January 2019

“Skipping these
important control
checks is equally likely
when there is a
collective focus to
achieve maximum
productivity in
anticipation of a
looming valuation
date”
Above: A primed roof and air and vapour control layer installation.
Whilst it may seem that the most organised
approach is to schedule all materials and labour
resources before the bond tests have been
completed, there is a risk that works may proceed
without the proper checks being undertaken. We
have seen this happen when labour resources
have targets to meet, or presume that pre-checks
have already been completed by others. However,
skipping these important control checks is equally
likely when there is a collective focus to achieve
maximum productivity in anticipation of a looming
valuation date.
If for any reason a problem with the attachment
to a structural deck is discovered during the
installation, inevitably there is a strong pressure
to attempt to continue with the same materials
and / or primers already on site, which may not
be suitable. It could be reasonably argued that
whilst changing materials at this stage may
introduce delays, those delays are likely to be a
lot shorter (and less costly), than having to
resolve the problem post-handover.
So what are the risk conditions? Is it only in the
winter time that bond tests are required before
commencing? No. This should be standard
practise so that everyone involved can be
assured that the appropriate application method
has been determined. For those using structural
hot melt products, this practise of bond tests
before commencement of the work appears
engrained in our culture. It is commonplace to
arrive at most sites and see test patches of
structural hot melt systems accompanied with
detailed records of the tests completed. But, why
is this practise not as engrained with other
technologies? It should be standard practise
across the board.
By progressing your installation without these
bond tests it is often viewed by main contractors
that you are accepting the condition of the deck.
And they may have a point.
Beyond simply waiting for the deck to fully cure
(which is another topic in itself), here are few
other conditions to consider:
Sub 5°C Conditions: During these lowtemperature
conditions, there is a risk that surface
condensation may exist on the structural deck. This
is one of the reasons why many products advise
that they should only be applied in greater than 5°C
conditions, despite the products themselves
functioning in sub-5°C temperatures.
Screeds: Sand-cement screeds are often used for
levelling purposes or providing a suitable roof fall.
The problem is that these products are like
sponges and absorb water every time it rains.
Interestingly, whilst it may seem more expensive
on paper to consider tapered insulation, there may
be a saving on the overall project package if you’re
able to get your waterproofing completed quicker,
allowing internal works to proceed and scaffolding
and other attendances to be struck earlier.
Zero Falls (less than 1:80): A minimum fall on
your roof will ensure that it drains and BS 6229
advises that to achieve a minimum 1:80 finished
“It is important to
ensure that the deck is
fully dried so that you
are bonding to the
concrete deck itself,
not a layer of water”
fall, you should design at either 1:60 or 1:40 to
allow for tolerances during the construction
(depending on how much information is available).
However, how often do we see zero-falls designs
which are designed at zero falls, rather than say
1:80 to achieve a close to zero fall (after
tolerances)? In these conditions both the drying
time of the structural deck, and keeping the deck
dry after rainfall, are likely to be troublesome.
However, in the condition of a zero-fall design it is
likely that this problem may be further
exaggerated, due to the formation of back-falls.
In all of these conditions, it is important to ensure
that the deck is fully dried so that you are bonding
to the concrete deck itself, not a layer of water,
which is not known for its adhesive properties.
If utilising a traditional gas-torch to dry your roof
deck, check the NFRC Safe2Torch guidance
document: www.nfrc.co.uk/Safe2Torch.
Contact Danosa
0845 074 0553
www.danosa.co.uk
@DANOSAUK
JANUARY 2019 TC 41