I need to fit two chunks of wooden worktop together with their grain
running at right angles. I know I *could* run the join at 45 degrees
but that involves all sorts of other problems and compromises.

So, do I need to allow the joint to move to allow for differential
expansion along and across the grain? It'll be in a fairly low
humidity environment but the temperature is likely to fluctuate quite
a lot (basically in line with outside temperature).

It's oak if that makes any difference.

--
Chris Green
·

On 09/04/2019 21:38, Chris Green wrote:
I need to fit two chunks of wooden worktop together with their grain
running at right angles. I know I *could* run the join at 45 degrees
but that involves all sorts of other problems and compromises.

So, do I need to allow the joint to move to allow for differential
expansion along and across the grain? It'll be in a fairly low
humidity environment but the temperature is likely to fluctuate quite
a lot (basically in line with outside temperature).

It's oak if that makes any difference.

the joint needs to be allowed to move. that means no glue or firm fixing
in more than one place and the rest of the joint allowed to slide.
Screws or dowels in slots are often used.
the joint needs to be near perfect because any filler will fail.

On 09/04/2019 22:04, Bob Minchin wrote:
On 09/04/2019 21:38, Chris Green wrote:
I need to fit two chunks of wooden worktop together with their grain
running at right angles.Â* I know I *could* run the join at 45 degrees
but that involves all sorts of other problems and compromises.

So, do I need to allow the joint to move to allow for differential
expansion along and across the grain?Â* It'll be in a fairly low
humidity environment but the temperature is likely to fluctuate quite
a lot (basically in line with outside temperature).

It's oak if that makes any difference.

the joint needs to be allowed to move. that means no glue or firm fixing
in more than one place and the rest of the joint allowed to slide.
Screws or dowels in slots are often used.
the joint needs to be near perfect because any filler will fail.

Yes, it _will_ move and almost certainly shrink. A mitre across all
600mm is not really a good idea - it will open up at the front. When I
was in the trade I used to (try to) get the fitters to hard fix the
front of the worktop and at the rear use washers or expansion brackets.
This was to keep the butt joints in the corners closed. If you hard fix
at the rear the corner joints open.

The joints themselves can be masons mitres or plain butts and cut with
whatever equipment you have. Good to use standard worktop connector
bolts. Good to use PVA which will partially seal the end grain and allow
some creeping movement before it breaks. Beware biscuits and other
arrangements which will give you a 'step' in the joint unless you are
confident you can smooth it down to match the rest of the worktop.

TW

TimW wrote:
On 09/04/2019 22:04, Bob Minchin wrote:
On 09/04/2019 21:38, Chris Green wrote:
I need to fit two chunks of wooden worktop together with their grain
running at right angles.Â* I know I *could* run the join at 45 degrees
but that involves all sorts of other problems and compromises.

So, do I need to allow the joint to move to allow for differential
expansion along and across the grain?Â* It'll be in a fairly low
humidity environment but the temperature is likely to fluctuate quite
a lot (basically in line with outside temperature).

It's oak if that makes any difference.

the joint needs to be allowed to move. that means no glue or firm fixing
in more than one place and the rest of the joint allowed to slide.
Screws or dowels in slots are often used.
the joint needs to be near perfect because any filler will fail.

Yes, it _will_ move and almost certainly shrink. A mitre across all
600mm is not really a good idea - it will open up at the front. When I
was in the trade I used to (try to) get the fitters to hard fix the
front of the worktop and at the rear use washers or expansion brackets.
This was to keep the butt joints in the corners closed. If you hard fix
at the rear the corner joints open.

The joints themselves can be masons mitres or plain butts and cut with
whatever equipment you have. Good to use standard worktop connector
bolts. Good to use PVA which will partially seal the end grain and allow
some creeping movement before it breaks. Beware biscuits and other
arrangements which will give you a 'step' in the joint unless you are
confident you can smooth it down to match the rest of the worktop.

Thanks all, I've gone with a (fairly) standard worktop connector near
the front edge and a couple of 'straps' further back which should be
able to move sideways a little. The expansion should then just change
the alignment at the back of the joint.


--
Chris Green
·