Repair notched joist by scabbing - glue ply to rough sawn joist

[andreas]

I have lifted some floorboards that were butchered by some one in the past and have found that a couple of the joists have been notched badly. Not really bad but I would like to add strength back for peace of mind.

I have read about scabbing using structural glue and ply either side of the joists but my question is that the joists are rough sawn and I had always been told that for good glue joints wood should be smooth.

Is there a particular glue that would be ok on rough sawn timber?

[Temp]

Google  "for joist repair plates" or "Bower beams"

 

https://www.permagard.co.uk/bower-beams-large?gad_source=1&gad_campaignid=20104758639&gbraid=0AAAAAD6l7u6eYbKpQcQBXyc85Smq5MoS8&gclid=CjwKCAjw87XBBhBIEiwAxP3_Axxih9ZPj7neGI8nFscH233n-kk6VjP3GPKyrL0vkQGshG4fCttAOhoCbzMQAvD_BwE

 

https://www.preservationshop.co.uk/product-category/timber-treatment/timber-repair-systems/

 

Edited Wednesday at 19:21 by Temp

[andreas]

9 minutes ago, Temp said:

Google  "for joist repair plates" or "Bower beams"

 

https://www.permagard.co.uk/bower-beams-large?gad_source=1&gad_campaignid=20104758639&gbraid=0AAAAAD6l7u6eYbKpQcQBXyc85Smq5MoS8&gclid=CjwKCAjw87XBBhBIEiwAxP3_Axxih9ZPj7neGI8nFscH233n-kk6VjP3GPKyrL0vkQGshG4fCttAOhoCbzMQAvD_BwE

 

https://www.preservationshop.co.uk/product-category/timber-treatment/timber-repair-systems/

 

Thank you I had seen those but I cannot slide the lower lip in below joist without damaging ceiling below, and notch in top of beam and has pipes in so I could not put a full top one in. The glued ply scabbing was suggested to me as I can slide in through lifted boards but they do not know about glue on rough sawn timber and I cannot find clear answer.

[Nickfromwales]

1 hour ago, andreas said:

Thank you I had seen those but I cannot slide the lower lip in below joist without damaging ceiling below, and notch in top of beam and has pipes in so I could not put a full top one in. The glued ply scabbing was suggested to me as I can slide in through lifted boards but they do not know about glue on rough sawn timber and I cannot find clear answer.

Do you have some pics, as it is possible you are worrying about nothing. We can see if there's defo an issue if we can see it  

[Temp]

Is the timber treated? Can be difficult to glue well to that.

 

Otherwise Id use a polyeurathane wood glue which foams up to fill any voids.

[andreas]

14 hours ago, Nickfromwales said:

Do you have some pics, as it is possible you are worrying about nothing. We can see if there's defo an issue if we can see it  

I do like to worry about nothing haha.

I will try and get some pictures this evening when home from work. 

 

[andreas]

11 hours ago, Temp said:

Is the timber treated? Can be difficult to glue well to that.

 

Otherwise Id use a polyeurathane wood glue which foams up to fill any voids.

I do not know if treated or not. House is mid 60s we think. Do you think the foaming PU is strong enough?

[SteamyTea]

Using modern adhesives is generally quite easy, though often messy.

My go to timber adhesive is now Lumberjack. It is a low expansion polyurethane, comes in a tube.

 

Many people say that foaming PUs are the way to go on rough surfaces, and making the surfaces wet helps.

I am not sold on this for structural usage. The more bubbling you get, the less adhesive there is holding it all together.

So while many modern PU adhesives say they use moisture to aid curing, I suspect that it also reduces shear and peeling strength.

 

Rough cut timber may need to have the worse of the splinters removes, and be made dust free. Washing with water is ok for this, but allow an hour or two for drying, you don't want it dripping wet.

The most important thing is the clamping together of the two parts. Don't be tempted to just clamp at ends and middle. Even low expansion foam adhesive can exert a lot of pressure. So lots of G-Clamps and some sturdy 50mm by 75mm (or deeper) thick timber to spread the loads (note plural, PUs expand, then contract).

Don't be tempted to take the clamps off before fully cured.

 

If you are worried, try it out on some test pieces. You will learn so much about using adhesive.

Edited 22 hours ago by SteamyTea

[saveasteading]

If the notches are near the ends then it probably doesn't matter structurally. Where are they?

 

The plates shown by @Temp would be great but your point is valid and important.  So you could instead simply fix the flat plate equivalent to both sides, using several screws. More thought needed if that suits. I wouldn't bother with glue at all.

Standard at any BM or at SFix or ToolS.

 

 

Or you could use plywood instead  Again multiple screws are more important than glue.

 

Or, replace the flooring locally with plywood, again screwed down.  This becomes a top flange for the joists.

 

 

[sharpener]

Have had to do a similar job as a result of bodging by plumbers.

 

Plywood is probably not a good material for this as half the grain runs in the wrong direction, you want all the grain running parallel to the joist so it will be maximally strong in bending.

 

I put a sister joist of half the width on each side of it using long Timberlok screws. Bolting through would have been better but I could not get a drill in to make the clearance holes.

 

The theory of bolted joints is that the bolts or screws pull the joint tightly together, then the shear loads are transferred by the friction between the faces (and not by the bolts).

 

Consequently rough faces will improve the friction. I don't think adhesives are much help in this scenario though I did use Evostik Resin W - which has long been my favourite woodworking adhesive, I think it has a new name now.