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We are building a new house colonial style with surrounding Verandah. The timber deck boards will run parallel with the external wall with a spacer board cut in a 45 degrees angle at the change of direction, there will be butt joints at the corners into the spacer board. The sub frame for the deck is intended to be 90x45 H3 pine My concerns are that the decking boards will expand and contract, and we will be requested to replace the boards. If instructed to install the tongue and groove flooring, I wish to be able to provide a document that supports NOT installing T & G externally.

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Extract From Specification below H.27 VERANDAH DECKING Allow to lay %100x25 Merbau tongue and groove flooring parallel to the length of verandas. Top nail boards with stainless steel nails over %150x50 treated pine floor joists @ 450 cts laid on edge over set down concrete slab, or adjustable steel piers. Lay snake belly flashing over each joist prior to fixing flooring. Overhang final board with bullnosed edge and trim ends of joists with %100x25 hardwood board. Mitre boards in verandah corners and finish mitres against an %75 x 25 trimmer. Sand to 80 grit and apply 2 coats Cutek Extreme CD50 Clear.

Woodsolutions Answer

Tongue and groove flooring was often installed on verandah floors in earlier times but is not generally recommended today. Timber decking is installed with spaces between the boards to allow for swelling and shrinking in responses to changes in moisture content. Flooring is kiln-dried to a moisture content suitable for interior use, and is likely to swell if exposed to rain or high humidity outdoors. Tongue and groove boards might give satisfactory service if there is a significant roof overhang to exclude rain, the boards are coated all round prior to installation with a moisture excluding finish, and they are spaced apart 1.5 to 2.0mm to allow for swelling. It's also preferable if the verandah is not facing the prevailing weather. If the verandah floor is installed over a concrete slab set down, as per specification, the concrete should be dry before the flooring is installed. We are not familiar with "snake belly flashing" but perhaps that is to prevent moisture rising from the concrete. We suggest you draw these factors to the attention of the architect, since satisfactory performance is not guaranteed even with the precautions outlined above. 

Answered on :
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

Has anyone had any experience with using a product called Firecoat to retrofit an existing residence to bring it up to the BAL 29 requirements and/or had a building surveyor approve the use of the product to coat hardwood species that aren't listed as BAL 29 compliant to meet the standard?. The product has passed BAL40 rating testing however it seems very difficult to get acceptance of it as part of a cost effective solution to bring old buildings up to the requirements.

Woodsolutions Answer

WoodSolutions has not conducted testing of the Firecoat product and has no experience of its use. However, if you can obtain a certificate from a recognised testing laboratory, there shouldn't be any problem in achieving building approval. The Firecoat website states that Firecoat is "accredited with a BAL-40 rating by independent body, The National Association of Testing Authorities (NATA), Australia's leading accreditation body." This statement isn't quite correct. NATA provides accreditation of organisations that can perform testing, NATA doesn't actually do the tests. No doubt this is just careless wording and presumably Firecoat can provide a certificate of performance for your building surveyor. If the product achieves BAL-40 then it also achieves any lower rating such as BAL-29. As you are probably aware, fire resistance is only required for elements that are exposed to a potential fire, not for internal timber. BAL-29 areas require "bushfire-resisting timber" for exposed elements. If the hardwood in question happens to be one of the seven timbers in Appendix F of AS 3959 that are rated bushfire-resisting without treatment, then a fire retardant such as Firecoat is not required. Otherwise, any timber can be made bushfire-resisting by the application of a fire retardant coating that complies with AS 3959, Appendix F. 

Answered on :
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 large domestic blackbutt deck that requires sealing . We have been using Cutek Extreme CD50 on some vertical cladding but it is taking over 2 weeks to dry per coat in the Sydney winter. Is there a faster drying oil based coating we should consider ?
Woodsolutions Answer

We don't have detailed knowledge of Cutek Extreme CD50, but from Cutek's Safety Data Sheet it appears to be an oil and wax blend (paraffinic distillate), with copper 8 quinolinol as an anti-mould additive. This would seem to be a satisfactory finish for outdoor timber, and should live up to most of the claims made on the Cutek website. We agree with the general statement that CUTEK® Extreme CD50 "will not flake or peel and maintenance is fast and simple – no need to sand or strip". Other producers of exterior oil finishes could make the same claim, since oil finishes penetrate into the wood and don't form a film on the surface like paints and varnishes. Whether other oil finishes would be faster drying in your rather wet winter is hard to say. Ideally an oil finish should be applied to dry wood during dry weather. Perhaps you could test a small quantity of an alternative product by coating a timber sample and observing its drying rate. 

Answered on :
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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