DIY Doctor

Brickbuild garden shed - Mortar Bed/Joint Thickness

Postby enthusiasticnovice1 » Mon May 18, 2020 1:57 pm

Hi - I'm in the process of building a double skinned brick (tied) shed (3m x 2m x >2.5m). Having laid a concrete slab (compacted MOT sub-base, sharp sand and DPM) I noticed my slab was out of level with a 2inch variance between diagonal corners.

In retrospect I'd have built a frame poured a level concrete footing onto which to start my first course of bricks, or perhaps just distributed the variance between the mortar joints over the first three courses. Regrettably in my enthusiasm I did neither and instead I laid a thick (3:1) mortar bed (2"-4") levelling the variance and bedding the first coarse of bricks to a top line level.

I'm looking at an attractive level footprint (first coarse) bedded on a thick mortar bed joint. The footrprint is solid. The frogged bricks are stable and joints all filled.

I'm worried that the thickness of the mortar bed will compromise the structural integrity of the build - albeit only a relatively small garden shed. I've done a lot of reading about impact of air drying on mortar bed joints in excess of 1.25" (maximum) and approx compressive strength of 3:1 mortar mixes, but guidance is aimed at commercial or domestic builds.

Question: Do I tear it all up and start over, with either a level concrete footing, or a thin mortar bed evening out the variance over three coarses, or do I build-on? What are the real and present risks of proceeding based on visual assessment of the strength of the current bed laid?

I'd be grateful of some pragmatic guidance?

NOTE: The bed was laid in a frame hence the mess!
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Simply Build It

Postby stoneyboy » Tue May 19, 2020 9:21 pm

Hi enthuiasticnovice1
Since you used a 3:1 mortar mix your first course will be fine. Unless you have reasons to use such a strong mix e.g. you re using engineering bricks, I suggest a 5:1 mix with plasticiser would suffice.
Regards S
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Postby enthusiasticnovice1 » Wed May 20, 2020 5:04 pm

Thanks Stoneboy - I’m very great full for your response! I recognise it’s not been the master craftsman’s way, however you’ve reassured me somewhat that it may at least suffice! I chose 3:1 specifically because I wanted a strong mortar bed onto which to bond the first coarse and had thought 3:1 would be more appropriate as a regrettably thick mortar bed. Thanks again.
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