Hello

Sammy here - Looking for help with my walk in shower. One wall is an exterior wall with cellulose blown in insulation with poly over it. I have decided to redguard my whole shower to save my marriage in future years - So, I hear you can't poly your walls and use Redguard so do you take the poly down and put the CBU directly against the insualtion? This type of wood fiber insulation looks like it would suck water vapors like crazy so I'm a little worried about no vapor barrier...

Second question. What is the best thing to do in the corners and wall joints? Everybody in our area grouts them and leaves with no caulk or silicone. Since this is my own home I would like to do the right thing. I hear clear silicone is the best. Do you apply this into the joint and call it good? Does it need anything behind it? (I have 1/8" joints) Is it bad to grount everything and then silicone over the grout?


Any advice would help!

Thanks much
Sammy

i'm NOT a professional, so wait for others to respond.

but in the mean time

i would leave the walls and poly and insulation. the insulation is mildew proof (its treated with chemical). i would put up the CBU and redgaurd the shower side, a couple of coats and get in the cracks and seems good. then the water won't get behind your CBU and then will not get trapped between the two water proof areas.

the insulation is nice cause it will keep you warm in the shower.

as for the question about the caulking, well, i'm looking for this answer too!

Knucklez

It creates the possibility of vapor being locked between the 2 barriers.
I have some old photos on this site which clearly show poly and liquid membrane being used together. I have had my hands properly slapped and have long discontinued this method. But I'm still not sure about how much problem we'd have with a 3' wide wall having a double barrier, but like everyone else on this board ... I'm learning every day.


There are situations such as yours where I think it best to use a sheet of poly and then install cement board.

The most important thing about a shower pan is its ability to remove water quickly and effectively. So if you have a good presloped mortar bed with a liner properly installed into the drain assembly with clear weep holes ... waterproofing won't have much work to do and I wouldn't worry about it over cementboard. Other types of backerboard may require waterproofing so be sure what you're using.

Hi Guys, I have a couple of questions in relation to this topic as i too am in the midst of a shower renovation.

Firstly, what does "CBU" stand for?

Secondly, my shower alcove is where the old bath/shower was and it has two external walls. One long one - 5 foot long and one end which is about 3 foot long. They both have insulation and poly vapour barrier over them. Are you saying that when I install my cement board NOT to waterproof it with redguard which is what I was going to do before I tile it with 12 inch porcelain?

The third wall is an internal wall. This is where the shower head and tap/fosset is situated. There is no vapour barier on this wall. Is it required?

The tile supplier recommended waterproofing the cement board before tiling because he said if somehow water should get behind the grout and tiles the cement board will not disintegrate like drywall but will absorb water which will then be stuck somewhere at the base of your wood stud wall, vapour barrier and insulation and not be able to drain any where causing rot and mold eventually. Is this correct?

Silicone caulking. I was going to silicone all my internal vertical corners and not grout these. And also Silicon the bottom horizontal joint between the boottom row of tile and my acrylic pre-fab shower base. Is this correct?

I have a new post relating to the Shower base if any one can offer suggestions for please.

Thanks and successful tiling to all!

Mick

Cement Board Units .... panels of cement board.

If you're building a regular shower (not a steamroom) then leave the existing vapour barrier as is and patch where required ... (ie: staples, tears etc). Use cement board panels over top and use no waterproofing.

Not really .... build the shower right and it'll last as long as your home with no water or mold problems. I never use acrylic shower pans so I have no idea how good they are when incorporated into a complete shower system.

You'd better read the instructions with your base to see what they recommend, although I imagine that's a good idea.

The aim of your whole shower system is to direct water into the drain. Water will seep through tiles and grout, no doubt about it. The reason you use cement board backing is because it it not damaged by water. The poly behind the CBU should be free of holes and be tucked over the top of the shower pan so that water seeping along the CBU is guided into the pan and not somewhere behind it.

As for the corners I have found that if the corners are reinforced with an open weave fiberglass mesh embedded in a bit of thinset or redgard they don't move with respect to each other. That eliminates the need for silicone in the corners.