How to seal the bottom of shed walls?

Welcome to the Bunnings Workshop community @jjebw. It's fantastic to have you join us, and many thanks for your question about sealing your shed from the weather.

Looks like a perfect job for Sikaflex 11FC. It is a flexible jointing sealant designed to stick to concrete and steel. It'll seal that area well and is far superior to silicone. Just make sure you give the area a thorough clean before caulking it along the gap and seam between the floor and wall. If the steel is beginning to rust, it would be a good idea to seal the outside to stop water from migrating under the sheeting.

Please let me know if you have any questions.

Mitchell

Remarka6le

Can also recommend Sikaflex, I just used it recently when renovating our shed. Best advice is wait a couple of days after rain and clean it throughly. Apply a generous amount to the inside, clean as required. Apply a smaller amount to the outside, clean as required. Don't do it on a rainy day, try to do the project when you have at least another day of sunlight to allow it to seal properly.

Hello @jjebw

Would it be possible for you to post a picture of the other side of the shed wall? Is soil gathering on the face of the wall? Is vegetation overgrowing in that area of the shed? Is there a retaining wall next to the shed? I understand these are a lot of questions. But I'm proposing to look at the source of the water and perhaps pre-empt it from reaching your shed wall.

Standard solutions include putting in Vinidex 65mm x 20m Draincoil With Filter Sock or Everhard 3m EasyDRAIN Polymer Grate And Prejoined Channel. My only concern is that if we don't address these possible causes more water will enter your shed.

If you have any other questions we can help with, please don't hesitate to post them.

Eric

Jason

Hi @jjebw,

Just checking in to see how you are going with this project? I trust the advice you received was very helpful. Please let us know if you need any further assistance.

Jason

jjebw

Thanks for all the tips everyone, project took a couple of months. I used the Sikaflex and dug a trench around the side and put in some draining grates so hopefully it'll stop the rust.

Jason

Well done @jjebw. It looks like a fantastic result. Thanks so much for coming back and sharing some photos as this is a topic that has popped up on the site before. It will be really helpful to others to see what you have done.

Thanks again, we look forward to seeing what projects you tackle next. Please let us know if you need a hand with anything.

Jason

Great advice Mitchell, thank you.

Im putting a new shed on a fairly even slab. One of the shed's walls will be leaning flash against the house wall, so I won't be able to put the sealant on the outside of that wall. This is the wall likely to leak most at the bottom as there's likely to be some water dripping from the house wall and the shed roof into the narrow gap between the shed and the house wall (probably 2-3cm).

How much sealant should I be applying on the inside of the shed? Is there anything else I could do to waterproof it at the bottom?

Thank you in advance, all ideas and guidance are appreciated!

Welcome to the Bunnings Workshop community @MarcinW. It's wonderful to have you join us, and many thanks for your question about sealing a shed wall.

The methods described in this guide on How to waterproof a shed floor can be applied to the inside of the wall. Only a 5mm wide bead of sealant is required to cover any gaps between the shed wall and the concrete. Smooth the bead into a cove so it rides up onto the shed wall and out onto the concrete. The aluminium angle then provides an additional layer of protection in case any water manages to get under the shed wall. You might like to seal the wall first and check to see whether that is effective. If the issue persists, you can add the angle over the top.

Please let me know if you have any questions.

Mitchell

Thank you Mitchell for the welcome and advice! I'll go through this and likely to ask more questions :-)!

@MitchellMc Thank you again for the help and the idea!

Will the method described in the link you’ve shred also work if applied on the inside of shed (I can imagine the outside placement is much better as the water will firstly run off instead of sitting under the bottom edge…)?

The challenge I face is that the shed will sit with its two walls (long and short) directly agains the garage wall as the slab will not allow for a gap between. (I attach the photos of the slab and the adjacent walls).

Or is there a different/better method that would work under these circumstances? And do you think I should be paining/sealing the concrete first for a better adhesion/tighter seal?

Any idea and experience much appreciated!

Hello @MarcinW

You are in a unique position to apply the floor seal because the shed has not yet been anchored to the cement slab. I propose thinking about how you can put the Sika 300ml Grey Sikaflex 11FC Plus Polyurethane Adhesive Sealant under the bottom channel and start assembling from there. It's even possible to put the aluminium L channel in as well while the wall is not yet in the way.

I don't recommend sealing the floor at this point as the adhesive sealant works better when in direct contact with concrete. You can paint the slab later on when the shed is in place.

In regards to the gap between the concrete wall and the shed, I suggest building a small PVC gutter and attaching it to the shed. I recommend using Holman 32mm x 3m Class 12 PVC Pressure Pipes and Kinetic 32mm Galvanised BSP Pipe Saddle Clips - 10 Pack.

In order to build the gutter simply cut the 32mm pipe in half and use the saddle clips to hold it in place.

If you need further assistance, please let us know.

Eric

Terrific advice @EricL , thank you!

You’ve mentioned adding an aluminium L channel. Where would you put it, on the inside of the shed wall and attach with SikaFlex 11FC (ie same way as in the tutorial under link shared by @MitchellMc but on the inside)?

Thank you!

Hi @MarcinW,

It sounds like @EricL is suggesting that the L angle can be installed before the wall as per the guide. I believe he's mistakenly said channel instead of angle. I'm sure he'll let us know if he is thinking of another channel. However, if you're not confident installing it prior to the wall on the outside, then you could install it on the inside.

Please let us know if you have further questions.

Mitchell

Thank you @MitchellMc !

Regarding the installation of an L angle on the outside (between the garage wall and the shed wall), are you recommending to install it:

- on the ground against the wall first, caulk it (or caulk the shed wall) and then press the shed wall against it for the bond?

- install the angle on the shed wall first, then caulk it and push the entire shed (with the angle installed and caulked) against the garage wall?

The challenge I see is that I don’t know how to ensure the L angle is water tight if it’s on the outside as there’ll be no space between it and the garage wall to put the caulking gun in there to fill all small holes?

How would you go about it?

I'd suggest installing the angle on the ground against the garage wall and waiting for the adhesive/sealant to cure @MarcinW. You can then apply a bead of sealant along the bottom of the angle, or the shed wall, and push the wall up against it. The angle is just a secondary measure to ensure the area is sealed. On a new shed build, I feel the most important area to seal is directly under the walls. A nice thick bead of sealant needs to be applied to the concrete and the wall placed on top of it.

Mitchell

This is a great help. Thank you @MitchellMc and @EricL, I really appreciate it and hope it’ll also help others with similar shed projects.
It’s amaIng to hear from the experts so quickly and very very helpful! Great community!

I’ll keep you up to date on the outcomes and thank you again.

Do keep us updated, @MarcinW. I'll be looking forward to hearing how it went.

Reach out anytime you need assistance; we're here to help.

Mitchell

Sath

Moved into a house with a shed which had some concrete put in earlier to seal the shed base. I had water coming through and i put sealant inside and has stopped a lot of water coming in . But I can see water getting collected within the corrugated gaps. See attached pics. Should i remove the concrete covering and put in sealant or is there another way ? Worth putting in more drainage around? I am thinking is it worth spending effort/money on the old one or put in a new shed.water between the curvesconcrete covering already in

Welcome to the Bunnings Workshop community @Sath. It's great to have you join us, and many thanks for your question about sealing a shed.

Believe it or not, in a normal shed installation, that channel is designed to fill up with water and drain away. The outside edge of it is lower than the inside edge, so if it fills up with water, it will flow to the outside. However, your outside section is filled with concrete. Normally it wouldn't fill up as the water would drain out either end. Once again, though, the concrete has likely blocked that escape route.

If you remove some concrete from one end and locate that bottom U-shaped trim, you could drill a small hole in it just above ground level to allow the water to drain out. Have a look at the image I've included below. You've solved the issue of the water creeping under the trim, but now it is filling up. Try exposing the trim on the outside and drilling a hole in it.

Please let me know if you have any questions.

Mitchell

Sath

Many thanks Mitchell for your reply, Very clear indeed. How do i go out removing concrete without impacting the rim?

Hi @Sath

I suggest using a Kango Masonry Bit to drill into the concrete if you don't want to harm the rim. Upon reaching the aluminium rim you simply use a standard steel bit rated for cutting into steel.

My number one tip is to make sure to drill in a flat horizontal angle. If the angle is wrong, water will not seep out of the channel. One other method you can try is to use a larger drill bit allowing you to slightly swivel the drill to make a larger hole in the concrete.

If you need further assistance, please let us know.

Eric

Tyro

Hi jjebw

There are far more experienced people in the Workshop Comminity, but as a rust inhibitor I've always found WD40 or spray on fish oil great for the job.

As for the sand and dirt ... if it's coming in from under the walls, try running a thick band of silicone or gap filler around the outside edges on the floor.

Good luck!

Tyro

Congratulations jjebw

That's turned into a great space!

After my previous post I wondered if the sand coming in is beach sand? If so it will have salt in it. If so the salt is likely to be causing the rust. So maybe painting the shed with anti-rust paint might be needed. Your local Bunnings guru's will be the best ones to help you with that as they'll be familiar with similar environmental related problems and how to best deal with them.

Good luck!

Tyro

Hi MarcinW

I come from a very wet climate. How about deflecting the water run off before it can run down the walls? Maybe run some galvanised sheeting from under the house eves to the other side of the shed apex.

Hello @Tyro

That is an excellent suggestion let me tag @jjebw to make them aware of your recommendation.

Eric

Sath

@EricL @MitchellMc Working away with your suggestions, the leaks from the side panels have stopped. Tested with the rains 🙂

Now the shed doors are showing similar leaks, that is the channels collect water on the inside and starts pouring inside when it rains hard. See pics. How do i drain this?

Also there is a gap at the below the doors, Should i put a rubber seal ? inside of the shed door where it pours out of the channeloutside of the shed door

Hello @Sath

I believe that the moss and mould collecting in the channel has created a seal between the drain channels. This in turn now prevents water from draining out. I suggest washing the channels with 30 Seconds 1L Outdoor Cleaner Spray. Wash the door channel vigorously with your garden hose.

Once the channel has opened up, I suggest drilling a drain point on the door just as you did on the side channels of your shed. This should prevent water from gathering in it.

In regards to the rubber seal, I suggest having a look at the Moroday Rubber Seals in the store and see which one suits your needs.

If you need further assistance, please let us know.

Eric

CorinneW

How much can you roughly do with one tube