Seal Your Toe Ups

Written by Andrew Morrison

Moisture seal tape on a straw bale wall

It is important to seal your toe ups in order to stop the flow of air through your walls. This is not the same thing as “breathing walls” which we straw balers like to talk about as a good thing. That is entirely different. In a breathing wall, the concept is that air, pressurized from the interior of the house will slowly make it’s way through the walls, starting with the interior plaster, moving through the bales and finally escaping through the exterior plaster.

That’s all good because the interior plaster removes the majority of the moisture from the air and releases it slowly, back into the room, and through into the bales. It does that release in a slow and controlled fashion, so the system stays in balance. More on this process at another time. This blog post is about something entirely different: stopping moisture laden air from moving directly from the interior, conditioned space, into the bales.

The most common places for such infiltration is through the back of electrical plugs and other wall penetrations, at joints around partially exposed framing (picture interior timber frames exposed, yet also in contact with the plaster), and the floor to wall joint. For the back of the electrical plugs, either use a sealed electrical box typically used in exterior installations or shoot some minimally expanding foam into the box after the wiring has been completed but before the switches and plugs have been set. For the joint along the timber frame, be sure to reinforce the plaster with blood lath where it meets the wood and then consider using either a bead of caulking after the plaster has been applied and has cured, or a seal similar to the one used at the floor to wall joint.

As you can see in the picture above, the floor joint is covered with an adhesive flashing that folds from the floor to the toe up, sealing the gap that would otherwise be left to move moisture into the walls. This works very well, but there is one draw back…okay, maybe two. First, the floors and toe ups have to be very clean to allow the material to stick and seal the joint properly. That’s hard to accomplish on a job site. Secondly, if the floor is  finished slab, or some other finish material, you risk installing the adhesive material where it will be seen or leave a sticky residue on the floors.

A material I like to use in place of the adhesive flashing is a sill sealer. It’s a simply roll of foam that is installed underneath the toe ups at the time of their initial installation. Because it is a malleable foam, it fits any shape (within reason)  and seals it tightly. It’s also really easy to install, and the floors don’t have to be so clean you could eat off of them either.

Sealing these areas will increase your building envelope’s efficiency greatly and will extend the life of your bales. Two really good things to have in your house and for your peace of mind.

If you’re interested in really learning how to build with bales and you want to have perhaps one of the best weeks of your life in the process, then come to one of our workshops. We ALWAYS have a good time and you will gain the confidence to build your own house too. CLICK HERE to see what workshop locations and dates we have available this year!

15 Responses

  1. That can work too Jim, but you have the same issue of adhesion to the dirty floor. I think the best way is the sill sealer. If you want to add some caulking as a back up, that’s a good idea.

  2. Hi! I know my questions is not in the subject but iI want to ask you this: It is possible that the walls to be breakeble? I mean if something hit them.It is possible to make a hole until the straw?

  3. I come back again! I just order your dvd’s, but I don’t receive any confirmation about the order. I am so anctions to lern more abaut straw bale becose I want to begein in a few day’s. Sorry for my poor righting!

  4. is this foam sealer also what we call ‘backing rod’? I should think that might work well, especially if it were put in place beneath the 4×4 toe up was nailed down. Hitting the void with a line of expanding foam would also work well, but that turns into several cans of $10/shot foam dispensers.

  5. Did not know to do this and now have exterior browncoat and interior scratchcoat applied. Any kind of a “retrofit?”

  6. I feel this is a good reminder to choose sill sealer for toe ups. We built a small on-slab, load bearing strawbale structure with Dan Chiras at the Evergreen Institute last year and sill sealer is inexpensive and not labor intensive. Unlike caulk or sealing tape, sill sealer spans the width of the toe up ensuring maximum coverage, it saves time, can be installed by novice helpers and saves the back muscles from bending over to apply some other material. Thanks for the reminder!

  7. Great timing! I’ll be using this next weekend when I do my toe ups. Called around and it isn’t stocked in the Home Depots or Ace’s around here but Ace ordered it for me – at $3.49 for 50′ roll it will turn out to be a very cost effective solution! Thanks a bunch, Andrew!

  8. Hi Carol. No, you can still apply the felt paper if the sealer doesn’t completely cover the toe ups. This is just to seal vapor out of the walls where as the felt paper is to isolate the wood from the plaster.

    Hope you are well!

  9. Hi Don. Your climate is pretty darn mild and so I would not be that concerned about it. That said, you can use caulking to seal the floor to wall connection at this point or even after the finish coat (clear caulking I suppose would work best).

    On another note, do you have ay good bale sources around La Grande, OR?

  10. Hi Angy. Yes, if you hit the walls with say a well hit baseball, you can either dent or further damage the wall. The quality of the plaster and the substrate installation and the material used in the plaster will also effect the results of the impact. Earthen plaster is softer than lime, for example, and so won’t resist the damage as much.

  11. Hi Angy. I imagine by now you have received the confirmation if not the DVD. I am on the plane back from Portugal and will look into this when I get home to make sure all is okay. Thanks for letting e know and sorry about that.

  12. OK, there is a trade off. IF the sill sealer is used, then how does water (not moisture) escape (ie., water spills inside the house such as a water heater leak or someone literally spills a pitcher of beer on the floor at the wall)? I would expect that if the wall was weeping enough water to make it to the gravel, the wall would be about to fail anyway. I understand that this is an effort to try to get any condensing moisture from entering the base of the wall. The sill sealer, in cold climates, should only be installed on the interior toe up? Should the sill sealer be installed on both toe ups no matter the climate?

  13. I prefer using it only on the interior. It provides the vapor break needed, but does allow moisture out from the toe ups, need be. I agree that water flowing through the toe ups could signify a total failure in the wall, but what’s more common is that a hose bib leaked or failed within the water isolation box. This allows you the chance to fix it sooner rather than later.

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