Concrete blocks for retaining wall

[Bert Coules]

If I build a raised flower bed using dense concrete blocks it is advisable to paint or otherwise treat the inside surfaces before filling with earth? Many thanks.

[The Natural Philosopher]

Totally unnecessary. Concrete blocks of exterior grade are happy to go under the soil

[harryagain]

The problem is there is a lot of water loss by evaporation through the blocks. You can stop this by painting the inside with bitumous paint or lining with polythene. Also reduces frost damage if the blocks are dryer.

I hope you have left "weep holes" at intervals for drainage.

[JimK]

/The Natural Philosopher

- show quoted text - Totally unnecessary. Concrete blocks of exterior grade are happy to go under the soil /q

Perhaps but if the OP is planning to paint or render the outside of the retaining wall he would do well to address the penetrating damp issues that will occur..... BTDTGTTS

Jim K

[Bert Coules]

I have no definite plans as yet, but painting the outside is something I've thought about. With no internal treatment, does the penetrating damp affect even specialist masonry paint?

Bert

[meow2222]

FAIL.

NT

[Bert Coules]

I have absolutely no idea what that is meant to convey.

Bert

[harryagain]

The paint will be lifted off the wall by water pressure. It's not possible to fix this as there will aso be a "rising damp" issue,

If you want something that looks decent you will have to use other than concrete blocks and unpainted. It would be best frost resistant too.

[Bert Coules]

Ah, so even if I treat the inner face of the wall, water will soak up from the base through the footings?

What about blocks covered on the outer surface by some sort of facing? Stone slips, thin bricks, that sort of thing, fixed with waterproof adhesive rather than mortar?

Thanks for the thoughts.

Bert

[stuart noble]

It's a way of attracting attention. Just IGNORE :-)

[JimK]

retaining wall he would do well to address the > penetrating damp issues t hat will occur...

I have no definite plans as yet, but painting the outside is something I've thought about. With no internal treatment, does the penetrating damp affec t even specialist masonry paint?/q

IME yes, more than once! This was a weak mix rendered retaining low garden block wall (by others...) and it progressively looked mouldy, flaky, blew p arts off after frosts & was generally a bit crap. Annual painting with prop er stuff did not provide a solution. I "roofed"it in red cedar shingles in the end.

Jim K

[Bert Coules]

Ah, that's interesting, thanks Jim: cladding the outside is something I've considered (both on this new wall and the existing one that I mentioned in an earlier thread). So whatever you used to fix the shingles (mortar? adhesive?) wasn't affected by the penetrating damp?

Bert

[Bert Coules]

On reflection, did you fix battens and nail the shingles to them? ("Roofed" you said.) Stupid of me not to think of that.

Bert

[meow2222]

What you proposed will fail. No paint is going to stop evaporation adn thus salt crusting. If you want it to stay looking decent you need a waterproof layer on the inside.

NT

[JimK]

/Ah, that's interesting, thanks Jim: cladding the outside is something I've considered (both on this new wall and the existing one that I mentioned in an earlier thread). So whatever you used to fix the shingles (mortar? adhesive?) wasn't affected by the penetrating damp/q

Nah stainless steel screws into plugs in wall, with breathable roofing membrane between wall & shingles...

You need to include a vertical dpm or somesuch in your wall construction to hopefully avoid all that!

Good drainage under the raised bed, and some good dpm lining the 'back' of the wall, lapping a bit away from the wall at the base to 'steer' moisture away from the blockwork? You can get black dpm if you look about, rather than green or blues that seem to prevail.

Or how about a vertical layer of gravel to form a French drain around the inside of the wall??

Coping stones to reduce rain penetration from above maybe laid with mortar mixed with a waterproofer for belt & braces!?!

Jim K

[Bert Coules]

Thanks for the explanation.

Bert

[Bert Coules]

Jim, thanks for the detailed reply. One of the possibilities I considered (I've seen something like it done elsewhere) is to use those blocks with square holes ("Hollow blocks" are they?), fill the vertical cavities with soil and put ground-cover plants along the tops of the walls so they could trail down the outside, ivy-like. Under those circumstances the dampness of the outer surface might be a positive benefit, but I don't know just how much coverage of the vertical blockwork I could expect to achieve: any areas of bare blockwork that were left exposed might still look fairly raw and unattractive.

Bert

[JimK]

/One of the possibilities I considered (I've seen something like it done elsewhere) is to use those blocks with square holes ("Hollow blocks" are they?), fill the vertical cavities with soil and put ground-cover plants along the tops of the walls so they could trail down the outside, ivy-like/q

How high a wall we talking? Those hollow blocks are intended to have rebar through them to stitch courses together and then filled with concrete... not sure how strong the wall would be if blocks filled with damp soil, nor what would happen in winter wrt spalling etc?

Jim k

[Bert Coules]

Three courses: something like 26 inches overall height. I understand the objections, but as I say, I have seen it done - though that was only a passing visit and I've no idea of its success or otherwise long-term.

Bert

[JimK]

/Three courses: something like 26 inches overall height. I understand the objections, but as I say, I have seen it done - though that was only a passing visit and I've no idea of its success or otherwise long-term. /q

Or its' construction maybe? Might you have viewed those blocks 'end on' perhaps? As part of a much deeper & more usual hollow block retaining wall construction?

Just a thought:-)

Jim K