaning product that contains oxalic acid. The US Department of Agriculture's Forest Service has a helpful data sheet on the subject. It can be dowloaded via this link https://www.srs.fs.usda.gov/pubs/48449. Treating the timber with an oxalic acid solution is likely to be easier and more effective than the builder trying to sand the marks out. You may be able to stop further staining if you can find the source of the metal contamination and eliminate it. It could arise from cutting metal nearby, for example working on guttering or other metal items. Your builder can find a product with an oxalic acid base by checking the labels of deck cleaning products, or reviewing their Material Safety Data Sheets. 

Iron stain

Answered on 15-04-2021
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.

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