Floor­ing ad­he­sives and poor per­for­mance

David Hay­ward, ATFA Tech­ni­cal Man­ager, takes a look at ad­he­sives in the tim­ber floor­ing in­dus­try and points out some things that need to con­sid­ered with both prod­uct and in­stal­la­tion.

Australasian Timber - - ASSOCIATIONS - David Hay­ward ATFA Tech­ni­cal Man­ager.

IR­RE­SPEC­TIVE OF whether it is solid tim­ber, en­gi­neered or per­haps bam­boo floor­ing there are a range of ad­he­sives that are used to pro­vide part or at times all the fix­ing.

One of the most com­mon types of floor­ing ad­he­sive is the mois­ture cured polyurethane which of­ten comes in ‘sausages’ or ‘pails’ and are re­ferred to by the in­dus­try as ei­ther the ‘non foam­ing’ type and the ‘foam­ing’ type. The ‘non foam­ing’ type is more flex­i­ble and cures to a rub­bery like ma­te­rial and is able move to an ex­tent when floor­ing ex­pands or con­tracts. The foam­ing type is more rigid and can have the ben­e­fit of fill­ing voids be­neath the floor and sub­floor re­duc­ing the in­ci­dence of drummy spots. Due to as­pects such as this, some con­trac­tors pre­fer one over the other. Also en­ter­ing the mar­ket are the poly­mer ad­he­sives which too are flex­i­ble and like the polyurethane ad­he­sives also mois­ture cur­ing (from small amounts of wa­ter in the air, sub­floor or prod­uct). Mois­ture cur­ing ad­he­sives, par­tic­u­larly in Europe, the USA and to a lesser de­gree in Aus­tralia are also be­ing used which have prop­er­ties to act as a mois­ture vapour re­tarder and with acous­tic at­ten­u­at­ing prop­er­ties. So over the years we have seen many ad­vances in floor­ing ad­he­sives and we can be sure to see fur­ther de­vel­op­ments in the fu­ture.

In most cases when we ad­he­sive fix floors there are no is­sues and we go from job to job with­out think­ing too much about it. But all prod­ucts and fix­ing meth­ods have their lim­i­ta­tions so don’t get lulled into a false sense of se­cu­rity. All floor­ing prod­ucts dif­fer in terms of their ex­pan­sion and shrink­age prop­er­ties un­der changes in at­mo­spheric hu­mid­ity and all floor­ing prod­ucts also dif­fer in the forces they gen­er­ate when it comes to ex­pan­sion.

We need to re­mem­ber that ad­he­sive fixed floors dif­fer in na­ture to nail down floors. When a floor is nailed down the floor­board is able to slide over the sub­floor it is fixed to. Al­though the two are con­nected they act some­what in­de­pen­dent of each other. How­ever, when we full bed ad­he­sive fix a floor­board, it and the sub­floor be­come one. The ex­pan­sion prop­er­ties of the floor­board dif­fer from that of the sub­floor and the ad­he­sive can trans­fer very high forces be­tween floor and sub­floor.

Have you ever seen an en­gi­neered floor take on a crowned shape when laid in hu­mid­ity con­di­tions that are too high? The crowned shape oc­curs be­cause the face lamella ex­pands more than the core layer it is glued to and the board arches. This is shown in the first photo. Now when we full bed ad­he­sive fix solid tim­ber floor­ing on to say a ply­wood sub­floor we are in ef­fect cre­at­ing an ‘en­gi­neered’ prod­uct that is the width of the ply­wood sheet. Just like the face lamella on the en­gi­neered floor the tim­ber floor­ing ex­pands more than the ply­wood be­neath it. Con­se­quently, if hu­mid­ity con­di­tions are too high the sheet sub­floor can buckle off the joists. Photo 2 (Be­low right) demon­strates the re­sult.

Now even though these fail­ures oc­curred it does not mean that floors can­not be laid in high hu­mid­ity en­vi­ron­ments. How­ever, greater care is needed with choice of prod­uct, species and in­stal­la­tion method. Note that en­gi­neered floor­ing man­u­fac­tur­ers gen­er­ally have a hu­mid­ity range suited to their prod­ucts and that rec­om­mended in­stal­la­tion prac­tice can also vary de­pend­ing on en­vi­ron­men­tal con­di­tions. Low and medium den­sity solid tim­ber can­not gen­er­ate the same ex­pan­sion force as high den­sity tim­bers. With solid tim­ber the in­stal­la­tion prac­tice may in­clude ac­cli­ma­ti­sa­tion to re­duce ex­pan­sion forces af­ter in­stal­la­tion. So it is im­por­tant to think about each job, the species and fix­ing method to be used.

It is also im­por­tant to re­alise that par­tic­u­larly when ad­he­sive fix­ing high den­sity solid floor­ing the forces pass through the ad­he­sive to the sub­floor. It is not just the fix­ing of ply­wood sub­floors to joists that is im­por­tant but the likes of ply­wood sub­floors to con­crete slabs or if di­rect to slabs the in­tegrity of the slab sur­face and any lev­el­ling com­pound used. One fur­ther as­pect to note is that ad­he­sive fix­ing of solid tim­ber will also re­strain the boards from ex­pand­ing greater than with say nail fix­ing. This then gen­er­ates greater pres­sure at board edges within a floor. Un­der such pres­sure a floor can be more prone to peak­ing (boards with a cupped ap­pear­ance hav­ing raised board edges) and that high fea­ture grade floors may also be more prone to shear­ing through the likes of gum veins.

It is im­por­tant to re­alise that that we can lay many dif­fer­ent types and sizes of tim­ber floors be­cause we have ad­he­sives. How­ever, it is also im­por­tant to un­der­stand what the ef­fects are of us­ing ad­he­sives with dif­fer­ent floor­ing prod­ucts and the lim­its of those prod­ucts and the ad­he­sives be­ing used. It is im­por­tant to fol­low man­u­fac­turer in­struc­tions and use in­dus­try recog­nised prac­tices.

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