I am building a foundation for a tunnel greenhouse with Leca blocks. We have dug a trench about 70 cm deep and packed it with crushed stone at the bottom. Three courses of the wall will end up underground when everything is finished. My question concerns how best to treat the surface of the wall. As I understand it, it needs protection so that moisture doesn't penetrate and cause the blocks to crack when it freezes in winter. One solution I am considering is to apply red primer to the entire wall. The question is whether this is sufficient for the part that is underground or if I need to apply an additional layer there as well. I was thinking of plastering with a suitable mortar on top of the red primer. However, I would prefer not to do that on everything that will be underground, unless it is absolutely necessary for durability.
Does anyone have experience with this?
Grateful for any answers!
Does anyone have experience with this?
Grateful for any answers!
I'm not an expert, but I guess plaster is considered a type of protection? It's on the outside of the lecan, which means the lecan is not in direct contact with the ground.
Then I don't think you need to apply slurry on top of rödgrund. Rödgrund is essentially a base and slurry, so it probably doesn't serve any purpose to apply slurry (again) on top of the rödgrund.
Then I don't think you need to apply slurry on top of rödgrund. Rödgrund is essentially a base and slurry, so it probably doesn't serve any purpose to apply slurry (again) on top of the rödgrund.
I have no doubt that the plaster provides protection. The question is whether the redgrund is sufficient protection in terms of frost spalling.Thyro89 said:
Redgrund first and then rendering with something like a B mortar seems to be a common approach. It is suggested, for example, by Weber in their PDF about plastering. Rendering is just the method of applying the mortar. The different layers of plaster can still have different functions, even though the same method is used. However, I am also not an expert ☺️ so I reserve the right for any errors. What I really want to know is whether redgrund provides sufficient protection or if it is just intended to improve adhesion.
I don't think Lecablock are particularly sensitive to frost damage - I have stored blocks on damp ground during winter and never seen any damage. There is so much air in the blocks that the ice crystals can expand without problems and the clinker itself is a completely waterproof sphere.
Weber states that Lecawalls below ground should be thin plastered with max 2 mm A-bruk brushed in. The thin plaster seals against soil, water, and ants. No further treatment is needed.
Weber states that Lecawalls below ground should be thin plastered with max 2 mm A-bruk brushed in. The thin plaster seals against soil, water, and ants. No further treatment is needed.
Thank you Claes! Exactly what I wanted to hear 😀
I asked my local XL-bygg. They claimed that the red primer only provided better adhesion and that it was therefore unnecessary to apply it below ground. His suggestion, considering it was a greenhouse with plastic, was that I should place a platon membrane directly against the lecablocks instead. That would provide sufficient protection against moisture. Then render or plaster above ground.
I asked my local XL-bygg. They claimed that the red primer only provided better adhesion and that it was therefore unnecessary to apply it below ground. His suggestion, considering it was a greenhouse with plastic, was that I should place a platon membrane directly against the lecablocks instead. That would provide sufficient protection against moisture. Then render or plaster above ground.
Last edited: