Warning!
Polyboard is not like wood. It's a material which reacts
more to the change in temperature than wood. Thus, it
is necessery to consider this aspect when installing.
Naturally, a variation of a few degres will not affect
the material. However, Polyboard used indoors does not
generally raise problems.
When installing Polyboard outdoors, the challenge aspect
of cold winters and hot summers must be considred. Another
important concern is the exposure in the sun. Polyboard
will absorb more ultraviolet rays if you use a darker
color such as grey, green or brun.
Taking into account this fact there are some ways of putting
Polyboard and of taking advantage of the best methods
without incurring any problems. There are 2 suggestions
which were experimented and has produced very good results.
In both cases, the spacings of the joists should not exceed
12 inches and the sheet of Polyboard should mesure 18mm
(_ inch of thickness).
1-Polyboard
can be installed in the following manner. As shown in
the illustration, join the sheets at the mid-point between
2 joists and cut a strip (not too tight, allow ¼
inch of play on either side) of the same material to go
between the 2 joists and screw it from underneath, making
sure that the screws are short enough not to pierce through
both thicknesses. For a tighter joint, we suggest adding
a sealant or some glue to the joint. There are a number
of sealants that will do the job, but we have had good
results with Flextra brand sealants or all-purpose PL
construction glue.
 |
If the joint still seems too loose
despite this extra support, probably because there is
too much space between the joists (the ideal spacing is
no more than 12 inches) we recommend adding some small
brackets (3 or 4 inches long) underneath, as in the illustration.
But you should be careful to screw in only the part of
the bracket that connects with the joist, not
the part under the Polyboard. The bracket is
only meant to support the joint, not to hold it in place.
A 2-foot space between the brackets should be sufficient.
Once again, it is better to support all of the sheets
than the length of the house, if necessary, so the material
can expand when exposed to heat.
 |
2-The second one
consists in using the mouldings which you can get yourselves
at your Polyboard trader (image1 ). This moulding must
be assembled on top of the joist every 48 inches. Make
sure to use a rather strong joist to support the envisaged
weight including the weight of Polyboard. Your trader
of material will know how to advise you on the good dimension
of joist. The joist which will receive the moulding (
image2 ) must be installed 1/4 of inch lower either, or
another method would be to saw 1/8 of inch on top. Make
sure to keep a minimum hillside of 1/8 of inch every linear
foot towards the outside to allow the drainage of exceeding
water in case of hard rain.
 |
|
 |
| 1 |
|
2 |
Then insert the sheets of Polyboard
into the mouldings while pressing them firmly on the house
and screw along the house ( image3 ) and not somewhere else
and pull a joint of sealing ( image4 ). Several brands can
be adhered but we tried Flextra successfully. Attention,
the temperature in which you will install your sheets of
Polyboard will determine which correctness you will have
to insert them into the mouldings. Ideally warm sheets have
already set their expansion, then you can tighten them.
The contraction is easier to manage than the expansion.
 |
|
 |
| 3 |
|
4 |
You will notice that the moulding is
conceived so that it gets the water back under the sheet
of Polyboard (that water which would have been able to skip
under the top of the sheet). An hillside is important ,thus
this way the joist will allow an evacuation of the water
towards the outside and keep dried the bottom of your patio.
Also this way, Polyboard will not expand and contract without
you noticing it.
2-Another way consists in making,
on the top of the sheet ( image5 ), saw cuts with your circular
saw on half of the depth or approximately 7 to 9mm (about
5/16 ") of depth every 12 inches in length and in width
( image3 ). It will be important and especially nicer to
make lines very straight ahead. Then, as your joists are
also spaced out every 12 inches of the saw cut, it will
be just above supports and you will only have to screw in
the intersections of the saw cuts ( image6 ). This way turned
out effective and less expensive because the major part
of the inconvenience of the expansion comes from the exposure
of the sun on the surface of the sheet. The surface becomes
warmer than the bottom, thus it takes more expansion and
tends to bulge out. Thus, the saw cut becomes the joint
in case of expansion. It closes when the sheet is warm and
reappears when the sheet cooled down.
 |
|
 |
| 5 |
|
6 |
This way we can also protect the joist by taking care of
putting a piece of Polyboard 6mm of thickness about 4 inches
of width under the joints of sheet. Even there this joist
should be installed 1/4 of inch lower than the others (
image7 ) to compensate either cut the top of the joist .
This method allows the water to slide between sheets without
joining the joist. To seal the joint between sheets, it
is recommended to use a sealing which must be necessary
renew as needed.
 |
|
|
| 7 |
|
|
|
