Is it possible to install concrete board alongside plywood?

If it’s a ground floor bathroom then it’s possible , you will need to lay the concrete level to the floor board and just level out with tile adhesive to keep the floor even

First remedy the leak test and make sure no longer leaks. Secure all surrounding wooden areas with screws!!! Ensuring no more movement. Cut out all damaged wood and ensure joist are good. If not replaced effected damaged joist. Once all is dry and secure fit concrete parnell secure. You can now do as you please

No it can't be done the damp wet board would be removed and replaced with new boarding to match the original and sealed and then the tile backer board would be fixed on top to match and then retile to suit what is already down

Yes it could be done. I suggest first we change all the weak boards then we start the next process.

Shoud be stick first before tiling ditra matt

I would not recommend this as it then has no overlap bondaing to the tiles

inform the client that the existing floor has a weak sub floor and you recommend for him to change it and the work guarantee only cover the work done.

on the joint where ply and cement board connect, support joint with noggins to limit movement, apply flexible sealant/Adhesive to joint and use flexible adhesive and grout to fix tiles.

Detramat

It's not suitable, take it all up and use either bacher board with the flexible matting

Yes it should be fine

Wood, such as what is commonly seen on the subfloor of a home, is not an acceptable long-term substrate. When you come up against plywood subfloors in the bathroom or other areas of the home, a cement-based backer board must be installed on top of the wood.

It's better do replace all the board if it's weak

Concrete boards are a gimmick. Use the correct plywood prime it before tiling and use flexible rapid set adhesive. Fix the leak first mind on bath or your problems will only continue. Make sure to mechanically fix the plywood and but up tight against existing flooring. The use of flexible adhesive should allow for movement.

Yes, it's possible to replace the damaged section of your bathroom floor with concrete board and then retile it. However, it's important to make sure that the subfloor underneath the entire bathroom floor is structurally sound and able to support the weight of the concrete board and tiles.

Assuming the subfloor is solid, here are the steps to replace the damaged section of the bathroom floor:

Cut out the damaged section of the floor using a circular saw or jigsaw. Make sure to cut along the edges of the floor joists so that you have a clean, square hole.

Measure the size of the hole and cut a piece of concrete board to fit. Make sure the edges of the concrete board sit on top of the floor joists for support.

Screw the concrete board down to the floor joists using concrete screws or galvanized deck screws. Make sure the screws are flush with the surface of the concrete board.

Apply a waterproofing membrane over the concrete board to prevent moisture from seeping through to the subfloor.

Install tiles on top of the concrete board using a thin-set mortar. Make sure to use a waterproof grout to seal the joints between the tiles.

Once the tiles have been installed, you can install a transition strip or threshold to cover the joint between the new tile and the existing floor.

As for the joint between the concrete board and the chipboard/plywood, you can use a silicone caulk to fill the gap. Apply a bead of caulk along the joint and smooth it out with your finger or a caulk smoothing tool. This will help prevent water from getting underneath the new tile and causing damage to the subfloor

inform the client that the existing floor has a weak sub floor and you recommend for him to change it, and the work guarantee only covers the work done.

on the joint where the ply and cement board connect, support joint with noggins to limit movement, apply flexible sealant/ adhesive to joint and use flexible adhesive and grout to fix tiles.

Yes, this can be done. A new piece of ply will be laid and the concrete board(hardi backer)will go over it.Screw down the hardi backer with hardibacker screws and use an appropriate construction adhesive. You can tackle the joints with a 2 part wood filler.

Best to use a plywood instead

It's better to change whole the floor, but i you don't you have to lay down some kind of mat or net to tackle the joint, speciel metal netting just to avoid any kind of cracks

I would replace the sub floor the over plywood the whole area

Depends on the sizes of the cement boards and chip board affected. You can add extra noggings where they meet the Joints.

Use joint tape and it can be done

I be wound replace with chipboard and then use a backer board approximately min 10ml and lay with a flexible adhesive and screw with galvanised screws and washers.

You might have issues not long after laying a tiled floor directly onto timber as it moves with temperature change and humidity. Take up entire floor back to joists. Check joists for level (these can be realigned using additional min 50mm wide cls or similar attached to existing joists) Overboard with min 18mm ply with as few cuts as possible and fix to joists @ 3" centers using 35mm screws and not nails. Over lay the entire floor with a de coupling mat such as ditra and then your ready for tiling using S2 adhesive.

Cut damaged area out carefully and install the cement board correctly so it is supported on top of the wooden beams that supports the floor making sure it is strong enough to carry the weight once installed