Why do we need sand cushion under the foundation and how to do it

durability of any structure depends largely on the accuracy of laying the foundation, and not the last role in this played a sand cushion.One of the requirements for it, is to ensure the stability of the structures during periods of soil shifts due to changes in the depth of the water layers (groundwater).This happens usually in the off-season, when the snow melts and heavy rains that accompany each autumn.This may occur when a strong freezing of the soil.

Sand for

pillow It is in order to provide a "cushioning" the foundation of the building and make a sand pillow.Furthermore, sand well aligns the bottom of the trench.In fact, this layer of sand under the bottom (sole) of the foundation.Therefore, make a pillow after being prepared trench for the foundation.Its depth depends, among other things, on the composition of the soil on which the structure is erected.When it is prepared, its deepened by 15 - 30 cm, and the trench is filled with sand.

In some sources it is recommended to use sand and shallow middle fraction.However, the "experts" are advised not to do so, and take the coarse sand.Fine sand gives a great "shrink", whereas with large this is not happening.You can also use an ordinary river sand ( "average").

Features and tips

If poured wet sand, then tamp it is not necessary, it is compacted by yourself.If the sand is dry, you need to moisturize it and ramming.In the latter case it is poured "portions" and ram each.Quality pillow is easy to check - if a person walks on a sandy backfill and after him there are traces, the pillow is well compacted.

necessary to take into account the level of underground water.For each area there is its average value.If the place of laying the foundation, it is exceeded, the thickness of the sand layer should be increased.It is necessary to pay attention not only on the evenness across the sandy surface, but also on its "horizontal".Therefore, in the process of tamping pads need to control using the building level.

However, we must take into account what type of foundation will be laid.The article given an overview of the sand cushion.But there are nuances depending on the foundation.For example, what form is better to make a pillow (perhaps trapezoidal?).Therefore, in each particular case it is necessary to examine this issue in more detail.