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Materials are often selected at the design stage to allow strength and
material characteristics to be incorporated into the design. Some
aspects of material selection which are required for design or for
specification on the drawings have been covered in "Design & Detailing" but
are addressed in greater detail below.
Please click on the following links to gain information on each of these
material groups:
Timber Selection
Timber for the Structure
Strength
Quality
Durability
Note on the lack of relationship between stress grade and durability
Note on durability
and preservative treatment
Stability/Weathering Characteristics
Suitable Structural Timbers
Timber for the Decking
Note on subframe and decking
timbers
Sealants
Fixings
Stainless Steel Fixings
Finishings
Click on the following link for a downloadable
Deck Master® Decking
Materials Advisory, as reference
before, or when, talking to your decking materials supplier.
Timber Selection
Timber requirements for building a deck fall into two categories:
-
timber for the structure
- decking subframe and roof structure and
-
decking timber
In the traditional delivery of decking projects the
choice of:
- structural timber is often made on the basis of
initial strength
with price an important factor
eg strength or “F ratings” are often the primary means
of specification
- decking timber is often made on the basis of price
and initial appearance
eg quality of machining, a colour preference or a
rustic appearance - characteristics which have no bearing on long term
performance, especially in weather exposed applications.
However, the choice of decking and subframe timber is not as simple as
it seems. To a greater degree than many other building materials the
performance and longevity of both subframe and decking timber is dependant
on the characteristics of the timber species incorporated into the project -
characteristics which vary markedly between species.
To access subframe and decking timber for your project, which will give
satisfying performance over a long life, there are a number of factors which
must be considered and appropriately specified.
The requirements for subframe and decking timber are covered in greater
detail below:
Please note that some of the information below which
is also relevant to design and material specification is also provided on
the "Design and Detailing" page.
Timber for the structure
Stress grades are often used as a primary specification for structural
timber used externally, above or in ground. However, stress grades are an
imperfect guide for overall suitability of timber for fully weather exposed
conditions.
Specifying timber requirements according to strength (or stress grade) will
only ensure that the timber supplied is of sufficient strength, when milled,
to perform a structural purpose. It will not ensure that the
timber will be suitably durable for the application or geographical location
or sufficiently stable that excessive shrinkage or distortion will not cause
aesthetic or structural problems.
In
addition to strength, other characteristics, such as quality, durability, shrinkage,
and weathering properties, are also important and should be specified to
ensure satisfactory
performance over the life of the deck. More detailed information on
these characteristics is provided below.
As the structural timber is often not directly exposed to the weather and is
generally orientated vertically so that the water does not pool in any
defects, it can be of a lesser quality and allow a greater range of species
than the decking timber.
Suitable structural timber can be sourced in hardwood or softwood, however
different hardwoods and softwoods are not equally suitable for every
application and the specifier, builder or purchaser must ensure that
the subframe and decking timber specified is fit for the purpose and
conditions for which it is to be used - in the long-term.
Strength (Stress Grade)
Commonly available stress grades in unseasoned structural hardwood are F14
and F17 with F7 being commonly available in seasoned softwood.
In hardwood, the timber strength specified may depend on availability in
your area, however, F14 should be the minimum stress grade specified in,
considering the type and extent of natural characteristics allowed under the
grading rules for the various stress grades. F17 Hardwood is preferred for
weather exposed conditions as it generally includes a lesser number and size
of natural characteristics, which can be a source of accelerated
deterioration when exposed to the weather.
Note on lower hardwood stress grades: In some areas, hardwood structural
timber may only be readily available in lower stress grades and lower
durability.
Unseasoned structural timber in F11 stress grade may be suitable, provided
that it is:
• minimum durability class 2 (above ground classification);
• of low shrinkage or seasoned;
• well ventilated;
• not used in conditions of consistent high humidity and
• used in combination with other good building practices, particularly the
sealing of cut ends and sealing of the tops of joists with a waterproof
membrane to shed water away from the joist.
For structural timber of durability class 2, these requirements would be
necessary to satisfy the performance requirements of the BCA.
In softwood, seasoned F7 should be the minimum stress grade specified.
Softwood structural timber also should be well ventilated; and used in
combination with other good building practices, particularly the sealing of
cut ends and sealing of the tops of joists with a waterproof membrane to
shed water away from the joist. Check with your supplier whether any
limitations on use, or particular construction techniques, are appropriate
for conditions of regular high rainfall and humidity.
Quality
Timber supplied to a stress grade will contain natural characteristics, such
as knots, to the extent allowed in the grading rules and will not guarantee
supply to a visually attractive standard that you may consider appropriate
for your situation.
You may prefer that the posts supporting the roof structure and the roof
timbers be of a higher standard of appearance, containing few and small
characteristics, whereas the decking subframe may only need to be of the
specified structural standard, as it is concealed from view.
If you require a high standard of appearance in addition to appropriate
strength, specify ‘Structural Appearance Grade’. Structural appearance grade
timbers are more expensive than structural grade timbers. If the appearance
of your structural timber is an issue which is important for your project,
speak to your timber merchant about the visual standard of the timber which
would be supplied.
Durability
Natural durability is the ability of the heartwood of a timber species to
resist decay and insect attack and is determined by the “extractives” eg
oils, waxes and resins which fill the capillaries, changing sapwood into
heartwood as the tree grows.
Durability ratings have been determined from the performance of samples of
heartwood both in-ground and above-ground at a number of test sites around
Australia, from expert opinion and from experience of in-service
performance.
Durability is categorized into 4 durability classes – from Class 1 for
highly durable species to Class 4 for non-durable species, with each
durability class having a probable life expectancy for “outside above
ground” and “in ground contact” (AS reference) .
It would be expected that the life expectancy of timber above-ground would
be better than in-ground, reflected in the above-ground rating for a species
being the same as or better than the in-ground rating.
We recommend that only durability class 1 hardwoods, or appropriately
treated seasoned softwoods be considered for use for each of the in-service
conditions “outside above ground” and “in ground contact”.
Where the underside of the structure is greater than 400mm above the ground
this should be considered an above-ground application and subframe timbers
shall be selected durability class 1 (outside above ground classification)
structural hardwoods with sapwood treated to H3 (hazard level 3); or
structural softwoods treated to H3.
Where the underside of the structure is less than 400mm above the ground,
this should be considered an in-ground contact application and subframe
timbers, shall be selected termite resistant durability class 1 structural
hardwoods (in ground contact classification) with sapwood treated to H5; or
structural softwoods treated to H5.
In extreme exposure conditions subject to regular
rainfall or high humidity such as in tropical areas, structural timber and
decking should be durability class 1 hardwoods (in ground contact
classification). Where regular rainfall is expected, consider
protecting your deck with a roof with wide overhangs.
Posts extending into footings shall be selected termite resistant durability
class 1 hardwoods (in ground contact classification) with sapwood H5 treated
or H5 treated round softwood posts. H4 treatment may be acceptable where the
application is not critical and the posts can be replaced when they
deteriorate.
Note that using termite resistant species does not negate the requirement
for termite protection in accordance with the Building Code of Australia.
Note on the lack of relationship between stress grade and durability
There is no direct relationship between stress grades and durability- a
higher strength timber will not necessarily be more durable – an example is
Tasmanian Oak which is a low durability hardwood with a relatively high
stress grade.
Strength and durability should be
considered and specified separately or by proxy by specifying a species to
achieve the required durability characteristics eg F14 or F17 Spotted Gum -
Spotted Gum is a durability 1 species (outside above ground classification)
which is also very stable.
Note on durability and preservative treatment
• Durability classes only refer to
the heartwood (diagram).
• Sapwood is considered to be non-durable and must be preservative treated
to improve its durability.
• When timber is treated, the preservative chemical only penetrates and
protects the sapwood.
• Treatment of sapwood does not improve the durability of heartwood.
• The sapwood of some timbers, such as cypress, cannot be preservative
treated and hence can not be made durable. Decking from species with
untreatable sapwood but which satisfy the requirements for durability,
stability and weathering characteristics shall be supplied sapwood free.
• Because hardwoods only have a small sapwood band the durability (and hence
longevity) of treated hardwood is as per the durability of the species from
which the timber section is produced.
• Because softwoods have a large sapwood band, the durability (and hence
longevity) of the treated softwood is as per the durability of the treated
sapwood, provided there is minimal heartwood present.
Shrinkage
If using unseasoned hardwood structural timber, use only low shrinkage
timbers ie less than 8% tangential shrinkage. Ideally, a single
species, or alternatively mixed species but with similar characteristics,
shall be used to ensure that similar shrinkage occurs in all the structural
members.
Unseasoned hardwood structural timber from high shrinkage species
(tangential shrinkage greater than 10%) is sometimes supplied for the
decking subframe. High shrinkage species are subject to collapse, distortion
and excessive reduction in section size during on-site seasoning. High
shrinkage and widely varying differential shrinkage between species, over
time can result in unevenness in the decking surface, unsatisfactory
appearance and even structural problems.
If using unseasoned hardwood, confirm with your timber supplier that low
shrinkage species will be supplied.
“Surface checking” will occur in unseasoned hardwood as the outside of the
section dries out quickly and shrinks while the inside of the section dries
more slowly. Surface checks will close up in the long term as the whole of
the section dries out. In low shrinkage timbers the surface checking is
normally not severe and we would advise against using filler to fill surface
checks as the filler will be squeezed out as the checks close over time.
If using softwood structural timber, use only seasoned timber for reduced
distortion of the structural members and greater stability and uniformity of
the overall subframe.
Stability/Weathering Characteristics
Weathering is the gradual deterioration of the timber surface from the
combined effect of exposure to ultra-violet (UV) radiation in sunlight and
water from rainfall. The combined effect is for colour change, a loosening
of the timber fibres and a gradual wearing away of the surface.
The swelling and shrinking associated with wetting and drying can cause
surface and deeper level checking, and exposure to the heat from direct
sunlight can cause distortion of decking. The effect of hot, direct sunlight
on saturated timber after rain can be particularly severe. The natural
properties of some timbers, in resisting excessive swelling and shrinking,
surface checking and distortion, make them more suited to weather-exposed
conditions than other timbers. Similarly, some timbers have natural
properties which are not suited to weather exposed conditions and their use
should be avoided.
Maintaining an effective surface coating will improve the performance of the
timber work, protecting it from weathering damage.
Suitable Structural Timbers for
the Decking Subframe
Structural timbers for the subframe of weather
exposed decks should be:
· highly durable
· low shrinkage (if
unseasoned) or seasoned
· stable and
· treated to the appropriate hazard level if section contains
sapwood.
Note on durability
- if clear
of the ground (>400mm) use durability class 1 hardwoods (outside above
ground classification to AS 5604 – 2003 or F7 seasoned
structural softwood treated to H3
- if in-ground or close to ground (<400mm) use durability class 1 hardwoods
(in ground contact classification to AS 5604 – 2003) or F7 seasoned
structural softwood treated to H4/H5 – softwood posts in ground should be
treated round posts.
- if subject to regular rainfall and high humidity, such as in tropical
areas, use durability class 1 hardwoods (in ground contact classification to
AS 5604 – 2003)
Note on shrinkage for unseasoned hardwood
– to be less than 8% tangential shrinkage
Note on treatment
- H3 for above ground applications or H4/H5 for
in and close to ground applications
Suitable hardwoods for structural timberwork include
(please refer to the essential notes below):
- For above ground, (in average conditions) (1): Spotted Gum
and Black Butt (2)
- For above & in ground (3): Iron
Bark, Forest Red Gum (4), Grey Gum (5), Grey Box (Gum-topped
Box), White Mahogany, Tallowwood and Gympie Messmate.
Note that the above are “standard trade names"
(Technical Pamphlet 1 - Building Timbers - properties and recommendation for
their use in Queensland - published by Queensland Forest Service). Ensure
that species with similar or local names but with inferior properties are
not substituted for the species listed above. Any regional high shrinkage
examples of these hardwoods are to be avoided – discuss with your timber
supplier.
Structural
timber in softwood, shall be seasoned, minimum F7 stress grade,
preservative treated to H3 for above ground use or H4/H5 for close to or
in-ground contact.
·The list of suitable timbers in hardwood, above, is not
exhaustive. Contact your local timber supplier for information on suitable
structural timbers which are available in your area.
·High shrinkage unseasoned timbers and/or low durability timbers
and/or timbers with untreated or untreatable sapwood are generally not
suitable for structural timbers in weather exposed conditions.
·In some areas, hardwood structural timber may only be
readily available in lower stress grades and lower durability. Structural
timber in F11 stress grade may be suitable for use in above ground
conditions which are not extreme, provided that it is: minimum durability
class 2 (outside above ground classification); of low shrinkage or seasoned;
well ventilated; not used in conditions of regular rainfall or high humidity
and used in combination with other good building practices, particularly the
sealing of cut ends and sealing of the tops of joists with a waterproof
membrane to shed water away from the joist. For structural timber of
durability class 2, these requirements would be necessary to satisfy the
performance requirements of the BCA.
·Softwood structural timber also should be well
ventilated; and used in combination with other good building practices,
particularly the sealing of cut ends and sealing of the tops of joists with
a waterproof membrane to shed water away from the joist. Check with your
supplier whether any limitations on use, or particular construction
techniques, are appropriate for conditions of regular high rainfall and
humidity.
(1) These species are classified in AS 5604 -
2003 as durability 1 outside above ground and durability 2 in ground
contact.
(2) Blackbutt (Eucalyptus Pilularis) is not to
be confused with, and should be used in preference to, New England Blackbutt
(Eucalyptus Andrewsii) which has a lower durability and higher shrinkage
than Blackbutt. Blackbutt is best used under cover.
(3) The species are classified in AS 5604 -
2003 as durability 1 outside above ground and durability 1 in ground
contact.
(4) Forest Red Gum (Eucalyptus tereticornis) –
sometimes referred to in Queensland as “Blue Gum” - is a high durability &
low shrinkage timber suitable for external use & is not to be confused with
“Sydney Blue Gum” (Eucalyptus salilgna) which is a low durability & high
shrinkage timber unsuitable for weather exposed use.
(5) Grey Gum (Eucalyptus Propinqua) is a high
durability & low shrinkage timber suitable for external use & is not to be
confused with “Mountain Grey Gum” (Eucalyptus Cypellocarpa) which is a low
durability & high shrinkage timber unsuitable for external use.
Please click on the following link for information on
suitable structural timber for the desking subframe:
Timber for the decking
The decking timber should be manufactured from timber of suitable quality,
durability and stability and treated to the appropriate hazard level for the
application.
As a minimum, decking timber should be:
• seasoned (less than 18% moisture content to avoid excessive shrinking on
the job)
• stable (not swelling and shrinking excessively in response to moisture
changes or distorting from the effects of heat or moisture changes) and
• of appropriate durability - for above ground applications use minimum
durability 1 (above ground conditions) treated to H3 or for close to ground
applications -durability 1 (in ground) treated to H5).
Some timber species are:
• more stable than others when exposed to hot conditions and or moisture,
maintaining their shape and resisting distortion and
• more durable than others lasting longer in exposed conditions.
Good decking timber for exposed conditions combines both high durability and
stability ie it will last a long time and will be relatively stable,
performing well over its life. Examples of species which would be suitable
for above ground applications and in all weather conditions include:
• Spotted Gum,
• Ironbark (red and grey),
• Grey Gum (not Mountain Grey Gum)
• Gympie Messmate
• White Mahogany
• Tallowwood and
• Kwila (Merbau).
Ironbark, Gympie Messmate and Tallowwood are durability 1 (in ground contact
classification) species and would be suitable for close to ground
applications.
Other decking timbers available in your area may be suitable, (seasoned
decking with appropriate durability, stability and treatment) – refer to your
local timber supplier for recommendations to suit your application ensuring
you advise whether the deck will be exposed to or protected from the weather.
If using decking of standard moisture content, in areas of low or high
humidity, make suitable allowance for the corresponding shrinkage or
expansion which will occur.
If decking is to be installed in areas of consistent extreme low humidity,
eg in drier far western areas or in areas of consistent extreme high
humidity, eg in rainforest areas, then decking with an appropriate moisture
content shall be ordered, or standard decking acclimatised to the local EMC
(equilibrium moisture content) by strip-stacking before installation. The
equilibrium moisture content (EMC) is the moisture content at which the
timber no longer loses moisture to, or gains moisture from, the atmosphere.
The EMC varies with seasonal changes, so it is normal to quote a range for a
location. Minimal shrinkage or expansion will occur if timber is used with a
moisture content within the EMC range for a location.
Mt Isa, in north-western Queensland, has an average
EMC of 9-10% and timber shrinkage associated with moisture loss to the
atmosphere, from say 18% down to 9% is likely to produce excessive gapping,
possibly board distortion and reduction in hold-down from the fixings.
The greatest enemies of exposed timberwork are heat and moisture.
Decks directly exposed to the heat of the sun will have a surface
temperature many degrees hotter that surfaces protected from sunlight.
In Northern Australia you could expect deck temperature in summer to
exceed 65 degrees (C) and some timbers are more naturally stable when
exposed to heat than others. To the best of our knowledge there is no
test or standard for stability. Knowledge of which timbers are more
stable than others is then a matter of experience and general knowledge
within the timber industry. This knowledge does exist and reputable
suppliers will be able to advise you on which decking timbers will performs
best in the conditions you are intending to use them.
Decking projects in high humidity or rainfall areas require greater
attention to design, detailing, construction and regular maintenance.
Consider using durability 1 hardwoods (in-ground contact classification), or
protecting your deck with a roof with wide overhangs.
Note on subframe and
decking timbers
Different timbers, whether that be Spotted Gum, Black Butt, Merbau, Belau or
Treated Pine, will not deliver the same performance in exposed conditions.
Our suggestion is to make your purchasing decision for decking and subframe
timber (and of course construction), on the basis of the performance you are
looking to achieve not on price.
If you are not being told by your supplier that there is a difference in the
performance of different timbers, or you are not being provided with a
quality timber as an option for your project, our advice would be to find
another supplier who will provide you with information on the different
properties of different timbers and suggestions based on what you need for
your conditions, assisting you to make an informed choice.
Sealants
Joist Sealers
If a deck is exposed to the weather, moisture will be trapped between the
underside of the decking and the tops of the joists. Without a sealer,
moisture will absorb into the the tops of the joists where it cannot dry out
easily. The tops of the joists will deteriorate over time, creating a
hollowing out which reduces the hold-down strength of the fixings and may
require replacement of the joists when the decking is replaced in the
future. There is greater deterioration at the fixings where moisture
can follow the path of the fixing and penetrate deeper into the joist.
With a joist sealer, the moisture absorbed into the joist is reduced or
eliminated extending the life of the joist and effectiveness of the fixings.
Joist sealers also seal around the shank of the fixing, reducing deep
penetration of moisture.
2 example of joist sealers:
Malthoid - a bitumen impregnated felt dampcourse which is placed on
top of the joist and folded down on the edges for water shedding. Also
seals around fixings.
Joistrip - a unique rubber profile specifically designed to seal the
tops of timber joists. Incorporates wings to shed water. Also
seals around fixings. (www.joistrip.com)
Fixings
All bolts, screws, nails, brackets, framing anchors
and other hardware in fully weather exposed conditions should be hot-dipped
galvanized or stainless steel (depending on severity of conditions) to
ensure satisfactory long-term performance of the fasteners.
Electroplated or zinc-plated fasteners are not
suitable for long-term performance in fully weather-exposed conditions as
the plating will deteriorate, particularly in contact with preservative
treated timbers.
Commercially available framing anchors are generally made from galvanised
sheet from which the shape of the bracket is punched and then folded to
shape. Commercial galvanised brackets are not suitable for use in extreme
applications such as in the coastal zone, around pools or in weather exposed
applications.
In extreme applications Stainless Steel fixings are recommended - see below
for more information.
Selection of the correct fixing and fixing method is critical to the
satisfactory long-term performance and appearance of timber decking.
In weather exposed domestic applications subject to light foot traffic,
decking shall be hand nailed or screwed, with two fixings per board at
each joist.
Nails shall be domed head (DH), twist shank (TS) type in stainless
steel (SS) (preferred) or hot-dipped galvanised (HDG) (depending on
severity of exposure conditions).
For hardwood joists, use 50x2.8mm DHTS nails (as above)
For softwood joists, use 65x3.15mm DHTS nails (as above)
Screws shall be
stainless steel and of suitable head type, size and style to ensure secure
fixing but with limited shearing failures while driving eg
50 x 10G SS Decking Screws (refer Product and Services Directory for
details)
Although 50x2.5 stainless steel domed head gun nails are readily
available and commonly used for fixing decking, hand
nailing with the nail type and size listed above will provide
greater initial hold-down and there is sufficient history of use to be
confident of long term performance. If required your nail supplier may
be able to provide additional information on gun nails for decking and a
recommendation as to their suitability. Your local Deck Master
will have experience of the effectiveness of Stainless Steel Domed Head
Twist Shank gun nails in the decking and subframe materials available
in your area.
T-Nails (eg 50x2.2 Finishing Nails or 50x2.5 Flooring Nails) shall not
be used to fix decking as the zinc plating may deteriorate rapidly and
the shank diameter is too fine for suitable hold-down,
resulting in boards moving or ‘rocking’ and nails working up.
Plain steel or zinc plated nails shall not be used to fix decking or
in any external application, as they are likely to rust, causing
staining and gradual deterioration of the nail and the timber around it.
If unsure of the suitability of certain fixings for exposed conditions, refer to your supplier for further information in the context of the requirements of the BCA.
Problems with inappropriate fasteners may not be
apparent in the short or medium term. Corrosion of fixings can lead to
long-term problems such as loss of hold-down forces to stop decking
distorting or serious structural problems from the corrosion and potential
failure of brackets or bolts supporting posts, bearers or joists.
Stainless Steel
fixings
In corrosive environments such as in coastal areas,
around pools or in fully weather exposed conditions, all fixings, including
connector nails, shall be stainless steel.
Stainless steel hand nails are generally available ex
stock from the larger building materials suppliers in coastal areas.
Outside of the coastal zone, where there is less demand, stainless steel
fixings are available but may have to be sourced as a special order.
Stainless steel domed head twist shank gun nails are
readily available from larger building materials suppliers and hire
companies. Although fixing with these nails is becoming the standard
fixing method due to the speed of fixing and perceived performance of the
nail, hand nailing (with a similar but larger shank nail) provides a
stronger hold down and is likely to perform better over a longer life.
Use of
stainless steel, rather than hot-dipped galvanised, nails will also simplify
sanding of the deck, as part of long-term maintenance, as less care would
need to be taken to avoid damaging the protective coating on the nail head.
Stainless
steel brackets are manufactured by the major bracket manufacturers, and if
not in on the shelf of your local building materials supplier, they can be
sourced as a special order.
Finishings
Protective timber finishes
It is important that a suitable finish be applied and maintained to protect
the surface of the timber from weathering and to maintain an attractive
appearance.
Timber finishes are of two types:
• Penetrating Finishes such as water repellents, decking oils and decking
stains – which penetrate into the surface of the timber and do not form a
significant surface film.
• Film Building Finishes, such as clear surface coatings, heavy-bodied
stains and paints - which form a surface film and do not penetrate
into the surface of the timber to the same degree as oils and stains.
You should decide before commencing, where you will use a penetrating oil or
stain, clear film building finish, heavy bodied stain or paint and consistently use that system for
sealing and finish coats as you may not be able to change the system part
way through. For example, a paint system may not be able to be applied over
a preparatory oil or stain finish and similarly an oil or stain finish would
not be effective if applied over a paint prime coat.
Decking oils and stains provide a more natural appearance and do not form a significant surface film
which can be damaged or peel or become slippery when wet.
Decking stains generally contain coloured pigments
and obscure the appearance of decking to a greater degree than decking oils,
but provide greater protection and need recoating less regularly.
Clear film building finishes require greater care in preparation and
application, have a glossy natural appearance and can last a number of
years, properly prepared and applied. Clear film building finishes may
not provide suitable service if used on unseasoned timber work or timber
work which has not had time to weather - check with your supplier for
additional information.
Paint finishes hide the natural appearance of timberwork. However, they
provide high levels of weathering protection, provided they are properly
applied and maintained. A paint system properly applied and maintained on
structural timber can give protection for up to 8 years. Note - this does
not apply to decking and possibly not to horizontal surfaces.
In "average" conditions, you should expect protection for 9 to 12 months
from oils and 12 to 18 months from stains and several years from film
building finishes properly applied. In severe conditions, such as
around pools, recoating is likely to be necessary at shorter intervals.
Although decking oils and stains require recoating at relatively short
intervals, the recoating process is relatively simple and speedy.
Because of the different properties, appearance and advantages of oils, stains
clear finishes and
paints, it is common practice for exposed structural timber to be protected
with a paint system for outward appearance and longevity, whilst the decking
timber is protected with an oil, stain or clear film building decking finish.
Concealed structural timbers, eg joists, are generally left uncoated with
natural durability and sealing of the tops of the joists and end grains
being sufficient to ensure suitable performance and longevity.
Penetrating oil or stain finishes or clear film building finishes are commonly used to protect decking from
weathering.
Paint finishes may be suitable for protecting decking in some situations,
however the paint can become slippery when wet and the protection relies on
the paint film remaining intact.
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