In fact, straw has excellent adhesion, and therefore you can plaster it with anything - everything will be equally well applied and adhered to.
However, today we will look at two main types of plasters: cement and clay.
Some people mistakenly believe that clay is not strong enough for straw house and, in order to strengthen its strength, they decide to plaster the house with cement plaster.
And everything seems to be fine, the house is perfectly protected from external influences, but what is the danger?
The bottom line is that clay plaster reliably protects thatched walls and does not allow moisture to pass through.
Cement plaster easily allows moisture to pass into the thatched walls and back, forming condensation.
To give a more detailed answer to this question, let us turn to chemical properties these plasters. There is such a thing as hydrophilicity. In general, it shows how much the material loves and attracts water.
So, clay is more hydrophilic than straw, and therefore, all the water that is in the straw is drawn into itself by the clay, and then it evaporates.
At the same time, cement is less hydrophilic than straw and therefore, straw begins to absorb all the moisture that is in the walls. What does this mean? After the straw absorbs all the moisture, it will begin to become covered with mold, mildew, and eventually, it may simply begin to rot.
Now the second question: where can moisture come from in the walls if the wall is reliably plastered?
Moisture tends to move from hot air to cold air. Moreover, she moves from high pressure to a lower one. As a rule, the pressure in the house is always much higher than outside, so all the moisture that is in the house (from the shower, kitchen, plants, sweat, etc.) gets inside the walls.
Further, if the wall is plastered with clay, then it retards the movement of water in the wall and at each stage less and less moisture reaches the straw. But even the moisture that gets there is pulled back into the wall by the clay, due to its hydrophilicity.
If the wall is plastered with cement, it does not have such waterproof properties and allows much more moisture to pass to the thatched walls themselves, which is successfully absorbed by the straw in the future.
Therefore, one conclusion can be drawn: based on them chemical features For these materials, it is not advisable to plaster the straw with cement, because in the future this can lead to its rotting.
At the same time, clay plaster is much healthier, cheaper and easier to work with and, in addition, will reliably protect your thatched walls from destructive moisture.
Some builders plastering straw walls without a reinforcing base. This is possible where “sticky” plaster with the addition of clay acts as a fastening solution. With less sticky plaster (cement-based), a metal mesh is usually used, especially in areas prone to damage such as corners and around windows. (Fig. 1 ).
As an ecological reinforcement for plaster, you can use reed mesh or thin wooden strips (approximately 1x3cmx2m), nailed vertically or in a cross diagonally every 3-4 cm to vertical (5x5 cm), evenly distributed wooden strips ("shingles"). These vertical the strips are cut into the surface of the blocks (such grooves can be made with the sharp end of a hammer) and firmly attached to the internal posts or the tops of each subsequent row of blocks are fastened (Fig. 2) using a “straw needle”. Vertical corner guides are made in a similar way.
Separation of walls and ceilings.
When filling the joints of walls and ceilings use wooden system gratings described above or a metal mesh attached on both sides to the frame (Fig. 4). "loose straw" is softly stuffed into the spaces between the slats and then plastered over.
Plastered ceilings have good fire resistance to attics insulated with straw blocks. It is best to use metal mesh in this situation, although you can do without it.
Plastering.
Plastering can be done by hand or using a plastering station. Straw walls allow most plastering techniques to be applied. Application plaster mortar can be produced different ways- spread or throw on with various tools. Spreading is easy, but only applicable when using thick solutions. Throwing is much more difficult.
Plastering cement-based is the most well-known, but not as easy to use as lime-, gypsum- and other clay-containing “mud” techniques.
The following components are usually used to make cement-based plaster:
One part Portland cement;
One part slaked lime;
Eight parts of clean, sifted sand.
80% of pure water from the total volume of all components is added to the container. Then sand and lime are poured in. Everything is mixed for one minute. Cement and water are then added as necessary. Mixed again for 10 minutes to create a good, sticky mass.
Plaster is applied in 2-3 layers (in the final layer the amount of sand is reduced to 6 parts). After completion of work, humidity should be maintained cement plaster for several days. This will increase its strength.
Clay-containing “mud” plaster is made from tested clay with a sufficient amount of sifted sand. To prevent cracking, this mixture is mixed with straw in a ratio of 3-5 parts sand to one part clay.
Straw and compressed straw blocks have three real “enemies” - high humidity, fire and rodents. Let's call them “obvious” shortcomings.
Building a house using straw bales may seem like a crazy idea at first. And, by the way, for some, this alone is a serious limitation - not many can handle the risk of being branded a “black sheep.” But still, this is not the only and not the main disadvantage and risk when building a thatched house.
Straw and compressed straw blocks have three real “enemies” - high humidity, fire and rodents. Let's call them “obvious” shortcomings.
The disadvantages are obvious
1. Risk of rotting at high humidity
Straw with a moisture content of more than 20% begins to mold, the stems rot and collapse, so it is so important to keep the straw blocks dry before construction begins, lay them dry and quickly seal them with plaster.
During construction. The straw walls are only partially ready, so they are covered with cellophane film against rain
This also implies that thatched walls cannot be left open. At the same time, the choice of coatings is also limited: cement-sand plaster, clay-sand plaster, gypsum plaster, gypsum sheets, wooden panels
The danger of mold exists for both unplastered and poorly made walls.
In areas with a constantly humid climate, you will need high-quality vapor barrier for internal surfaces external walls. Wide roof overhangs will protect the house from heavy rain.
2. Fire
Plastered compressed straw blocks are highly fire resistant and have been officially rated as having a very high fire resistance rating. A properly protected thatched wall is superior in fire safety to a wooden one. But straw scattered around a construction site can easily cause a fire. You need to be especially careful with straw in attics, attics, and near fireplaces.
This is confirmed by the story of a woman whose house burned down during construction.
"A house was being built for permanent residence(autumn 2005). I bought the plot ready ground floor. The frame was secured to the foundation with 14x220 anchors. The blocks were tied with two simple twines; they were not pressed properly, because... During installation, a lot was gutted... The outer wall was covered with DSP, and the inner walls were covered with boards at intervals. A straw house burned down. Fire in a straw house during construction. Fire in a straw house during construction.
In the photo you can see to what stage the house was built before it burned down (they managed to make a subfloor on the second floor and interior partitions). At this stage, the builders began to place glass insulation on the foundation on the 1st floor, heating blowtorch(April 2006). According to them, the windows on the second floor were open. After some time it began to smoke under the casing and floor. They began to blow it up and flood it, but they couldn’t, the fire spread very quickly and burned the whole house. There are many versions, but I think there was a draft of hot air and, most importantly, a violation of fire safety regulations...”
Prevention measures:
- no smoking on the construction site
- quickly clean up scattered straw
- always have a fire extinguisher on hand
- do not use open fire sources until the walls are plastered
- use tightly compressed straw blocks
- After laying the blocks, plaster them outside and then inside the house before starting interior decoration.
3. Rodents
“The mice will eat it” is a very common statement about thatched houses. Why is it so widespread? Because mice can actually settle in straw in search of food and warmth. True, not in any straw, and not really in straw :) It is inconvenient for mice to settle directly in straw blocks - they are prickly, but in the voids between the block and, for example, a plasterboard, they can.
By the way, rodents are not the only small pests that can help you tear your house apart :) There are also birds and insects that can also choose straw as their habitat.
Prevention measures: use rye or rice straw for insulation (mice do not eat it and do not live in it), insulate everything possible ways access to straw.
Disadvantages little mentioned, but really existing
4. Design limitations
When using a load-bearing frame, the design limitations are small, but they do exist, and they relate primarily to the number, location, width and height of openings.
5. Thick walls
Width straw block makes the walls quite thick. One of the difficulties with walls of such thickness is the need to expand the foundation and increase the roof area. In houses with more thin walls creating exactly the same useful internal space requires less resources.
Straw walls. Thick thatched walls protect well from frost, but increase the foundation and roof...
6. Few standard projects
Unlike houses built using other technologies, there is a clear shortage standard schemes straw bale construction. This means that the development of a project for the construction of a thatched house will most likely have to be ordered individually, and you will have to look for understanding architects-designers-builders.
In some countries there are still no building codes(in Belarus it is regulated by SNIP, in the Russian Federation and Ukraine it also seems to be).
7. Deadlines and money
You need to immediately have a certain amount on hand in order to quickly solve “must-have problems.” I will give one dialogue from the forum that well illustrates this point.
- ... one BUT: if I build a log house and I run out of money, I can live in it unfinished, but a thatched house requires both external and interior decoration, and right away.
- The cost of minimal finishing for living in a house is so insignificant that it does not deserve separate discussion. If there is money for the frame, roof and windows, then there will be crumbs for plastering.
- Something tells me that it will cost at least $5 per square, - and there are a lot of squares in the house!
- Necessarily! No less than 5! If you don’t apply your hands yourself, but walk and poke with your finger, it’s uneven here, apply some oil there...
8. Deadlines and money - 2
We have suitable straw closer to August, and if there is not enough money, then we may not have time to do everything before winter. And in winter external walls Plastering cannot be done. Therefore, there is the prospect of overwintering straw under the roof of an unfinished house or outbuilding on the site, and then risk No. 1.
9. “Pointing finger”
Due to the fact that the technology of construction from straw blocks is not yet very widespread, it will be necessary to monitor the progress of work much more and more carefully in comparison with construction from “traditional” materials: so that builders do not smoke, do not work with a burner, and that fertilizers are nearby with straw (for example, ammonium nitrate - spontaneous combustion is possible upon contact with sawdust or straw), and so that children with matches do not appear nearby...
P.S. Disadvantages of thatched houses with a load-bearing frame
You may have already heard that a thatched house can be built framed or frameless. To be honest, I still have little idea of the process with such a frameless house, but people call the disadvantages of straw construction with load-bearing frame, so let’s mark them just “for show”. So, this is an additional waste of time, money, work force, materials to create a supporting system, when the blocks themselves could support the weight of the roof, as well as the need to create a foundation that carries the weight of the blocks and concentrated loads from the vertical posts. published
While excavating the basement (which will also be part of the air conditioning system), we had the opportunity to compare soil samples from different depths. It turned out that after a small fertile layer there is a rather thick layer of oily clay. To determine the composition of the clay, a small experiment was done: two clay samples from different depths were placed in separate glass jars and filled with water with a little salt added. The contents of the cans were thoroughly mixed to obtain a liquid clay mortar, which should then separate into fractions (the addition of salt serves to accelerate the precipitation of the solution). After the mixture settles, i.e. will be separated into silt and sand, it will be possible to approximately determine the composition of the clay. But this is all theory, and in practice I was not able to see a clear boundary between the layers in both cases. On the contrary, almost the entire height of the sediment was occupied by silt, and there was almost no sand. Thus, we will have to add sand to our clay for use as plaster.
In order to determine the proportions of the composition for clay plastering, two test batches were made with different proportions of clay and sand. The composition of the first sample: one part clay, one part sand and one part finely chopped straw (in a loose, uncompacted state). The second sample is the same, but there are two parts of sand. The resulting mixtures were plastered on a straw bale from different sides.
Both plaster samples adhered to the straw bale without any problems. In the second case, it was felt that there was more sand in the mixture, but no problems arose in applying the plaster to the straw. To appreciate the difference you need to wait until the mixture dries completely. In fact, before building a house, I thought about buying pottery clay in bags for plastering on straw. If you can use your own clay, that will be great. True, the color of our clay is slightly different from what was intended, but this is not a problem - you can add a little kaolin to the finishing layer of plaster inside the house.
The result of the experiment is as follows: after the clay dried on the straw, it turned out that both samples had approximately the same adhesion and strength. A mixture with a higher sand content on the surface forms a more granular structure; “extra” grains of sand are quite easily separated from the surface, but in terms of strength this sample is in no way inferior to the first. Chopped straw included plaster mixture reinforces it, increases strength and adhesion, and prevents cracking.
After such an experiment, it was decided to plaster with clay in the following proportion: 4 volumetric measures of sand, 5 clay, 4 crushed straw without compaction and required amount water to achieve the desired consistency of the mixture. The first layer of clay plaster has a rather rough surface, but this is good, because it is not possible to level straw bale walls in one pass. The rough surface of the first layer promotes better adhesion of the second layer to the first. In order for the first layer of clay plaster to adhere properly to the straw base, you need to try to press the clay into the straw as deeply as possible. And one more note regarding filling the frame of the house with clay and straw. The denser the straw bale, the better: it springs less during plastering and holds its shape well. I had the opportunity to compare plaster on bales with different densities. So, working with loose bales is much less convenient.
p style="text-align: justify;">Straw bales for insulating the frame do not have perfectly right angles, and therefore, even when tightly laid, voids remain between them. We stuffed these voids with straw and a small amount thick clay. After applying the first layer of plaster, all the unevenness of the wall clearly appears, and individual straws sticking out are also visible. We remove them with an electric trimmer, which at the same time knocks down the protruding tubercles of the plaster, which makes its surface rougher. After trimming, we plaster the wall surface with clay again. To apply the second layer, we change the proportions of the mixture: 5 parts clay, 3 parts sand and 1 chopped straw.
To build the walls of a house from clay and straw, two layers of plaster are enough. In some cases, when after the first pass too deep holes clearly appear on the wall, before finishing layer It makes sense to fill these holes separately, but in general two layers is sufficient. Straw in the walls is a very effective and natural insulation material. Clay binds bales no worse than cement mortar for the case brickwork, despite the fact that there is no clay between the bales. The final exterior finish of the house will be siding (after the straw and clay walls have completely dried).
I had been planning to post this article for a long time, but I kept putting it off because... this year I didn’t manage to finish what I started - my walls were plastered only on the outside once, and then only incompletely... Next - 15 steps in the process of plastering a thatched house...
1. Before plastering the walls should be straightened- for example, big wooden hammer; I also saw an example of how the “excess” was cut off with a grinder or chainsaw. First we do it from the street side - there will always be time inside :) .
2. Then you can do it again check the gaps between the blocks and in the openings - and fill them with straw or a mixture of chopped straw and clay.
3. Next, we cover the frame with mesh so that the plaster holds tighter.
You can use metal or plastic. There is one problem with the first one - it starts to get jammed inside the house mobile connection. Therefore, my plans were for the lower part of 1 meter to be metal, and everything above to be plastic. However, in practice it turned out that the outside was covered with a plastic mesh 2 meters high.
You can plaster the walls either on top plaster mesh, and without it, rubbing the plaster into the straw - the second option is labor-intensive, but cheaper (you don’t need to buy a mesh - although the consumption of plaster is 15-20 percent higher, so it’s worth doing the math, perhaps).
In addition, sometimes instead of a mesh they make a thin sheathing of slats or shingles.
4. For attaching the mesh We use metal wire or nylon cord and stitch the blocks together with the mesh. This is not necessary, in principle. I started doing this, but then I realized that she would hold on just fine anyway.
5. Cover the openings with film. I think it's clear why.
6. Install scaffolding. This item is also optional - it depends on the height of your walls, of course. One of the most .
7. Check the clay for plasticity- if you plaster with clay, of course.
At first I was going to do this, but in the end I settled on lime plaster for the external walls.
8. Prepare the plaster mixture.
9. Check the mixture for readiness:) This is also not difficult - you can plaster a piece of the wall and wait for it to dry. If cracks appear, you need to reduce the amount of clay.
10. Plaster 1 time - rough.
Everyone knows from films how mud huts were made in Ukraine - in big holes a bunch of people mix the clay with their feet, and then women and children throw lumps of this mixture with all their strength into the walls with their hands. In general, there is a lot of fun here :) But you can also use special devices for applying plaster - it won’t be as romantic, but it will be faster.
In the case of lime plaster, such fun, alas, is cancelled...
11. Leveling the thrown plaster with a grater board. There is an article about tools for more details.
12. Waiting for drying within about 7-10 days.
13. Plaster 2 times.
14. Plaster 3 times - finishing.
IN upper layer plaster can be added linseed oil(about 5% by weight of the plaster) - it will become a good breathable and at the same time moisture-proof impregnation. You can also add dye to the third layer of plaster.
15. If desired, paint the walls, for example acrylic paint.
Some for final painting use potassium silicate ( liquid glass), which also forms a waterproof film. By adding pigment to it, you will get the desired color.
These are the steps I came up with - everything seems simple and it’s quite possible to do it yourself. Write in the comments - let's discuss!
The wall of a thatched house after the first layer lime plaster Typhoon Master No. 28
