Can our frame hold light clay straw, and plaster?

Hello, my partner and I are in the process of placing an order for Natural Hydraulic Lime (NHL) to plaster the light clay straw walls on our tiny home frame. However, when we got our estimate for the NHL we realized we would need to use significantly more than we anticipated, and are now concerned that our frame won’t be able to hold the weight. The footprint of the house is 16x9x10, and sits on concrete pier blocks, below 10×6 wooden beams, connected with metal bolts. The frame itself is made up using 2×4’s, and has a loft and gabled roof. The walls are 10 ft tall.

We plan to apply a thicker coat of earthen plaster, followed by the NHL at 7/8ths of an inch.
Do you think our frame can hold the weight of the plaster?

Thanks!
Tyler Morning

Hi Tyler, welcome to Permies!

Could you give a better description of the design, maybe a sketched photo of the footprint. How many concrete blocks, what are the spans? When you say 2x4 frame is this the wall or the floor? How thick are your walls going to end up?

Is the weight of the wall going to be on 2x4s or will it be on the beams themselves? Maybe a photo if you have things in place already.

Hi, thanks so much for your questions. I don't have a sketch, but I'm attaching a photo.
There are 4 concrete blocks, each is 9x9 inches on the bottom, and 12x12 inches at the base.
Floor is OSB, on 2x6 joists, and 2x4s frame the walls, which will be a little under 6 inches thick when they are done, if we stick with light clay straw.

On the two long walls the weight of the walls will be on the 6x10 beams directly. On the short walls their isn't a lip for the plaster at the base of the walls, so it will cling directly to the wall.

I think I have an idea of what it looks like. The 16 foot span is probably where problems lay in wait. That is very far for a 6x10. I would put another support under the center of each side to reduce this to 8' spans. This will also help distribute 1/3 of the weight into other point loads. I don't know what type of soil you have, or what weather conditions are like, but with point loads like that and directly on the surface you may have lifting or sinking over time. If it freezes where you are those footers will definitely heave a bit over time since they are set directly on the ground.

Is the timber you have used able to withstand water on it?
Will it rot if it gets damp?
If so, lime plaster may not be a good idea.

If you are in the South as it appears, freeze-thaw is not an issue, but load from the piers on the soil is. What is the soil under the piers? Unless it is compacted gravel going down fairly deep, I would expect the whole structure to sink into the ground over time. I wonder if even a single pair of added piers would be enough. I am sure that would support the main beams well, but I think you need more area of ground contact to spread the load. I would dig out under new pier locations a foot or so and twice as wide as the pier, add crushed gravel (not smooth round pea gravel), and compact it to give good support. I would also use shims after placing the pier to take up the slack from sliding the pier into place and put load on it.

A 9' span for 2x6 floor joists is not bad for an outbuilding, and I think you will be alright there. The edge joist will have little floor live load, so it has more to spare for the wall dead load, especially if you doubled the joists under the walls.