timber coping - fastening to concrete walls?

Campanula UK Z8March 19, 2011

I have built raised beds out of concrete blocks which will be rendered. For coping, I had a quantity of pressure treated joists, 200x50mm which I have stained and oiled (gah, 4 coats each of stain and Danish oil and three of wax!) I want to attach them to the beds without screwing through the tops - I can use L brackets as there is a generous overhang (the blocks are 100mm wide) but I also want to actually stick them with something. At first, I though I could unibond the timber and bed them on mortar but am hoping for suggestions. Obviously, I don't want to use anything which comes in little tubes or corning guns - there is 30m of running length. I wondered about tile adhesive? Basically, anything which comes in 5 litre tubs ought to be a feasible amount. Ideas?

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dan_staley(5b/SS 2b AHS 6-7)

I'm struggling with the description of the purpose of the wood (and the fact that English is better than American) - are you intending to put the wood on top (nice)? If so, I'm wondering how you are going to overcome the moisture and temperature differential with an adhesive.

That is: in my experience material differences make adhesives a problem. I can't think of what will work here, and you may want to countersink and take the screw down and secure into the block with an adhesive that the trades use. There are several that are excellent, but in my view the key is to countersink the drill hole such that the head and screw lies below the surface.

If you must do it, you'll have to do some tests with different adhesives. I use some around the yard that work with like:like material, but unlike materials want to blow out with moisture or cold. Maybe a test area for a year is in order...


    Bookmark   March 20, 2011 at 11:18PM
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What you might consider is attaching some kind of fixing (vague enough?) to the concrete blocks with a receiving fixing on the underside of the timber. For instance a bolt with a metal plate at the sharp end glued and mortared to the top of the wall and a keyhole shaped hole cut into the underside of the timber. The head of the bolt goes into the round part of the keyhole and you then hammer the timber along into the slot. You will have to line this up accurately and be prepared for some minor adjustments.

    Bookmark   March 21, 2011 at 8:56AM
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flora_uk(SW UK 8/9)

I am assuming the wooden coping is to make the wall into a seat. I think that an adhesive would eventually give way, not so much because of temperature differentials in our climate but because of damp. There there is a danger of water getting under the wood and sitting there causing rot. Wooden coping that I have seen is generally raised above the wall in some way to allow air to pass between the wood and the wall. You would need to screw the wood down onto wooden spacing blocks using countersunk brass or galvanized screws. You can get domed tops which make the screws look quite stylish.

Here is a link that might be useful: Wooden wall seating

    Bookmark   March 22, 2011 at 6:23AM
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