How to Strengthen Gipsum (GifaFloor) flooring joins

[Mmark]

Can I bond something, like steel plates, to the underside of structural 18mm Gipsum flooring g&t board joins, to strengthen the loading bearing? And will they last and be worth while?

Our joists are not exact centres. The structural GifaFloor 18mm are 50% reduction in load if not supported, this takes it to under 1kn for a bedroom, which is borderline. The UFH spreader plates were already laid before we found out. So looking for a way to mitigate risks.

 

[Deleted member 174758]

For steel plates to be strong enough to add stiffness I feel that they will have to be so thick that they would add considerably to the loading of the floor and might cause more problems (in terms of drooping) than they cure. Steel sheet isn't particularly stiff and doesn't glue to timber all that well so the durability of any bond between such dissimilar would also be suspect - and that's without taking into account the differences in coefficient of expansion between the two materials which might contribute to delamination during a very hot summer or very cold winter. You'd probably be better off doing what joiners sometimes do to carry new timber stud walls which needs to run parallel with the joists atop an existing floor, but not above an existing joist, and that is to introduce a series of solid struts (or blocking) between the joists (i.e. spanning the gap) where the joints in your flooring occur (i.e. at right angles between adjoining joists). If the floor is already installed his will mean working from beneath. Where the joints are right next to and parallel to a joist and not more than 50mm off it, a piece of 2 x 2 or 3 x 2 CLS could be screwed into the side of the joist and to the flooring. Not an ideal fix, but should work as it's the same technique as is used for flooring repairs after sparkies or plumbers have been digging holes in them. TBH depending on the section of your joists I might also consider introducing a full row of solid strutting to stiffen the whole floor side to side in the room, in view of the fact that your flooring (from another thread) is only 18mm thick

 

[Mmark]

For steel plates to be strong enough to add stiffness I feel that they will have to be so thick that they would add considerably to the loading of the floor/QUOTE]
Thank you for the reply. After speaking to Knauf support, I’m taking your advice and asking the builders to take up the UFH spreader plates and add support battens down. Luckily we don’t have to take up the whole floor. There are 13 gaps, we just need to support under gaps 7, 8, 9 and 10, prior to that we can get it to land on joists.

The builders also did not provide perimeter support on one of the edges. I really want to avoid taking up all the UFH to install battens along the side. I’ve been looking for L shaped angled bracket that will attach to the wood, under the plasterboard, to add some perimeter support. However I’m struggling to find one thick enough, that will be able to enough additional support on the side. Any ideas (links) ?

Mark

 

[catlad]

I might be missing the point but can't you add 18mm t&g flooring over the existing flooring to make it stronger?

 

[Mmark]

I might be missing the point but can't you add 18mm t&g flooring over the existing flooring to make it stronger?

I need to keep the tog down, for the UFH to work with carpet. It’s why I switched from chipboard t&g to gifafloor, as it got the over all tog below 2.

 

[Mmark]

I managed to find this document, which is a detailed stress test setup and results for GifaFloor FHB18 and FHB32.
https://www.ribaproductselector.com/Docs/4/233054/external/COL889433.pdf

It aligns with what an architect told me. That the point loads is not the point they break, but the point at which deflection is more than 3mm. After 3mm tiles would pop off. They take the load way beyond the recommended capacity of 2kn, up to 6.99kn - they say it has a safety factor of 2. Looking at this document the weakest points are not the T&G of say point M4 but actually the perimeter edges of points, where T&G is not in play - see points E1 and R4. Although point M4 is the side join of a board, so there is no unsupported join end T&G testing, which would form a T shape

A different document says for end joins without joist support you should reduce the point load capacity by 50% for FHB25 and above. What I cannot find is anything that says it's also reduced by 50% for FHB18? Also why 50% where did this rule of thumb come from? Is there something analogous for chipboard?

I know with wooden floorboards if joins are not on joists, the boards sag over time and creek. Are fibrous boards subject to the same problems or less so? The architect says that in reality, for many renovation projects, the joists do not align with joins and builders don't typically take time to correct this, so I shouldn't worry, especially as it's also small bedroom (4mx3m) with through traffic.