Help!: Putting down hardiebacker board

[Hulloo]

Hey people hope u can advise me.....I am currently installing a new shower room in my house. Im upto the stage of tiling the floor. The floor is made up of wooden floorboards on wooden joists.

The floor was slightly unlevel so i decided to use everbuild self leveling compound after priming with SBR bonding and securing down any loose floorboards. This has given a great result.

The next stage is to lay down the 12mm cement based hardie backer boards.

To give the boards that extra security before screwing down using the galvanised screws, I have decided to lay the boards down on a very thin bed of dri wall adhesive (Had a spare bag lying around) then screw down when set.

My question is if i follow the above procedure would i first need to prime the self levelled floor with PVA for the dri wall to give the hardie backer a secure fix? If so what ratio mix of PVA to water and for how long should I leave it before laying the boards......

Many thanx, hope u can help.....

[Mike]

the correct order should have been strenghthen and screw down floor boards, if then solid enough (no deflection) prime and lay down hardi boards with 1 part flexi adhesive and screws then slc if required. also we don't use p.v.a in tiling , the primer you mentioned is ok though

[Hulloo]

Is it no good then to use the spare dri wall bag i have? As I have already laid the slc what would u suggest i do next? Many thanks for the quick reply

[Phil Hobson]

I would forget the PVA and the drywall adhesive, use SBR to prime, then a flexible tile adhesive to glue and screw the boards

[doug boardley]

Mikes method is the correct procedure.

[Hulloo]

I would forget the PVA and the drywall adhesive, use SBR to prime, then a flexible tile adhesive to glue and screw the boards

Ok thanks i will do. Just a couple of things.....How should I dilute the SBR and how long shall i leave it before laying the boards....Many thanks, u have been great help

[Hulloo]

Oh and 1 final thing sorry to be a pain, when laying the boards with the floor adhesive should i use a notched trowel or lay them on a full bed....Many thanx

[Mike]

what about the slc already on the floor boards doug/phil?

[Mike]

a notched trowel will be fine and when the board is screwed down it should be a solid bed then

[Hulloo]

a notched trowel will be fine and when the board is screwed down it should be a solid bed then

What ratio should i mix the SBR to prime the slc with and alo how long should I leave the SBR before laying the boards down?

[Phil Hobson]

As Mike says, the correct method is as he states, if the slc is the type that can be used over timber then you don't have a problem. The boards can be glued and screwed using a notched trowel, but if your slc is not suitable for timber you may have to lift it and go the route Mike suggests. Not many slc products are usable on wooden floors

PS. most SBR dilute 3:1 with clean water, but check with manufacturers instructions

[Mike]

it will say the ratio on the can, probably 3 or 4 water to 1 sbr. leave it till its soaked into the slc, (shouldn't take long though) i'd be cautious of the slc though as you'll be screwing through it, it may crack between the floor boards and backer boards

[Hulloo]

[QUOTE=Phil Hobson;534737]As Mike says, the correct method is as he states, if the slc is the type that can be used over timber then you don't have a problem. The boards can be glued and screwed using a notched trowel, but if your slc is not suitable for timber you may have to lift it and go the route Mike suggests. Not many slc products are usable on wooden floors[/

The SLC was suitable for wooden floors

[Mike]

i would suggest trying a few screws through the slc and into the floorboards to make sure the slc don't crack as you won't be able to see once you overboard

[Hulloo]

i would suggest trying a few screws through the slc and into the floorboards to make sure the slc don't crack as you won't be able to see once you overboard

the slc already has a few thin crack lines......is this not a good thing? as per man instructions the floorboards were primed with SBR....Would the flexi tile adhesive between the backer boards and SLC resolve this?

[Mike]

what would worry me is that the boards are flexing and the slc is cracking and becoming loose. it's not ideal but hard to judge without seeing it. you went the wrong way round with the slc and may be taking a chance tiling over it. it may be ok though, it's a hard one to call. do you have any pictures of the slc?

[Phil Hobson]

Good news, you should be OK, one tip, cut all your boards first and dry lay, leave a 5mm gap around the perimeter, also stagger the boards ( brick bond) leave 2mm/3mm gap between boards, take up one board at a time, glue and screw each board so the adhesive is still wet. Once you have glued and screwed all the boards. Tape all the joints with an alkali resistant tape, depending on the make of your boards, this will prevent cracking on the joints

[Hulloo]

what would worry me is that the boards are flexing and the slc is cracking and becoming loose. it's not ideal but hard to judge without seeing it. you went the wrong way round with the slc and may be taking a chance tiling over it. it may be ok though, it's a hard one to call. do you have any pictures of the slc?

the boards will be screwed down at 20mm center so would that cause much flexing?

[Mike]

you think the slc will be ok on the floor boards phil? i won't argue with you . you got more experience than me

[Mike]

the boards will be screwed down at 20mm center so would that cause much flexing?

you'll need a lot of screws for that! do you mean 20 cms

[Phil Hobson]

Sorry missed a couple of posts there, if you are sure the slc is suitable for timber the cracks could be shrinkage. Hope you sort it

[Hulloo]

you think the slc will be ok on the floor boards phil? i won't argue with you . you got more experience than me

It was everbuild 701 i think, and it did state it was suitable for wooden floors if first the floor was secured and primed with SBR

[Hulloo]

you'll need a lot of screws for that! do you mean 20 cms

LOL my bad i think the epoxy grout has got to me

[Mike]

sounds like you should be ok then. good luck and if you stick to the rest of the instructions the jobs a good 'un. if you're not sure about anything just ask (before you do it preferably lol)

[Phil Hobson]

you think the slc will be ok on the floor boards phil? i won't argue with you . you got more experience than me

Sorry Mike, we keep overlapping posts. The slc I use is called Levelflex and is fibre enhanced (very flexible) I would have no problem using it over floor boards prior to over boarding, but the way you described it is the correct way. Just trying to save some time and effort.

[Hulloo]

Good news, you should be OK, one tip, cut all your boards first and dry lay, leave a 5mm gap around the perimeter, also stagger the boards ( brick bond) leave 2mm/3mm gap between boards, take up one board at a time, glue and screw each board so the adhesive is still wet. Once you have glued and screwed all the boards. Tape all the joints with an alkali resistant tape, depending on the make of your boards, this will prevent cracking on the joints

Must i use flexi adhesive to secure the boards down seeing as the screws will be holding them in place. Reason i'm asking is i have the 1 back of flexi adhesive enough to cover the area of floor tiles require but have quite i bit of the non flexi wall/floor adhesive leftover......Just me being a cheapskate

[Mike]

you must use flexi adhesive as the wood can expand and contract and the flexi adhesive will allow for that. don't risk the floor failing for the sake of a tenner!

[Phil Hobson]

As Mike, don't skimp now

[Bathfix Bob]

Makes you wonder though how many people (trades included) use dri wall adhesive to glue the hardie backer boards down, it sure is cheaper than tile adhesive at *** a bag.

[Mike]

Makes you wonder though how many people (trades included) use dri wall adhesive to glue the hardie backer boards down, it sure is cheaper than tile adhesive at £16 a bag.

surely you can get decent adhesive for less than that bob?