Blockwork against I beam

solway

Active Member
Blockwork sitting on top of I beam. Iv tried filling the void with timbers at every 300-400 covering with building paper/roofing felt and covering again with riblathe. All joints crossed at least 400mm. We have tried filling the void with cement board aswell doing thin coat with mesh and topped with sand+cement but always after a few month's hairline cracks appear at the 2 ends where the I beam sits on the concrete pad and some cracks where the timbers were inserted behind the felt or cement board.
We're starting a job tomorrow and there is an I beam above the front door 4 metres long. I'm sick of the other ways not working so I was thinking of filling the void in the I beam with an external insulation board (void 50mm deep) and cover with double layer of fibre mesh and 6mm basecoat 150mm onto the blockwork and topcoat with sand + cement. I rang an ewi engineer in our local area and he said sand +cement has never been tested over polystyrene insulation boards. He reckons they will swell with heat/moisture. My answer was so does timber and this is the way they advise people to tackle these details. Has anyone ever tried basecoat over insulation followed by sand+cement topcoat.
 

Attachments

  • 1495023344861.jpg
    1495023344861.jpg
    61.1 KB · Views: 1,057
  • 1495023366595.jpg
    1495023366595.jpg
    41.6 KB · Views: 384
  • 1495023401257.jpg
    1495023401257.jpg
    42.7 KB · Views: 379
Expansion coefficient differing betwixt materials is the problem. The job needs something to take the place of the timber. Has anyone tried that thick plastic you can get for decking nowadays? Just a thought.
 
Someone on here advised me to use exact gap expanding foam to stick cement board in it, still to do it on mine so not sure if it works.
 
Ya we always lap at least 150mm onto the blockwork. The timber is the problem so is there another way to form grounds to fix on cement board/felt+riblathe. I don't know,filling the void with polystyrene insulation seems OK to me but will it expand when up against the sun/rain/frost/humidity???
 
Cut down hardi backer board...fix inside RSJ with foam fix, base coat over with mesh embedded.

Done a few this way never had a problem.
 
Rend Aid with mesh embedded. Topped with Weber OCR.

We only meshed stress points...and the RSJ.
 
Top